Dụng Cụ Chỉnh Hình Và Chân Tay Giả Trong Phục Hồi Chức Năng (Ấn Bản Thứ 3)

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595
Understanding Prosthetic Feet
Kevin Carroll, John Rheinstein, and Elicia Pollard
Just as every person is unique, every person with an
amputation presents a different set of characteristics that
should be considered when selecting a prosthetic foot. This
selection should be made carefully as safety, performance,
and patient satisfaction can be impacted if the foot is not
well matched to the patient.1 To make an effective selection
among the multitude of choices offered by prosthetic foot
manufacturers and to succeed in matching the right foot to
the right recipient, it is important to thoroughly consider
each individual's current and potential abilities and needs.
The rehabilitation team should carefully review a patient's
medical and prosthetic history while keeping in mind the
performance features, specifications, and appearance of
available feet. Past research studies offered data concerning
foot performance and patient preferences, but studies have
not yet provided pathways to successful foot selection based
on clinical evidence.2–4
The aim of providing a prosthetic foot is to maximize every
patient's rehabilitation potential so that they may return to
their daily activities and work at a level comparable to their
peers. Ideally, the function of a prosthetic foot should match
that of an anatomical human foot.5 It should offer shock
absorption, compliance to uneven terrain, push-off, and
shortening during the appropriate points in the gait cycle,
all in a lightweight, low-maintenance package. In reality, no
prosthetic foot available today matches the human foot in all
these characteristics. The final choice is always a compromise,
as no single prosthetic foot performs optimally for all activi­
ties and conditions. The most appropriate foot is one that best
serves the user's unique needs at the time of selection.
Once a specific foot design is selected it must be ordered
to meet the specific weight and activity level of each ­person.
If patients experience physical or lifestyle changes, the foot
should be replaced to match their new functional needs.
For example, a weight gain of 20 or more pounds or sub­
stantial increase in activity or loads carried may result in the
catastrophic failure of the structural element of a foot. All the
parts of a prosthetic system, especially feet, should be checked
regularly for wear and tear and replaced immediately if any
cracks or other signs of structural failure occur. It is difficult
to predict the useful life span of a foot because of the wide
range of users and the way they are used.
FACTORS IN SELECTING A PROSTHETIC FOOT
When working with a patient to design an appropriate pros­
thesis, the rehabilitation team (physiatrist, surgeon, primary
care physician, physical therapist, and prosthetist) should
assess and consider a number of factors that influence com­
ponent selection. In addition, explaining the function and
features to the user and why a foot was selected can enhance
their satisfaction.
Functional Level
• Medicare guidelines describe functional levels into
which all persons with lower-limb amputation fall and
are widely accepted by most payers.6 This classification
­system determines the medical necessity for ­components
such as feet and other additions to the prosthesis and is
based on the patient's current and potential functional
abilities
Medicare policy states, “A lower limb prosthesis is cov­
ered when the patient: (1) Will reach or maintain a defined
functional state within a reasonable period of time; and (2)
is motivated to ambulate. ” Clinical assessments of patient
rehabilitation potential must be based on the following
­classification levels:
Level 0: Does not have the ability or potential to ambu­
late or transfer safely with or without assistance and
a prosthesis does not enhance their quality of life or
mobility.
Level 1: Has the ability or potential to use a prosthesis
for transfers or ambulation on level surfaces at fixed
cadence. Typical of the limited and unlimited household
ambulator.
21
LEARNING OBJECTIVES
On completion of this chapter, the reader will be able to:
1. Define the Medicare functional levels.
2. Explain key factors analyzed when prescribing a prosthetic
foot.
3. Define the fundamental characteristics of the different
types of prosthetic feet.
4. Formulate a prescription recommendation for a prosthetic
foot based on the patient's needs.

596
Section III  Prostheses in Rehabilitation
Level 2: Has the ability or potential for ambulation with
the ability to traverse low-level environmental barriers
such as curbs, stairs or uneven surfaces. Typical of the
limited community ambulator.
Level 3: Has the ability or potential for ambulation with
variable cadence. Typical of the community ­ambulator
who has the ability to traverse most environmen­
tal barriers and may have vocational, therapeutic, or
exercise activity that demands prosthetic utilization
beyond simple locomotion.
Level 4: Has the ability or potential for prosthetic ambu­
lation that exceeds basic ambulation skills, exhibiting
high impact, stress, or energy levels. Typical of the
prosthetic demands of the child, active adult, or athlete.”
Note: Persons with bilateral amputation are not strictly
bound by the functional level classification requirement.
Potential functional ability is based on the reasonable
expectations of the prosthetist, and treating physician, con­
sidering factors including, but not limited to the following:
• the patient's past history (including prior prosthetic use
if applicable);
• the patient's current condition including the status
of the residual limb and the nature of other medical
problems; and
• the patient's desire to ambulate.
Ideally, the rehabilitation team examines and interviews
the patient and reaches a consensus as to the potential
functional level each patient is most likely to achieve. The
key word in reaching such a decision is “potential,” which
­challenges the team to predict future outcomes based on past
performance and other unknowns. This decision has real
implications for patients as it determines what type of foot
they will receive. Therefore, if the rehabilitation team believes
that a person currently performing at K2 level will at some
future date achieve K3 category, the patient should receive a
K3-level prosthesis immediately. Not only will this allow the
person to work toward achieving the K3 performance with
an appropriate foot, but it will save cost over the long run by
eliminating the need to purchase two different feet. In addi­
tion to the factors mentioned below, the Amputee Mobility
Predictor instrument, designed to measure ambulatory
potential of lower-limb amputees, can also help to determine
future potential.7
Activities of Daily Living and Work Requirements
No single foot can meet a person's needs in all situations.
By determining the most frequent and important activi­
ties a balance of performance features can be achieved. For
example, someone who works in an office and who also plays
golf on weekends should be provided with a multiaxial ankle
to accommodate uneven terrain.
Patient’s Weight
Sizes and strengths are available for patients ranging from
a baby to those adults weighing more than 500 pounds
(Figure 21-1). Weight should be recorded at every patient
encounter to insure that a foot is still appropriately matched
to the patient. The assumption that an extremely heavy
patient cannot be fitted with a prosthesis is no longer true.
Because a growing population of patients is overweight,
manufacturers are offering prosthetic feet for heavier
patients. A prosthetic foot expected to support heavier
weights must be specially crafted for increased strength and
durability; consequently, the prosthesis itself is larger and
heavier because of the additional material included in the
foot, pylon, and socket.
Obesity makes prosthetic fitting more difficult; however,
the results achieved by overweight people can be very inspi­
rational. Even patients weighting more than 300 pounds
should not give up hope. Although initially confined to
a nursing home bed, rehabilitation teams that work with
overweight patients can fit them with a prosthesis, assist
them with standing, begin therapy, and within just a few
months have the same bedridden patients walking in and
out of the prosthetist's office on their own. It is not uncom­
mon for functional K1-level patients to progress to K2
level with appropriate care and therapy. Patients are often
deconditioned from the illnesses that precipitated their
amputation and can make great strides as long as they are
motivated.
Amputation Level and Residual Limb Characteristics
Foot selection can bear directly on the health of the person's
residual limb. Ground reaction forces that are transmitted
through a person's body can be damaging to the person's
residual limb, knee, hip, or back. Choosing a foot with
compliant heel action can reduce these impact forces. The
foot and pylon may also offer vertical shock absorption fea­
tures, which reduce impact on the residual limb. In general,
short or painful residual limbs are fit with feet that are
softer to attenuate ground force transmission through the
prosthesis. To benefit from feet that store and return energy,
a user must walk with a minimum velocity to load the foot so
that energy can be returned. If this is not possible because of
physical restrictions in strength, range of motion, or ­balance,
a lower-functional-level foot should be provided.
FIGURE 21-1  Very small children's feet. (Courtesy of Hanger Clinic,
Austin, TX.)

Chapter 21  Understanding Prosthetic Feet
597
Comorbidities
The deflection dynamics of a foot can have an effect on the
health and well-being of a person's joints. Excessive toe stiff­
ness can cause hyperextension of the knee. The contralateral
limb should also be taken into consideration as too soft of a
prosthetic toe can cause increased impact on the sound side.
Environmental Stresses and Durability
People exposed to extreme environments need a foot that will
not deteriorate under those conditions. If conditions are very
harsh, a separate prosthesis may be required. Any foot that is
not properly maintained or not dried after getting wet can fail
prematurely.
Shoe Choices (Heel Heights and Shoe Shape)
A heel height-adjustable foot (Figure 21-2) can make a signi­
ficant difference for someone who wants to wear high heels or
switch between different heel-height shoes, depending on the
formality of the occasion or work requirements.
Although a heel-height adjustable foot can flatten for bare­
foot walking, the prosthetic foot shell will wear out quickly if
it is used without a shoe. Seasonal aspects are also important;
providing a split between the big toe and its neighbor may
not seem important in the fall or winter, but is very noticeable
in the summer when the user wants to wear thong sandals
(Figure 21-3).
Feet that are too wide may prove difficult to get into a shoe
and a foot that is too narrow may move around in the shoe
causing instability. Asking the patient to bring the shoes they
intend to wear to clinic can reduce uncertainty about foot size
and shape. Patients who have been prescribed a diabetic shoe
should be encouraged to wear only those shoes.
Interaction with Other Prosthetic Components
The foot is part of a closed chain in which ground reaction
forces are transmitted through the prosthesis. The character­
istics of the foot will affect the way a prosthetic knee and hip
joint respond to ground forces. For example, a foot with a stiff
heel will send more flexion force to the knee at heel strike.
Prior Prosthetic Feet and Gait Habits
Patients who have become accustom to the characteristics
of a foot over many years may have difficulty adapting to a
new foot. If a change is warranted, the patient should under­
stand that a period of adjustment is required of any new
foot. Therapy is recommended anytime a new prosthesis or
component is provided.
Psychological Influences and Personality Traits
The wearer's age has less to do with the choice of prosthe­
sis than the wearer's attitude. For example, an 80-year-old
might be running marathons, while a 45-year-old with less
determination remains wheelchair-bound. The difference
may lie solely in their state of mind. A prosthesis wearer's
personal preferences, practical goals, and lofty ambitions
should all be considered when selecting a foot. Many people
are able to expand their capabilities and motivation dramat­
ically once they are fitting with an appropriate prosthesis that
allows them to improve range of activities.
Skin Tone
Each of the feet described in this chapter is available with a
protective cover or foot shell that gives the appearance of a
foot in addition to protecting the structural element of the
foot. Today's foot shells have a more natural appearance and
greater durability than did their predecessors. Most have
toes and are available in three basic flesh tones. Flexible
skins can be added that closely approximate the patient's
skin tone.
Cost
Foot choices may be limited by insurance coverage and the
patient's ability to pay. In general, higher-functional-level feet
cost more.
All of the factors mentioned above should be consid­
ered when narrowing the selection of appropriate prosthetic
choices for your patient. It is important to thoroughly discuss
with the patient all aspects of the choices available to them, and
ensure that everyone on the rehabilitation team ­understands
FIGURE  21-2  Heel height-adjustable foot. (Courtesy of Hanger
Clinic, Austin, TX.)
FIGURE  21-3  Feet with split toes. (Courtesy of Hanger Clinic,
Austin, TX.)

598
Section III  Prostheses in Rehabilitation
the patient's wishes and his plans for future or potential activ­
ities. Each person has different values as to what is important
to them. Ideally, more than one foot can be tried so that an
individual can make a choice based on actual performance as
well as the considerations mentioned above.
PERFORMANCE FEATURES AND APPEARANCE
OF AVAILABLE PROSTHETIC FEET:
A COMPACT GUIDE
K1 Feet
The solid-ankle, cushion-heel (SACH) (Figure 21-4) foot is
the most basic prosthetic foot available. It is recommended
only for those with limited functional ability and potential to
ambulate. The SACH foot is provided primarily for transfers
and limited ambulation. This foot's immovable ankle and soft
heel give it the ability to absorb the impact of heel strike but
provides minimal energy return. There are numerous man­
ufacturers who produce a version of the SACH foot, simply
crafted from a wooden or plastic block with a soft cushion
under the heel segment and rubber toes. Because the SACH
foot has no moving parts, little maintenance is required until
the foot is worn out, at which time it should be replaced.
No device is indestructible, however, and with our increas­
ingly overweight society, care should be taken to provide a
foot with the appropriate weight category to avoid damage or
failure. A carbon composite foot (see “K3 Feet” below) may
be required if a SACH foot cannot be made strong enough to
support an extremely obese patient.
K2 Feet
Some of the of prosthetic feet used for persons with amputa­
tion who are at the K2 functional level are as follows:
• Ossur Flex-Foot K-2 Balance (Figure 21-5, A)
• Otto Bock 1M10 Adjust (Figure 21-5, B)
• Endolite Navigator
• Trulife Kinetic
• Dycor FMA
• College Park Celsus
There is an array of different feet suited for persons with
amputation at function level K2 who are able to walk inside
their homes and outside in the community at a slow pace. Most
K2 feet are lightweight, have a flexible keel, a multiaxial ankle,
and provide some energy return. A full-length toe mechanism
lends stability while providing smooth transitioning from
heel strike to toe-off. These feet have foam-rubber cushions
that assist the wearer with soft plantarflexionby providing a
smooth transition from heel strike to mid-stance. The feet
also allow for some transverse rotation. The flexibility of
the ankle on most of these feet can be softened or stiffened
by changing the rubber cushions. More features and adjust­
ments also mean that more attention and maintenance must
be provided. Function level K2 patients should be reassessed
regularly by the rehabilitation team to determine whether
they can progress to function level K3. Additional therapy
and motivation may be all that is need to push them to the
next level.
K-3 Feet
Many of the manufacturers of prosthetic feet for persons with
amputation at the K3 functional level are as follows. Each
offers a number of different foot configurations within this
category:
• Carbon fiber composite feet with energy-storing dynamic
response:
• Ossur Flex-Foot
• Otto Bock
• Freedom Innovations
• Ohio Willow Wood
• Endolite
FIGURE 21-4  K1 foot: the solid-ankle, cushion-heel (SACH) foot.
(Courtesy of Hanger Clinic, Austin, TX.)
A
B
FIGURE  21-5  Prosthetic feet for persons with amputations at
the K2 functional level. A, Flex-Foot Balance. B, Otto Bock 1M10
Adjust. (Courtesy of Hanger Clinic, Austin, TX.)

Chapter 21  Understanding Prosthetic Feet
599
• Microprocessor feet:
• Ossur
• Endolite
• Fillauer
• iWalk
Functional level K3 feet are appropriate for patients with
the ability or potential to do all daily activities and walk with
variable cadence. They are fabricated from lightweight flexible
carbon fiber, which is very responsive and extremely durable.
Compared to a SACH foot, they reduce energy consumption;
offer increased ankle motion; reduce sound side loading; and
store and return more energy.3 There are nearly 100 different
designs available in this category, which vary based on the
shape of the carbon fiber and the addition of other materials
to absorb shock and rotational forces. They can be fitted with
or without an integrated pylon. Because they are designed
with no moving parts, they offer low-maintenance but should
be checked semiannually for wear and to determine if they
still meet the needs of the patient.
The integrated pylon foot (Figure 21-6) is the lightest of all
foot prostheses. It is one continuous carbon fiber composite
material unit from the toe to the top of the pylon, including a
heel segment that allows significant plantarflexion/dorsiflexion.
Some of these feet also provide inversion/eversion and rota­
tion through a longitudinal split that bisects the foot, a urethane
cushion, or a floating sole plate. Alignment capabilities are
somewhat limited by the integrated pylon as adjustments must
be made just below the socket rather than at the ankle. Wedges
can be added at the foot to compensate for this shortcoming.
Energy-storing feet without the integrated pylon offer
the same features as those described above but also allow the
­prosthetist to perform alignment adjustments at the ankle
where the foot is joined to a separate pylon. This permits greater
alignment flexibility; however, it adds slightly more weight than the
integrated pylon prostheses. These feet can also be matched with a
separate ankle joint that provides plantarflexion/dorsiflexion and
eversion/inversion by adding a flexible link between the pros­
thetic foot and the pylon. Although add-on ankles add weight to
the prosthesis and require regular maintenance, many patients
consider it a small price to pay for the more natural feel of an
ankle moving as they ambulate.
Another advantage an ankle joint can offer is the ability for
users to adjust their own heel height (Figure 21-7). Patients
who enjoy a versatile shoe wardrobe can switch from a tennis
shoe or casual slipper into a dressy high-heeled shoe easily, by
pushing a button on the side of the ankle, concealed by the cos­
metic covering. The ankle is allowed to bend into the desired
position and then safely locked. The foot still provides normal
gait and energy-storing capability in any height position.
Other beneficial functions include shock and torsion
absorption that are designed into the foot or added in the pylon.
These features are especially important for high-activity
people and those performing repetitive motions. They reduce
the vertical and sheer forces that are transmitted to the ­residual
limb by allowing these motions to take place in the component
rather than inside the socket. Hydraulic damping is another
ankle add-on that permits increased fluidity of sagittal plane
movement (Figure 21-8).
Microprocessor feet (Figure  21-9) are the latest devel­
opment in prosthetic foot technology, and have opened an
exciting new spectrum of possibilities for many persons
with lower-extremity amputation. In contrast to traditional
prosthetic feet that are passive, microprocessor feet actively
respond to changes in the environment. If the wearer ascends
an incline, the foot automatically provides dorsiflexion, and
continues to do so for the extent of the incline. Similarly, the
foot automatically responds with plantarflexion during the
descent on a downhill grade. The Endolite Élan, Fillaurer
Raize, and Ossur Proprio all perform these functions.
The newly introduced BiOM foot is designed to replace
the propulsive function of the gastroc-soleus muscles; its use
FIGURE  21-6  K3 foot with integrated pylon—Freedom Innovations
Silhouette. (Courtesy of Hanger Clinic, Austin, TX.)
FIGURE  21-7  K3 foot with hydraulic ankle—Endolite Echelon.
(Courtesy of Hanger Clinic, Austin, TX.)

600
Section III  Prostheses in Rehabilitation
results a near-normalized gait for persons with transtibial
amputation. The BiOM generates power during plantar flex­
ion, propelling the prosthesis forward. The the first published
research study demonstrated a significant reduction in
metabolic cost, which allows persons with amputation to walk
with greater economy and symmetry.8 The BiOM generates
its powered plantarflexion by using a combination of micro­
processors, sensors, motors, and springs. It reacts in real time
to changes in speed and terrain.
Microprocessor feet are heavier than most traditional feet.
They are powered by an onboard battery that requires nightly
recharging. The range of motion of microprocessor feet is
thus far limited to this single axis capability, but inversion
and eversion flexibility are likely to be available in the future.
Contraindications for microprocessor feet are exposure to
water, dirt, and extreme heat.
K-4 Feet: High Activity
A number of specialized prosthetic feet (Figure  21-10)
are available for the serious athlete and weekend runner.
Different configurations are available for sprinting and run­
ning. The sprinting foot, with a stiffer, springy character, is
designed for powerful bursts of speed, such as a 100-meter
or 200-meter race. The running foot combines stiffness that
is gentler and serves as a distance running foot for ­marathon
or half-marathon challenges. Choice of design depends on
FIGURE  21-8  Dynamic Response Foot with Vertical Shock and
Torque Absorbing Pylon-Flex-Foot Re-Flex Rotate with EVO.
(Courtesy of Hanger Clinic, Austin, TX.)
B
D
A
C
FIGURE  21-9  Microprocessor foot. A, BiOM. B, Ossur Proprio. C, Endolite Élan, Miamisburg,
OH. D, Fillaurer Raize, Chattanooga, TN. (Courtesy of Hanger Clinic, Austin, TX.)

Chapter 21  Understanding Prosthetic Feet
601
the patient's activity and special interest. Their unique design
makes them appropriate for running or sprinting but they are
not recommended for everyday wear.
Specialized activity feet are available for sportsmen and
athletes. Multiaxis feet are recommended for golfers and hik­
ers who traverse uneven terrain. A swim foot is available that
can be locked in plantarflexion for use with a swim fin. Swim
ankles that offer additional flexibility may also be added to
a waterproof foot for added efficiency in the water. A short,
rock climbing foot is sold with a specialized climbing shoe.
SUMMARY
Selecting the most appropriate prosthetic foot can be a com­
plex clinical decision because of a variety of factors, includ­
ing a patient's current and potential functional level patient's
specific needs, the wide array of choices available, and cost.
A small oversight in the selection process can make a signif­
icant difference in the level of success the patient achieves.
Rehabilitation team professionals, together with the patient
family members, and caregivers, should analyze and evalu­
ate the best prosthetic options for advancing mobility that
is functional, efficient, practical, and safe in persons with
lower-extremity amputation. Advances in energy-storing
materials and microprocessor technology offer persons with
lower-extremity amputation improved function in daily
activites as well as high-activity-performance in sports such
as running, swimming, golfing, biking, and hiking.
A
C
B
D
FIGURE 21-10  Specialized prosthetic feet. A, K3 foot with multiaxial ankle and rotation (College
Park Venture, Fraser, MI). B, Swim foot with moveable ankle. C, Adult climbing foot. D, Running feet.
(A, B, and D Courtesy of Hanger Clinic, Austin, TX; C, courtesy TRS, Inc, Boulder, CO.)
CASE EXAMPLE 1
An Individual with a Transtibial Amputation
A. J., a former marine soldier, was 20 years old when
he endured traumatic injuries after driving his motor
vehicle over a landmine. He was one of three people who
survived the explosion. A. J. was flown to Germany for
emergency surgery and later transferred to a military
medical center in Washington, DC. He severely injured
his left leg, incurred damage to his right tympanic mem­
brane, and lost his left thumb. After multiple surgeries,
bone infection in his left leg, and months of rehabilitation,
doctors decided to amputate his leg below the knee. A. J.
was offered honorable discharge because of his injuries.
He accepted the discharge and returned to his hometown
where he continued rehabilitation.
In high school A. J. had been a competitive athlete for
his track team and he maintained an average weight of 180
pounds. One year after the accident, the 5-foot 11-inches-
tall former soldier weighs 206 pounds and is ambulating

602
Section III  Prostheses in Rehabilitation
REFERENCES
1. Powers CM, Torburn L, Perry J, et al. Influence of prosthetic foot
design on sound limb loading in adults with unilateral below-knee
amputations. Arch Phys Med Rehabil. 1994;75(7):825–829.
2. van der Linde H, Hofstad CY, Geurts AC, et  al. A systematic
­literature review of the effect of different prosthetic components
on human functioning with a lower-limb prosthesis. J Rehabil
Res Dev. 2004;41:555–570.
3. Cummings DR, Kapp S. State-Of-The-Science Conference on
­prosthetic feet and ankle mechanisms. Available at:
oandp.org/jpo/library/index/2005_04S.asp.
4. Czerniecki JM. Research and clinical selection of foot-ankle
­systems. J Prosth Orthot. 2005;17(4S):358.
5. Perry J. Gait Analysis: Normal and Pathological Function.
Thorofare, NJ: Slack; 1992.
6. DMERC Region A Lower Limb Prostheses Policy #LLP20030401,
The DME MAC Jurisdiction, A Supplier Manual. Available at:

mr_lcd_archived/L11464_2003-04-01.pdf.
7. Gailey RS, Roach KE, Applegate EB, et  al. The amputee
­mobility predictor: an instrument to assess determinants of the
lower-limb amputee's ability to ambulate. Arch Phys Med Rehabil.
2002;83(5):613–627.
8. Herr HM, Grabowski AM. Bionic ankle–foot prosthesis normal­
izes walking gait for persons with leg amputation. Proc Royal Soc B.
2012;279(1728):457–464.
Until the development of her neuropathic ulcer, Mrs.
R. T. lived independently in a second-floor apartment
of an urban retirement community in a small city, drove
her own car to a nearby park to walk for exercise at least
3 times each week, and participated in many activities at
her local senior center. Since her surgery, she has been
living with her daughter in a nearby suburb, using a
wheelchair (propelling it herself) for mobility, and receiv­
ing home care physical therapy to build her strength and
endurance. She reports that she is able to transfer between
bed and wheelchair independently but requires assistance
to get into and out of the car. She is anxious to receive a
prosthesis, but wonders if she has the ability to return to
community ambulation without the need of an assistive
device.
Mrs. R. T. is 5 feet, 3 inches tall and weighs 150 pounds.
She admits that her memory “is not what it used to be” and
has recently been diagnosed with mild cognitive impair­
ment, but she has no clinical signs of dementia. She has
significant osteoarthritis of her fingers and wrists, as well
as in both of her hips.
Questions to Consider
• To what extent would Mrs. R. T.'s age, height, weight,
and lifestyle impact the selection and maintenance of a
prosthetic foot?
• What K-level best reflects Mrs. R. T.'s functional poten­
tial? Why have you selected this K-level?
• What prosthetic foot design would be most appropriate
for Mrs. R. T.'s first prosthesis?
• What environmental challenges might Mrs. R. T.
encounter if she is able to resume her pre-ulcer activi­
ties? How might the challenges be similar or different
in an urban versus suburban community?
• How does the prosthetic foot that you have chosen
simulate the functional characteristics of a human
foot?
• What are the effects of a prosthetic foot on gait? How
does a prosthetic foot's function during gait differ dur­
ing running?
• What specific recommendations should be given to meet
Mrs. R. T.'s needs and assist her in meeting her goals?
CASE EXAMPLE 2
An Older Adult with Amputation due to Infected
Non-healing Neuropathic Ulcer
Mrs. R. T. is a 79-year-old with long-standing diabetes and
peripheral arterial disease who developed a neuropathic
ulcer at the first metatarsal head of her right forefoot
6 months ago. Despite conservative attempts to heal the
wound using a total contact cast, and subsequent vascular
bypass surgery to restore blood flow to the distal extrem­
ity, the wound failed to heal and osteomyelitis developed.
Mrs. R. T. underwent standard transtibial amputation
2 months ago, managed postoperatively with removable
rigid dressing to protect the surgical site and control
postoperative edema. Although the surgical incision was
slow to heal, her surgeon has determined that it is now safe
to begin prosthetic training, and she has been referred for
prosthetic prescription.
­independently with a transtibial prosthesis. A. J. has accepted
the loss of his left leg and is ready to return to a “normal”
life. He is determined to run again and plans to enroll at a
local college. A. J. currently lives with his mother in a small
one-story house in a rural community and has not driven a
vehicle since the accident.
Questions to Consider
• To what extent would A. J.'s age, height, weight, and
lifestyle impact the selection and maintenance of a
prosthetic foot?
• What prosthetic foot design would be most appropriate
for athletic challenges?
• What environmental challenges might A. J. encounter
on a college campus? What environmental challenges
might he encounter in a rural community?
• How does a prosthetic foot simulate the functional
characteristics of a human foot?
• What social issues might A. J. face as he enters college?
How would a prosthetic foot affect his psychosocial health?
• What specific recommendations should be given to
meet A. J.'s needs and assist him in meeting his goals?

603
Postsurgical Management of Partial Foot and the Syme
Amputation
Edmond Ayyappa and Heather Worden
Partial foot and Syme-level amputations present advantages
and challenges to the patient and the rehabilitation team.
Preservation of the ankle and heel (in partial foot amputa­
tion) and most of the length of the lower limb (in Syme ampu­
tation) has an important advantage of distal weight-bearing
capability: The individual with partial foot or Syme-level
amputation is often able to ambulate without a prosthesis if
necessary. The prosthesis, however, provides protection for
the vulnerable distal residual limb for patients with vascular
compromise and neuropathy.
The length and shape of the residual limb present three
challenges for successful fitting and prosthetic training
for patients with partial foot or Syme amputation: suspen­
sion of the prosthesis on the residual limb, distribution of
weight-bearing forces within the prosthesis, and attachment
and alignment of the prosthetic foot. This chapter defines
the most common partial foot and Syme amputations, and
reviews the prosthetic management options currently avail­
able. Also identified are specific indications and contraindi­
cations for the various prosthetic designs.
PARTIAL FOOT AMPUTATIONS
Until the advent of antibiotics, disarticulation through the
joints of the foot reduced the risk of sepsis and shock and
improved the prognosis for healing compared with amputa­
tions that transected bone. The earliest partial foot amputation
was recorded in 434 bc by the Greek historian Herodotus,1
who told of a Persian warrior who escaped death while in the
stocks by disarticulating his own foot. He hobbled 30 miles to
a nearby town, where he was nursed to health until he could
construct a prosthesis for himself. Later he became a sooth­
sayer for the Persian army but ultimately was recaptured by
the Spartans and killed.
At present, partial foot amputations include a wide vari­
ety of ray resections, digit (phalangeal) amputations, and
metatarsal transections (Figure 22-1). Midfoot amputations
include surgical ablation at the Chopart and Lisfranc levels
(Figure 22-2).2 Chopart disarticulation involves the talocal­
caneonavicular joint and separates the talus and navicular
as well as the calcaneus and cuboid.3 Lisfranc disarticulation
separates the three cuneiform bones and the cuboid bone
from the five metatarsal bones of the forefoot.
The three hindfoot amputations are the Pirogoff, Boyd, and
Syme. The Pirogoff amputation is a wedging transection of the
calcaneus, followed by bony fusion of the calcaneus and distal
tibia with all other distal structures removed. In a Boyd ampu­
tation, the calcaneus remains largely intact rather than being
wedged before arthrodesis with the tibia. Today these ampu­
tations are infrequently performed on adult patients. Neither
provides an easy fit with a prosthesis. The Boyd amputation
has received positive clinical reviews when used in the man­
agement of congenital limb deficiencies in children in which
the amputated limb is shorter than the sound limb.4,5 In this
case, there are usually fewer postoperative complications, such
as scarring and heel pad migration, and less susceptibility to
the bony overgrowth common in children with congenital limb
deficiencies. The Syme amputation is performed more fre­
quently in adults because of the ease of prosthetic management
22
LEARNING OBJECTIVES
On completion of this chapter, the reader will be able to do
the following:
1. Differentiate among the various disarticulation and trans­
action surgeries used when amputation of the forefoot,
midfoot, or rearfoot is necessary.
2. Describe usual gait performance and limitations of indi­
viduals with a partial foot and with the Syme amputation.
3. Compare the advantages and disadvantages of prosthetic
options for individuals with partial foot amputation.
4. Compare the advantages and disadvantages of the various
prosthetic designs for persons with the Syme amputation,
including donning and pressure tolerance.
5. Compare how the various nonarticulating and dynamic
response Syme prosthetic feet mimic the three rockers
of gait.
6. Describe typical static and dynamic alignment variables or
issues affecting gait for patients with a Syme or partial foot
prosthesis.
7. Use knowledge of prosthetic options to suggest prosthetic
prescriptions and plans of care for patients with partial
foot and Syme amputation.

604
Section III  Prostheses in Rehabilitation
at this level (Figure 22-3). Because of the length of the residual
limb in Pirogoff and Boyd amputations, the attachment of a
prosthetic foot lengthens the limb when a prosthesis is worn. A
heel lift on the contralateral sound limb is usually necessary to
counteract this artificially long prosthetic limb.
Proximal partial foot amputations often result in equinus
deformities because of muscular imbalance created by sev­
ered dorsiflexors and intact triceps surae.6–8 Nevertheless,
many individuals with a partial foot amputation function
extremely well. In one survey, physicians and prosthetists
reported that patients with partial foot amputation func­
tion better than those with the Syme amputation.9 Although
surgeons and prosthetists have long supported the Syme
amputation in preference to the Lisfranc or Chopart ampu­
tations, many patients with midfoot amputation achieve
high levels of function. For example, Jack Dempsey, a pro­
fessional football player with a midfoot amputation, set sev­
eral all-time field goal records wearing a custom-designed
kicking boot.10
Gait Characteristics After Partial Foot Amputation
A person with a partial foot amputation typically has vascular
insufficiency, is usually between the ages of 60 and 70 years,
has compromised proprioception and sensation, and has
weak lower limb musculature. After a Syme or partial foot
A
B
C
FIGURE  22-1  Examples of amputations involving the forefoot.
A, This digit (phalangeal) amputation involves disarticulation at
the tarsal–metatarsal joint. More distal digit amputations remove
either the distal phalanx or the middle and distal phalanges. B, In
this complete transmetatarsal amputation, transaction occurred just
proximal to all five metatarsal heads. C, Ray resections involve dis­
articulation of one or more metatarsals and their phalanges from the
tarsal and neighboring metatarsals. Ray resections often require skin
graft to achieve adequate tissue closure.
A
B
C
FIGURE  22-2  In a Chopart amputation (A) there is disarticula­
tion of the midfoot from the forefoot at the level of the talus and
­calcaneus. In a Lisfranc amputation (B) there is disarticulation of the
forefoot (metatarsals) from the midfoot (tarsals). (C) In a transmeta­
tarsal amputation, there is transaction through the length of one or
more metatarsals, usually just proximal to the metatarsal heads.
A
B
C
FIGURE  22-3  A, The Syme amputation involves removal of the
inferior projections of the tibia and fibula and all bone structures
distally while preserving the natural weight-bearing fat pad of the
heel. B, The Chopart amputation preserves the talus and calcaneus.
C, The Lisfranc amputation has disarticulation of metatarsals from
the midfoot.

Chapter 22  Postsurgical Management of Partial Foot and the Syme Amputation
605
­amputation a patient may be able to ambulate without a pros­
thesis but has a loss of the anterior lever arm in ambulation
and an inefficient, somewhat dysfunctional gait. The primary
need immediately after amputation is to protect the remaining
tissue, which is vulnerable to vascular or neuropathic disease.
The neuropathic walker developed at Rancho Los Amigos
Medical Center locks the ankle in a custom-molded, foam-
lined, thermoplastic ankle-foot orthosis (AFO) (Figure 22-4).
A rocker bottom is contoured to promote a smooth rollover
as a substitute for the second and third rockers of gait, and
the orthosis provides optimum protection for the insensate
residual foot. For patients with adequate protective sensation,
the risk of tissue breakdown is less and a custom shoe insert
with in-depth or postoperative shoes often provides adequate
protection.
A review of gait in partial foot case histories showed varia­
tions in single-limb support time directly related to the reduc­
tion of the forefoot lever arm of a partial foot and subsequent
increase in the force concentration on the distal end during
terminal stance, reflected as reduced time in single-limb sup­
port on the limb with amputation (Figure 22-5).11
In a person with a whole foot, a fully intact anterior
lever arm preserves elevation of the center of mass at ter­
minal stance. With normal quadriceps strength and eccen­
tric control, slight knee flexion (15 to 20 degrees) provides
shock absorption as weight is rapidly transferred onto the
limb during loading response (Figure  22-6). Most people
with dysvascular partial foot and a Syme amputation demon­
strate significant weakness of the quadriceps. This functional
weakness threatens eccentric control of the usual knee flex­
ion angle that occurs during loading response. To compen­
sate, the patient may keep the knee extended during loading
response. This strategy shifts the ground reaction force vec­
tor to a position anterior to the knee joint axis, thus reducing
the workload of the quadriceps. Although this compensa­
tory strategy enhances early stance phase stability, it sacrifices
the shock absorption mechanism at the knee and hip joints,
increasing the likelihood of cumulative joint trauma at both
joints (see Figure 22-6, B). Neuropathic impairment of pro­
prioception and sensation may further complicate control of
the knee in early stance. In addition, compromised forefoot
support increases center of gravity displacement. A penalty of
higher energy cost results.
A recent study of the gait of persons with partial foot
amputation included 18 patients with transmetatarsal
amputations, 11 with one or more metatarsal amputa­
tions, 15 with ray resections, and two with either a Lisfranc
or a Chopart amputation.11–13 One portion of the analy­
sis focused on the mechanics of the residual limb rockers.
Partly because of a delay in the forefoot rocker, patients with
all types of partial foot amputations walked with a signif­
icantly slower velocity than control subjects with healthy,
intact feet (Figure 22-7). Peak ankle dorsiflexion was also
significantly delayed for all three partial foot groups com­
pared with those with intact feet. Although the control
group with intact lower limbs reached peak ankle dorsiflex­
ion at a point 43% into the gait cycle, patients with partial
foot amputation did not reach peak dorsiflexion angle until
nearly the halfway point of the gait cycle (Figure 22-8). This
delay in reaching peak dorsiflexion subsequently delays
forward progression over the shortened stance limb and the
transition to double-limb support.
FIGURE 22-4  The neuropathic walker provides maximum pro­
tection for the denervated foot at risk for amputation. The com­
bination of custom-molded multidurometer liner, locked neutral
ankle, and rocker bottom permits a rollover with minimal plantar
pressure and shear.
Level of Amputation
Chopart
45
0
10
20
30
40
50
60
70
80
90
100
Lisfranc
54
54
Trans-
metatarsal
No
Amputation
70
% Gait cycle in single-limb support
FIGURE 22-5  Percent of the gait cycle spent in single-limb support
for patients with midfoot Chopart or Lisfranc amputations and fore­
foot transmetatarsal amputation. Healthy older adults with intact
feet typically spend between 65% and 75% of their gait cycle in
single-limb support.

606
Section III  Prostheses in Rehabilitation
The rise rate of the vertical ground reaction force is the
amount of force that occurs in 1% of the gait cycle and can be
expressed as Newtons divided by the percent of the gait cycle.
After controlling for variation in velocity, the rise rate of the
vertical ground reaction force from mid to terminal stance
(as the force pattern nears its F2 peak) was significantly lower
for all three amputation groups compared with the control
group (Figure  22-9). Peak vertical ground reaction forces
were ­significantly higher for the sound limb than the affected
limb, likely reflecting an abrupt unloading of the partial foot
amputation limb.
The forefoot lever arm of the trailing limb typically pro­
vides anterior support and results in adequate terminal stance
support time (Figure 22-10). This results in appropriate step
length of the advancing limb. By contrast, inadequate ante­
rior support of the trailing limb of the partial foot amputee
reduces the lever arm, resulting in ­premature toe break and
forefoot collapse. The step length of the advancing limb may
be correspondingly reduced (Figure 22-10, B).
FIGURE 22-6  A, During loading in normal gait, knee flexion pro­
vides a significant shock absorption mechanism to protect the proxi­
mal joints. B, The patient with weakness associated with dysvascular
disease avoids knee flexion to increase stability, with a penalty of
increased trauma to the proximal joints as a consequence of repeated
higher impact loading.
Normal quad
strength
Controlled
knee flexion
reduces
joint impact
Impact of
limb loading
A
Weak
quads
No knee flexion
(patient locks
knee to reduce
instability)
Impact of
limb loading
B
Level of amputation
RR
62
0
10
20
30
40
50
60
70
80
90
100
MT
57
61
TM
NC
100
% of normal mean velocity
FIGURE  22-7  Reduced gait velocity in patients with partial foot
amputations. On average, patients walked at 62% of gait velocity of
control subjects with intact lower limbs. MT, Metatarsal amputation
of one to four rays; NC, normal control subjects; RR, ray resection; TM,
complete transmetatarsal amputation.
Level of amputation
0
10
20
30
40
50
60
70
Point of peak dorsiflexion
(% of gait cycle)
RR
51
MT
52
49
TM
NC
43
FIGURE  22-8  For persons with partial foot amputations, maxi­
mum dorsiflexion is delayed during stance phase of the gait cycle.
Although control subjects with intact feet achieved a maximum dor­
siflexion angle at a point 43% into the gait cycle, those with partial
foot amputation did not reach the maximum dorsiflexion angle until
halfway through the cycle. The consequence of this delay is a slowed
forward progression of the body's center of mass and transition
to the subsequent period of double-limb support. MT, Metatarsal
amputation of one to four rays; NC, normal control subjects; RR, ray
resection; TM, complete transmetatarsal amputation.

Chapter 22  Postsurgical Management of Partial Foot and the Syme Amputation
607
An inverse relation exists between surface area and peak
pressure when body weight is loaded on the foot during stance.
This relation is especially important for individuals with par­
tial foot amputation during terminal stance. As the plantar
surface area of the supporting forefoot is reduced, the mag­
nitude of the pressure is increased.11–13 The reduced forefoot
lever arm also creates abrupt weight transfer to the contralat­
eral side and can reduce step length, stride length, and veloc­
ity. Without prosthetic support, the advancing sound-side step
length diminishes. Fear, insecurity, and pain aggravated by
increased pressure near the amputation site collectively create
an abrupt transfer of weight to the sound side, thus increasing
the magnitude of the initial vertical force peak.14
In normal gait, the weight line is positioned more and more
anterior to the knee joint as the gait cycle moves from midstance
into terminal stance and preswing phases (Figure 22-11). As a
result, the limb is held in a passive, energy-efficient extended
knee position, effectively supporting body weight and increas­
ing stability in late stance. The length of the forefoot lever
arm is one of the key determinants of this support. For per­
sons with partial foot amputation, the lever arm of the foot is
greatly reduced, leading to a less-effective, premature loss of
support at the end of stance phase. This shorter lever places
the ground reaction force closer to or behind the knee in late
stance (Figure 22-11, B). Because much of the passive stability
provided by a normal forefoot lever in late stance is absent, the
quadriceps must contract to maintain stance phase stability,
contributing to an increased energy cost of walking for per­
sons with partial foot amputation.
Pinzur and colleagues15 described a functional relation
between gait velocity and the level of amputation at the foot.
As the amputation level becomes more proximal (as the length
of the residual foot decreases), changes in temporal and kinetic
gait characteristics include reduced sound-side step length,
decreased velocity, increased energy cost, and increased verti­
cal load on the sound side. An inverse ­relation exists between
the length of the remaining portion of the forefoot and the
time spent in single-limb support on the amputated side.14
When the level of amputation is proximal to the metatarsal
heads, medial support is lost at loading response. This may
require orthotic “posting” to limit resultant valgus defor­
mity. Patients with partial foot amputation frequently have
plantar flexion contracture develop from muscle imbalance.
Any plantar flexion contracture, in turn, increases pressure
at the distal residual limb during terminal stance, causing
­discomfort, pain, and risk of ulceration.16 A contracture is
even more problematic for individuals with Hansen disease
Level of amputation
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
Peak vertical GRF
(N/% gait cycle)
RR
11.3
MT
11.9
11.0
TM
NC
9.7
FIGURE 22-9  Comparison of peak vertical ground reaction force
(GRF) of the intact limbs of patients with partial foot amputations
and persons without amputation, expressed as Newton divided by
% of gait cycle. MT, Metatarsal amputation of one to four rays; NC,
normal control subjects; RR, ray resection; TM, complete transmeta­
tarsal amputation.
FIGURE 22-10  A, The forefoot lever arm contributes to a normal step
length. B, Reduction of the forefoot support after partial foot amputa­
tion produces a consequent reduction in contralateral step length.
Normal
toe break
Normal
lever arm
Normal
Step length
A
Premature
toe break
Lever arm
reduced
Step length
reduced
B

608
Section III  Prostheses in Rehabilitation
or diabetic neuropathy because they already have compro­
mised sensation.17,18 Shoes worn without prosthetic replace­
ment of the missing forefoot quickly become disfigured,
collapsing at a displaced toe break, further endangering
the vulnerable areas of the residual limb.19 The areas of the
­residual foot most vulnerable to tissue damage during walk­
ing include the distal end, first and fifth metatarsal heads,
navicular, malleoli, and tibial crest. The longitudinal and
transverse arches, the heel pad, and the area along the pre­
tibial muscle belly are pressure-tolerant areas for loading in a
custom shoe or prosthesis.
Prosthetic Management
During the 1800 s, digit amputations were fitted by a wood
or cork sandal with a leather ankle lacer.20,21 Partial foot
amputations were sometimes fitted with a socket and keel
fashioned from one piece of carefully chosen root wood,
the grain of which followed the curve of the ankle. This was
referred to as the natural crook technique. Another com­
monly used historical design incorporated steel-reinforced
leather sockets.22
In recent decades, a wide variety of prosthetic options for
individuals with partial foot amputation have emerged. The
prescribing physician and patient care team must familiar­
ize themselves with the broad array of options available in
prosthetic components and design so that prescription con­
siderations can best accommodate the special needs of each
patient. Because of variability in level of amputation, sensi­
tivity or insensitivity of the residual limb, concurrent foot
deformity, and patient activity, no single prosthetic prescrip­
tion can be used for all patients with foot amputation.23 As
the amputation level becomes more proximal and the length
of the residual foot decreases, prostheses are more likely to
incorporate supramalleolar containment or more superior
support. This is especially true as a patient's activity level
increases. Commonly used prosthetic approaches include toe
fillers placed inside the shoe, a foot orthosis or an arch sup­
port, the University of California Biomechanics Laboratory
(UCBL) orthosis to control heel position, and a boot or slip­
per made of flexible urethane resin (Smooth-On, Easton,
PA). Cosmetic restoration of silicone and several variations
of AFOs are also in common use.
The length and degree of flexibility of the prosthetic fore­
foot affect the anterior lever arm and consequently foot and
ankle motion. The biomechanical goal is to allow anterior
support in the area of the lost metatarsals as well as a con­
trolled fulcrum of forward motion as the foot-ankle complex
pivots over the area of the lost metatarsal heads in the third
rocker of late stance. An additional goal is to minimize pres­
sure at the amputated distal end within the socket or shoe.
Toe Fillers and Modified Shoes
If a simple filler is prescribed, an extended steel shank or
band of rigid spring steel should also be placed within the
sole of the shoe, extending from the calcaneus to the meta­
tarsal heads. The challenge that faces the prosthetist is to
match the appropriate degree of forefoot flexibility to the
needs of each patient. For an energy-efficient and cosmetic
gait, relative plantar rigidity should give way to at least 15
degrees of forefoot flexibility distal to the metatarsal heads.
The extended steel shank is helpful in providing a lim­
ited degree of ­buoyancy that substitutes for the lost ante­
rior support of the foot.24 Stiffening the sole with a spring
FIGURE  22-11  A, Normal energy-efficient passive knee support
in late stance relies on a locked or rigid forefoot that limits further
dorsiflexion at the ankle and a normal forefoot lever arm to maintain
the ground reaction force anterior to the knee during late stance. B,
After partial foot amputation, the reduced forefoot lever arm often
leads to increased quadriceps activity to compensate for reduced
passive knee support and ensure stability in late stance.
Single limb
support
Long lever arm
A
Resultant
passive
knee
support
Locked ankle
limits excessive
dorsiflexion
Single limb
support
Short lever arm
B
No passive
knee support
Increased
quad
activity

Chapter 22  Postsurgical Management of Partial Foot and the Syme Amputation
609
steel shank increases the lever arm support, but often at
the expense of additional pressure on the distal end of the
residual limb.25
For a patient with a more complex partial foot amputa­
tion, a rocker bottom shoe modification distributes force
over a greater area and advances stance more quickly and
efficiently. A curved roll or buildup on the plantar surface
of the shoe encourages tibial advancement while minimiz­
ing weight-bearing pressures on the distal amputated end
(Figure  22-12). For optimal function the plantar contour
of a rocker bottom should follow a radius originating from
the knee joint center but break or roll more abruptly just
distal to the metatarsal heads. Although a rocker bottom
assists rollover, it also compromises symmetry of gait. It is
often prescribed for individuals with chronic pain or in con­
junction with a custom-molded accommodative interface
for those with a neuropathy-related risk of reamputation.
Extra-depth shoes have 6 to 8 mm or more of space inside
the shoe on the plantar surface to accommodate an orthotic
insert or prosthesis and may be useful for patients with digit
or ray amputations.23
Custom-molded shoes, when used in conjunction with a
filler and shank, improve the comfort level and reduce the risk of
ulceration in many dysvascular patients with amputation. They
are not as subject to forefoot collapse, provide major protection
to the endangered foot, and may last longer than stock shoes.26
Custom Shoe Inserts and Toe Fillers
A custom-molded, flexible, plantar shoe insert is one of the
options for individuals with amputation of the hallux or first
ray. This orthotic approach is typically used in combination
with extra-depth shoes. The goal is to provide a flexible ante­
rior extension to compensate for a missing or shortened first
ray to improve the third rocker and yet support and protect
the amputation site during the simulated metatarsophalangeal
hyperextension in late stance and preswing.27 This provides
some relief for metatarsal head pressure, supports the arch,
and probably assists in normalizing the ground reaction force
pattern during terminal stance and preswing. It may incorpo­
rate a toe filler to prevent premature forefoot shoe collapse.28–30
Toe fillers consist of soft foam material such as room-temper­
ature vulcanized elastomer, which fills the voids in the toe box
of the shoe. They provide limited extension of the shoe life and
a moderate degree of cosmesis. They also act as spacers, keep­
ing adjoining toes properly positioned and reducing abnor­
mal motion that can otherwise lead to ulceration. The toe filler
alone provides limited mechanical advantage. A spring steel
shank within the sole of the shoe and extending from mid­
calcaneus to the metatarsal heads can further improve gait.
An alternative to the spring steel shank is a longitudinal sup­
port built into a flexible custom insole. Either support device
must end at the metatarsal heads to allow hyperextension of
the metatarsophalangeal joints. A foot orthotic with arch sup­
port and filler is preferable to the simple filler because it can
be used in different shoes and because it provides plantar sup­
port to an already compromised weight-bearing surface.31
Custom insoles can also be made from a sawdust and epoxy
resin instead of foams and thermoplastics.
The UCBL orthosis, a foot orthosis that encapsulates the
calcaneus, was developed at the UCBL during the 1960s and
was comprehensively described in 1969.32,33 The UCBL ortho­
sis is designed to provide better control of subtalar and fore­
foot position than are custom-made shoe inserts, reducing
motion and thus friction with a closer fit or purchase over the
calcaneus and forefoot (Figure 22-13).34 The UCBL orthosis
design can be effectively incorporated into a custom orthosis
and filler for persons with partial foot amputation.
FIGURE 22-12  A supramalleolar leather lacer, worn inside a high-
top extra-depth shoe with toe filler and rocker bottom, is an effective
prosthetic choice for this patient with a Chopart amputation.
FIGURE  22-13  The custom-molded University of California
Biomechanics Laboratory orthosis attempts to obtain a purchase over
the os calcis and is thought to influence alignment of the subtalar
joint. This patient has ray resection of the hallux and first metatarsal.

610
Section III  Prostheses in Rehabilitation
CASE EXAMPLE 1
A Patient with a Unilateral Hallux Amputation
B. B. is a 49-year-old male with a 14-year history of diabe­
tes. He has controlled his diabetes and has never had any
complications secondary to his diabetic condition. B. B.
noticed that he had stepped on a tack which he removed
approximately 3 to 4 days after the incident. He noted there
that was no pain but he did notice that when he manipu­
lated the great toe, the nail bed looked different than usual,
slightly irritated, and the skin did not behave like the skin
on his other toes. He neglected to receive medical attention
because he was already taking antibiotics for a preexisting
infection. Ten days after the initial incident B. B. underwent
an amputation involving a disarticulation of the first meta­
tarsophalangeal joint of the right foot, resulting in a hallux
amputation (Figure 22-14).
Questions to Consider
• Considering his medical situation and awareness of his
diabetic condition, what concerns might exist about the
residual foot? Which part of the foot is most vulnerable
to future complications?
• What is the primary mechanism for an increase in energy
consumption with any digit amputation, and what is par­
ticularly concerning about a great toe (hallux) amputation?
• How will his shortened foot affect progression through­
out the gait cycle with respect to each phase of gait and
the specific three rockers of the foot?
• What would be the most optimal prosthetic recommen­
dation? What are the primary goals of the prosthesis?
How should the rehabilitation team assist him in caring
for his new amputation as well as in prevention of future
proximal amputations?
Recommendations
After obtaining all additional information from B. B. and from
all medical sources concerning B. B., it was noted that the he
had medically significant bilateral callusing of the heels, as well
as over metatarsals 2, 3, and 5. He had a Morton toe on the left
foot, as well as tight Achilles tendon bilaterally. He was wearing
a size 11 wide shoe but measured for a size 11.5. It was noticed
overall that his right foot was considerably swollen relative to
his left foot. After reviewing his condition the treatment team
recommended extra-depth diabetic shoes with bilateral cus­
tom foot orthoses. The custom foot orthoses consisted of a hal­
lux filler for the right, bilateral deep heel cups, a metatarsal bar
on the left, and bilateral relief at the second metatarsal head
(Figure 22-15). After fitting him with his new shoes and foot
orthoses, he was able to ambulate free of any pain or discom­
fort. He stated he felt like he was able to “walk faster compared
to before the orthoses” as a consequence of the increased stabil­
ity, positioning and comfort that the prescription provided in
comparison to walking without foot orthoses.
FIGURE 22-14  The patient was seen for an initial evaluation post­
operatively. Patient came to the clinic after seeing podiatry, where
his feet were examined and routine maintenance and care was per­
formed. Note the significant bilateral callusing of the heels, as well
as over metatarsals 2, 3, and 5 with areas of treatment (bandages).
FIGURE 22-15  Superior, lateral, and bilateral images of a foot orthosis with the toe filler. The patient
was able to ambulate without pain and stated that with the foot orthoses, as well as his correct fitting
shoes, he was able “to walk faster compared to before the orthoses.”

Chapter 22  Postsurgical Management of Partial Foot and the Syme Amputation
611
Cosmetic Slipper Designs
The slipper, one variation of which has been referred to as
the slipper-type elastomer prosthesis, is fabricated from semi­
flexible urethane elastomer.35 A similar design in silicone may
not provide adequate forefoot support without the addition of
an extended steel shank in the patient's shoe. Another simi­
lar variation is made from a combination of silicone Silastic
(Dow Corning, Midland, MI), polyester resin, and prosthetic
(polyurethane) foam. These designs provide much of the sup­
port and control of the UCBL approach but with added cos­
mesis. These designs may be appropriate for individuals with
transmetatarsal amputations or disarticulations. They are
ideal for swimming or water sports because most are water
impervious, cosmetic, and capable of providing a flexible
whip action, which is useful with swim fins.
Some slipper-type prostheses are cosmetic restorations
made of silicone or vinyl and based on a “life cast,” or an alginate
impression of a human model (Figure 22-16). This prosthesis
is made for patients who consider cosmesis paramount. This
custom prosthesis is most often produced in special manufac­
turing centers and frequently requires a considerable amount
of time for delivery. It can be ordered with hair, freckles, and
in a large variety of skin tones; however, it is most often a less-
than-perfect match when compared with the intact contralat­
eral foot. The patient should always share responsibility in the
color swatch selection. The material itself is easily stained and
changes color with time when exposed to sunlight. The cos­
metic restoration provides little ambulation advantage but does
increase shoe life. It may be appropriate for patients with trans­
metatarsal amputations who place a premium on cosmesis.
Prosthetic Boots
The prosthetic boot, with laced or hook-and-loop material
ankle cuff closures, has greater proximal encompassment to
reduce distal motion and increase control (Figure  22-17).
This design is appropriate for individuals with a Lisfranc or
transmetatarsal disarticulation or amputation. One variation,
the Chicago boot, or Imler partial foot prosthesis, combines
a thermoplastic UCBL-type heel cup with a flexible urethane
prosthetic forefoot.36,37 Other designs incorporate urethane
with a modified solid-ankle, cushion-heel foot; some are fab­
ricated from leather, laminated plastic, or Silastic elastomer
(Dow Corning), Plastazote (Bakelite Xylonite Ltd, London,
UK) combinations, as an insert for a boot, or as an outer boot
with inner filler to accommodate bony prominences.38–41 Such
boots often have an anterior or medial tongue and laces or
some other means of obtaining a firm purchase above the
ankle.42–45 Some variation of the prosthetic boot may be the
general prosthesis of choice for most patients with midfoot
amputations.
Ankle-Foot Orthoses
The AFO is another option for persons with partial foot
amputation. The polypropylene or copolymer shell sup­
ports the plantar aspect of the foot, incorporates the heel, and
extends up the posterior leg to the belly of the gastrocnemius
(Figure 22-18). A circumferential anterior strap stabilizes the
limb in the AFO. As an alternative metal uprights may be
attached to a shoe but have obvious cosmetic drawbacks. The
AFO, whether metal or plastic, provides advantages of the
arch support/UCBL orthosis and boot with maximum con­
tainment and a lever arm for support and substitution of the
rocker mechanism. It offers enhanced stability and control
because of its high proximal trim line. It has been an excellent
solution for many patients with partial foot amputation and
may be the prosthesis of choice for the active patient with a
Chopart or Lisfranc amputation. Supramalleolar thermoplas­
tic or laminated versions are fit with Tamarack (Blaine, MN) or
Gillette (Gillette Children's Specialty Healthcare, St. Paul, MN)
FIGURE 22-16  The life cast prosthesis provides excellent cosmesis
with little or no biomechanical assistance. Without additional rein­
forcement a silicone slipper-style prosthesis does not provide ade­
quate forefoot support.
FIGURE  22-17  A prosthetic boot, composed of epoxy-modified
acrylic resin combined with supramalleolar containment and free
motion, single-axis ankle joints may be helpful at the transmetatar­
sal level. Without the circumferential containment above the ankle,
patients often report joint pain toward the end of the day.

612
Section III  Prostheses in Rehabilitation
joints to provide free plantar and dorsiflexion motion. This
biomechanical solution is popular for the higher activity level
of midfoot amputations. In the presence of acute ankle pain, a
patient with a Chopart amputation was successful with a rear-
entry ground reaction force AFO with rigid ankle.
FIGURE 22-18  A posterior leaf spring andle-foot orthosis with toe
filler and anterior strap is successful for many patients with partial
foot amputation.
CASE EXAMPLE 2
An Individual with a Bilateral Chopart Amputation
A. E. is a 64-year-old man with a 23-year history of periph­
eral vascular disease, diabetes, and recurring foot ulcers. He
underwent a Chopart amputation of his left lower extremity
7 years ago and has since successfully worn an orthopedic
shoe with a toe filler. When needing to walk for long dis­
tances, A. E. uses a straight cane on the right to reduce dis­
tal anterior discomfort of his residual limb. Twelve months
ago a neuropathic ulcer developed on his right plantar
forefoot. Despite conservative management with felted
foam and a Darco heel wedge shoe, the ulcer failed to heal
and ultimately became infected and developed into osteo­
myelitis. He underwent the Chopart amputation without
complication, healed successfully, and now is able to stand
unsupported without shoes or orthosis (Figure 22-19). He
is able to ambulate in shoes with prosthetic fillers; however,
he walks with a remarkably slow velocity and an observable
shortened step length.
Questions to Consider
• Given his medical history, what concerns exist about
the condition of his residual feet? What areas are most
vulnerable to pressure from repetitive loading during
walking in Chopart residual limbs?
• Are there muscle imbalances as a result of a Chopart
amputation that place him at risk for development of
contracture? How should joint excursion of his short­
ened feet be examined? What indicators of muscle
performance are important to assess? What measures
should be used to assess muscle function and strength?
How should any impairments be addressed?
• How will his shortened feet affect his progression through
the gait cycle? Will he have compromise of the first
rocker from initial contact through loading response? Of
the second rocker from loading response through mid­
stance to terminal stance? Of the third rocker in terminal
stance into preswing? Why will there be shortened step
and stride length of the opposite swing limb?
• What are the major goals for prosthetic intervention for
A. E.? What specific recommendations should be made
and why? What is his prognosis for functional ambu­
lation? Should an assistive device be recommended
for long-term use? Why or why not? How should the
­efficacy of intervention be assessed?
FIGURE 22-19  An individual with bilateral the Chopart ampu­
tation is able to stand steadily. Because of the short forefoot lever,
however, the “sway envelope” for dynamic postural control is likely
narrowed. Plantar flexion contracture, if present, would compro­
mise stability and increase pressure at the distal plantar surface of
the residual limb. In this illustration, the patient is wearing several
layers of socks before putting on his prostheses.

Chapter 22  Postsurgical Management of Partial Foot and the Syme Amputation
613
SYME AMPUTATION
In 1867, E. D. Hudson, the surgeon general of the United
States, described the Syme amputation with a litany of super­
latives: “No amputation of the inferior extremity can ever
compare in value with that of the ankle joint originated by
Mr. Syme. Twelve years of experience with that variety of
operation have afforded me assurance that it is a concept
which is complete in itself and not capable of being improved
in its general character.”46
The Syme, or tibiotarsal, amputation is a disarticulation
of the talocrural joint. The forefoot is completely removed,
but the fat pad of the heel is preserved and anchored to the
distal tibia. This allows distal end bearing and some degree
of ambulation without a prosthesis (Figures  22-21 and
22-3).47 It gained popularity during the late 1800 s primar­
ily because the likelihood of survival with this technique
was substantially greater than with other surgical choices,
given the reduced degree of sepsis and shock that occurred
when bone was not severed.48
Two possible problems exist in amputations at the Syme
level: migration of the distal heel pad (which may be surgically
avoidable) and poor cosmetic result (which can sometimes be
partially addressed by removal of the malleoli). For a posi­
tive outcome, the vascular supply must be adequate to ensure
healing. The resurgence of popularity of the Syme amputation
today is from an increased awareness of its energy efficiency
in gait compared with transtibial levels as well as improved
vascular evaluation techniques and medical procedures that
increase the likelihood of more distal primary wound heal­
ing.49,50 In addition, the dramatic weight-bearing potential of
Recommendations
After reviewing his overall gait performance and discussing
his functional needs, the team recommends bilateral rocker
bottom walking boots (Figure 22-20). (Walking boots are
most often recommended for individuals with a single-limb
Chopart amputation.) After prosthetic fitting with bilateral
rocker boots, temporal parameters significantly improved
over orthopedic shoes. Although A. E. had identical cadence
with both conditions (shoe and boot), his step length dra­
matically increased and single-limb support time decreased
when wearing the rocker boots. The overall result is a sig­
nificantly higher gait velocity. Although he initially used
a straight cane on the left for balance and to reduce ante­
rior distal pressures of his newly amputated limb, A. E. is
now able to ambulate functional distances without assistive
devices. He uses his cane only when in crowds to “buy him­
self more space” and reduce the likelihood he will be bumped
or jostled by others.
FIGURE 22-20  This individual with a bilateral Chopart amputa­
tion has been fit with bilateral rocker bottom walkers. The rocker
bottom mimics second and third rockers of the gait cycle, whereas
the extension of the anterior lever provides additional dynamic
stability in gait. These combine to increase stride and step length
for improved functional mobility and a more energy-efficient gait.
FIGURE 22-21  This individual has had a Syme-level amputation
of the left lower extremity and a first ray (hallux) resection in the
right lower extremity. Early weight-bearing before prosthetic fitting
can aggravate migration of the heel pad after the Syme amputation,
even though migration is primarily a function of surgical technique.

614
Section III  Prostheses in Rehabilitation
a well-performed Syme surgery (with or without a prosthe­
sis) has always been considered.51 Pressure-sensitive areas of
the Syme residual limb include the tibial crest, lateral tibial
flair, fibula head, and the bony prominence around the distal
expansion.52,53 Pressure-tolerant areas include the ­midpatella
tendon, medial tibial flair, and anterior tibialis.
Postoperative Care: Walking Casts
To avoid medial migration of the heel pad in the postop­
erative period, gait training and other therapy that involve
weight bearing should be encouraged only after delivery of
the prosthesis. The prosthesis is designed to hold the ankle
and bulbous distal residual in an appropriate relation. A fully
mature residual limb is less likely to displace. Early prosthetic
fitting may involve a definitive prosthesis or a temporary
walking cast with a patten bottom (Figure 22-22). The tem­
porary walking cast may be especially preferred if the patient
has edema, is obese, or has other medical conditions in which
significant volume loss is anticipated. The initial walking cast
should be applied as soon as the sutures have been removed,
usually within 2 weeks of surgery. The successful application
of the Syme walking cast requires a more thorough knowl­
edge base in prosthetics than might be readily appreciated.
Application of a walking cast should be done by a clinician
with a solid prosthetic background.
Prosthetic Management
The prosthesis for the Syme amputation must be strong
enough at the ankle section to withstand the forces of tension
and compression that are produced by the long tibial lever
arm throughout the gait cycle and at the same time provide
an acceptable degree of cosmesis over the bulbous expan­
sion at the ankle. All prosthetic designs strive to encompass
the tibial section above the distal expansion firmly and still
permit donning and doffing. Although prostheses designed
for Syme amputations may be appropriate for Pirogoff and
Boyd amputations, use of such prostheses requires that a lift
be placed on the contralateral shoe to achieve bilateral limb
length symmetry.
Before World War II, most patients with Syme amputa­
tions were fit with anterior lacing wooden sockets or leather
sockets supported by a superstructure of heavy medial and
lateral steel sidebars.53,54 The prostheses most frequently fab­
ricated today include the Canadian, medial opening, sleeve
suspension, and flexible wall (bladder) designs.
Canadian Syme Prostheses
The Canadian Syme prosthesis design was introduced dur­
ing the 1950s as the first major improvement over the tra­
ditional steel-reinforced leather (Figure  22-23).55–58 When
viewing the ankle in the coronal plane, no obvious build­
ups, windows, or hardware is present to increase the ankle
diameter. The Canadian Syme prosthesis has a removable
posterior panel to facilitate donning and doffing. This don­
ning window extends from the apex of the distal expansion,
moving proximal as far as necessary to provide clearance for
the bulbous end.59 Breakage may be higher than with other
FIGURE 22-22  The patten bottom in a walking cast is used when
the clinic team anticipates gross volume changes in a patient with a
Syme amputation.
FIGURE  22-23  The Canadian Syme prosthesis has a posterior
opening access panel that diminishes its strength at the ankle. It may
be inappropriate for heavy-duty wearers.

Chapter 22  Postsurgical Management of Partial Foot and the Syme Amputation
615
Syme prostheses because the ankle area, which undergoes the
most compression and tension during ambulation, is weak­
ened by the ­window cutout around the ankle in the posterior
region. Modern carbon fiber and acrylic lamination materi­
als and techniques have aided in meeting this challenge.60,61
The Canadian prosthesis is a relatively cosmetic approach,
but more recent options have limited its use.
Medial Opening Syme Prostheses
The medial opening Syme prosthesis, also known as the Veterans
Administration Prosthetic Center Syme prosthesis, followed the
introduction of the Canadian Syme prosthesis. Developed at
the New York City Veterans Administration Medical Center
in 1959,62 it has a removable donning door that extends prox­
imally from the distal expansion to a level approximately
two thirds of the height of the tibial section on the medial
side (Figure 22-24).63 Like the Canadian design, the medial
opening prosthesis is relatively cosmetic at the ankle and
compares favorably with the Canadian design. The medial
placement of the donning panel provides much more oppor­
tunity for anteroposterior strengthening of the prosthesis.
All other factors being equal, this design is stronger than the
Canadian and is the approach of choice for many patients
with The Syme amputation.
Sleeve Suspension Syme Prostheses
The sleeve suspension Syme prosthesis is sometimes referred to as
the stovepipe Syme prosthesis because of the cylindrical appear­
ance of its removable liner (Figure 22-25). It is ­constructed with
an inner flexible insert or sleeve that has filler material in the
areas just proximal to the distal expansion.64,65 Before slipping
into the outer shell or socket, the wearer first pulls on the flex­
ible liner.66 The outside sleeve then telescopes within the outer
prosthetic shell. In another version the leather and foam inner
sleeve does not cover the entire residual limb but wraps around
the leg and fills up the void areas above the expansion.67 The
sleeve suspension prosthesis is bulky and not very cosmetic, but
its strength is significantly better because no window is present
to create a structural weakness. It is often chosen for the obese
or very heavy-duty wearer or for the patient with recurring
prosthetic breakage with other designs. It is more adjustable and
forgiving than the other Syme designs and is often chosen when
major fitting problems are anticipated.
Expandable Wall Prostheses
The flexible, expandable wall, and bladder Syme prosthe­
ses, of which several varieties are available, vary more by
FIGURE  22-24  The Veterans Administration Prosthetic Center
Syme prosthesis has a medial opening window, and has long been a
popular approach to fitting the the Syme amputation.
B
C
A
FIGURE 22-25  A, A mature Syme residual limb. The sleeve sus­
pension Syme prosthesis has a full-length liner (B) that slips into the
prosthetic socket (C). This design accommodates adjustments well.
It offers excellent strength at the cost of cosmesis and is an excellent
option for the obese or heavy-duty wearer.

616
Section III  Prostheses in Rehabilitation
materials used than by mechanism of action. All are based
on the concept of an inner socket wall just proximal to the
distal expansion that is elastic or expandable enough to
allow entry of the limb into the prosthesis and still provide
a level of total contact around the ankle once donned.68,69
This design normally requires a double prosthetic wall.
The original bladder Syme prosthesis, described by Marx70
in 1969, obtained expansion by using flexible polyester
resin in the neck area. The more recent Rancho Syme pros­
thesis uses a flexible inner socket, supported by a frame or
superstructure of laminated thermosetting plastic. The use
of flexible thermosetting plastics and silicone elastomer for
expandable wall sockets has gradually eclipsed the use of
Surlyn (DuPont, Wilmington, DE) and other thermoplas­
tics as a material of choice for the inner liner. Expandable
wall Syme prostheses are slightly bulkier and less cosmetic
at the ankle than their Canadian or medial opening coun­
terparts because they require a flexible inner socket and
a rigid exterior superstructure. The fabrication process is
more involved, and fitting adjustments to the flexible inner
socket can be difficult. Creating either a silicone elastomer
or a Surlyn inner socket flexible enough for comfortable
donning and doffing may significantly limit its durability.
The Syme residual limb presents greater pressure distri­
bution challenges to a prosthetist than do other types of
lower-limb prosthetics. A test socket is especially recom­
mended for all Syme prostheses. Because the act of don­
ning and doffing with this system is relatively simple, it
may be the prosthesis of choice for patients with upper
limb dysfunction or cognitive impairment.
Tucker-Winnipeg Syme Prostheses
The Tucker-Winnipeg Syme prosthesis, rarely seen in the
United States, ignores the traditional requirement of com­
prehensive total contact by introducing lateral and medial
donning slots.71 The design is well suited for children. It is
contraindicated for patients with severe vascular disease
and for others who are prone to window edema. A loss of
total contact can also affect proprioception and control of
the prosthesis. In general, the method permits a prosthe­
sis that is relatively cosmetic, easy to don, and not prone
to the noises that are sometimes created by rubbing at the
window covers of the medial opening and Canadian Syme
prostheses.
Prosthetic Feet for Syme Prostheses
One of the challenges in selecting prosthetic components
for patients with a Syme amputation is fitting a prosthetic
foot and ankle bolt within the very limited space under the
residual limb while still maintaining equal leg lengths and
a level pelvis. The rare exception to this is when bilateral
ankle disarticulation has occurred; Syme bilaterality fits
many more choices of foot designs. When there is unilat­
eral Syme amputation, great care must be given to the mini­
mal amount of space available between the distal end and
shoe so that a heel lift on the contralateral side would not
be necessary.
Determining the Prosthetic Clearance Value
In determining whether a particular Syme's foot can
accommodate a patient, the available space between the
distal end of the residual limb and the floor is measured
with the pelvis level, and the anatomical clearance value is
derived. Most Syme feet are attached to the socket by a foot
bolt screwed upward from below the prosthetic heel into a
Syme nut, a threaded disk that is laminated into the socket.
The nut, shaped to approximately match the contours of the
distal residual limb, is approximately ⅝ inches tall, and this
height must be considered when constructing the prosthe­
sis. In addition, the typical Syme foot has a liner with distal
end thickness which is ⅛- to ¼-inch thick. To determine
the applicability of a particular foot for a patient the space
between the bottom of the heel of the foot and the top of
the foot is added to height of the Syme nut and the liner
and end-pad thickness. This measurement is the prosthetic
clearance value.
Nonarticulating Syme Feet
Many prosthetic feet used for transtibial amputation have
been adapted for the Syme amputation. The first was the
solid-ankle, cushion-heel (SACH) foot, patented in 1863 by
Marks and further developed at the University of California
at Berkeley after World War II. It was introduced as a com­
ponent of the Canadian Syme prosthesis in the 1950s. The
Syme SACH is distributed in the United States primar­
ily by Kingsley (Kingsley, Costa Mesa, CA). It is available
in a regular men's shoe heel height and a running shoe
heel height.
The SACH foot design simulates plantar flexion as the
patient rolls over a compressible heel, but because of a rigid
wooden (typically maple) keel, it is neither flexible nor elastic
in late stance. The SACH-type Syme foot was the historical
foot of choice for patients with a Syme amputation in previ­
ous decades, and remains a highly durable, cost-effective foot
design today.
The stationary-ankle flexible-endoskeletal (SAFE) Syme
foot has the advantage of providing a modest inversion
and eversion component of motion, through elasticity of
the forefoot, and is useful for uneven terrain ambulation.
Not including the thickness of the Syme's nut, the SAFE II
(Campbell-Childs, White City, OR) Syme foot requires 1⅜
inches of space between the distal end and the floor or shoe
with pelvis leveled.
Dynamic Response Syme Feet
In the last decade a variety of dynamic response foot designs
have emerged for more active Syme walkers. The Impulse
Syme's Foot (Ohio Willow Wood, Mt. Sterling, OH) has a
Kevlar (DuPont, Wilmington, DE) keel with carbon deflection
toe-spring plates and a weight limit of up to 250 lb (113 kg).
The toe spring is a carbon-epoxy composite. A unique manu­
facturing technique allows carbon fibers to be optimal ori­
ented and avoid wrinkling, buckling, and deformation. The
most interesting part of the foot is alignment adjustability.
Ohio Willow Wood also has a Carbon Copy II Syme foot

Chapter 22  Postsurgical Management of Partial Foot and the Syme Amputation
617
available in two heel heights and with all the toe resistances
and sizes of the standard (non-Syme) Carbon Copy II. The
Carbon Copy II is available with a medium heel density for
patient weights up to 250 lb (113 kg).
The Steplite Foot (Kingsley) provides a compressible heel
design with the buoyancy of a carbon keel. It is quite durable
and applicable to almost every patient with a Syme amputation
because it requires only 1⅝ inches of prosthetic clearance value.
That accounts for 1 inch for the foot itself and ⅝ inch for the
nut and socket thickness. The low-profile version accommo­
dates a typical man's heel height. The “Strider” is made for a
man's running shoe, and “Flattie” is a narrow foot for females
that accommodates a flat heel. The Steplite provides a buoyant
elastic forefoot but, like many Syme feet, is limited in its heel
compression.
Ossur (Aliso Viejo, CA) offers a low-profile carbon Syme
foot version for a very active prosthetic wearer weighing up to
285 lb (129 kg). The same foot can be worn by a low-activity
amputee weighing up to 365 lb (165.5 kg). The Ossur Low
Profile requires 2 inches of clearance from the floor to the
distal end of the socket and is designed with a flexible double-
spring keel. It uses a fenestrated heel that allows greater com­
pression, thus reducing shock. The upper spring bumper is
coated with Teflon (DuPont), which reduces squeaks, a char­
acteristic not uncommon to feet with more than one keel in
the forefoot. Another Syme foot that may be used for patients
up to 500 lbs (227 kg) is the Vari-Flex (Ossur) which requires
only 1¾ inches of space under the socket and is attached
using epoxy filler and lamination.
Another dynamic elastic foot choice for the active indi­
vidual is the Seattle Light Foot (Seattle Orthopedic Group,
Seattle, WA).
Almost all prosthetic feet for Syme prostheses have ankles
that are essentially locked. This characteristics results in
increased work for the quadriceps for controlled knee flexion
during loading response. Incorporation of several degrees of
adjustable articulated plantar flexion (at the risk of increas­
ing the weight of the prosthesis) might improve function for
certain patients.
Alignment Issues
With most prosthetic feet, the small area between the dis­
tal residual limb and floor limits the prosthetist's ability to
refine the special relation between the socket and foot in the
dynamic alignment phase. Adjustable alignment devices,
similar to those available for transtibial prostheses, have his­
torically not been compact enough to fit in the available space
between the prosthetic foot and the end of the socket. Two
component options have been introduced with the goal of
addressing this limitation.
A novel functional alignment device for the Impulse
Syme available from Ohio Willow Wood permits some
degree of dynamic alignment by enabling the prosthe­
tist to adjust the angular positions of the foot during the
fitting process. This Impulse Syme socket adapter kit
(Figure  22-26) allows angular adjustments during the
dynamic alignment phase of between 4 and 8 degrees,
depending on the direction. In addition, ⅛-inch carbon
spacers allow for length additions up to ⅜ inch. It is used
with a 1-inch Syme “dished” nut contoured to interface
with the distal end of the limb.
The SL Profile and the Lo Rider Syme feet (Otto Bock,
Minneapolis, MN) provide angular adjustability by a pyr­
amid. Unfortunately, the height of the pyramid may pre­
clude their use on many patients with a Syme amputation.
The newest and very promising addition is the 1 C20
ProSyme's (Otto Bock), which can be fit on most patients
and is a moderately dynamic urethane carbon fiber foot
for Syme amputees up to 275 lb (125 kg) (Figure 22-27). It
has a wide range of alignment adjustability as well as heel
height changes.
Placing the Syme foot in slight dorsiflexion relative to
the shin section mimics normal gait patterns, encourages a
smooth cosmetic and energy-efficient rollover during stance
phase, and optimizes the weight-bearing potential of the
socket contours. For individuals with quadriceps weakness,
the dorsiflexion angle can be reduced to minimize ­excessive
FIGURE 22-26  The Impulse Foot is a dynamic response foot sys­
tem for Syme prostheses. This foot is particularly useful when pros­
thetic clearance value is limited. The adaptable design allows the
prosthetist to fine tune during the dynamic alignment process to
achieve a gait pattern that is energy efficient and cosmetic. (Photo
courtesy Ohio Willow-Wood, Inc., Mt. Sterling, Ohio.)
FIGURE  22-27  The IC20 Pro Symes, similar to the Impulse, is
unique in its alignment adjustability. Angular and linear alignment
as well as heel height adjustments make it an exceptional choice.
(Photo courtesy Otto Bock, Minneapolis, Minn.)

618
Section III  Prostheses in Rehabilitation
demands on the quadriceps. The telltale clinical sign of exces­
sive demand is trembling of the knee during midstance.
Although early alignment recommendations placed optimal
initial dorsiflexion up to 12 to 15 degrees, current practice is
to set the foot at a smaller angle of approximately 5 degrees.72
The long Syme residual limb does not easily accommodate
itself, cosmetically or functionally, to more than 5 degrees of
dorsiflexion.
Alignment can be significantly compromised when
knee flexion contracture is present. To prevent break­
age and ­premature wear from the anterior lever arm, the
degree of anterior (linear) displacement of the socket
over the foot is generally reduced from that of a trans­
tibial prosthesis.
The Syme socket is positioned in an angle of adduction
that matches the anatomical adduction angle of the tibia.
The adduction of the socket should be positioned to create
as smooth a transition as possible at the ankle and knee so
that the prosthetic foot rolls over with the sole flat on the
floor. The optimal spatial relation in the coronal plane is
one that creates a slight varus moment. Socket adduction
angle, foot eversion angle, and linear displacement affect
the external varus moment at the knee during midstance.
For an efficient and cosmetic gait, the knee must displace
approximately 12 mm laterally at midstance. Insufficient
displacement implicates malalignment, most often at an
inadequate eversion angle. Excessive displacement may
be the result of malalignment or lateral collateral ligament
laxity at the knee. The most successful strategy to address
chronic weight-bearing ulceration at the knee that has not
responded to a silicone liner, or to address major laxity of
the collateral ligaments, is the addition of orthotic com­
ponents (external knee joints and a thigh lacer) to provide
extra support and protection.
CASE EXAMPLE 3
A Patient with Bilateral Dysvascular Syme Amputation
H. P. is a 56-year-old man with an 18-year history of insulin-
controlled diabetes. Eight years ago, a left hallux ray resection
failed to heal and became infected, necessitating a left Syme
amputation. After healing, he became proficient with a Syme
prosthesis, ambulating functional distances without assis­
tive devices. One year ago a large neuropathic wound devel­
oped under the second through fourth metatarsal heads of
his right foot. The wound failed to heal despite several trials
of total contact casting. H. P. and his vascular surgeon agreed
that a Syme amputation on the right would improve his func­
tional status and allow him to return to work as a junior high
school teacher and baseball coach. Amputation occurred
7 months ago, and both residual limbs are well healed. He has
Rancho-style expandable wall Syme prostheses with SACH
feet (Figure 22-28). He has been on an exercise program and
is walking 2 miles per day. He ambulates at a relatively high
speed (120 steps/min) and can walk long distances (more
than 1 mile) at that velocity. He has poor socket fit wearing
10-ply socks. Stress cracks can be seen on the foot. The team
agrees that a change in prosthetic design and components
would improve his function and satisfaction.
Questions to Consider
• Given his medical history, what concerns exist about the
condition of his residual feet? What areas are most vul­
nerable to pressures from repetitive loading during walk­
ing in Syme residual limbs?
• What types of muscle performance at his knee and hip
are important to assess? What measures should be used
to assess muscle function and strength? How will any
impairments be addressed?
FIGURE 22-28  This patient is wearing bilateral Rancho-style
expandable wall Syme prostheses with solid-ankle, cushion-heel
feet. Note the wide diameter at the ankle, necessary to accommo­
date the bulbous distal residual limb during donning. His pros­
theses incorporate a patellar tendon-bearing design at the knee,
and he wears neoprene suspension sleeves as auxiliary suspen­
sion. Note also the widened base of support that he has adopted
to enhance stability in quiet standing. Reflective markers have
been placed at the pelvis, greater trochanter, lateral lower thigh,
lateral prosthesis, lateral malleolus, and the shoe in preparation
for comprehensive gait analysis.

Chapter 22  Postsurgical Management of Partial Foot and the Syme Amputation
619
SUMMARY
This chapter explored the options for prosthetic management
for patients with partial foot and Syme amputations. Because
of the variability in surgical procedures, condition of the resid­
ual limb, and altered biomechanics of the residual limb in gait,
no single best option exists for prosthetic design. Instead, the
characteristics of each patient (weight, skin condition, desired
activity level, and length of residual limb) must be carefully
considered in prosthetic prescription. The goal is to find the
best match of the person's status and needs from the grow­
ing array of prosthetic design options for the partial foot and
Syme amputations. This places an increasing demand on the
knowledge base of medical professionals. More than ever, the
physician, physical therapist, and prosthetist are challenged to
function as a cohesive team, drawing on each other's strengths
to achieve the best possible outcome for each patient.
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Recommendations
The clinical team determines H. P. is a candidate for a
dynamic response foot and a design consistent with an
active lifestyle. The paying agency will want to know the
item description as well as the associated Medicare code.
For example, this amputee is provided with a Syme's pros­
thesis (L5050), test socket (L5618), acrylic socket (L5629),
medial opening window (L5636), expandable wall (Rancho
style) (L5630), extended patellar-tendon bearing brim
design socket (L5632), total contact (L5637), ­suspension
sleeve (L5685), ultralight ­construction (L5940), Freedom
Innovation FS-2000 Low Profile Foot (L5981) and ­alignable
system (L5910), and six prosthetic socks for each limb
(Figure  22-29). After delivery of the limbs, H. P. reports
immediate improvement of long-­distance walking.
FIGURE 22-29  The same individual as in Figure 22-28 after
receiving his new prostheses with dynamic response feet.
Distance between heels has been reduced in both standing
and walking, stride length has increased substantially, and he
reports greater comfort and ease in walking long distances
required for his job and leisure activities.

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Section III  Prostheses in Rehabilitation
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Prosthet. 1974;28(4):59–63.
35. Stills M. Partial foot prosthesis/orthosis. Clin Prosthet Orthot.
1988;12(1):14–18.
36. Imler CD. Imler partial foot prosthesis IPFP—the Chicago boot.
Orthot Prosthet. 1985;39(3):53–56.
37. Imler CD. Imler partial foot prosthesis IPFP “Chicago boot.”
Clin Prosthet Orthot. 1988;12(1):24–28.
38. Wilson MT. Clinical application of TRV elastomer. Orthot
Prosthet. 1979;33(4):23–29.
39. Fillauer K. A prosthesis for foot amputation near the tarsal-
metatarsal junction. Orthot Prosthet. 1976;30(3):9–12.
40. Pullen JJ. A low profile pediatric partial foot. Prosthet Orthot Int.
1987;11(3):137–138.
41. Rubin G, Danisi M. A functional partial-foot prosthesis. ISPO
Bull. 1972;3(7):6.
42. Collins JN. A partial foot prosthesis for the transmetatarsal level.
Clin Prosthet Orthot. 1988;12(1):19–23.
43. Rubin G, Danisi M. Functional partial-foot prosthesis. Bull
Prosthet Res. 1971;10(16):149–152.
44. Staros A, Goralnik B. Lower limb prosthetic systems. In:
American Academy of Orthopaedic Surgeons, eds. Atlas of Limb
Prosthetics. St. Louis: Mosby; 1981:293–295.
45. LaTorre R. The total contact partial foot prosthesis. Clin Prosthet
Orthot. 1987–1988;12(1):29–32.
46. Hudson ED. Mechanical Surgery; Artificial Limbs, Apparatus for
Resections, by U.S. Soldiers. New York: Commission of the Surgeon-
General; 1867 (Library of Congress Call No. RD 756.H86).
47. Jansen K. Amputation—principles and methods. Bull Prosthet
Res. 1965;10(4):19–20.
48. Harris RI. The History and Development of the Syme's
Amputation: Selected Articles from Artificial Limbs. Huntington,
NY: Krieger; 1970.
49. Burgess EM, Romano RL, Zettl JH. The Management of Lower-
Extremity Amputations. Washington, DC: U.S. Government
Printing Office; 1969.
50. Wagner FW. The Syme amputation: surgical procedures. In:
American Academy of Orthopaedic Surgeons, eds. Atlas of Limb
Prosthetics. St. Louis: Mosby; 1981:326–334.
51. Quigley M. The Rancho Syme prosthesis with the Regnell foot.
Clin Prosthet Orthot. 1988;12(1):33–40.
52. Hanger HB. The Syme and Chopart Prostheses. Chicago:
Northwestern University Prosthetic-Orthotic Center; 1965.
53. Wilson AB. Prostheses for Syme amputation. Artif Limbs.
1961;61(1):52–75.
54. Leimkuehler J. Syme's prosthesis—a brief review and a new fab­
rication technique. Orthot Prosthet. 1980;34(4):3–12.
55. Foort J. The Canadian type Syme prosthesis. UCBL Technical
Reports. 1956;30:75–76.
56. Murphy EF. Lower extremity components. In: American
Academy of Orthopaedic Surgeons, eds. Orthopedic Appliance
Atlas. Vol 2. Ann Arbor, MI: J.W. Edwards; 1960:212–217.
57. Voner R. The Syme amputation: prosthetic management. In:
American Academy of Orthopaedic Surgeons, eds. Atlas of Limb
Prosthetics. St. Louis: Mosby; 1981:334–340.
58. Boccius CS. The plastic Syme prosthesis in Canada. Artif Limbs.
1961;6(1):86–89.
59. Department of Veterans Affairs. Syme Amputation and
Prosthesis. Toronto: Department of Veterans Affairs, Prosthetic
Services Centre; 1954.
60. Dankmeyer CH, Doshi R, Alban CR. Adding strength to the
Syme prosthesis. Orthot Prosthet. 1974;28(3):3–7.
61. Radcliffe CW. The Biomechanics of the Syme Prosthesis: Selected
Articles from Artificial Limbs. Huntington, NY: Krieger; 1970.
62. Schwartz RE, Bohne WO, Kramer HE. Prosthetic management
of below knee amputation with flexion contracture in the child.
J Assoc Childrens Prosthet-Orthot Clin. 1986;21(1):8–10.
63. Iuliucci L, Degaetano R. V.A.P.C. Technique for Fabricating a
Plastic Syme Prosthesis with Medial Opening. New York: New
York University Medical School; 1969.
64. Byers JL. Fabrication of Cordo, Plastizote, or Pelite remov­
able liner for closed Syme sockets. Bull Prosthet Res. 1972;
10(18):182–188.
65. Warner R, Daniel R, Lesswing A. Another new prosthetic
approach for the Syme's amputation. Int Clin Info Bull. 1972;
12(1):7–10.

Chapter 22  Postsurgical Management of Partial Foot and the Syme Amputation
621
66. Byers JL. The closed Syme socket with removable liner. ISPO
Bull. 1973;7:4–5.
67. McFarlen JM. The Syme prosthesis. Orthot Prosthet. 1966;
20(3):23–27.
68. Eckhardt AL, Enneberg H. The use of a Silastic liner in the
Syme's prosthesis. Int Clin Info Bull. 1970;9(6):1–4.
69. Meyer LC, Bailey HL, Friddle D. An improved prosthesis for
fitting the ankle-disarticulation amputee. Int Clin Info Bull.
1970;9(6):11–15.
70. Marx HW. An innovation in Syme prosthetics. Orthot Prosthet.
1969;23(3):131–141.
71. Lyttle D. Tucker-Syme prosthetic fitting in young people. Int
Clin Info Bull. 1984;19(3):62.
72. Hanger of England. Prosthesis for Below-Knee Amputation—
Roelite Instruction Manual. Bath, UK: Trowbridges; 1982.

622
23
Transtibial Prosthetics
David Knapp
23
LEARNING OBJECTIVES
On completion of this chapter, the reader will be able to do
the following:
1. Describe the principles underlying current transtibial
socket design.
2. Discuss the pros and cons of the various options for pros­
thetic suspension.
3. Identify key weight-tolerant and pressure-intolerant sur­
faces of a typical transtibial residual limb.
4. Identify key determinants of appropriate transtibial pros­
thetic alignment.
5. Recognize and differentiate the various factors that may
lead to transtibial prosthetic gait deviations.
6. Suggest appropriate strategies to address transtibial gait
deviations.
PROSTHETIC EVALUATION
When evaluating a candidate for transtibial prosthesis, a
comprehensive physical examination that includes a detailed
history interview is essential. The typical physical examina­
tion includes: inspection, palpation, evaluation of muscle
performance—manual muscle testing (MMT); and active
and passive range of motion (ROM) testing—sensory test­
ing, and skin integrity assessment. The interview assesses the
individual's cognitive level, age, health history, vocation, avo­
cation, and home living status. This is also an ideal time to
discuss rehabilitation goals with the individual and the rest
of the clinical team. Setting realistic goals that are challeng­
ing but offer opportunities for incremental victories can go a
long way toward reaching a successful outcome. Each mem­
ber of the clinical team—therapist, physician, person with
amputation, and prosthetist—has information and input
that is useful in the rehabilitation process. The best outcome
will be the result of a collaborative endeavor involving all the
team members. There are no hard-and-fast rules that deter­
mine the rehabilitation potential; the decision to move ahead
with prosthetic fitting is made on an individual basis.
When determining prosthetic candidacy, the individual's
motivation and belief that they are capable of walking are
determinant factors. The rehabilitation process will require
both physical and mental effort, and sometimes involve
working through pain and discomfort. When persons with
amputation have the desire and drive to walk again, there
is very little the team can do to dissuade them. Likewise, if
the person does not believe that walking might be possible,
efforts to enhance recovery may be in vain. Involving the per­
son with recent amputation in an amputee support group, or
requesting a peer visitor from a local prosthetist, can provide
some inspiration and encouragement that therapists, family
members, or prosthetist's who have not experienced amputa­
tion simply cannot offer. Peer visitors are individuals of simi­
lar age, gender, and amputation level that have been through
the rehabilitation process and have successfully reintegrated
into the communities (work, leisure, social) that are impor­
tant to them. Peer visitors are available to spend time with
those with recent amputation and share their first-hand expe­
riences. The Internet hosts a variety of organizations that pro­
vide support and information for persons new to amputation
and prosthetic use, and is a good resource to find local groups
that may be beneficial.
Because amputation is often the result of trauma or dis­
ease, there are often comorbidities that complicate the overall
management of the person with amputation. There are a vari­
ety of options available to the prosthetist to provide a func­
tional prosthesis, even when presented with a residual limb
that is not ideal. Mild to moderate knee flexion contractures
and weakness, for example, may be accommodated for by
altering the alignment of the prosthesis. Skin issues, such as
adherent scarring and eczema, can be addressed by selecting
the appropriate interface material., Pressure on skin and soft
tissue over prominent bones can be relieved by altering the
socket shape. There are also prosthetic options for those with
severe upper-limb dysfunction that will enable the individual
to don and doff his or her prostheses independently. It is only
with careful consideration of the person's complete profile
that the clinical team can recommend the components and
design that will lead to the most optimal prosthetic outcomes.
This clinical analysis includes choosing the features that
are most appropriate for the individual's current status and
their anticipated level of function. The most appropriate
prosthesis is the prosthesis that suits the person's individual
requirements. One size does not fit all: the ideal prosthesis for
one person may be completely useless to another.
Prosthetic design is often a compromise of weight ver­
sus function. Adding features that may seldom be used will

Chapter 23  Transtibial Prosthetics
623
increase the weight and maintenance requirements of the
device. Increased weight leads to increased energy expendi­
ture and premature fatigue.1 On the other hand, exclusion of
features that the person will need on a regular basis may lead
to excessive stresses on the limb, premature component wear
or breakdown, and inefficient gait. The clinical team should
agree on the indivdual's functional goals so that the prosthesis
can be designed to meet them. With the materials and fabri­
cation techniques that are available to contemporary prosthe­
tists, those using a prosthesis can walk farther, with greater a
energy efficiency than ever before.
Generally speaking, persons who undergo ­transtibial
amputations are likely to return to their previous level of
function.2 Those with dysvascular disease, or those who
have additional comorbidities because of injury or disease
need special consideration when developing their rehabili­
tation goals and anticipated level of function. The Center for
Medicare Services created a hierarchical system to classify
the functional potential of persons with lower limb ampu­
tations. This system, referred to by “K-levels,” is summa­
rized in Table 23-1.3 Note that each functional level uses the
phrase “has the ability or potential” in the description. This
highlights the fact that individuals cannot reach their full
potential until their prosthesis is provided and rehabilita­
tion has been successful. For certain benefits to be covered
under Medicare, the individual must be certified by his or
her prosthetist and physician with the appropriate K-level.
This is to prevent prescription of prosthesis with costly
components that person will not be able to manage or use
effectively.
EARLY PROSTHETIC MANAGEMENT
Goals for postoperative management of the transtibial ampu­
tee include (a) to maintain full ROM of the hip and knee,
(b) to facilitate rapid healing of the suture line, (c) to main­
tain or improve cardiovascular and pulmonary condition­
ing, (d) to enhance static and dynamic balance; and (e) to
faciltiate functional strength in the remaining musculature.4
Table 23-2 breaks the lifelong rehabilitation of the amputee
down into nine distinct stages and summarizes the goals for
each stage.
TABLE 23-1  Classification of Functional Potential of
Patients with Lower-Limb Amputations
K-Level
Medicare Functional Classification Level
K0
The patient does not have the ability or potential
to ambulate or transfer safely with or without
assistance and a prosthesis does not enhance
quality of life or mobility.
K1
The patient has the ability or potential to use a
prosthesis for transfers or ambulation on level
surfaces at fixed cadence. Typical of the limited
and unlimited household ambulator.
K2
The patient has the ability or potential for
ambulation with the ability to traverse low-level
environmental barriers such as curbs, stairs, or
uneven surfaces. Typical of the limited community
ambulator.
K3
The patient has the ability or potential for
ambulation with variable cadence. Typical of
the community ambulator who has the ability to
traverse most environmental barriers and may
have vocational, therapeutic, or exercise activity
that demands prosthetic utilization beyond simple
locomotion.
K4



The patient has the ability or potential for prosthetic
ambulation that exceeds basic ambulation skills,
exhibiting high impact, stress, or energy levels.
Typical of the prosthetic demands of the child,
active adult, or athlete.
From Centers for Medicare and Medicaid Services. Medicare
Region C Durable Medical Equipment Prosthetic Orthotic Supplier
(DMEPOS) Manual. Columbia, SC: Palmetto GBA, 2005.
TABLE 23-2  Phases of Rehabilitation for Persons
with Amputation
Phases
Hallmarks
1. Preoperative
Medical and body condition assessment,
patient education, surgical-level
discussion, functional expectations,
phantom limb discussion
2. Amputation
surgery and wound
dressing
Residual limb length determination,
myoplastic closure, soft-tissue coverage,
nerve handling, rigid dressing
application, limb reconstruction
3. Acute postsurgical
Residual limb shaping, shrinking,
increasing muscle strength, restoring
patient's sense of control
4. Preprosthetic
Wound healing, pain control, proximal
body motion, emotional support,
phantom limb discussion
5. Prosthetic
prescription and
fabrication
Team consensus on prosthetic prescription
6. Prosthetic training
Prosthetic management and training to
increase wearing time and functional use
7. Community
integration
Resumption of family and community
roles; regaining emotional equilibrium;
developing healthy coping strategies,
recreational activities
8. Vocational
rehabilitation
Assessment and training for vocational
activities, assessment of further
education needs or job modification
9. Followup
Lifelong prosthetic, functional, and
medical assessment; emotional support
From Esquenazi A, DiGiacomo RD. Rehabilitation after amputation.
J Am Podiatr Med Assoc. 2001;91(1):13-22.

624
Section III  Prostheses in Rehabilitation
One common complication of transtibial amputation
surgery is a loss of full knee extension. Failure to promote
full extension of the tibiofemoral joint can lead to delays
in prosthetic fitting while ROM is restored. If the lack of
knee extension remains, a permanent joint contracture can
alter the prosthetic fitting process. The clinical team gener­
ally encourages rigid dressings that extend well above the
knee and hold the knee in full extension. It has been shown
that rigid removable dressings (RRDs) provide more favor­
able outcomes than elastic bandages when used to control
postoperative edema and to provide protection to the sur­
gical site.5 In some regions, persons with new amputation
are fitted with immediate postoperative prostheses (IPOP)
in the operating room or soon after surgery. The immedi­
ate postoperative prosthesis is intended to serve the same
purpose as the RRD with the additional feature of allow­
ing supported weight bearing for early mobility. Because of
the gross changes to the limb that are anticipated in the first
few days after amputation, the IPOP sockets are designed to
allow some weight-bearing forces direct to the medial tib­
ial flare and patellar tendon because these structures are far
from the surgical site and are not likely to be impacted by
post operative edema. It is important to note that weight
bearing while in an IPOP should be at the level of toe touch
partial weight bearing: Full weight bearing is discouraged as
there is generally not enough area to distribute the full body
weight in a manner that the skin will tolerate for extended
periods of time. Full weight bearing through an IPOP car­
ries risk of damage to the healing surgical construct, and
subsequent delayed healing and prosthetic fitting. Assistive
devices should be used to encourage partial weight bearing
while allowing functional use of the remaining muscles.
The limb will change rapidly throughout the early reha­
bilitation process and the prosthetist and therapist should
closely monitor the fit and alignment of the IPOP. Adding
extra layers of socks to the residual limb will accommodate
early changes in limb volume. Eventually this will become
counterproductive and a replacement socket should be
ordered. Immediate postoperative prostheses are fabricated
with modular components that allow changes to be made
easily.
The surgeon may decide that an IPOP is not an option
for the individual because of factors including excessive soft-­
tissue damage or delayed wound healing, a RRD should be
utilized.6 One variant of the RRD is a custom-molded plaster
socket with a prefabricated plastic collar that encapsulates the
indivdual's limb from the distal end up to approximately two-
thirds of the thigh. There also are other variants, including a
completely prefabricated plastic socket that is adjustable or a
custom-molded plastic socket that is made from a digital scan
of the limb.7 Regardless of the variation of RRD chosen, the
goals are the same: the RRD (a) keeps the knee in full exten­
sion to prevent contracture, (b) protects the limb from exte­
rior trauma, and (c) controls swelling through total contact.
This removable device is worn over at least one layer of cotton
sock and is held in place with Velcro straps (Figure 23-1). It is
also fenestrated to allow airflow and release moisture. The
device can be worn 23 hours a day and can be removed easily
for dressing changes and bathing.
PROSTHETIC PRESCRIPTION
A prosthetic prescription is a detailed description of all the
features of the completed prosthesis: (a) socket design, (b)
skin-socket interface, (c) suspension strategy, and (d) addi­
tional modular components. For transtibial prostheses, the
components are limited to feet, shock absorbers, torque
absorbers, and dynamic pylons.
The socket is the interface between the residual limb and
the prosthesis; all the forces from the ground during gait are
transferred to the limb through the socket. All the forces from
the limb needed to control the motion of the prosthesis are
transferred to the prosthesis through the socket. Much care
and time should be spent on socket design and fitting, as a less
than ideal fit can quickly lead to pain, injury, and lack of func­
tion. The socket design, interface, and suspension need to be
considered together as their functions are often interrelated
and interdependent upon one another. A soft liner, for exam­
ple, can function both as an interface and as the suspension
for the prosthesis. In the same way, a socket that is designed
with a different interface may contraindicate certain suspen­
sion options. Forethought regarding how those three design
elements intermingle will increase the probability of produc­
ing a comfortable and functional prosthesis for the indivudal.
Prosthetic Sock
Supracondylar
Cuff
Cotton
Stockinette
Plaster
Cast
FIGURE  23-1  Cross sectional diagram of a Rigid dressing for
transtibial amputation. Cotton stockinette is placed over the resid­
ual limb, and padding is placed over vulnerable areas (i.e., suture
line, bony prominences). The residual limb is then wrapped with
several layers of plaster-of-Paris impregnated gauze. Rigid dressings
can be used until the suture line closes. They have been shown to
reduce postoperative complications and accelerate the rehabilitation
process. (Reprinted with permission from: Below Knee Prosthetics,
Prosthetics-Orthotics Program, University of Texas Southwestern
Medical Center at Dallas, TX, 1988, p. 7-7).

Chapter 23  Transtibial Prosthetics
625
SOCKET DESIGNS
Early transtibial prostheses were fashioned by hollowing out a
block of wood and attaching metal single-axis knee joints and
a leather thigh corset. The sockets were referred to as “plug-
fit” sockets because they were open-ended and the limb fit
into the socket like a plug fits in a drain. The attached thigh
corsets took advantage of the conical shape of the thigh to
transfer weight proximally and transmit mediolateral forces
to and from the limb. Although many persons with amputa­
tion were quite functional with this system, the lack of con­
tact on the distal end of the residual limb often led to painful
edema in that area. Additionally, the joints and corset added
bulk and weight to the prosthesis and unnecessarily restricted
knee motion.8
Patellar Tendon-Bearing Socket
By the end of World War II, the large number of veterans
who suffered limb loss during combat inspired prosthetists
to experiment with new materials and techniques to improve
prosthetic comfort and function. In 1959, a symposium was
held at the University of California Biomechanics Laboratory
to promote the development of transtibial socket fitting. The
result was the patellar tendon-bearing (PTB) socket design.
This design has been used successfully over the past five
decades to strategically load the limb in areas that are more
pressure tolerant, namely the patellar tendon and medial tib­
ial flare, and relieve the tissue over bony prominences like the
tibial crest and head of the fibula. In most cases, this elimi­
nated the need for proximal weight bearing.9
The main goal of the PTB socket design was to increase
the surface area on the residuum that is available for weight
bearing so as to eliminate the need for the knee joints and
thigh corset. The PTB socket was described as “total contact,”
which meant that there were supposed to be no voids or air
pockets between the limb and socket. This design allowed
weight bearing to occur in any area that capable of support­
ing a load. The term patellar tendon-bearing originates from
the use of a patellar “bar” that is built into the socket at the
level of the center of the patellar ligament, midway between
the patella and the tibial tubercle (Figure 23-2). The socket
is aligned in approximately 5 degrees of knee flexion, which
allows the bar to act as a weight-bearing surface within the
socket. The proximal trim line of the posterior wall is located
just proximal to the patellar bar to stabilize the limb in the
anteroposterior direction and to prevent the limb from slid­
ing to far down into the socket. The posterior trim line should
be lower on the medial side to accommodate the insertion of
the medial hamstring during knee flexion.
The other major weight-bearing surface in the PTB socket
is the medial flare of the tibia. The proximal end of the tibia
broadens out medially and, when stabilized by pressure from
the lateral wall of the socket, can effectively accept loading.
It is necessary to simultaneously create a relief for the fibular
head, which is at the same level, to avoid any pressure on that
bony structure. Filling the distal end of the socket with a com­
pliant foam material provides the slight pressure ­during full
weight bearing, which is necessary to control distal edema.
The medial and lateral walls of the PTB socket extend up to
the level of the adductor tubercle to provide lever arms for
mediolateral stability. The PTB technique is still used success­
fully today, and many modern fitting techniques incorporate
at least some of the attributes of the original PTB design.
Total Surface-Bearing Socket
The total surface-bearing (TSB) socket strives to further dis­
tribute the weight-bearing load over the entire surface of
the limb, even in areas that had been traditionally consid­
ered to be pressure intolerant. Strategic compression of soft
tissue and relief for bony prominences are the tools used to
direct more force into areas of the limb that can tolerate it,
and less force into areas that are prone to skin breakdown.
The intent in designing a TSB socket is to distribute uniform
pressure over the entire surface of the limb.10 It is expected
however, that during a typical step while walking, the pres­
sure in any given location will change from a negative pres­
sure during swing phase to high pressure in stance that, if
sustained, would cause tissue damage. Because the forces on
the limb change quite dramatically throughout the gait cycle,
that dynamic pattern must be anticipated so as to use those
forces to design the reliefs for pressure-intolerant areas; larger
forces means more tissue compression, which require larger
reliefs. The other factor to consider is the density and struc­
ture of the tissues comprising the limb. Tissue properties vary
widely, and there are temporal effects too; muscle tissue, for
example, behaves one way while relaxed and very differently
while contracting. Once they are accommodated, the relative
locations of these tissues within the socket must be preserved;
FIGURE 23-2  The patellar tendon bar and medial tibial flare are
the major weight-bearing areas of the PTB socket; this total-contact
socket design has been used for more than 60 years for a comfort­
able prosthetic fit persons with transtibial amputation. (Reprinted
with permission from: Below Knee Prosthetics Manual, Prosthetics-
Orthotics Program, University of Texas Southwestern Medical
Center at Dallas, TX, 1988, p. 4-2).

626
Section III  Prostheses in Rehabilitation
this not only provides a good environment for the tissues, but
also allows accurate control of the prosthesis.
To fully accommodate the dynamic tissue loading that
occurs in a prosthetic socket, the prosthetist must consider
both the shear and the normal forces on the limb. Shear
forces run parallel to the limb surface and are best mitigated
through the use a socket interface. Interface materials, such
as socks, sheaths, flexible liners, and gel liners, offer a con­
tinuum of shear reduction on the skin surface. The best mate­
rials to minimize shear are those found in gel liners. Normal
forces are those that are applied perpendicular to the surface
of the limb. The socket walls should be contoured according
to the type of tissue in the area and the anticipated loading
patterns. Because there is no way to reduce the force on the
limb without restricting the inidividual's activities, the best
way to reduce pressure is to distribute the forces over as broad
a surface as possible. The actual forces on the limb are a com­
bination of shear and normal forces that occur together in
various proportions.
Ambulation is a dynamic event in which the forces on the
limb are continually changing; for this reason the prosthetic
socket must be designed to function under a variety of load­
ing patterns. The socket must be designed and fitted under
physiologic conditions that match that of the intended use.
Soft-tissue compression will vary with load; the socket con­
tours must reflect the anticipated load so as to prevent exces­
sive loading on bony prominences. Throughout the gait cycle
the forces and moments on the socket and limb change con­
tinuously. There is a flexion moment during loading response,
a varus moment throughout midstance, an extension moment
in terminal stance, and a flexion moment again in preswing
(Figure 23-3). The forces on the limb range from a compres­
sive force of 1.2 times body weight in stance, to a distractive
force slightly higher than the weight of the prosthesis in swing
phase.11 A well-fitting prosthesis must provide tolerable pres­
sure distribution in all of those varied loading conditions.
Soft tissue, muscle tissue, and bone contours must each be
accounted for in a specific way to achieve a good fit. Soft tissue
can tolerate moderate compression so the prosthetist will pre­
compress that tissue in the socket. Muscles can tolerate mild
compression but should be encouraged to contract with each
step so less precompression should be applied. The shape of
muscle tissue changes when it contracts. Flexible materials can
be used over muscle bellies that allow for the geometric vari­
ability. Finally, bony prominences must be given extra volume
within the socket so that when the tissue around them com­
presses during loading, the pressure will not exceed the toler­
able limit.
The load-bearing capabilities of the limb can also be
affected by the surgical technique used for the amputation.
The Ertl procedure, named after Dr. Janos Ertl Sr., is a surgi­
cal procedure that involves creating a bone bridge between
the distal end of the tibia and fibula, as shown in Figure 23-4
(see Chapter 19 for more detail). The goal of this procedure
is to create a tougher, more force-tolerant limb. One prob­
lem that this technique aims to solve is nerve impingement.
Transtibial amputees are prone to nerve compression between
the long bones of the lower leg.12 Forces within the socket
push the tibia and fibula together and compress ­anything
in between. If the tibial nerve is trapped between the bones,
Terminal Stance
Loading Response
Midstance
FIGURE 23-3  The magnitude and direction of the forces on the socket change throughout stance
phase, concentrating pressure in predictable areas. At initial contact and loading response there is an
anterior force at the proximal posterior knee and distal anterior residual limb. At midstance weight
bearing forces create proximal-medial and distal-lateral pressures. At the end of stance phase the
anterior force moves to the proximal anterior knee and distal-posterior residual limb. (Adapted with
permission from: Below Knee Prosthetics Manual, Prosthetics-Orthotics Program University of Texas
Southwestern Medical Center at Dallas, TX, 1988, p. 5-5).

Chapter 23  Transtibial Prosthetics
627
pain can result. By fusing the bones together at the distal end,
the relative motion between them is minimized thereby pro­
tecting the soft tissues that are located between them. Many
individuals who have had this type of surgical procedure
can bear weight directly on the distal end of their limb. This
end-bearing capability allows the prosthetist to distribute the
person's weight differently and potentially provide a prosthe­
sis that does not extend as far proximally; this can increase
comfort over standard weight-bearing areas and increase the
range of knee flexion available to the individual. However, the
increased surgical time and subsequent increase in infection
risk are often cited as reasons to forgo the Ertl procedure sur­
gical technique.13
INTERFACE MATERIALS
The material that separates the limb from the socket is referred
to as an interface. Interfaces play an important role in lower-
limb prosthetics. Interfaces can offer shock absorption, they
can mimic soft tissue to provide an extra layer of cushioning
for those who are bony, and they can help to mitigate shear
forces on the limb. Interfaces influence the hygiene, ease of
donning, and maintenance requirements of the prosthesis as
well. With new materials being developed continuously, there
are many interface options for the prosthetist; a discussion of
commonly used interface materials is presented here.
Hard Socket
Early prostheses were made from hard materials like wood,
which did not offer much cushioning. Persons with amputa­
tion used layers of cotton or wool socks to provide a soft inter­
face between their limb and the hard socket. There are several
advantages to this system: the socket is relatively thin, so the
it is easily concealed under clothing; a clean sock can be used
each day, or changed times throughout the day if needed; the
number and ply of socks can be adjusted to accommodate for
limb volume fluctuation during the day; and the socket itself
is very durable. Because there are no compressible surfaces,
the fit is reliable; it will not become “packed down” in high
pressure areas. It is nonporous, easy to clean, and relatively
maintenance free. It also does a fair job of eliminating shear
as the coefficient of friction between the socks and socket is
relatively low compared to that between the socks and skin.14
This type of socket is most challenging to fit and is not rec­
ommended for mature limbs that have lost much of their
soft-tissue protection over bony prominences. It is also more
difficult to adjust than other socket styles.
Socks and Sheaths
Prosthetic socks can be made from various combinations
of cotton, nylon, wool, Lycra, polyester, and spandex. Some
manufacturers have recently started using silver fibers in their
socks as well to enhance the antimicrobial properties of their
socks and sheaths (Figure 23-5). The prosthetic sock provides
shock absorption, decreases the shear forces on the limb, and
wicks away moisture. To further decrease friction, a nylon
sheath is often recommended as the initial layer and the
thicker socks would be donned over the sheath. The sock also
provides the individual with a method to control socket fit;
as the residual limb matures and shrinks, additional sock ply
may be required to restore the fit and comfort of the socket.
FIGURE 23-4  In the Ertl procedure, a weight-tolerant transtibial
residual limb is constructed by joining the distal ends of the tibia
and fibula with a bone bridge that is constructed from a piece of
the fibula. Radiograph of a healed bone bridge (tibia–fibula synos­
tosis) several months following a transtibial amputation using the
Ertl approach. (Reprinted with permission from Dionne CP, Ertl WJ,
Day JD. Rehabilitation for those with transtibial osteomyoplastic
amputation. J Prosthet Orthot. 2009;21[1]:64-70.)
FIGURE  23-5  Prosthetic sheaths are very thin stocking-like gar­
ments worn between the skin and prosthetic sock or socket liner.
They are used to reduce friction, disperse moisture, and con­
trol bacterial growth. (Reprinted with permission from Kingsley
Manufacturing Co, Costa Mesa, CA)

628
Section III  Prostheses in Rehabilitation
Prosthetic socks come in various ply thicknesses for conve­
nience to the prosthetic wearer; for example, a person can
wear one five-ply sock rather than having to don five individ­
ual single-ply socks. New prosthetic wearers are typically pro­
vided an assortment of one-, three-, and five-ply socks from
which they can select. The socks can be layers one on top of
the other to achieve the appropriate number of ply.
Soft Inserts
Closed cell foam, used because they do not absorb moisture,
can be molded over a model of the limb to create a soft insert.
This insert lines the entire socket and terminates just proximal
to the socket trim lines (Figure 23-6). For increased protection,
a distal end-pad, which is an extra layer of soft material at the
bottom of the insert, can be used to cushion the distal end of
the tibia. Soft inserts provide an extra layer of cushioning that
is needed for more mature limbs that lack adequate soft-tis­
sue thickness. They can be worn over a nylon sheath, which
is a very thin nylon stocking similar to women's stocking, or
over any number of sock ply. Wearing the insert directly over
the skin without a sock may lead to excessive shear and skin
breakdown because of the relative motion between the limb
and insert. Single durometer inserts provide a uniform com­
pression profile whereas multidurometer inserts, made from
layers of different materials with varied properties, can take
advantage of the force-altering characteristics of each layer. For
example, a material that has high plastic deformation might
offer good shock absorption but would wear out very quickly
if used alone. Mating that material with one that has low com­
pression resistance would prevent some of the plastic deforma­
tion and extend the useful life of the insert. Soft inserts that
can deform during the donning process can be used to accom­
modate anatomic irregularities that would not be able to slide
directly into a rigid socket. For example, an insert for a limb
with a bulbous distal end can be made thicker in the narrow
area above the bulge so that the diameter of the finished socket
would not impede donning. Another example is the wedge
needed for supracondylar suspension; this wedge can be inte­
grated as part of the soft insert to facilitate ease of donning.
Flexible Inner Socket
If PTB theory is to direct weight bearing into specific areas
of the limb and away from others, then the flexible inner
socket is the incarnation of that idea. With this system, an
inner socket is made over a model of the limb from a flexible
material that will stretch upon the application of force. Then
a rigid frame is built around the inner socket, corresponding
to areas of the residual limb where weight bearing is desirable.
The result is a socket that flexes away from forces in non–
pressure-tolerant areas, but remains rigid in the force-tolerant
areas. Because flexible sockets in rigid frames can eliminate
compressive forces in any specific area, this system is useful
for persons with particularly bony residual limbs and those
with severe localized sensitivity. They are not recommended
for residual limbs with adherent scarring, however, because
pressure differentials created by the frame tend to amplify the
shear forces on the limb.
Expandable Wall Socket
When the limb is amputated at or below the ankle, the resulting
long residual limb present an interesting challenge to the pros­
thetist. The proximal trim lines of the prosthesis can be lowered
to a more distal position on the limb because there is a long
lever arm for prosthetic control during ambulation. However
the distal residual limbs is larger in diameter than they are in
the more proximally because the malleoli are still present. The
prosthetist can accommodate for a larger distal size by creating
a removable wall in the socket that is replaced after the pros­
thesis is donned, by using a specially designed soft liner, or by
creating an expandable wall socket. The expandable wall socket
is made from an elasticized material that stretches enough for
FIGURE 23-6  This soft insert is partially removed from the supra­
condylar suprapatellar socket. There are pull loops mounted on the
medial and lateral wings to help with doffing the prosthesis. Once
inserted into the rigid socket, the thicker portions of the insert lock
over the femoral condyles and suspend the prosthesis. To remove the
prosthesis, the user must pull up on the insert while pushing down
on the socket. (Photo courtesy of David A. Knapp, CPO, Hanger
Prosthetics & Orthotics, Inc., North Haven, CT)

Chapter 23  Transtibial Prosthetics
629
the individual to push his or her limb through in weight bear­
ing, and tightens up over the malleoli to provide suspension.
This socket is too flexible to attach a foot to, so a rigid frame is
made over the flexible socket with a small space between them
in which the expansion can occur. This is a self-suspending
socket that can be very comfortable for the person. It is diffi­
cult to fabricate this style socket, and it is even more difficult to
make adjustments to the fit once it is fabricated. More informa­
tion on these designs can be found in Chapter 22.
Gel Liner
The term gel liner is loosely used in the field to describe a liner
that is made from a material that exhibits gel-like properties.
There are three basic varieties of these liners: (a) silicone elas­
tomers, which are highly cross-linked at the molecular level;
(b) silicone gels that have a relatively low amount of crosslink­
ing; and (c) urethanes. The properties of these materials vary
and are relevant to the prosthetist and person with amputa­
tion because they directly affect the forces that are transmitted
through them to the residual limb. Of particular interest are
certain properties of gel liners including: coefficient of friction,
compressive stiffness, and shear stiffness. Silicone gels have
the lowest compressive and shear stiffness values; this makes
them useful in reducing compressive loading and eliminat­
ing shear forces on the limb. Lower shear stiffness would be
beneficial for a bony limb, but might compromise stability by
creating excessive motion on a limb that has more biological
soft tissue. Silicone elastomers present the highest compressive
stiffness values, so they are best suited to supporting loading
without deformation. Elastomers would be beneficial for use
on a limb that has a high proportion of soft tissue. Urethanes
show the highest coefficient of friction with skin, a property
that is useful for preventing localized skin tension and shear.15
Understanding these properties, allows the prosthetist to
choose a material that is complementary to the socket design
and effectively leverages the force transmission properties of
the material against the soft-tissue characteristics of the limb.
Gel liners are a key component of TSB sockets. Gel liners
are designed to be worn directly on the skin or over a thin liner
referred to as “liner liners.” Liner liners are thin nylon sheaths
with silver fibers that are meant to be worn between the skin
and gel liner to prevent skin irritation caused by the warm
moist environment of the gel. Although great effort is made
to eliminate relative motion between the limb and socket, a
small amount of motion is unavoidable. Gel liners have a high-­
friction inner surface, where it is in contact with the limb, and
a low friction outer surface where it meets the socket. This
encourages whatever small amount of motion is present to
occur on the outer surface of the liner and minimizes motion at
the liner–skin interface. The colloidal nature of the gel absorbs
the shear that is not dissipated by the liner–socket interface so
that only a small percentage reaches the skin (Figure 23-7).
Incorporation of a locking pin at the distal end of the gel liner
allows the liner to be used for suspension as well. This type of
liner is referred to as a “locking liner” as opposed to a “cushion
liner” that has no pin. The pin mates with a locking mechanism
built into the socket to suspend the prosthesis.
Roll-on liners should fit snugly, but not tightly. As the
liner is stretched, a shear profile is established on the limb.
A tighter fit creates higher frictional forces and if the pres­
sure distribution is not equal, the frictional forces on the skin
will be uneven, leading to blisters and skin problems. This can
occur with a very bony limb, unless the liner is custom made
for the individual. Custom made gel liners are created over
a mold of the residual limb. This is indicated for unusually
shaped limbs, those with deep invaginations, or those that
need specifically located reliefs or cushions.
SUSPENSION
Another important consideration when designing a prosthe­
sis is the method by which the prosthesis is held to the limb;
this is referred to as the “suspension.” When prosthesis is
suspended perfectly, there is no relative motion between the
socket and the limb. When motion occurs because of a faulty
or inadequate suspension system, the limb is subjected to an
entirely different loading pattern. This motion is referred to
as “pistoning” as it bears some resemblance to the motion of
a piston in the cylinder of an internal combustion engine.
Pistoning can lead to pain, skin breakdown, and reduced con­
trol of the prosthesis. Great care should be taken to minimize
motion within the socket. There are several strategies for sus­
pension, they can be used individually as the primary mode
of suspension or more than one technique can be used simul­
taneously to provide auxiliary suspension.
Waist Belt
A waist belt connected by an elastic strap to the thigh cor­
set was used to suspend early transtibial sockets. Waist belts
encircle the pelvis between the iliac crests and the greater
FIGURE 23-7  A cushion liner (left) provides shock absorption and
a low shear interface, the distal connector found on a locking liner
(right) adds a means of suspension as well. (Reprinted with Permission
from Ohio Willow Wood Company, Mount Sterling, OH).

630
Section III  Prostheses in Rehabilitation
­trochanters. These adjustable belts have buckles on the ante­
rior aspect that mated with an inverted Y-strap that is attached
to the socket; this allows them to be donned separately and
then joined together. Because this system crosses the hip and
knee joints, flexion and extension of these joints must be
accommodated by an elastic component. Further accommo­
dation of knee flexion is accomplished by the inverted Y-strap
(Figure 23-8). The Y-strap is fitted over the patella so that the
two arms of the Y move posteriorly during knee flexion to
reduce elongation of the elastic strap. The person can adjust
tension in the strap based upon individual comfort. Pistoning
in the socket is controllable with enough tension in the elas­
tic. Tension in the strap decreases with hip flexion so that the
strap has slack while the person is seated. Hip extension pro­
duces tension in the strap and will aid in limb advancement
as it assists hip flexion in preswing.
Joints and Corset
The joints and corset feature (first discussed in the section
on Socket Design) provides suspension as well as a weight-
bearing element if the thigh corset is properly fitted over the
femoral condyles. A skillfully molded corset can gain pur­
chase over the smaller circumference of the thigh just prox­
imal to the knee joint. The stiff leather corset is fabricated
with either straps or laces that can be tightened as the wearer
dons the prosthesis. This permits the limb to pass through the
corset and then be held securely in position once the corset
is ­tightened. The knee joints, which are typically made from
steel, provide a secure connection to the socket. When the
condyles are prominent, this can serve as the primary means
of suspension and a waist belt is not needed. As the prosthetic
knee joints are positioned slightly posterior to the anatomi­
cal knee joint center, tension in the cuff to decreases over the
condyles as knee flexes, thereby enhancing sitting comfort
(Figure 23-9). The joints and corset system can also include a
posterior check strap that limits full knee extension. This can
be used to eliminate the terminal impact at the end of swing
phase, which can be audible, and to prevent excessive wear on
the prosthetic knee joints. The thigh cuff allows for full func­
tional range of knee flexion but will cause binding in the pop­
liteal fossa when the knee is flexed beyond approximately 110
degrees. Joints and corset may be the suspension of choice for
persons with ligamentous instability of the knee.
Cuff Strap
A cuff strap is a flexible leather cuff that attaches to the
medial and lateral walls of the socket at the same point that
orthotic knee joints would attach, that is, just posterior and
proximal to anatomic knee center (Figure 23-10). The cuff
has an adjustable strap that completely encircles the thigh just
FIGURE 23-8  Waist belt and inverted Y-strap suspends the prosthe­
sis through tension in the elastic strap between the belt and Y-strap.
The strap is fitted to allow hip and knee flexion during swing phase.
The elastic recoil of the strap during swing phase assists swing limb
advancement of the prosthesis. (Reprinted with permission from: Below
Knee Prosthetics Manual, Prosthetics-Orthotics Program, University of
Texas Southwestern Medical Center at Dallas, TX, p. 5-15)
FIGURE 23-9  Thigh corset with knee joints is used when the resid­
ual limb is not capable of supporting the full weight of the patient,
for example, for someone with a very short residual limb, or with
significant scarring or fragile skin over traditional weight bearing
surfaces. It may also be used for persons with mechanically unsta­
ble knee joints secondary to ligamentous insufficiency. (Reprinted
with permission from: Below Knee Prosthetics Manual, Prosthetics-
Orthotics Program, University of Texas Southwestern Medical
Center at Dallas, TX, 1988, p. 4-7)

Chapter 23  Transtibial Prosthetics
631
­proximal to the patella. After the person dons the socket, the
cuff is secured in place so that prosthesis will hang from the
cuff while standing and walking. The anatomic structures that
provide the suspension are the patella and the femoral con­
dyles. To create a strong hold, the medial and lateral walls of
the socket need to be lower than the standard height; because
this reduces mediolateral stability, cuff strap suspension it is
not a good choice for short residual limbs. An elastic com­
ponent may be added to the strap over the patella to increase
sitting comfort. This system is simple, quick to fabricate, and
provides a secure suspension for the prosthesis while accom­
modating an unencumbered angle of knee flexion. The cuff
does not provide any weight-bearing or mediolateral stability.
Cuff strap suspension may be problematic for Persons with
much muscle or adipose tissue arounp the lower thigh
Supracondylar Suspension
Suspension can be achieved by incorporating the femoral con­
dyles completely within the rigid transtibial socket. By extend­
ing the medial and lateral trim lines of the socket approximately
2 cm proximal to the adductor tubercle, the medial–lateral
dimension of the top of the socket can be made narrower
than the knee joint; this prevents the knee joint from moving
upward out of the socket by capturing the femoral condlyes.
Supracondylar suspension also adds significant medial–lateral
stability to the prosthesis by increasing the length of the lever
arm proximal to knee center. This technique, when combined
with a PTB-style socket, is collectively referred to as “PTB-SC.”
This type of socket can be difficult to don because the
width of the proximal opening is smaller than the width of
the condyles. This problem can be addresed in two ways:
either by making the medial wall detachable, or by including
the supracondylar wedge in a soft insert. The first method
uses a steel bar that is formed into the prosthesis. The entire
medial wall of the prosthesis, along with the steel bar, can be
removed for donning. Once the limb is in the socket, the bar
slides back into a channel in the distal portion of the socket
and locks into position with a ball detent (Figure 23-11). The
second method uses a flexible liner that has a wedge built into
it proximal to medial condyle. The rigid socket is fabricated
over the liner such that the medial–lateral dimension of the
proximal end of the socket is equal to the widest dimension
of the knee. This allows donning of the flexible liner first,
then with slight compression of the liner, the limb and liner
together slide into the socket and are locked in pace through
pressure and friction (Figure 23-12).
It is necessary to have at least a 1-cm difference between
the medial–lateral dimension of the knee joint and that of the
thigh just proximal to the adductor tubercle so as to provide a
secure supracondylar suspension. Widening the socket in the
region just posterior to the condyles serves to loosen the grip
over the condyles while seated in 90 degrees of knee flexion.
It is noteworthy to mention that the high medial and lateral
walls of this type of socket are apparent even through long
pants when the knee is flexed. Some individuals might find
this unsightly and unacceptable.
FIGURE 23-10  The cuff strap suspension uses the proximal aspect
of the patella as well as the femoral condyles to achieve suspen­
sion of the prosthesis on the residual limb. (Reprinted with permis­
sion from: Below Knee Prosthetics Manual, Prosthetics-Orthotics
Program, University of Texas Southwestern Medical Center at
Dallas, TX, 1988, p. 4-7)
FIGURE 23-11  One option to ease the process of donning a supra­
condylar or supracondylar/suprapatellar socket is to remove a thick
medial wedge when the residual limb is pushed into the socket. This
wedge is repositioned once the limb is within the socket. A ridge in
the socket along the proximal edge of the wedge holds it in place
during ambulation. (Reprinted with permission from: Below Knee
Prosthetics Manual, Prosthetics-Orthotics Program, University of
Texas Southwestern Medical Center at Dallas, TX, 1988, p. 4-6)

632
Section III  Prostheses in Rehabilitation
Supracondylar/Suprapatellar
By extending the trim line of the anterior aspect of the
PTB-SC socket up to the level of the medial and lateral walls,
the proximal surface of the patella also can be used to assist
suspension (Figure  23-13). The patellar tendon-­bearing–
supracondylar/suprapatellar (PTB-SCSP) socket allows the
formation of a quadriceps “bar” above the patella that pro­
vides suspension and resists hyperextension. The continuous
trim line at the proximal brim also increases the rigidity of the
medial and lateral walls, further enhancing suspension. The
advantages and disadvantages of this variation match those
of the PTB-SC with the exception that it is even more visible
under clothing when the knee is flexed.
Sleeve
One of the most versatile means of suspending a prosthesis is
with a knee sleeve. A suspension sleeve provides suspension
through two biomechanical principles: friction and vacuum.
The sleeve extends approximately 20 cm proximal and distal
to knee center, and is fitted over the proximal end of the pros­
thetic socket (Figure 23-14). The sleeve should fit snugly but
not hinder circulation. Sleeves can be made from a variety of
materials, depending upon the goals of the prosthetic design.
Neoprene and elastic fabric are common materials used for
sleeves because they contour nicely to the anatomy and pro­
vide a high coefficient of friction with the skin. These sleeves
FIGURE  23-12  Another option for donning supracondylar or
supracondylar/suprapatellar sockets is removal of the medial wing of
the socket. This allows the wide condyles to pass through the narrow
proximal dimension of the socket. The medial wing is repositioned
after donning; the metal flange holds the medial wing in place, to
achieve the proximal purchase over the femoral condyles used to
suspend the prosthesis. (Reprinted with permission from: Below
Knee Prosthetics Manual, Prosthetics-Orthotics Program, University
of Texas Southwestern Medical Center at Dallas, TX, 1988, p. 4-6)
FIGURE 23-13  The quadriceps bar of the patellar tendon-bearing–
supracondylar/suprapatellar socket resists knee hyperextension and
enhances suspension. It also stiffens the wings to improve purchase
over the condyles, further enhancing suspension of the prosthesis
on the residual limb. (Reprinted with permission from: Below Knee
Prosthetics Manual, Prosthetics-Orthotics Program, University of
Texas Southwestern Medical Center at Dallas, TX, 1988, p. 4-4)
FIGURE 23-14  Roll on knee sleeves provide a fairly cosmetic, low
profile, versatile means of suspension. Sleeves use friction against
the shell of the prosthetic socket distally and the wearer's skin prox­
imally to suspend the prosthesis on the residual limb. (Reprinted
with permission from: Below Knee Prosthetics Manual, Prosthetics-
Orthotics Program, University of Texas Southwestern Medical
Center at Dallas, TX, 1988, p. 4-9)

Chapter 23  Transtibial Prosthetics
633
use friction only to suspend the prosthesis because they allow
for air to flow through them, in and out of the socket. This
is useful for dissipating perspiration and keeping the limb
cooler, but it also allows undesirable motion to occur between
the socket and the limb. Over time, this can lead to pain and
skin breakdown. The sleeve can be worn over a sock, which
can be good for hygiene; however, this will affect the coef­
ficient of friction between the sleeve and the limb, which
could lead to suspension failure. Sleeves permit functional
ROM for the knee, but because they bunch up in the popliteal
fossa, they can restrict knee flexion beyond approximately
100 degrees.
Suction
Modern sleeves are referred to as “sealing sleeves” because
they are made from nonporous materials that seal the proxi­
mal end of the socket against the skin so that no air can flow
into, or out from, the socket. This creates a suction suspen­
sion. One-way air valves are commonly used in conjunction
with sealing sleeves to allow air that is trapped during don­
ning to escape from the socket. Sealing sleeves provide excel­
lent suspension when combined with a TSB socket style.
Once the socket is sealed, very little pistoning can occur
because there are no voids between the limb and socket. For
the sleeve to seal, the sleeve must touch the skin directly for
at least the top 5 cm. The skin must be free from deep scars
or invaginations in that area, as they would provide a path
for air to enter under the sleeve. Because the sealing sleeves
rely on an airtight seal to function, they are highly suscep­
tible to failure as a consequence of leaks. Even a small hole in
the sleeve can allow air to flow into the socket, defeating the
vacuum and impairing suspension. Although sleeves are not
very durable, they can be replaced without any special tools
or equipment.
The soft tissue of the residual limb behaves like a incom­
pressible fluid. For the limb to move within the sealed vol­
ume of the socket, the volume of the limb itself would have
to change. This can only happen if fluid moves into or out
from the limb through the bloodstream, a process that is too
slow to be accomplished within the short interval of swing
phase. Therefore, the cyclic alteration between compres­
sion in stance and tension in swing slowly draws fluid into
the limb and pushes it back out, assisting normal circula­
tion. Suction suspension may provide a means for improv­
ing healthy circulation in the residual limb and controlling
limb volume.
Locking Liners
The first references to locking liners involve the use of a roll-
on silicon liner, referred to as an “Icelandic roll-on suction
socket” (Iceross).16,17 The use of the term suction for this type
of suspension is incorrect, however. The liner is primarily
held on by friction because it is not possible to maintain a
vacuum within a flexible structure. If friction is eliminated
through the use of a lubricant, the liner can be pulled off the
limb. It is more accurate to describe this type of suspension as
a locking mechanism. These roll-on gel liners are compliant
enough to contour nicely to the shape of the residual limb and
include a threaded hole at the distal end. This hole serves as a
point of attachment for the suspension hardware.
There are three basic options for the hardware:
1. Early sockets used a ring that was screwed into the distal
end of the liner. When the ring came through a special
opening in the distal end of the socket, the prosthetic
wearer could pass a thin bar through the ring so that
it could be retracted back into the socket. This system
is still good for individuals who have difficulty doffing
the prosthesis because it allows them to remove the bar
and then use both hands to push the socket off. This
system requires additional clearance under the limb to
accommodate the diameter of the ring and the associ­
ated attachment fixture. The bar is also a separate com­
ponent, so it can easily get lost. The individual should
be instructed to store the bar in the prosthesis and take
it out only during the donning process.
2. Difficulties with the ring gave rise to using a strap that
is manually fed through a hole in the distal end of the
socket and then secured to the outside of the socket
(Figure 23-15). The strap must be of sufficient length
to be put through the hole before the limb enters the
socket. This eliminates the need to carefully align the
sleeve during donning as the limb will be drawn down
into the socket by tension in the strap. It also eases don­
ning force required to push into the socket because the
limb elongates and decreases in girth under tension. As
no locking mechanism is mounted on the distal end, no
additional clearance is needed, leaving precious space
for other components. One variant of this system uses
a lanyard and a special lock mechanism to secure the
lanyard in the distal end of the socket, the lanyard is
permanently attached to the locking mechanism so it
needs to be disconnected from the liner each time the
liner is taken off.
3. Most modern sockets use a pin-and-lock mechanism.
This pin can range from approximately 3 to 10 cm in
length. It works in conjunction with a locking mecha­
nism built into the distal end of the socket that engages
when the individual dons the prosthesis. Some wear­
ers experience frustration with this as it can be diffi­
cult to align the pin so that it engages with the locking
mechanism. To remove the prosthesis, the prosthetic
wearer must disengage the pin manually while push­
ing the socket off with the other hand. There are sev­
eral variants of locking mechanisms: some offer an
audible “click” to indicate that the pin has engaged but
will only lock in a limited number of positions, others
use a clutch mechanism or a smooth pin that allow for
an infinite number of locking positions. Ideally, only
one position should be needed, that is when the limb is
positioned correctly in the socket. However, as an indi­
vidual's limb volume varies throughout the day, it is not
uncommon for there to be an additional “click” or two
as they spend more time weight-bearing in the prosthe­
sis (Figure 23-16).

634
Section III  Prostheses in Rehabilitation
Locking liners allow some pistoning to occur.18 The amount
of motion can be dramatic when loose tissue is present at the
distal end of the residual limb. As the limb is lifted off the
ground in swing phase, the weight of the prosthesis pulls on
the pin causing the liner and limb to elongate in length and
contract in girth. This effect is most apparent at the distal
end. This “milking” motion creates unnecessary stress on the
distal end of the limb and can lead to pain, edema, and skin
breakdown.19 This is especially problematic for limbs with
adherent scar tissue as the liner will attempt to pull the tissue
away from the bone. This type of suspension is not ideal for
a newly amputated limb as the distal end is not fully healed.
This problem can be averted if suction, rather than the pin, is
used to hold the liner to the socket wall.
Semirigid Locking Liner
A semirigid locking liner is used to combine the convenience
of a locking liner with the benefits of full suction suspension.
The indivdual first dons an interface, which can be a sheath,
sock, or cushion gel liner that the prosthesis was designed to
fit over; then puts on a thin flexible custom molded socket that
has a locking liner rolled over it; and finally steps into the rigid
frame to engage the locking mechanism. The locking liner seals
the limb in the flexible socket and virtually eliminates piston­
ing of the limb within the socket. Because the locking liner is
under the rigid frame rather than stretched over it, the life of the
locking liner is greatly extended. Having the socket under the
liner prevents deformation of the locking liner so that piston­
ing is virtually eliminated and the distal tissue is protected. To
further enhance the suction of this system, an expulsion valve
can be incorporated into the flexible socket; this allows any air
that is trapped in the socket during donning to be removed
(Figure 23-17). This one-way valve provides a path for air to
move from inside the socket to the outside of the locking liner.
Wearing a sock or a liner that has a fabric exterior helps any
remaining air to migrate toward the valve and out of the socket.
Elevated Vacuum
As the advantages of suction suspension are clearly docu­
mented in the literature,20,21 there has been considerable inter­
est in using external vacuum pumps to increase the level of
suction (decrease the pressure) within the socket. These sys­
tems are referred as “elevated vacuum.” Pumps can be either
electric (battery-operated), or mechanical. The mechanical
pumps use the natural cycle of compression during stance
FIGURE 23-15  An example of a distally mounted strap or lanyard
that can be used to pull the limb, within its liner, into the socket.
(photo courtesy of David A. Knapp, CPO, Hanger Prosthetics &
Orthotics, Inc., North Haven, CT)
FIGURE 23-16  An example of the pin that is attached to the liner,
and the locking receptacle incorporated into the distal socket for a pin
lock suspension system. Pin locks are extremely popular because of
their effectiveness and relative ease of use. (Photo courtesy of David A.
Knapp, CPO, Hanger Prosthetics & Orthotics, Inc., North Haven, CT)

Chapter 23  Transtibial Prosthetics
635
and distraction during swing to pull air from the socket dur­
ing gait. Electric pumps have the added benefit of being able
to accurately control the level of vacuum within the socket
by turning on and off at preset thresholds (Figure  23-18).
Elevated vacuum maintains limb volume by preventing
fluid loss that occurs during prolonged weight bearing.22
The elevated vacuum environment within the socket leads
to decreased motion, and therefore to fewer skin problems,
improved prosthetic control, better balance, and enhanced
comfort.18 It has also been shown that elevated vacuum
sockets have lower peak pressures and lower impact forces
than traditional suction sockets.23 To achieve elevated vac­
uum, a sealing sleeve is required to prevent air from entering
through the proximal end of the socket. Some wearers report
a decrease in the amount of available knee flexion once the air
has been evacuated from the socket; this is likely caused by
tension in the sealing sleeve as it spans the entire knee joint.
IMPRESSION TECHNIQUES
The first step in creating a well-fitting socket is capturing an
accurate impression of the residual limb. This can be done in
a variety of ways ranging from plaster bandages to noncon­
tact optical scanners. Each technique has its own set of advan­
tages and disadvantages and there is no one best method for
every limb. All methods share the common goal of capturing
a model of the limb that accurately represents the location
and geometry of each aspect of the limb. Capturing a static
impression of the limb is quite simple and any method will
suffice if done properly. The challenging task is to capture the
dynamic nature of the biological tissue by compressing the
soft tissues during the process to simulate the conditions that
will be on the limb during weight-bearing.
Hand Casting
During hand casting, the limb is gently wrapped with a plas­
ter bandage and the prosthetist pushes in key weight-bearing
areas while the plaster is setting up. How much compression
is needed and which areas to compress are determined based
on the prosthetist's individual knowledge, skill, and experi­
ence. Multistage casting procedures involve molding spe­
cific regions of the limb individually and then joining them
together once the individual sections are set up. This allows
the prosthetist to position the limb in multiple postures dur­
ing casting to capture unique features; for example, the inser­
tion of the hamstrings can be molded during active knee
flexion when they are most prominent (Figure 23-19). For
more details about casting, the reader is referred to Chapter 6.
Pressure Casting
Another way to precompress the tissue is to use a pressur­
izing technique.24 This involves placing the limb into a vac­
uum or pressure chamber while the plaster is setting up
(Figure 23-20). A vacuum chamber is typically a latex blad­
der that is pulled over the wet cast and sealed on the thigh.
A vacuum pump attached to the distal end removes all the
air between the cast and bladder; this allows the atmospheric
pressure to compress the limb up to approximately 14 psi.
Alternatively, a pressure chamber is a clear cylinder with a
FIGURE 23-17  Close-up of valve on the distal end of flexible socket
of the semirigid locking liner system. This system takes advantage of
the benefits of full suction and the convenience of a locking mecha­
nism. (Photo courtesy of David A. Knapp, CPO, Hanger Prosthetics
& Orthotics, Inc., North Haven, CT)
FIGURE  23-18  This figure shows a microprocessor controlled
device that draws air out of the socket to maintain elevated vacuum
necessary for effective suspension of the prosthesis on the resid­
ual limb. Electronic vacuum pumps are reliable and can accurately
maintain specified levels of vacuum. (Reprinted with permission,
Hanger Prosthetics & Orthotics, Inc., Austin, TX)

636
Section III  Prostheses in Rehabilitation
latex bladder attached. The limb, with the unset plaster wrap,
is placed in the bladder and air is pumped into the space
between the cylinder and bladder; pressure in the cylinder
can be increased to 30 to 40 psi, providing additional com­
pression. In either method, the differential pressure between
the limb and the environment serves to apply uniform pres­
sure over the entire surface of the limb. This leads to the most
tissue compression in the softest areas and the least amount
of tissue compression in the bony areas. The amount of dif­
ferential pressure required will vary with the indivdual's
weight, and the prosthetist will use the least amount of pres­
sure required to achieve the optimal fit. Once the plaster has
hardened, the pressure is released and the limb is removed
from the chamber.
Optical Scanning
Optical scanners can be used to capture the three-­dimensional
external shape of the limb to within 1 mm of accuracy
(Figure 23-21).25 They are quite useful in situations when cast­
ing is impossible or impractical such as immediately following
surgery or with bulbous limbs that cannot be removed from a
plaster cast without cutting or distorting the cast. Digital mark­
ers and alignment lines can be attached to the virtual model to
reference the location of bony landmarks and pressure sensi­
tive areas. Although it is not possible to compress the skin by
hand while scanning because the hand would block the view
of the surface, the isobaric techniques described in the previ­
ous paragraph can be used to precompress the soft tissue.
ALIGNMENT
Alignment refers to the spatial orientation of the prosthetic
socket relative to the foot. This alignment will influence
the magnitude and direction of the ground reaction force
throughout the gait cycle. There are four goals in prosthetic
alignment: (1) facilitating heel strike at initial contact; (2)
providing adequate single limb stability during stance phase;
(3) creating smooth forward progression (rollover) during
the transition from early to late stance phase; and (4) insuring
adequate swing phase toe clearance.26 These goals are reached
through dynamic alignment of the prosthesis, during which
the person walks on a prosthesis that is fitted with an adjust­
able device that allows for alignment changes in all three
planes. Although “normal” gait is not a goal, modern com­
ponents do allow many persons with transtibial ­amputations
FIGURE 23-19  Three-dimensional image of a limb captured with
optical scanner during the prosthetic prescription process. This
computer model of the limb's surface is accurate to within 1 mm.
(photo courtesy of David A. Knapp, CPO, Hanger Prosthetics &
Orthotics, Inc., North Haven, CT)
FIGURE 23-20  Pressure casting provides an isobaric environment
to pre-compress the tissue and achieve an optimal socket fit. This
figure shows the flexible pressure chamber and the pump that is used
to increase the pressure during casting. (Reprinted with permission
from Ossur Americas, Foothill Ranch, CA)
FIGURE 23-21  An example of a noncontact optical scanner uses
a laser to capture a three-dimensional image of the surface of the
limb. It is particularly useful in applications where casting is con­
traindicated. (Photo courtesy of David A. Knapp CPO, Hanger
Prosthetics & Orthotics, Inc., North Haven, CT)

Chapter 23  Transtibial Prosthetics
637
to evade detection of gait abnormalities or deviations by all
but the most skillful gait observers. Prosthetic alignment can
also be used in conjunction with socket fit to address pres­
sure issues within the socket. Because of this socket fitting
and dynamic alignment must occur simultaneously. Effective
fitting and alignment requires an iterative process as chang­
ing one aspect can affect many others. The end result is often
a compromise. For example, the foot may require excessive
dorsiflexion in order for the person to achieve sufficient swing
clearance, even though this may contribute to an higher than
optimal knee flexion moment during loading response. The
prosthetist must understand biomechanics of the limb and
gait cycle and weigh these factors appropriately to make the
best decisions.
The modular components that connect the socket, pylon,
and foot allow the prosthetist to make angular changes to the
alignment. Socket flexion or socket extension refer to tilt­
ing the proximal end of the socket forward or backward in
the anteroposterior direction respectively. Socket abduction
moves the proximal end of the socket medially while socket
adduction moves it laterally. Adjustments around the ankle
can be described with standard anatomic terminology: inver­
sion, eversion, plantarflexion, and dorsiflexion. Changes to
the alignment can refer to the motion of the socket relative
to the foot, or vice versa. Dorsiflexing the foot for example,
causes socket flexion, while everting the foot leads to the
same motion as adducting the socket.
The socket can also be shifted medially or laterally in the
frontal plane and anteriorly or posteriorly in the sagittal plane,
these are referred to as linear changes. These, too, are relative
changes; a lateral shift of the socket for example, is equal to a
medial shift of the foot. This type of adjustment is useful dur­
ing static alignment to ensure that the foot is directly under
the indivudal's knee. Linear adjustments can be made by either
using a special component that permits this type of shift, or
by using a pair of standard pyramid connectors and making
equal but opposite angular adjustments (Figure 23-22).
Bench Alignment
The first step in the alignment of a transtibial prosthesis is to
position the socket in what is known as “bench alignment.”
This is the alignment that serves as the starting point for the
dynamic alignment process. Standard bench alignment has the
socket in 5 degrees of flexion and 5 degrees of adduction while
the top of the prosthetic foot is level in both the frontal and sag­
ittal planes and the medial border of the foot is parallel to the
line of progression. When viewed in the sagittal plane, a plumb
line should fall from anatomic knee center and pass through
the foot at a point one-third of the foot length from the back of
the heel. In the frontal plane, the line should go from midpa­
tella through the center of the heel. The reason for the 5 degrees
of socket flexion is to elongate quadriceps, muscles slightly so
that they are better prepared to accept the full weight of the
body and to aid in shock absorption during loading response.
The 5 degrees of adduction ensures that the foot is sufficiently
inset to create the appropriate varus moment during stance;
this properly loads the proximomedial and distolateral aspects
of the limb that are best able to carry those forces. Standard
bench alignment is not used when joint contracture or defor­
mity is present; instead, the actual limb alignment is marked
during the casting procedure and that alignment is used as the
starting point in the dynamic analysis.
Height
Once the prosthesis is bench aligned, the person dons the
prosthesis, and stands with equal weight bearing on both
lower extremites. The first measurement examines the length
of the prosthesis. The goal is to achieve relatively equal leg
length, comparing the intact and prosthetic limbs There are
two accepted ways to assess the height: statically and dynami­
cally. In a static assessment, the individual is asked to stand
with feet shoulder-width apart, knees fully extended, and
bearing equal weight on either limb. The distances from
each iliac crest to the floor can be measured and compared.
FIGURE 23-22  The adapter under the socket allows the prosthetist
to slide the socket anteriorly/posteriorly, and medially/laterally, with
respect to the prosthetic foot position, during dynamic ­alignment.
This socket in this image is shifted approximately 1.5 cm anteriorly
(left). (Photo courtesy of David A. Knapp, CPO, Hanger Prosthetics
& Orthotics, North Haven, CT)

638
Section III  Prostheses in Rehabilitation
An alternative is to evaluate whether left and right iliac crests
appear to be level. The measurement should not be taken
in the supine position because the length of the prosthesis
changes during weight bearing as a consequence of flexion
of the dynamic components and compression of the inter­
face material. In a dynamic assessment, the person is asked
to walk and the entire body is observed, especially the head
and torso. Many factors will affect the motion of the head and
torso so it is best to focus only on gross asymmetries that can
be corrected by changing the length of the prosthesis. When
the static and dynamic height measurements are different, a
clinical decision is made to determine the optimal length for
the prosthesis to provide the best function for the individual.
It is not uncommon for the prosthesis to be up to 1 cm shorter
than the sound limb under static conditions.
Dynamic Alignment
Alignment changes can be made with the standard modular
connectors that are used to fasten the components of the pros­
thesis together. A standard pyramid connector (Figure 23-23)
can be set anywhere within an approximately 20 degree arc of
adjustability. This means, for example, that the socket can be
flexed up to 10 degrees or extended up to 10 degrees from the
neutral starting position. This is accomplished by loosening
one screw and then tightening the opposite screw the same
amount. Each pyramid permits adjustment in two orthogo­
nal planes. For simplicity, the prosthetist will typically rotate
the pyramid so that the adjustable planes are aligned with the
frontal and sagittal planes. Transverse plane rotation is almost
always infinitely adjustable; the standard connectors can
accommodate any foot position. When the dynamic align­
ment differs greatly from bench alignment, it may be necessary
to add a special alignable component to the prosthesis. This
component will accommodate a larger window of adjustment
and allows for linear changes in addition to angular changes.
For example, the foot can be inset relative to the socket sim­
ply by sliding the foot medially and retightening the connec­
tor. This device is to be used during the dynamic alignment
only and then removed during the final fabrication procedure.
Small linear adjustments can also be made without that special
component by performing equal but opposite angular adjust­
ments on two adjacent pyramid connectors; however, this
method will simultaneously affect the height of the prosthesis.
During the dynamic analysis, the prosthetist will ask the
individual to walk in a safe environment, typically within
the parallel bars, and observe the motion of the prosthesis
throughout the gait cycle. Adjustments are made to minimize
gait deviations and create a smooth and stable gait pattern. The
prosthetist will attempt to create an energy efficient stride by
minimizing the horizontal and vertical excursion of the center
of mass. Goals for the optimal alignment are stance stability,
swing clearance, equal step length, and energy efficiency. Socket
fit and suspension play an important role in providing stabil­
ity, so final adjustments to both of those aspects are included
as part of the dynamic analysis. Although dynamic alignment
is typically done on a flat, level surface, many prosthetists will
also attempt to simulate other terrains that an individual will
encounter in their daily lives. Ramps, stairs, and uneven sur­
faces all require slightly different alignments for optimal per­
formance. Final alignment is often a compromise of function
on the varied terrain that an amputee will encounter.
As the question of whether or not the alignment of the
prosthesis is “good” or not is ultimately answered by the func­
tion and contentedness of the person wearing the prosthesis,
there is a fairly broad range of alignments that can be consid­
ered acceptable.27 In an effort to standardize what is ultimately
a subjective estimate of proper alignment, the concept of ver­
tical alignment axis and alignment reference center has been
proposed. The vertical alignment axis is a vertical line that
passes through the geometric center of the socket at the level
of the midpatellar tendon. The alignment reference center is
the point along the line from the center of the foot through the
tip of the shoe, one-third of the way forward from the back of
the heel. To align the prosthesis, the individual is asked to fully
weight bear on the socket while the socket is supported on a
padded stand. The person determines the socket axis based
upon the most comfortable weight-bearing position. When
the socket is aligned with the socket axis in the most com­
fortable position and the vertical alignment axis goes directly
through the alignment reference center (Figure  23-24), the
prosthesis is generally accepted to be “well-aligned.”
Electronic Alignment
Technology has been developed to assist the prosthetist in
objectifying the alignment process and thereby making pros­
thetic alignments more repeatable and predictable. Electronic
sensors imbedded in the prosthetic components are capable
of transmitting real-time gait data to a nearby computer. The
computer processes these data and superimposes a graph of
the actual forces and moments for one complete gait cycle
over a set of “normal” data (Figure 23-25).28 Displaying the
­otherwise invisible forces and moments on the prosthesis cues
FIGURE  23-23  An example of the component that attaches the
prosthetic foot to the pylon. This pyramid is set to its maximum
limit of approximately 10 degrees of plantarflexion. (Photo courtesy
of David A. Knapp, CPO, Hanger Prosthetics & Orthotics, North
Haven, CT)

Chapter 23  Transtibial Prosthetics
639
FIGURE 23-24  The vertical alignment axis and alignment reference center (ARC) of a transtibial
prosthesis. Note that the socket axis is set in slight flexion from vertical. The center of the socket
should be at the center of the cross section of the socket at the level of the patellar tendon bar. The
alignment reference center is one-third the distance from the posterior edge of the shoe worn on the
prosthetic foot. (Reprinted with permission from Lin C, Wu YC, Edwards M. Vertical alignment axis
for transtibial prostheses: a simplified alignment method. J Formos Med Assoc. 2000;99[1]:39-44.)
Dorsiflexion
Moment
Plantarflexion
Moment
Loading Response
Midstance
Terminal Stance
Pre-Swing
FIGURE 23-25  This graph shows sagittal plane moment data collected for three cycles of stance
phase by an individual walking with a prosthesis as compared with the typical pattern of walking
by persons with intact lower extremities (shaded area). (Reprinted with permission from Orthocare
Innovations, Oklahoma City, OK;
Compas-Mastery-Lesson-2-Excessive-Valgus.pdf)

640
Section III  Prostheses in Rehabilitation
the prosthetist to focus in on specific variances and consider
their possible causes. This can prevent undetected problems
with alignment from causing long-term damage to the indi­
vdual's limb. For example, an excessive varus moment at the
knee can lead to premature medial compartmental osteoar­
thritis over a long period. These objective data can be printed
and kept in the person's file to be referenced if problems arise
or changes are necessary in the future (Figure 23-26).
ADDITIONAL FEATURES
There is an assortment of modular components that can
be added to a prosthesis between the socket and the foot to
enhance certain features and function of the prosthesis. These
include shock absorbers, torque absorbers, and dynamic
pylons. The downside of such components are that they
weight and require sufficient clearance between the socket
and foot. They may limit foot choices for that reason and are
typically used in cases where excessive shock is expected or
when an acceptable gait pattern is not attainable with existing
feet alone. Care should be taken to mount these components
as proximal as possible on the prosthesis to minimize the
inertial effects of the additional weight during swing phase.
Torque Absorber
When rotational motion in the socket is causing discomfort
or excessive stress on the skin, a torque absorber can be used
to decrease the rotational torque from the ground reaction
force. A torque absorber is a component that uses a viscoelas­
tic bumper to allow a limited amount or rotation to occur at
the foot without displacing the socket. The amount of rota­
tion is proportional to the torque and can range up to 30
degrees in either direction. This is especially useful in sports
applications, such as golf and tennis, that require a wide range
of rotation during the activity. Torque absorbers may also be
beneficial for turns encountered in normal daily ambulation,
especially for persons with fragile skin (Figure 23-27).
Shock Absorber
Although much of the functional shock absorption needed
for gait is attainable with controlled knee flexion in loading
response, some individual's benefit from additional verti­
cal excursion afforded by the addition of a shock absorber.29
This component uses a viscoelastic spring to dampen the
ground reaction forces by slowing down their transmis­
sion to the limb. As weight is transferred to the prosthesis,
the shock absorber compresses relative to the magnitude of
the ground reaction force. This reduces impact by spreading
the force out over a longer time interval. This compression
leads to a reduction of the overall prosthesis height during
early stance.
Dynamic Pylon
Typical prosthetic pylons are rigid and only function as an
attachment between the socket and foot to establish the
correct overall height. Dynamic pylons allow for energy to
be stored as spring tension as they flex through midstance
and terminal stance. This energy is released in preswing to
assist with hip and knee flexion and promote toe clearance
and limb advancement. This energy return allows the indi­
vidual to walk with less energy consumption and increased
­efficiency, meaning that they can walk farther and longer. The
angle of flexion in a dynamic pylon is small and is difficult
to observe during casual ambulation. The effects are more
­readily ­apparent during jogging or running (Figure 23-28).
FIGURE 23-26  The prosthesis is fitted with an electronic sensor that
can capture real-time gait data and transmit them to the clinician's
computer. (Reprinted with permission from College Park Inc., Frasier,
MI; )
FIGURE 23-27  An example of a extra component that is mounted
directly under the socket to reduce amount of torque and shock that
is transferred from the ground to the limb. It replaces all or part of
the pylon, depending on available length. (Reprinted with permis­
sion from Ossur Americas, Foothill Ranch, CA;
com/?PageID=13468)