Phẫu Thuật Tạo Hình Grabb & Smith’s (Bản Cập Nhật – Kevin C. Chung)

Polyester
Polyesters are polymers containing an esther group and usually refer to the compound polyethylene
terephthalate. This material is a high-molecular-weight polymer that is primarily used as knitted mesh
such as Mersilene mesh (Ethicon, Inc., Somerville, NJ) for hernia repair. Mersilene is a nonabsorbable
mesh with high tensile strength that allows for tissue ingrowth and has also been used for chin and nasal
augmentation. Certain polyesters such as poly-4-hydroxybutyrate are bioderived, in that they are
produced by microorganisms and have been used in biodegradable mesh products such as Phasix (Bard
Davol, Warwick, RI). 22
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Polyethylene
Polyethylene is the most commonly produced plastic. There are multiple different types of this polymer
differentiated primarily by their density and branching. The molecular weight of polyethylene influences
its mechanical properties, which can range from 40,000 daltons (low density) resulting in a ductile
material used for bags, to ultrahigh-molecular-weight polyethylene (2–6 million daltons) used for
orthopedic hip implants. Importantly, the material is inert and has low tissue reactivity and long-term
structural stability when used as implants.
Polyethylene implants are typically used for facial reconstruction and augmentation. These are usually
high-density porous implants (e.g., Medpor, Stryker, Kalamazoo, MI), which permit vascularization as
well as soft tissue and bony ingrowth with pore sizes ranging from 100 to 250 µm in diameter. 23 This
porosity results in incorporation of the implant and prevention of migration, though simultaneously
makes incorporated implants difficult to remove. High-density porous polyethylene implants are utilized
in cranioplasty, ear reconstruction, and orbital implants as well as reconstruction and augmentation of
the mandible, malar eminence, nose, and frontal bone among others areas. 24 Complications with these
implants include infection, exposure, extrusion, and visibility, which are highly reliant on the vascularity
of the surrounding tissues and the placement technique. 25
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PMMA
PMMA is a nondegradable acrylic resin formed by mixing liquid methyl methacrylate monomer with the
accelerator, PMMA powder. The resulting strong but light high-molecular-weight polymer is chemically
inert, rigid, nonconductive, and easily handled. The material is not porous, and therefore does not allow
of tissue ingrowth and osteoconduction when utilized on its own. PMMA is most commonly used for
cranioplasty owing to its rigidity and lack of significant movement or mechanical stress in this region. 26
This material can be molded in situ or can be preformed as a custom implant. PMMA is also used for
stabilization of chest wall. It can be added to or sandwiched between mesh reinforcement for some tissue
incorporation and durability.
A significant exothermic reaction occurs during curing of PMMA that can reach temperatures of 40 to
56°C. Active cooling of the surrounding tissues with saline is therefore required to prevent thermal tissue
necrosis. Furthermore, curing in vivo can results in a small amount of shrinkage that must be accounted
for and can also release the unbound monomer systemically, which is toxic.
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Polypropylene
Polypropylene is similar to the chemical structure of polyethylene but with the inclusion of a methyl
group. Polypropylene is most widely used as a high-tensile, nonabsorbable suture and mesh.
Polypropylene mesh is typically used for bridging repair of fascial defects or reinforcements of hernia
repairs as well as chest wall reconstruction. These meshes are macroporous and therefore allow for tissue
ingrowth, but also can have an increased risk of adhesions if placed intraperitoneally.
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Expanded Polytetrafluoroethylene
Expanded polytetrafluoroethylene (ePTFE) or Gore-Tex (W.L. Gore, Flagstaff, AZ) is created by
expanding a linear polymer of fluorine and carbon molecules to create a microporous structure. ePTFE is
a modification of PTFE that is a more lightweight and pliable material with good biocompatibility, a high
strength-to-weight ratio, and a similarly low coefficient of friction. Owing to its microporous structure,
the material has significantly less tissue ingrowth compared with macroporous mesh and a higher
propensity for encapsulation. 14
ePTFE products have a variety of applications in plastic surgery. Woven microporous meshes are used in
abdominal and chest wall reconstruction. Solid blocks can be carved and adapted for volume restoration
in facial reconstruction and augmentation such as with malar, chin, and nasal implants.
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Polyurethane Urea
Polyurethane urea is a multiblock copolymer with good mechanical properties and biocompatibility.
These polymers have been modified to form slow-degrading, filament-based meshes that serve as
scaffolds for tissue ingrowth. The Artelon CMC Spacer (Artimplant, Vastra Frolunda, Sweden) is a fabric
of the polymer designed for interposition between the metacarpal and trapezium for treatment of basal
joint arthritis by stabilizing the carpometacarpal joint by augmentation of the capsule and joint
resurfacing. 27
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Silicone
Medical-grade silicone is formed from PDMS, a polymer of organosilicone. Silicone is biologically inert,
does not dissolve in the environment found within the body, and is nontoxic. The mechanical properties
of silicone, most practically its viscosity, are altered by changing the length of the polymer and its
molecular weight. Cross-linking of PDMS chains has also become a clinically useful chemical alteration
that creates a firmer gel used for form-stable, highly cohesive implants.
Silicone is a widely used material across multiple different specialties in medicine and is used as
components of thousands of medical products. Short polymer chains of PDMS result in a low-viscosity
liquid form of silicone. Liquid silicone has been used extensively as a soft tissue filler but causes several
adverse effects including ulceration, cellulitis, abscesses, foreign body migration, and granulomas. 28
Liquid silicone injections are not Food and Drug Administration approved and must be avoided.
The polymerization of Dimethyl sulfoxide into longer chains is used to form silicone gels for implants.
Silicone has had a tumultuous past in the field of Plastic Surgery owing to the temporary restriction on
silicone gel implants by the Food and Drug Administration over concerns on toxicity and association with
connective tissue disease in 1992. Since then, however, studies have demonstrated the safety of silicone
breast implants with regard to a lack of toxicity and association with connective tissue disease 29 with a
cessation of the ban in 2006. Silicone implants are now utilized for a wide spectrum of indications in
Plastic Surgery including breast reconstruction, breast augmentation, facial reconstruction and
augmentation, ear reconstruction, gluteal augmentation, and joint and flexor tendon reconstruction.
Because silicone implants are not porous, they become encapsulated with scar tissue. This foreign body
reaction can have significant consequences for the long-term implications of silicone implants as fibrosis,
and encapsulation can result in contracture of surrounding tissues, aesthetic distortion, and pain.
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Biodegradable Polymers
Biodegradable polymers are designed to break down into natural byproducts such as water and carbon
dioxide. The most common biodegradable polymers include poly (lactic acid), poly (glycolic acid) (PGA),
and poly (lactic-co-glycolic acid), which are degraded into lactic or glycolic acid.
Formulations of these materials and their combinations, such as Vicryl mesh (Polyglactin 910; Ethicon,
Inc., Somerville, NJ) are used for support in abdominal and chest wall reconstruction as well as breast
reconstruction. Biodegradable plates and screws consist of similar polymers and are useful in craniofacial
surgery and fracture fixation in pediatric patients in whom bone growth limits the use of permanent
devices. 30 Other devices such as biodegradable suture anchors (e.g., Endotine, Coapt Systems, Inc., Palo
Alto, CA) consist of a mix of poly (lactic acid) and PGA.
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Indications by Body Region
Prosthetic implants have a wide range of indications for both reconstructive and aesthetic purposes. The
following sections summarize the most common uses of prosthetic implants in plastic surgery by body
region and indication (Table 9.3).
TABLE 9.3
Common Prosthetic Implant Indications and Materials in Plastic Surgery
Facial Reconstruction
Skeletal reconstruction (titanium, porous polyethylene, ePTFE, silicone)
Osteosynthesis hardware (titanium, biodegradable polymers)
Arch bars (stainless steel)
Ear reconstruction (polyethylene, silicone)
Eyelid weights (gold, platinum)
Facial Augmentation
Solid implants (porous polyethylene, ePTFE, silicone)
Mesh (polyester)
Anchoring devices (titanium, biodegradable polymers)
Calvarial Reconstruction
Osteosynthesis hardware (titanium, biodegradable polymers)
Cranioplasty (titanium, calcium phosphate ceramics, PMMA, polyethylene)
Breast Reconstruction and Augmentation
Breast implants (silicone)
Tissue expanders (silicone)
Support scaffolds (titanium, biodegradable polymers)
Chest Wall Reconstruction
Mesh (polypropylene, ePTFE, polyglycolic acid, biodegradable polymers)
Rigid reconstruction (PMMA)
Abdominal wall reconstruction
Mesh (polyester, polypropylene, ePTFE, biodegradable polymers)
Lower Extremity
Gluteal implants (silicone)
Hand
Osteosynthesis hardware (titanium, stainless steel)
Joint replacement (polyurethane urea, silicone, pyrolytic carbon, polyethylene)
Tendon reconstruction (polyester/silicone)
Skin
Tissue expanders (silicone)
ePTFE, expanded polytetrafluoroethylene.
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Facial Reconstruction
Bony Skeleton
Osteosynthesis of the facial skeleton is usually performed with different titanium hardware consisting of
load-bearing and load-sharing plates, secured with screws to provide rigid or semirigid fixation. In the
setting of pediatric reconstruction, hardware composed of biodegradable polymers may be chosen for
facial growth without having to remove hardware. Temporary implants in the form of internal and
external titanium distraction devices are also commonly used in craniofacial surgery for manipulation of
the skeleton after osteotomies.
Implants to restore the devoid facial skeleton are commonly used in orbital blowout fractures to
reconstruct the orbital floor. These implants usually consist of titanium, porous polyethylene, or a
combination of both and can be custom fabricated to the individual defect. A variety of other implants,
typically porous polyethylene, can also be used to restore bony contours in the face such as the mandible,
malar eminence, and zygoma. 24 These implants are placed in the subperiosteal plane to prevent
disruption of the overlying structures, visualize skeletal contours, maximize soft tissue coverage, and
ensure a well-vascularized environment.
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Ear
Reconstruction of the cartilaginous framework of the ear is most commonly required for defects and
malformations secondary to anotia, microtia, and trauma such as burns. Cited benefits of alloplastic
reconstruction include limitless material, age independence, decreased patient discomfort, and improved
ear definition. 31 Moldable implants usually consist of porous polyethylene, which have been
revolutionized by the utilization of a temporoparietal fascial flap to provide well-vascularized coverage
of the implant and minimize complications of infection and extrusion.
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Eyelid
Eyelid weights are commonly used for treatment of paralytic lagophthalmos secondary to facial nerve
palsy. Original implants were stainless steel, 32 which were later replaced with gold 33 and platinum. The
implant is typically placed in a pocket deep to the orbicularis oculi and can be secured to the tarsal plate,
without disrupting the insertion of the levator apparatus. Complications include implant migration,
extrusion, skin ulceration, capsule formation, implant visibility, over/undercorrection, and infection.
Platinum has been suggested to be superior, as its higher density allows for a smaller, thinner profile
implant, with potentially lower rates of extrusion. 34
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Facial Augmentation
Aesthetic augmentation of the facial skeleton is typically performed with alloplastic prosthetic implants.
Similar to reconstruction, implants are fixated to the underlying bone in the subperiosteal plane to
minimize injury to nerves and directly visualize bony contours. The most common implants are porous
polyethylene, ePTFE, and silicone; the last does not allow for tissue ingrowth and heals with fibrous
encapsulation. Common areas of augmentation include the malar eminence, infraorbital rim, and
paranasal regions in the midface, as well as almost all anatomic areas of the mandible including the
mentum, body, angle, and ramus. 35
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Calvarial Reconstruction
Calvarial reconstruction often utilizes titanium plates and screws for osteosynthesis of traumatic fractures
or for fixation of osteotomy sites. Osteosynthesis of the skull in pediatric patients may utilize
biodegradable hardware to allow for skull growth. Temporary stainless steel hardware has also been
utilized in infants such as the use of stainless steel springs to promote outward expansion of the skull in
sagittal craniosynostosis. 36
Prosthetic implants have proven to be valuable in large calvarial defects given the lack of adequate
autologous replacements. Alloplastic cranioplasty materials most commonly are calcium phosphate
ceramics including hydroxyapatite and derivatives of calcium phosphate cement pastes. Use in large
quantities in areas with potential bacterial contamination has been associated with an increased risk of
complications. 37 Customizable cranial implants with both PMMA and polyethylene, as well as titanium
implants, have also been described for adult cranioplasty with low major complication rates (Figure 9.2).
38 Preoperative radiation has been shown to be the strongest independent predictor of postoperative
complications. 39
FIGURE 9.2 Cranioplasty with custom prefabricated 3D-printed implant made of titanium mesh and calcium phosphate tiles
designed with virtual surgical planning (OssDsign AB, Uppsala, Sweden) and secured with titanium mini-plates.
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Breast
Implants
First generation Cronin-Gerow implants from 1963 had a teardrop-shaped silicone rubber shell filled with
silicone gel and a posterior Dacron patch for fixation. Subsequent generations of implants have
progressively improved to provide more natural results while minimizing complications such as silicone
leakage, capsular contracture, palpability, and visibility. Modern day implants consist of an elastic
silicone shell and highly cohesive silicone gel filling or a hard outer shell filled with saline (Figure 9.3).
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FIGURE 9.3 Tabbed tissue expander (A; Mentor, Irvine, CA) being filled with saline (B) during first stage of two-stage breast
reconstruction.
Silicone implants are approved for breast augmentation in patients age 22 years or older or for breast
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reconstruction in women of any age. Complications of silicone breast implants include capsular
contracture, infection, extrusion, rippling, double-bubble deformity, and rupture. 29 Implants with
textured surfaces have lower rates of capsular contracture; however, only when placed in the
subglandular and not submuscular plane. 40 Fifth generation cohesive gel implants have increased cross-
linking allowing for the production of anatomic implants that retain their shape. These highly cohesive
implants tend to have lower rates of contracture and rippling but higher rates of malposition and
seromas.
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Capsular Contracture
As silicone breast implants are not porous, the foreign body reaction to these implants is one of fibrous
encapsulation. Capsular contracture is an exaggeration of this response with the immune system playing
a central role believed to be triggered by multiple factors including subclinical infection and biofilm. This
response can have significant clinical implications with severe cases resulting in aesthetic deformities and
pain secondary to contracture, which requires total capsulectomy and implant exchange. Several risk
factors have been identified including smooth implants, periareolar incisions, subglandular placement,
and postoperative hematoma, among others. 41
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Breast Implant–Associated Anaplastic Large Cell Lymphoma
Breast implant–associated anaplastic large cell lymphoma (BIA-ALCL) is a rare T cell lymphoma
associated with primarily textured breast implants. 42 Patients most commonly present with a delayed-
onset seroma (>1 year) and less commonly a capsular mass. Any suspicious cases require aspiration of
periprosthetic fluid and/or biopsy of masses sent for cytology, histology, flow cytometry, and CD30+
immunohistochemistry. Most localized cases have a good prognosis with complete capsulectomy and
implant removal. Successful management of this disease is highly reliant on identification, treatment, and
proper reporting by plastic surgeons.
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Support: Polypropylene and Vicryl Mesh
Various synthetic materials have also been described to provide implant support in dual-plane
reconstruction. These include polypropylene-based (TiLoop Bra [pfm medical, Köln, Germany]) and
biodegradable polymer–based (Polyglactin 910 [Ethicon, Inc., Somerville, NJ]) products as cheaper
alternatives to biologic materials such as acellular dermal matrix. Superiority in outcomes between
biologic and synthetic products has yet to be determined in large, prospective studies.
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Chest Wall
Prosthetic implants can be useful tools in reconstruction of chest wall owing to the strength, rigidity, and
adaptability of certain materials to the three-dimensional contours of the thoracic cage. Proposed criteria
for the need for skeletal reconstruction of the chest wall include the absence of four or more ribs or a
defect greater than 5 cm in size owing to the potential for developing a flail chest. 43
Several types of implantable materials have been utilized in chest wall reconstruction. Polypropylene
meshes such as Marlex (CR Bard, Murray Hill, NJ) and Prolene (Ethicon Inc., Somerville, NJ) are
commonly used for tissue ingrowth whereas ePTFE (Gore-Tex, Gore, Flagstaff, AZ) can be used to
provide a watertight closure. 44 Multiple other polymers such as PGA and poly (lactic acid) serve the
same purpose. PMMA can be used to create a rigid, moldable reconstruction and can be sandwiched
between layers of macroporous mesh for tissue incorporation.
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Abdominal Wall
Mesh plays a critical role in abdominal wall reconstruction by providing support for primary repair of the
musculofascial wall or serving as a bridging material. Reinforcement of primary midline repairs with
mesh has been shown to significantly decrease the rate of recurrence in ventral hernia repair in a
multicenter, randomized controlled trial. 45
Synthetic mesh materials can be divide into three categories: (1) macroporous mesh (e.g., polypropylene;
Figure 9.4), which allows for tissue ingrowth but also has a high risk for adhesions of placed
intraperitoneally; (2) microporous mesh (e.g., ePTFE), which does not have tissue-growth and heals with
a capsule; and (3) composite mesh that contains an additional coating such as cellulose or collagen to
decrease adhesions when placed intraperitoneally. Recently developed biosynthetic meshes are made of
fully absorbable synthetic polymers (Bio-A [Gore], Phasix [Bard/Davol], TIGR [Novus Scientific]) and are
aimed at providing better support of the abdominal wall than biologic matrices while still undergoing
tissue ingrowth and resorption.
FIGURE 9.4 Abdominal reconstruction with synthetic macroporous polypropylene mesh (©Ethicon, Inc. Reproduced with
permission).
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Lower Extremity and Gluteal Region
Augmentation
Silicone implants have been utilized for augmentation of different lower extremity structures. Gluteal
augmentation with silicone implants is the most well-studied region. A variety of different placement
techniques exist, usually differing in plane of placement with the most common approaches being
intramuscular or subfascial implant placement. 46
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Hand
Osteosynthesis
A variety of different titanium plates and screws are available for rigid fixation of phalangeal, metacarpal,
and carpal fractures. Stainless steel Kirschner wires are also frequently used in hand surgery for
percutaneous pin fixation of bone fragments.
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Joint Replacement
Sequelae of rheumatoid arthritis, osteoarthritis, trauma, and even infection may necessitate the
replacement of joints in the hand. Arthroplasty is most often performed in the basal joint (osteoarthritis)
and the metacarpophalangeal and interphalangeal joints (rheumatoid arthritis). Traditional alloplastic
arthroplasty has utilized silicone joint replacement, though complications include synovitis,
displacement, and giant cell reactions. Polyurethane urea joint replacements (Artelon CMC Spacer;
Artimplant, Vastra Frolunda, Sweden) have also been introduced; however, evidence is still lacking on
the superiority of outcomes among different materials. Other implant materials include pyrolytic carbons
and polyethylene-based products.
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Tendon Reconstruction
Two-stage tendon reconstruction involves the placement of temporary tendon implants. The use of a
prosthetic implant overcomes the problem of a scarred tendon bed through the foreign body response to
the implant that results in a well-organized pseudosheath, allowing for tendon graft gliding. These
implants consist of variations silicone rods with different cores, such as polyester. Permanent tendon
implants have also been described but are limited owing to unreliable fixation to the bone distally and
native tendon proximally.
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Skin (Tissue Expanders)
Tissue expanders are used frequently throughout the body owing to the benefits of mechanical and
physiologic creep in providing adequate skin for closure of a defect. Two-stage breast reconstruction
utilizes tissue expanders that consist of an outer silicone shell and internal port to allow the breast pocket
to reach the appropriate size for implant placement without placing excess stress on the breast skin
envelope. Other common locations for tissue expansion are the scalp, forehead, neck, and back. Tissue
expansion is particularly useful in infants with lesions that have a high size-to-body surface area ratio
such as congenital nevi and vascular malformations.
The success of tissue expansion relies on a thorough knowledge of appropriate incision for insertion, 47
planes of implant placement, use of correct expanders, appropriate expansion timing, design of expanded
skin flaps, and management of complications. Tissue expansion often initially causes skin erythema and
mottling without fever or signs of infection in which expansion should be continued. On the other hand,
pain and erythema may suggest the need for fluid removal whereas fever, purulence, and signs of
infection require expander removal.
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Future Directions
There is still a significant need to continue to improve the characteristics of implantable prosthetics.
Although creating an autologous equivalent is the standard, today’s products are still by no means the
ideal implant first outlined in the 1950s. Recent research advances in prosthetics aim at creating new
materials while utilizing well-known products for different indications. As technology moves forward,
research must be focused on further understanding the interaction between the implant and the host at
the macroscopic and molecular level to continue to work toward optimizing the biocompatibility of
implants.
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Questions
1. A 13-month-old child with a giant congenital nevus of the flank undergoes uncomplicated
placement of a 10 × 15 cm subcutaneous rectangular tissue expander in preparation for subsequent
reconstruction with adjacent tissue. After initiation of expansion in the following weeks, the parents
of the child are worried that the skin over the expander looks red. Upon examination, there is slight
erythema of the skin overlying the expander without warmth or surrounding skin changes and with
no palpable fluid collections. The child is afebrile and well appearing and does not appear to be in
pain. The next appropriate step in management of this patient involves
a. Starting intravenous antibiotics
b. Removing the tissue expander
c. Continuing with expansion
d. Starting oral antibiotics
e. Aspirating fluid from the tissue expander to send for culture
2. A 24-year-old patient presents with dissatisfaction of his facial appearance. Examination reveals a
retruded chin, and alloplastic chin augmentation is planned. Compared with porous polyethylene
implants for facial augmentation, silicone implants have
a. Lower infection rate
b. Decreased concern for migration
c. Better contour to the facial skeleton
d. Easier removal
e. Increased visibility
3. A 23-year-old woman presents for consultation regarding breast augmentation. The patient has
small, symmetric breasts, without breast ptosis. She desires to be at least two bra sizes larger. Breast
augmentation with form-stable anatomic implants is planned with placement in the subglandular
plane. Which of the following answer choices best describes the advantages of using textured,
anatomic implants compared with smooth, round implants in this patient?
a. Decreased risk of malrotation
b. Decreased risk of postoperative capsular contracture
c. Superior cosmetic result
d. Decreased risk of seroma
e. e. Increased risk of rippling
4. A 56-year-old man undergoes resection of a large left anterior chest wall sarcoma, and you are
consulted intraoperatively for reconstruction. The resection includes the full-thickness chest wall
with five ribs and the left half of the sternum. Intraoperative defect size is 10 × 20 cm. He has not
received any other neoadjuvant treatments. Which of the following is the best choice for
reconstruction?
a. PMMA sandwiched in polypropylene mesh and left latissimus dorsi flap
b. PMMA sandwiched in polypropylene mesh and left vertical rectus abdominis myocutaneous
(VRAM) flap
c. Polypropylene mesh and left latissimus dorsi flap
d. Polypropylene mesh and left VRAM flap
e. Acellular dermal matrix and left latissimus dorsi flap
5. A 60-year-old woman with a history of right breast cancer and bilateral mastectomy and implant-
based reconstruction 6 years ago presents to your office complaining of right breast discomfort. The
patient initially had a two-staged reconstruction with placement of highly cohesive textured
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implants. She denies any changes in size of her breasts, skin changes, fever, or recent trauma to her
breasts. On examination, she has no significant abnormalities. A magnetic resonance image is
obtained, which reveals a moderately sized right periprosthetic fluid collection. Which of the
following is the most appropriate next step in management?
a. Fine-needle aspiration of the collection to send for culture
b. Fine-needle aspiration of the collection to send for CD30+ immunohistochemistry
c. Explantation of bilateral breast implants and total capsulectomy
d. Admission to the hospital and intravenous antibiotics
e. Observation
1. Answer: c. Skin undergoing tissue expansion can often become slightly hyperemic upon initial
expansion. Although skin erythema should always raise suspicion for infection with an underlying
foreign body, the absence of other signs of infection in this case including surrounding cellulitis,
pain, warmth, or fever makes infection unlikely. If the erythema persists or is worsening, further
workup for an infection is warranted. However, mild skin changes are expected, and expansion
should proceed normally in the absence of other symptoms. Starting antibiotics would be the correct
choice if an early infection was suspected. Although the traditional dogma for any tissue expander
infection entails explantation, more recent studies have shown that mild cellulitis without exposure
can be salvaged with oral antibiotic regimens. 1 In these cases, aspiration of fluid for culture can also
help guide antibiotic therapy. Severe infection, impending implant exposure or extrusion, requires
explantation of the expander, washout of the pocket, antibiotic therapy, and delayed reimplantation
after the infection has cleared.
2. Answer: d. Polyethylene and silicone implants are commonly used in facial augmentation. Both
implants are usually placed subperiosteally to maximize soft tissue coverage, minimize damage to
overlying neurovascular structures, and directly visualize bony contours. Both implants are
contoured to the facial skeleton and have different profiles that can be selected and adjusted as
needed. Porous polyethylene allows for tissue ingrowth and therefore is theoretically better
vascularized and has less of a risk of migration than silicone implants if not secured to bone. Because
silicone implants are not porous, they do not allow for tissue ingrowth and therefore are easier to
remove.
3. Answer: b. Fifth generation breast implants have increased cross-linking that results in a highly
cohesive implant that maintains this shape. Textured implants have been shown to have decreased
rates of capsular contracture than smooth implants; however, only when placed in the subglandular
plane. This difference is not significant in implants placed in the submuscular plane. Textured
anatomic implants have not been demonstrated to have superior cosmetic outcome. In fact,
evaluation by both plastic surgeons and nonmedical professional has not been able to identify
anatomic versus round patients in photographs of patients with breast augmentation. Anatomic
implants have a higher rate of malposition than round implants owing to their asymmetric shape,
which is visible with rotation. Highly cohesive fifth generation implants have also been shown to
have higher rates of seroma and decreased rates of rippling.
4. Answer: a. The patient has undergone a large chest wall resection that involves five ribs and a
portion of the sternum. He has a composite defect that includes the skin, soft tissue, and bone.
Patients who undergo resection of four or more ribs or have a bony defect greater than 5 cm are at a
higher likelihood of developing flail chest. Therefore, mesh and dermal allograft alone will not
provide adequate rigidity in this patient. PMMA is frequently used in chest wall reconstruction as a
polymer that can be molded but cures into a rigid structure. In certain cases, rigidity of the chest wall
secondary to fibrosis after radiation therapy may preclude the need for rigid chest wall
reconstruction, as flail chest is less prevalent in this cohort. However, this is not the situation in this
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patient who has not previously received radiation. As the patient had resection of the sternum as
well as ribs on either side, there is likely compromise of the internal mammary vessels, which would
prevent the use of a flap based on the superior epigastric vessels. Therefore, the best answer choice
provides a rigid reconstruction with PMMA sandwiched in macroporous mesh to allow for some
tissue ingrowth as well as durable soft tissue coverage with a latissimus dorsi myocutaneous flap.
5. Answer: b. More than 500 worldwide cases of BIA-ALCL have been reported. This rare T cell
lymphoma is primarily associated with textured implants and usually presents with a delayed-onset
seroma and less commonly a capsular mass. Patients who present with a seroma greater than 1 year
postoperatively should raise suspicion for BIA-ALCL. Appropriate steps in diagnosis include
sending periprosthetic fluid for CD30+ immunohistochemistry. Additional diagnostic tests from
fluid aspirate include cytology, flow cytometry, and histology. If a mass is present, it should also be
biopsied and sent for pathology. Observation is not correct, as the presentation of seroma greater
than 1 year postoperatively in a patient with textured implants is highly suggestive of BIA-ALCL.
Although explantation of implants and total capsulectomy is the treatment for BIA-ALCL localized
to the implant pocket, this would be premature without a diagnosis of BIA-ALCL. This patient does
not report any symptoms concerning for infection and the examination is otherwise benign. An
indolent infection is possible but unlikely this later postoperatively.
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Voorhees, AB. The development of arterial prostheses. A personal view. Arch Surg. 1985;120:289-295.
Major, MR, Wong, VW, Nelson, ER, et al. The foreign body response: at the interface of surgery and bioengineering. Plast Reconstr Surg.
2015;135:1489-1498.A review of the mechanisms behind the foreign body response to implants and the current strategies to manipulate these pathways.
Bellon, JM, Bujan, J, Contreras, L, Hernando, A. Integration of biomaterials implanted into abdominal wall: process of scar formation and
macrophage response. Biomaterials. 1995;16:381-387.
Jordan, SW, Fligor, JE, Janes, LE, Dumanian, GA. Implant porosity and the foreign body response. Plast Reconstr Surg. 2018;141:103e-112e.
Chen, Q, Thouas, GA. Metallic implant biomaterials. Mater Sci Eng R. 2015;87:1-57.
Healy, KE, Ducheyne, P. A physical model for the titanium-tissue interface. ASAIO Trans 1991;37:M150-M151.
David, L, Argenta, L, Fisher, D. Hydroxyapatite cement in pediatric craniofacial reconstruction. J Craniofac Surg. 2005;16:129-133.
Burstein, FD, Williams, JK, Hudgins, R, et al. Hydroxyapatite cement in craniofacial reconstruction: experience in 150 patients. Plast Reconstr
Surg. 2006;118:484-489.
Constantz, BR, Ison, IC, Fulmer, MT, et al. Skeletal repair by in situ formation of the mineral phase of bone. Science. 1995;267:1796-1799.
Miller, L, Guerra, AB, Bidros, RS, et al. A comparison of resistance to fracture among four commercially available forms of hydroxyapatite
cement. Ann Plast Surg. 2005;55:87-92.
Deeken, CR, Matthews, BD. Characterization of the mechanical strength, resorption properties, and histologic characteristics of a fully
absorbable material (poly-4-hydroxybutyrate-phasix mesh) in a porcine model of hernia repair. ISRN Surg. 2013;2013:238067.
Spector, M, Flemming, WR, Sauer, BW. Early tissue infiltrate in porous polyethylene implants into bone: a scanning electron microscope
study. J Biomed Mater Res 1975;9:537-542.
Yaremchuk, MJ. Facial skeletal reconstruction using porous polyethylene implants. Plast Reconstr Surg. 2003;111:1818-1827.
Rubin, JP, Yaremchuk, MJ. Complications and toxicities of implantable biomaterials used in facial reconstructive and aesthetic surgery: a
comprehensive review of the literature. Plast Reconstr Surg. 1997;100:1336-1353.
Zanotti, B, Zingaretti, N, Verlicchi, A, et al. Cranioplasty: review of materials. J Craniofac Surg. 2016;27:2061-2072.
Nilsson, A, Wiig, M, Alnehill, H, et al. The Artelon CMC spacer compared with tendon interposition arthroplasty. Acta Orthop. 2010;81:237-
244.
Singh, M, Solomon, IH, Calderwood, MS, Talbot, SG. Silicone-induced granuloma after buttock augmentation. Plast Reconstr Surg Glob Open.
2016;4:e624.
Spear, SL, Murphy, DK, Allergan Silicone Breast Implant USCCSG. Natrelle round silicone breast implants: core study results at 10 years.
Plast Reconstr Surg. 2014;133:1354-1361.Ten-year results of Allergan core study on silicone implants used in breast reconstruction and breast
augmentation. The study provides important data on rates of common complications after these procedures such as infection, malposition, capsular
contracture and need for implant removal/replacement.
Eppley, BL, Morales, L, Wood, R, et al. Resorbable PLLA-PGA plate and screw fixation in pediatric craniofacial surgery: clinical experience in
1883 patients. Plast Reconstr Surg. 2004;114:850-856; discussion 857.
Reinisch, J, Tahiri, Y. Polyethylene ear reconstruction: a state-of-the-art surgical journey. Plast Reconstr Surg. 2018;141:461-470.Detailed
summary of the author’s evolution of technique for polyethylene ear reconstruction from experience with over 1500 patients.
Sheehan, JE. Progress in correction of facial palsy with tantalum wire and mesh. Surgery. 1950;27:122-125.
Illig, KM. A new method of lagophthalmos surgery. Klin Monbl Augenheilkd Augenarztl Fortbild. 1958;132:410-411.
Silver, AL, Lindsay, RW, Cheney, ML, Hadlock, TA. Thin-profile platinum eyelid weighting: a superior option in the paralyzed eye. Plast
Reconstr Surg. 2009;123:1697-1703.
Yaremchuk, MJ. Improving aesthetic outcomes after alloplastic chin augmentation. Plast Reconstr Surg. 2003;112:1422-1432.
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van Veelen, MC, Kamst, N, Touw, C, et al. Minimally invasive, spring-assisted correction of sagittal suture synostosis: technique, outcome,
and complications in 83 cases. Plast Reconstr Surg. 2018;141:423-433.
Gilardino, MS, Cabiling, DS, Bartlett, SP. Long-term follow-up experience with carbonated calcium phosphate cement (Norian) for
cranioplasty in children and adults. Plast Reconstr Surg. 2009;123:983-994.
Wolff, A, Santiago, GF, Belzberg, M, et al. Adult cranioplasty reconstruction with customized cranial implants: preferred technique, timing,
and biomaterials. J Craniofac Surg. 2018;29(4):887-894.
Reddy, S, Khalifian, S, Flores, JM, et al. Clinical outcomes in cranioplasty: risk factors and choice of reconstructive material. Plast Reconstr
Surg. 2014;133:864-873.
Liu, X, Zhou, L, Pan, F, et al. Comparison of the postoperative incidence rate of capsular contracture among different breast implants: a
cumulative meta-analysis. PLoS One. 2015;10:e0116071.
Calobrace, MB, Stevens, WG, Capizzi, PJ, et al. Risk factor analysis for capsular contracture: a 10-year Sientra study using round, smooth,
and textured implants for breast augmentation. Plast Reconstr Surg. 2018;141:20S-28S.
Clemens, MW, Brody, GS, Mahabir, RC, Miranda, RN. How to diagnose and treat breast implant-associated anaplastic large cell lymphoma.
Plast Reconstr Surg. 2018;141:586e-599e.CME article summarizing diagnostic criteria for BIA-LCL, appropriate workup for suspected cases of BIA-
ALCL, and proper treatment and reporting of documented cases.
McCormack, PM. Use of prosthetic materials in chest-wall reconstruction: assets and liabilities. Surg Clin North Am 1989;69:965-976.
Arnold, PG, Pairolero, PC. Chest-wall reconstruction: an account of 500 consecutive patients. Plast Reconstr Surg. 1996;98:804-810.A large case
consecutive case series of chest wall reconstruction using both autologous and alloplastic materials. The study outlines basic principles of chest wall
reconstruction and highlights reconstructive options.
Luijendijk, RW, Hop, WC, van den Tol, MP, et al. A comparison of suture repair with mesh repair for incisional hernia. N Engl J Med.
2000;343:392-398.A multicenter randomized controlled trial of mesh reinforcement versus primary repair only of primary and first recurrent ventral
hernias less than 6 cm in length or width. Mesh reinforcement of repairs was found to have a 75% lower recurrence rate irrespective of hernia size.
Mofid, MM, Gonzalez, R, de la Pena, JA, et al. Buttock augmentation with silicone implants: a multicenter survey review of 2226 patients.
Plast Reconstr Surg. 2013;131:897-901.
Zide, BM, Karp, NS. Maximizing gain from rectangular tissue expanders. Plast Reconstr Surg. 1992;90:500-504.
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C H A P T E R 1 0
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Principles of Nerve Repair and Reconstruction and
Neuroma Management
Carrie A. Kubiak and David L. Brown and Theodore A. Kung
Key Points
Appropriate management of nerve injuries is dictated by correct identification of the degree of nerve
injury and the time since injury.
Acute nerve transection injuries are best treated with primary, tensionless repair.
Restoring appropriate alignment of corresponding fascicles in the proximal and distal nerve
segments is important for optimizing outcomes in primary neurorrhaphy.
In crush or avulsion nerve lesions where the zone of nerve injury is unclear, the viability of injured
nerve should be allowed to demarcate before definitive reconstruction is attempted.
Electrodiagnostic studies (EMG/NCV) can be used to help diagnose nerve injuries as well as track
nerve regeneration.
Autologous nerve grafts are the most reliable method to reconstruct segmental nerve gaps.
Nerve transfers should be considered in proximal injuries and when there is concern that
degradation of neuromuscular junctions will occur prior to reinnervation.
Peripheral nerve injuries result in a myriad of symptoms, ranging from minor sensory disturbances to
devastating loss of function. Debilitating chronic pain can be difficult to manage even with surgical
intervention. The mechanism, level, and severity of the trauma directly contribute to the expected
morbidity, prognosis, and recommended treatment following peripheral nerve injury. Recent advances in
microsurgical techniques, graft materials, and nerve transfer strategies have greatly improved our ability
to address peripheral nerve injuries, but reliable restoration of sensation and motor function can still be
difficult to achieve. Outcomes following nerve repair or reconstruction can be optimized by ensuring a
timely diagnosis and treatment, performing meticulous alignment of nerve ends during surgery, and
following appropriate rehabilitation protocols. This chapter discusses the pathophysiology of nerve
injury and summarizes the various operative strategies that are employed after trauma to peripheral
nerves.
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Peripheral Nerve Anatomy
Peripheral nerves consist of three main cell types. Neurons facilitate the transfer of information to and
from the central nervous system, conveying both afferent sensory stimuli as well as efferent motor
signals. Axons are extensions from the neuron cell bodies that reside in the spinal cord and spinal
ganglia. Axons are either myelinated or unmyelinated and are grouped together spatially in bundles
known as fascicles. Anterograde and retrograde axonal transport transfers structural proteins, as well as
communicate between the cell body and the target end organ through cycling of neurotransmitters. 1
Supportive glial and stromal cells play an important role in the support and function of peripheral
nerves. Schwann cells are the principal glial cells of the peripheral nervous system and produce the
myelin sheath to myelinated axons. Myelin acts as an insulating coating to axons, efficiently augmenting
the propagation of action potentials and increasing the conduction velocity in a process known as
saltatory conduction. Stromal cells form the connective tissue scaffold around neurons and glial cells. 2
The endoneurium is the innermost layer of loose connective tissue that surrounds individual axons and
their supporting Schwann cells to provide nourishment through microvessels. The perineurium serves to
bundle axons together to form fascicles and is a major contributor to peripheral nerve tensile strength. A
fascicular group consists of two or more fascicles surrounded by perineurium. The internal epineurium is
the connective tissue that envelops individual fascicles and group fascicles. The epineurium is the
outermost layer and is the tissue that defines an anatomically distinct peripheral nerve. Finally, the
mesoneurium is a thin layer of loose areolar tissue that connects the peripheral nerve to surrounding
structures and permits smooth gliding during bodily movements (Figure 10.1).
FIGURE 10.1 The normal peripheral nerve consists of myelinated and unmyelinated axons organized into bundles of fascicles.
Peripheral neural tissue is supported by three major connective tissue sheaths: the endoneurium, perineurium, and epineurium.
Peripheral nerves are supplied by a series of segmental nutrient arteries that feed into a network of blood
vessels within the nerve. The vasa nervorum vessels run superficially and longitudinally along the
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epineurium. These vessels send branches to intraneural vessels located within the interfascicular
perineurium and in turn join a multitude of capillaries that extend into the endoneurium. This extensive
communication maximizes the blood supply within the nerve and permits mobilization of a segment of a
nerve for a length up to 45 times its diameter. 3
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Physiology of Peripheral Nerve Injury
Loss of axonal continuity leads to an irreversible cascade of cellular and inflammatory events known as
Wallerian degeneration. 4 This process begins within 24 to 48 hours of injury and involves complete
axonal degeneration distal to the site of injury. Additionally, axonal degeneration occurs for a short
distance proximally. An influx of calcium and sodium ions triggers the sequence of axonolysis.
Disruption of both anterograde and retrograde transport systems leads to a buildup of proteins and
subsequent swelling of the nerve on both sides of the injury. 5 Schwann cells transform into a more
dedifferentiated and reactive phenotype 6 and begin to break down their own myelin, phagocytose
debris, and recruit macrophages to the site of injury. 7 These macrophages in turn promote a positive
feedback loop that further stimulates Schwann cell proliferation through the release of growth factors. 8
Wallerian degeneration proceeds until empty endoneurial tubes remain, devoid of axonal or myelin
material. In the proximal nerve segment, Wallerian degeneration halts at the closest intact node of
Ranvier, which also serves as the site of subsequent axonal growth. 9
To begin regeneration, dedifferentiated Schwann cells proliferate along the residual endoneurial tubes
and create columns known as Bands of Büngner. These longitudinally aligned Schwann cells provide a
supportive microenvironment and serve to guide regenerating axons to their appropriate distal target
organs. 10 For this reason, superior clinical outcomes are observed when endoneurial tube remains intact.
11 Schwann cells further support regenerating axons via release of cytokines and neurotrophic factors that
stimulate axonal growth. 12 Axonal regeneration is mediated by a host of neurotrophic factors that are
released from local tissue including sensory and motor targets. 13 A divided neuron may form up to 50 to
100 axonal sprouts in an effort to reinnervate its target tissue. Each regenerating axon forms a growth cone
consisting of multiple filopodia that guide outgrowth during regeneration. Proteases are also released
from the growth cone to aid in the removal of any physical barriers hindering its path. Clinically, the site
of axonal regeneration can be localized by tapping along the course of the peripheral nerve. A positive
Tinel sign occurs when an electric shock or pins and needles sensation is produced. Elongation proceeds
until the axons reach intact endoneurial tubes within the distal nerve segment that serve to guide growth
towards the end organ. When functional connections are not made in a timely fashion, axons can
degenerate in a process known as pruning. Axons that continue to grow aimlessly will form a
disorganized and painful mass known as a neuroma. 14 Studies have shown that more severe nerve
injuries lead to greater scarring and disordered axonal regeneration. 15
Axonal regeneration occurs at a rate of approximately 1 to 3 mm per day or just slightly more than an
inch per month. 16 Therefore, when the location of nerve injury is known, one can predict the amount of
time regenerating axons will take to reach their end organ. In distal peripheral nerve transections,
regenerating axons will need to grow a relatively short distance. However, with more proximal
peripheral nerve injuries, the time for regenerating axons to reach their targets can be estimated at many
months to several years, resulting in Schwann cells losing their ability to facilitate nerve regeneration and
distal endoneurial sheaths collapsing. 17 This precludes successful reinnervation even with the most
optimal surgical techniques. For this reason, the level of peripheral nerve injury is critically relevant to the
expected functional outcome. Muscle fibers will undergo irreversible loss of neuromuscular junctions and
progressive fibrosis if not reinnervated with 1 to 2 years. In contrast, sensory end organs do not undergo
such degeneration and can be reinnervated many years later with satisfactory results.
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Classification of Nerve Injury
In 1943, Seddon described three degrees of peripheral nerve injury: neuropraxia, axonotmesis, and
neurotmesis. 18 Sunderland later expanded this classification to five degrees based on histologic and
structural changes seen within the nerve after injury 19 (Table 10.1, Figure 10.2).
TABLE 10.1
Classification of Peripheral Nerve Injuries is Based on the Level of Anatomic Disruption
Seddon
Classification
Sunderland
Classification
a
Nerve Anatomy b
Recovery
Surgery
Myelin
Axon
Endoneurium
Perineurium
Epineurium
Neurapraxia
First degree
−
+
+
+
+
Full spontaneous recovery
within days to months
None
Axonotmesis
Second
degree
−
−
+
+
+
Full spontaneous recovery;
regenerates at a rate of 1–3 mm
per day
None
Third degree
−
−
−
+
+
Partial spontaneous recovery;
regenerates at a rate of 1–3 mm
per day
None
Fourth
degree
−
−
−
−
+
No spontaneous recovery;
regenerates at a rate of 1–3 mm
per day after appropriate
surgical intervention
Nerve
repair,
graft, or
transfer
Neurotmesis
Fifth degree
−
−
−
−
−
No spontaneous recovery;
regenerates at a rate of 1–3 mm
per day after appropriate
surgical intervention
Nerve
repair,
graft, or
transfer
Sixth degree
−
+/−
+/−
+/−
+/−
Recovery depends on
combination of degrees of nerve
injury
Variable
aDegree of nerve injury determines likelihood of spontaneous recovery and/or need for surgical intervention.
b+ Indicates structure is intact; − indicates structure is injured.
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FIGURE 10.2 Classification of nerve injuries. A. Uninjured nerve consists of myelinated axons surrounded by endoneurium. B.
In first-degree injury, axons are demyelinated but intact. C. In second-degree injury, axons are injured and undergo
degeneration. D. A third-degree injury includes damage to axons, myelin, and endoneurium. E. A fourth-degree is a complete
scar block that prevents regeneration. F. A fifth-degree injury is a division of the nerve. G. A sixth-degree injury is a combination
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of any of the five levels of injury within the same nerve.
Neuropraxia is equivalent to Sunderland first-degree nerve injury. In this condition, the axons within the
nerve remain intact, but a temporary, localized conduction block results from segmental demyelination.
Acutely, neuropraxia can ensue after stretching injuries or blunt force trauma, whereas chronic etiologies
of neuropraxia include longstanding compression neuropathies at locations where peripheral nerves pass
through tight anatomic spaces (e.g., carpal tunnel syndrome). Axonal integrity is preserved, neurons
maintain their connections to end organs, and Wallerian degeneration with subsequent axonal
regeneration is not required for restoration of function. Electrodiagnostic studies (EDS) will show normal
electromyographic (EMG) findings with decreased nerve conduction velocities and increased latencies.
Recovery time is dependent on remyelination of the axons by Schwann cells and requires approximately
6 to 8 weeks.
In axonotmesis, there is focal demyelination as well as axonal injury with Wallerian degeneration.
Axonotmesis is a component of Sunderland second-, third-, and fourth-degree injuries and is usually
caused by severe traction or crush injuries. Second-degree injury is characterized by the disruption of the
continuity of axons but with preservation of intact endoneurial tubes. Regenerating axons are guided by
their original endoneurial tubes that lead them directly to their target tissues, and therefore full functional
recovery can be expected. Third-degree injury involves damage to the axon, myelin sheath, and
endoneurium. The perineurium is intact, and the fascicular structure remains patent. Because the
endoneurial sheaths are violated, scarring may serve as a physical barrier to regenerating axons.
Functional recovery is variable and often incomplete. In fourth-degree injury, there is injury to the
myelin, axon, endoneurium, and perineurium, and only the epineurium remains intact. Common causes
of fourth-degree nerve injury include traction and iatrogenic nerve injection. Spontaneous recovery does
not occur due to interposed fibrosis, and surgical intervention is required.
Sunderland fifth-degree injury is equivalent to Seddon neurotmesis. This type of injury is the complete
transection of axons and all connective tissue layers, commonly due to a sharp laceration. Surgical
intervention is required, and functional outcomes are more unpredictable. Although the Sunderland
classification is a useful paradigm for organizing peripheral nerve injuries into differing severities, it does
have limited clinical utility. For instance, there is no diagnostic test to distinguish between second-, third-,
and fourth-degree injuries, as these can only be diagnosed histologically. 20 Therefore, Mackinnon and
Dellon introduced a sixth-degree category, which represents a mixed injury pattern. 21 Sixth-degree injury
represents a combination of any of the previous five levels of injury within the same nerve. Sixth-degree
injury results in variable recovery that is dependent on an accurate diagnosis and timely intervention.
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Diagnosis
A critical factor in the management of peripheral nerve injuries is the timeliness of both diagnosis and
surgical treatment. Therefore, a thorough clinical assessment and history is performed to establish the
location, nature, and severity of the injury. This includes testing motor, sensory, and pain fibers of the
suspected injured nerves. When possible, muscles innervated by the nerve should be evaluated
individually. The extent of motor nerve injury is determined by assessment of muscle strength, range of
motion, and atrophy. Sensory impairments can be identified by decreased sensation, hypersensitivity, or
allodynia in the distribution of the nerve territory. In the classic ten test, patients rank the magnitude of
sensation in the affected region compared with that in the contralateral region using a scale from 0 to 10.
Quantitative sensory testing can also be performed as a means to detect the perception threshold for
mechanical stimuli in patients with injured peripheral nerves. 22 This approach utilizes the pressure-
specified sensory device 22 to objectively quantify sensory innervation by measuring pressure thresholds
for perception of static and moving one- and two-point discrimination of the skin in the distribution of
the injured nerve. Vibration instruments and Semmes-Weinstein monofilaments are also used to evaluate
the sensory innervation and are most useful in evaluating chronic compressive neuropathies.
The exact site of nerve injury can be identified by clinical examination or through the use of
electrodiagnostic or imaging studies. The progress of axonal regeneration can be localized by tapping
along the course of the peripheral nerve. This finding is known as a positive Tinel sign and is experienced
as an electric shock or pins and needles sensation. Over the course of several weeks, distal migration of a
Tinel sign demonstrates ongoing regeneration and suggests that functional improvements may be
expected as long as the distance from the site of nerve injury to the target end organs is not exceedingly
long. Nerve block may also play an important role in establishing a diagnosis and discerning the location
of injury. Blocks are performed by injecting local anesthetic to anesthetize specific peripheral nerves to
identify the source of pain or allodynia. Symptomatic improvement after injection helps to isolate the
affected nerve, but the test is fairly nonspecific. 23
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Electrodiagnostics
The term electrodiagnostic studies (EDS) encompasses both nerve conduction studies (NCS) and EMG.
These tests are often performed together and provide useful information about the location of nerve
injury as well as severity and prognosis. NCS are used to assess both motor and sensory function by
measuring the conduction velocity of action potentials traveling through a nerve. To measure conduction
velocity in motor axons, a transcutaneous electrical stimulus is given and subsequently compound
muscle action potentials (CMAPs) from the corresponding distal muscle are recorded. For sensory axons,
recording skin electrodes are placed within the cutaneous territory of a sensory nerve to record the
transmission of the stimulus. Slower conduction velocities or increased latencies indicate the presence of
demyelination and reflect at least a first-degree Sunderland nerve injury. The position of the distal
recording electrodes can be repositioned at various places over the length of the peripheral nerve to
localize the conduction block. Amplitude of the recorded CMAPs provides an estimate of the number of
intact motor axons activating muscle fibers. Small or absent CMAP amplitudes indicate that some degree
of axon loss has occurred. The amplitude of the recorded compound sensory nerve action potential
similarly provides a reflection of the number of intact sensory axons.
The addition of needle EMG studies provides further insight regarding the condition of peripheral
nerves. In this test, a needle is inserted into a target muscle to measure muscle activity at rest and during
voluntary contraction. 24 Fibrillations and positive sharp waves (PSWs) on needle EMG indicate axonal
loss and therefore at least second-degree Sunderland injury, but these findings may not be apparent for
several weeks depending on how proximal the lesion is. 25 PSWs can be observed as early as 3 weeks after
nerve injury, whereas fibrillations are typically observed around 6 weeks after nerve injury. The presence
of fibrillations and PSWs on EMG are significant to the prognosis because they reveal that the distal
motor plates in the target muscle fibers are still available for reinnervation. The size, shape, and
recruitment pattern of motor unit potentials (MUPs) on needle EMG is helpful in determining the
duration of nerve injury and the expected potential for functional recovery. Immediately after
denervation, the number of motor units is reduced to a level that is commensurate with injury severity.
The reappearance of MUPs on EMG about 12 weeks after injury reflects the collateral sprouting of
adjacent, uninjured nerve fibers and thus represents second- and third-degree Sunderland nerve injuries.
These findings can become evident before any clinical signs of recovery are apparent. Owing to the
extensive nature of intraneural damage and scarring seen in fourth- or fifth-degree Sunderland injuries,
MUPs are not typically seen on EMG because all of the axons have lost continuity with their target muscle
fibers.
Electrodiagnostic studies may be obtained immediately after significant trauma to help determine the
presence and degree of nerve injury (Table 10.2). However, these studies are unable to distinguish
between severe axonotmetic and neurotmetic injuries in the acute setting. Total division of a peripheral
nerve may be better diagnosed with imaging studies such as ultrasound or magnetic resonance imaging.
NCS and EMG do play an important role in the timing of surgical intervention. For example, after a
suspected injury to a peripheral nerve, the presence of at least some motor units under voluntary control
shows that the lesion is incomplete, which implies a more favorable prognosis. On the contrary, the lack
of any signs of recovery on NCS or EMG after 3 to 6 months is usually an indication for surgical
exploration. Even when functional recovery is identified, these electrodiagnostic tests can also be
performed serially over time to help follow the progress of axonal regeneration and end organ
reinnervation.
TABLE 10.2
Electrodiagnostic Findings by Degree of Peripheral Nerve Injury
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Sunderland Classification of
Nerve Injury
Acute Nerve Injury
Chronic Nerve Injury
Fibrillations/PSWs
MUPs
Fibrillations/PSWs
MUPs
First degree
No
Normal
No a
Normal
Second degree
Yes b
Present: secondary to collateral
sprouting
No a
Present: secondary to
axonal regeneration
Third degree
Yes b
Present: secondary to collateral
sprouting
No a
Present: secondary to
axonal regeneration
Fourth degree
Yes b
No
No a
No
Fifth degree
Yes b
No
No a
No
Sixth degree c
Yes b
Variable
No a
Variable
aFibrillations and PSWs disappear after a period of chronic denervation.
bFibrillations and positive sharp waves (PSWs) are not identifiable until 3 to 6 weeks after nerve injury.
cElectrodiagnostic findings vary depending on the mixed severity and location of damage in sixth degree nerve injuries.
PSWs, positive sharp waves; MUPs, motor unit potentials.
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Management of Acute Nerve Injuries
The management of acute traumatic peripheral nerve injuries is largely dependent of the severity of
injury, the mechanism of trauma, and the distance from the injury to the target end organs. Intact but
contused nerves can often be expected to recover. Continued observation with close follow-up may be
appropriate before surgical intervention is warranted. However, with a more severe injury, prompt
surgical exploration and nerve repair may be the more suitable course of action.
In acute closed injuries, such as from blunt force trauma and blast mechanisms, peripheral nerves usually
suffer a contusion but remain structurally intact. Frequently, these are first-, second-, and third-degree
Sunderland injuries that are treated expectantly with sufficient time before surgery is considered. For
several weeks following the injury, patients should be seen frequently and serial examinations are
performed to look for any signs of recovery, such as a progressing Tinel sign and electrodiagnostic
evidence of recovery. These clinical findings help distinguish axonotmetic lesions that may recover
spontaneously from neurotmetic lesions that require surgical intervention. If there is confirmation of
return of function clinically or electrophysiologically, the patient should continue to be followed
expectantly, as recovery is still possible. If there is no return of function or if functional improvement
plateaus, nerve exploration may be considered. During this observation period, if none of these signs are
noted, it is more likely the patient sustained a higher grade injury (e.g., at least third degree) such that
axons either cannot find their way into distal endoneural tubes or their passage is blocked by intervening
scar tissue. Nerve exploration should be pursued and definitive surgical management will be dictated by
intraoperative findings. For example, neurolysis is indicated to excise pathologic scarring around and
within the substance of the peripheral nerve whereas a neuroma-in-continuity that is discovered is often
excised and reconstructed.
In contaminated wounds with acute crush or avulsion nerve injuries, the type and zone of injury can be
difficult to determine. In these scenarios, it is better to first debride any devitalized tissue and tack the
two nerve ends to a surrounding structure to prevent retraction. The wound and injured nerve are then
allowed to heal for at least 3 weeks for demarcation of the zone of injury. At the time of reexploration, the
extent of nerve injury will be more evident. The neuroma located at the proximal nerve segment must be
excised in bread-loaf fashion until a healthy fascicular pattern is seen. A similar technique is used for the
distal nerve segment, although there will be no neuroma present in this location. The resultant defect will
require either direct nerve repair or nerve reconstruction using a graft (Figure 10.3).
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FIGURE 10.3 Management of severe crush or avulsion injuries. A. When the zone of nerve injury is unclear, the nerve should
be allowed to demarcate for at least 3 weeks before definitive debridement of devitalized tissue is performed. B. Neuroma and
scar must then be excised in bread-loaf fashion until a healthy fascicular pattern is seen in both proximal and distal nerve
stumps. C. Only upon sufficient debridement should the nerve defect be repaired or reconstructed.
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Primary Repair
Acute, clean peripheral nerve lacerations are best repaired immediately. If the wound bed is well
vascularized and end-to-end approximation is possible, tension-free primary repair should be performed
within the first 2 to 3 days following injury. Transposition or mobilization of the nerve may be required to
minimize tension and facilitate repair. Excessive tension at the suture line results in compromise of
endoneurial blood supply, causing necrosis, fibrosis, and scar blockage of nerve regeneration. 3 This
diminishes the potential for successful functional recovery. Restoring appropriate alignment of
corresponding fascicles in the proximal and distal segment is similarly important for optimizing
regenerative outcomes in primary neurorrhaphy. Epineurial vascular landmarks are useful to ensure
optimal alignment of fascicles. If performed within 72 hours after injury, direct stimulation of distal
motor fascicles can further aid in mapping fascicular arrangements in the distal nerve stump. 26 After this
amount of time, the distal nerve segment is depleted of neurotransmitters, and direct stimulation will not
reliably result in muscle contractions. Intraoperative histologic staining of proximal and distal nerve ends
has been described as a means to align motor and sensory fascicles, although this process can take up to
an hour in even experienced hands. 27
Direct epineurial nerve coaptation with microsutures remains the standard surgical treatment for
peripheral nerve lacerations that can be repaired without undue tension. Microsutures (9-0 or 10-0) are
loosely placed through the external epineurium such that nerve ends and fascicular groups are kissing
and not bulging to the sides. Should bulging occur, trimming of the fascicles with microscissors will
facilitate end-to-end approximation within the endoneurial sheath (Figure 10.4). The fewest number of
epineurial sutures should be used for the repair to decrease iatrogenic harm to the nerve. In contrast, in a
fascicular repair technique, intraneural dissection is performed at the edges of the cut nerve and then
individual fascicles are realigned with microsutures. Adjunctive epineurial sutures may be placed or may
be omitted. However, the advantages that might be 
 gained from direct alignment of individual fascicle
segments may be offset by the higher chances of axonal injury during the procedure and increased
foreign body reaction caused by the greater suture material burden within the nerve. A more
conservative method of controlling the alignment of fascicles is known as group fascicular repair, whereby
identifiable groups of fascicles are aligned before a standard epineural repair is performed. Although this
modification is conceptually logical, clinical studies have not shown a clear superiority of one technique
over another. 28
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FIGURE 10.4 Primary nerve repair. A. In an epineural repair, the fascicles must be appropriately trimmed so that they do not
buckle, which will result in misdirection of the regenerating fibers. B. Well-performed nerve repairs will result in good alignment
of fascicles without the need for fascicular sutures.
An alternative repair technique utilizes tissue adhesives such as fibrin glue or poly(ethylene glycol)
hydrogel to supplement or replace epineurial sutures. Advantages of using adhesives for nerve repair
include its ease of use, reduced operative times, less tissue trauma, and less intraneural scarring
compared with using microsutures. 29 However, concerns remain about the lack of adequate tensile
strength after the application of these strategies alone. 30 Although animal studies have reported
superiority or at least equivalency to suture repair, 31 there are limited clinical data to support a complete
shift away from traditional microsurgical repair of nerve transection injuries.
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Autografts
When tensionless primary repair is not possible, an autologous nerve graft is preferred for nerve gap
reconstruction. A nonvascularized graft can be harvested from an expendable sensory nerve and is
interposed in the segmental nerve defect. The harvested nerve graft undergoes Wallerian degeneration
but maintains the supportive scaffold (i.e., endoneurium, perineurium, and epineurium) with Schwann
cell basal laminae, neurotrophic factors, and adhesion molecules to support regenerating axons. Axonal
regeneration through the nerve graft proceeds in a manner identical to that following primary
neurorrhaphy.
Utilization of a nerve autograft requires the sacrifice of a healthy, functioning nerve (usually sensory) for
reconstruction of a more important injured nerve (often motor). Autogenous nerve grafts can be
harvested from several sites, the most common being the sural nerve, medial antebrachial cutaneous
(MABC) nerve, and lateral antebrachial cutaneous (LABC) nerve. A sural nerve graft offers 30 to 40 cm of
graft length from each leg, whereas the medial antebrachial cutaneous nerve provides up to 20 cm of
length and the LABC up to 8 cm. These nerves are selected as donors because the sensory deficit is either
negligible owing to sensory innervation overlap or is considered acceptable compared to the potential
gain in motor function by using that nerve. The distal stump of the donor nerve can be sewn end-to-side
to an adjacent normal nerve to restore improved sensation to the donor dermatome. Expendable motor
nerves that can be harvested for autogenous grafting have a much more limited availability owing to
increased donor site morbidity. Harvest of motor nerves grafts are thus reserved for instances where no
sensory donors are available and nerve transfers would not provide a better option. A nerve innervating
a free muscle transfer can be considered as a possible graft (e.g., thoracodorsal nerve to the latissimus
dorsi muscle).
Autografts should be approximately 10% to 20% longer than the segmental defect in anticipation of
fibrosis-related graft shortening to ensure a tension-free repair. The autograft should be placed in
reversed orientation at the repair site to prevent loss of regenerating axons down side branches. If the
nerve graft diameter matches that of the segmental defect, the autograft can be simply interposed
between the two cut ends. Reconstruction of large diameter nerves often requires cable grafts. By aligning
multiple smaller caliber grafts (i.e., cable grafts) in parallel between corresponding fascicular groups, the
entire diameter of the large caliber nerve can be reconstructed. Autografts are associated with a number
of disadvantages including a separate donor site for the nerve graft harvest, the potential for neuroma
formation at the donor site, and occasionally insufficient donor nerve availability. Still, nerve autografts
are considered the standard for reconstruction of any segmental nerve defect.
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