Operative Technique in Plastic Surgery – Kevin C.Chung

and this can be particularly problematic in older patients. A “jaw
bra” can be used in neonates to minimize the open bite and assist
with feeding.13
Postoperative
■ After 6–7 days of distraction, the mandible is lengthened
sufficiently to improve the airway and allow extubation.
■ The neonate is monitored in the NICU to prevent airway
compromise.
■ The consolidation period is generally twice the activation period.
Prolonged consolidation theoretically leads to reduced relapse, but
at the expense of feeding difficulty.
POSTOPERATIVE CARE
■ The neonate is transferred to the NICU intubated.
■ Distraction activation is started on the day after surgery and proceeds at a rate
of 2 mm/d.8
■ The frequency of distraction is generally twice daily.
■ A pin driver is used for turning the activating arms (two turns of 360 degrees
correspond to 1 mm distraction) (FIG 4A).
■ After 1 week of activation, the mandible is advanced sufficiently to allow safe
extubation of the infant.
■ ENT is present to perform microlaryngoscopy/bronchoscopy, which
determines the safety of extubation.
■ Distraction is then continued at 1 mm/d because the skin tension has reached
its maximum at this point. Continued distraction at 2 mm may exceed skin
elasticity and lead to wound breakdown.
■ In older children, distraction is usually started after a 3-day latency period and
the rate is 1 mm/d.
■ Pin sites are washed daily with soap and water followed by topical antibiotic
ointment. The skin surrounding the pins appears red and stressed, but infection
is rare.
■ Weekly radiographs are obtained to monitor the progress of distraction and
hardware stability.
■ The end point of distraction is determined clinically with the aid of serial
radiographs to determine the position of the mandible and quantify the airway
improvement (FIG 4B).
■ The mandible is lengthened to a point anterior to the maxilla (slight class III

occlusion) in anticipation of minor relapse (FIG 4C).14
■ Distraction is generally completed within 3 to 4 weeks. The device is left in
place for an additional 6 to 8 weeks to complete consolidation.
■ At the end of consolidation (radiographic evidence of mineralization), the pins
(or the RED device) are removed under sedation in the operating room.
■ In older children or teenagers, orthodontic elastics may be used during the
activation or consolidation phase in an attempt to close the anterior open bite
created during the distraction process.
■ Feeding is resumed normally following surgery but may become increasingly
difficult as the mandible is advanced. A nasogastric tube is generally needed to
aid with feeding and is removed at the end of distraction.
OUTCOMES
■ Mandibular distraction is effective in the treatment of airway obstruction
associated with micrognathia.15 Given the high success rate with minimal
complications, it has become the standard of care for neonatal OSA (FIG
5A–E).
■ The procedure should be performed by a surgeon experienced in craniofacial
distraction, with the help of a multidisciplinary team.
■ The objective of mandibular distraction is to avoid tracheostomy or achieve
decannulation in patients who have previously received a tracheostomy. The
cost-effectiveness is clearly in favor of MDO over tracheostomy with less
morbidity.16
■ Patients with isolated PRS (nonsyndromic) generally require one mandibular
distraction procedure to clear the airway. Predictors for repeat distraction
include a syndromic diagnosis like TCS, Nager syndrome, Goldenhar, and
Stickler syndrome.8

FIG 4 • A. Driver engaging the distractor arms and
turning. B. Bedside radiograph demonstrating
advancement of the mandible and improvement of the
airway. C. A neonate at the time of distractor removal
demonstrating overcorrection of the mandible.

FIG 5 • A. Preoperative sagittal view CT scan
demonstrating mandibular micrognathia and narrow
airway. B. Airway improvement at the end of distraction,
showing overcorrection. C. Two-year postoperative view
demonstrating relapse, but with maintenance of airway
clearance. D. Three-dimensional CT scan before
distraction. E. Extent of mandibular advancement at the
end of the distraction.

■ In patients with underlying neurological problems and low muscle tone, MDO
generally has a lower success rate. Careful team discussion should precede
distraction in this patient population.2,6,8
COMPLICATIONS
■ Injury to the inferior alveolar nerve or the tooth buds from inaccurate selection
of osteotomy site or pin placement.
■ Temporomandibular joint ankylosis due to overloading of the TM joints. This
occurs less frequently with the internal technique than with the external
technique.
■ Infection is a rare occurrence. Pin site infections can be treated with local
wound care.
■ Pin dislodgement is a common complication. Use of transfixion pins that
penetrate both sides of the mandible offers better stability.17
■ Hardware failure and screw loosening is common with use of the RED device.
■ Permanent scars from percutaneous pin placement and skin stretching during
distraction (FIG 6).
■ These scars are generally well accepted by parents and preferable to
tracheostomy scars.
■ Anterior open bite is a common complication and can be problematic for
feeding.
■ Relapse is expected; slight overcorrection at the time of distraction is advised
(see FIG 5B,C).
■ Failure of distraction resulting in conversion to tracheostomy is seen in severe
cases of OSA. Predictors of failure include PRS without a cleft palate,
gastroesophageal reflux, and the need for Nissen fundoplication.11
■ Early consolidation may occur if the rate of distraction is too slow, requiring a
return to the operating room to repeat the osteotomies.

FIG 6 • Acceptable appearance of the scars 2 years
after distraction.
REFERENCES
1. McCarthy JG, Schreiber J, Karp N, et al. Lengthening of the human mandible
by gradual distraction. Plast Reconstr Surg. 1992;89:1-8.
2. McCarthy JG, Stelnicki EJ, Mehrara BJ, Longaker MT. distraction
osteogenesis of the craniofacial skeleton. Plast Reconstr Surg. 2001;107:1812-
1827.
3. Sarnat BG. Growth pattern of the mandible: some reflections. Am J Orthod
Dentofacial Orthop. 1986;90:221-233.
4. Chung MT, Levi B, Hyun JS, et al. Pierre Robin sequence and Treacher
Collins hypoplastic mandible comparison using three-dimensional
morphometric analysis. J Craniofac Surg. 2012;23(7 suppl 1):1959-1963.
5. Robin P. Glossoptosis: diagnosis, consequences and treatment. Bull Acad Natl
Med. 1923;89:37.
6. Mackay DR. Controversies in the diagnosis and management of the Robin
sequence. J Craniofac Surg. 2011;22(2):415-420.
7. Printzlau A, Andersen M. Pierre Robin sequence in Denmark: a retrospective
population-based epidemiological study. Cleft Palate Craniofac J. 2004;41:47-

52.
8. Denny AD. Distraction osteogenesis in Pierre Robin neonates with airway
obstruction. Clin Plast Surg. 2004;31:221-229.
9. Cohen MM Jr. Robin sequences and complexes: causal heterogeneity and
pathogenetic/phenotypic variability. Am J Med Genet. 1999;84(4):311-315.
10. Meyer AC, Lidsky ME, Sampson DE, et al. Airway interventions in children
with Pierre Robin sequence. Otolaryngol Head Neck Surg. 2008;138:782.
11. Murage KP, Tholpady SS, Friel M, et al. Outcomes analysis of mandibular
distraction osteogenesis for the treatment of Pierre Robin sequence. Plast
Reconstr Surg. 2013;132(2):419-421.
12. Grayson BH, McCormick S, Santiago P. Vector of device placement and
trajectory of mandibular distraction. J Craniofac Surg. 1997; 8:473.
13. Vecchione L, Smith DM, Losee JE. Neonatal mandibular molding: a novel
method of treating congenital open bite. Plast Reconstr Surg.
2010;125(2):648-651.
14. Denny AD, Talisman R, Hanson PR, Recinos RF. Mandibular distraction
osteogenesis in very young patients to correct airway obstruction. Plast
Reconstr Surg. 2001;108:302-311.
15. Tahiri Y, Greathouse ST, Tholpady SS, et al. mandibular distraction
osteogenesis in low-weight neonates with Robin sequence: is it safe? Plast
Reconstr Surg. 2015;136(5):1037-1044.
16. Kohan E, Hazany S, Roostaeian J, et al. Economic advantages to a distraction
decision tree model for management of neonatal upper airway obstruction.
Plast Reconstr Surg. 2010;126(5):1652-1664.
17. Molina F, Ortiz MF. Mandibular elongation and remodeling by distraction: a
farewell to major osteotomies. Plast Reconstr Surg. 1995;96:825-840.

42
CHAPTER
External Transfacial
Mandibular Distraction
Brian S. Pan
DEFINITION
■ Neonates with tongue-based airway obstruction encompass a heterogeneous
group of patients, the most common of which are those with isolated Pierre
Robin sequence (PRS).
■ Initially described in 1923, patients with PRS share a triad of signs that are
micrognathia, glossoptosis, and upper airway obstruction.1
■ The clinical strategies employed to treat these patients are (a) bypassing the
tongue base, (b) repositioning the soft tissues to alleviate the obstruction, (c)
and correcting micrognathia, the anatomic source of the obstruction.
■ Since the original description of mandibular distraction, both internal and
external approaches have been demonstrated to be safe and effective options.
■ The approach outlined herein includes further modifications to techniques
originally described by McCarthy2 and Denny.3
ANATOMY
■ The mandible is a unique bone composed of vertical and horizontal elements
that form a U-shaped construct.
■ The typical growth pattern of the pediatric mandible occurs in a superior and
posterior direction resulting in a downward and forward displacement of the
mandibular body and symphysis.4
■ From infancy through adolescence, the inferior alveolar nerve migrates
superiorly from the lingual, inferior border of the mandible to a more superior
position.
■ The primary morphological difference between the hypoplastic mandible in
PRS and the normal mandible is a small mandibular body. The ramus and

condyles tend to be of normal size.5
PATHOGENESIS
■ The incidence of PRS is difficult to define but is thought to be more frequent
than 1:14 000.6
■ Micrognathia is hypothesized to be the result of either a genetic growth
abnormality or a physical growth restriction.
■ Mandibular hypoplasia may be an isolated problem or related to a
craniofacial syndrome, the most common of which are Stickler syndrome,
velocardiofacial (VCF) syndrome, fetal alcohol syndrome (FAS), Treacher
Collins syndrome (TCS), Nager syndrome, hemifacial microsomia (HFM),
trisomy 21 and 22, and Kabuki syndrome.7
■ Intrauterine growth restriction causing head flexion, secondary to multiple
births, or oligohydramnios is also thought to limit mandibular growth.8
PATIENT HISTORY AND PHYSICAL FINDINGS
■ Neonates with tongue-based airway obstruction present along a spectrum of
severity.
■ Those patients with mild to moderate micrognathia may exhibit sonorous
breathing during sleep, apneic events, feeding difficulties, and poor weight
gain.
■ Neonates with more significant micrognathia not only will present with the
aforementioned signs and symptoms but may be in severe respiratory distress
and appear cyanotic. Sternal and suprasternal retractions and the use of
accessory muscles to breathe may also be apparent.
■ In such cases, urgent admission to a neonatal intensive care unit to stabilize
the airway is indicated.
■ In addition to a small mandible, glossoptosis is observed with a posteriorly
positioned tongue that collapses into the pharynx.
■ Patients with mild to moderate symptoms may fail to thrive due to the work of
breathing during sleep and while feeding.
■ The increased negative pressure required to inhale may also result in reflux
and aspiration of the gastric contents.9
IMAGING
■ A lateral cephalogram appropriately evaluates the hypoplastic mandible. The
degree of maxillomandibular discrepancy and the posterior airway space can

also be measured.
■ A three-dimensional computed tomography scan (3DCT) may also be
performed to further characterize the mandible and assess the location of the
inferior alveolar nerve and mental nerve foramina.
DIFFERENTIAL DIAGNOSIS
■ Although this diagnosis is typically made based on clinical findings and
physical examination, a genetic evaluation is an important component of the
multidisciplinary management of these patients.
■ This evaluation establishes an accurate diagnosis and anticipates future
medical needs if a syndrome is also present.
NONOPERATIVE MANAGEMENT
■ Prone and lateral decubitus positioning are the core maneuvers to assist with
airway patency while the child is awake and sleeping.
■ The use of tongue sutures, nasopharyngeal airways, palatal obturators, and
mandibular traction have also been described as effective conservative
measures. Their efficacy has been reported to be between 33% and 69% in
their respective patient populations.10
■ If long-term conservative care is indicated, close observation and a capable
caregiver are critical. Excess movement, coughing, and swallowing can easily
displace many of these devices leading to gagging, reflux, aspiration, and
potential loss of airway.
SURGICAL MANAGEMENT
■ The decision to operate is based upon the consensus of a multidisciplinary
team composed of representatives from neonatology, pulmonology,
otolaryngology (ENT), genetics, and plastic surgery.
■ In addition to the facial CT, a polysomnogram and direct evaluation of the
airway (microlaryngoscopy, bronchoscopy, or nasopharyngoscopy) are
typically obtained to aid in decision-making.
■ The main objective of the operation is to lengthen the mandible, thereby
advancing the attached soft tissues anteriorly, relieving the tongue-based
airway obstruction.
■ The main steps of the procedure include the following:
■ Expose the mandibular body, angle, and coronoid process bilaterally through
intraoral incisions.

■ Pass the first transfacial Steinmann pin caudal to the coronoid processes.
■ Pass the second transfacial pin just dorsal to the menton.
■ Perform bilateral mandibular osteotomies using an ultrasonic osteotome.
■ Apply external distractors.
■ The patient typically remains intubated following surgery and is transferred to
the NICU for postoperative management.
Preoperative Planning
■ Risks, benefits, and realistic expectations are discussed with parents prior to
surgery.
■ Risks include pin migration, tooth damage, injury to the inferior alveolar and
mental nerves, bony relapse, scarring, and the possible need for tracheostomy.
■ The operation is coordinated with ENT who will assist the anesthetist with
nasotracheal intubation if poor visualization of the larynx is anticipated.
Positioning
■ The patient is placed in a supine position with several small towels serving as
a shoulder roll.
■ A foam donut should be used to stabilize the head.
■ The nasotracheal tube is sutured to the septum to prevent inadvertent
extubation during the operation (FIG 1).
FIG 1 • A foam donut is used to stabilize the head. The
nasotracheal tube is sutured to the septum to prevent
extubation.

T E C H N I Q U E S
■ Exposure
■ Lidocaine with epinephrine is infiltrated into the lingual and buccal tissues
overlying the dorsal mandibular bodies, angles, and along the ascending
rami.
■ Exposure is achieved with a notched ramus retractor and a toe-in Obwegeser.
An incision is made over the ascending ramus and extended along the buccal
mandibular body (TECH FIG 1A).
■ Subperiosteal dissection is performed with a Freer elevator, exposing the
buccal surface of the mandible to identify the coronoid process, the ascending
ramus, the mandibular angle, and the body.
■ The lingual surface of the ascending ramus is then exposed to protect the
inferior alveolar nerve (TECH FIG 1B).
TECH FIG 1 • A. A notched ramus retractor and a toe-
in Obwegeser are used to provide exposure. An
incision is made over the ascending ramus and
extended along the buccal mandibular body. B. The
buccal surface of the coronoid process, the ascending
ramus, the mandibular angle, and the body are
exposed. The lingual surface of the ascending ramus
is then exposed to protect the inferior alveolar nerve.

■ Pin Passage
■ A 25-gauge needle is passed through the cheek to identify the most direct
path to the coronoid process (TECH FIG 2A).
■ This step is important to avoid traction on the skin from the Steinmann pin,
and the resultant scarring that may occur.
■ The site is then marked.
■ A 2-mm Steinmann pin is passed transmurally through the cheek into the
mandible just inferior to the coronoid process (TECH FIG 2B).
■ The pin is passed through the buccal mucosa, dorsal to the maxillary
tuberosity and caudal to the palate. The pin is advanced transorally and
through the contralateral side (TECH FIG 2C,D).
■ The ends of the pin are then protected.
■ The skin immediately dorsal to the menton is retracted cranially, and the
second Steinmann pin is inserted into the mandible through the floor of the
mouth, exiting the contralateral side (TECH FIG 2E).
■ This pin must be kept dorsal to the menton to avoid the mental foramina.
■ The pin should be placed close to the inferior edge of the mandible to
avoid the tooth roots but at least 2 to 3 mm above the inferior border to
prevent pin migration through the bone (TECH FIG 2F).

TECH FIG 2 • A. A 25-gauge needle is passed
through the cheek to identify the most direct path to
the coronoid process. B. A 2-mm Steinmann pin is
passed through the cheek into the mandible inferior to
the coronoid process. C. The pin is then passed
through the buccal mucosa, dorsal to the maxillary
tuberosity and caudal to the palate. The pin is
advanced transorally and then through the
contralateral side. D. Note the hemi-uvulae superior to
the Steinmann pin. E. The skin just dorsal to the
menton is then gently retracted cranially, and the
second Steinmann pin is then inserted into the
mandible exiting the contralateral side. F. The inferior
pin should be dorsal to the menton and avoid the
mental foramina. The pin should be placed close to
the inferior edge of the mandible to avoid the tooth
roots. Note the superior pin placement in relation to
the coronoid process.

■ Osteotomy and Completion
■ The skin on the contralateral side is also retracted cranially. The purpose of
this maneuver to prevent traction on the soft tissue and scarring as the
mandible is distracted.
■ The notched ramus retractor is then placed at the level of the coronoid
process, followed by a thin insulated ribbon retractor placed on the lingual
aspect of the mandible to protect the inferior alveolar nerve.
■ A toe-out Obwegeser is placed on the buccal aspect of the mandible to
expose the mandible for the osteotomy.
■ The osteotomy is then made using an ultrasonic osteotome and assessed for
completeness with a traditional 5-mm osteotome (TECH FIG 3A).
■ The external distractors are applied. The distractors are not advanced and are
set in a position that maintains the length of the native mandible.
■ The pins are then clipped (TECH FIG 3B).
■ The intraoral incisions are closed with dissolvable suture.
TECH FIG 3 • A. The osteotomy is performed similar
to a sagittal osteotomy below the level of the cranial
pin. It is initiated along the oblique ridge. A thin
insulated ribbon retractor should be used to retract the
lingual soft tissues and inferior alveolar nerve. B. The
external distractors are applied. The distractors are
not advanced and are set in a position that maintains

the length of the native mandible.
PEARLS AND PITFALLS
Physical
findings
■ Neonates with tongue-based airway obstruction present along a
spectrum of severity.
■ Feeding difficulties and poor weight gain in neonates with mild
micrognathia may indicate clinically significant obstructive sleep
apnea.
Technique
■ Steinmann pin placement is critical to avoid injury to tooth buds,
inferior alveolar and mental nerve, and to avoid pin migration
through the adjacent skin and mandibular border.
Postoperative
■ Postoperative extubation is typically safe within 3–5 d following
surgery depending on the degree of micrognathia.
■ The distraction callus consolidates 2 days for every day of
distraction.
■ A JawBra may be utilized to mold the mandible following
distractor removal if an anterior open bite is present.
POSTOPERATIVE CARE
■ The intubated child is transported to the NICU.
■ After a 24-hour latency period, distraction proceeds at 1 mm of advancement
performed twice daily for a total of 2 mm daily.
■ The pin sites are gently cleaned and antibiotic ointment is applied twice daily.
■ Extubation generally occurs between postoperative days 3 to 5.
■ Weekly cephalograms and physical examination are utilized to monitor the
progression of mandibular advancement, view the increase in posterior airway
space, and confirm the proper position of the Steinmann pins.
■ Distraction is complete when the mandible appears to have 5 mm of reverse
overjet based on a lateral cephalogram (FIG 2).
■ The distraction callus is consolidated 2 days for each day of distraction.

FIG 2 • Cephalograms are used to evaluate progression
of the mandibular advancement, view the increase in
posterior airway space, and confirm the placement of
the Steinmann pins. The distraction is completed when
the mandible appears to have 5 mm of reverse overjet
based on a lateral cephalogram and physical exam.
■ At the conclusion of the consolidation period, the external distractors and the
Steinmann pins are removed under general anesthesia.
OUTCOMES
■ Mandibular distraction osteogenesis (MDO) is safe and effective to treat
obstructive sleep apnea (OSA) secondary to tongue-based airway obstruction
from micrognathia.11
■ Compared to tracheostomy, the cost of treatment is markedly less due to the
decreased need for airway procedures and home care costs.12,13
■ In general, prematurity, low birth weight, preoperative intubation, and
syndromic diagnosis in addition to cardiac and pulmonary abnormalities, are
not predictors for failure, defined as conversion to tracheostomy.14

COMPLICATIONS
■ Infection is relatively uncommon due to the external placement of the
distractors.
■ Facial scarring is minimal unless pin traction occurs. This can be avoided with
proper skin retraction during the initial placement of the Steinmann pins (FIG
3A).
■ Improper pin and osteotomy placement can lead to tooth bud injury, pin
migration through the bone, and injury to the inferior alveolar nerve (FIG
3B,C).
■ Some relapse is anticipated due to the short consolidation period. This is
compensated for with 5 mm of overdistraction.
■ In our experience, anterior open bite has not been either a common short- or
long-term finding. If encountered immediately following distractor removal, a
JawBra is applied for mandibular molding.15
■ We have not found TMJ ankylosis to be a common complication associated
with this technique. By inserting the Steinmann pins anterior to condyles,
loading is avoided through the distraction process.
■ Failure of mandibular distraction with conversion to tracheostomy has been
associated in neonates with a diagnosis of PRS without a cleft palate and those
with gastroesophageal reflux and who required Nissen fundoplication.14
FIG 3 • A. Facial scarring is minimal unless pin traction
occurs due to improper skin retraction during the initial
placement of the Steinmann pins. Note the traction
scarring from the mandibular pin. B. Note the
placement of the pin beneath the tooth buds. C.
Following removal of the pin, the tooth buds are spared.

REFERENCES
1. Robin P. Glossoptosis: diagnosis, consequences and treatment. Bull Acad Natl
Med. 1923;89:37.
2. McCarthy JG, Schreiber J, Karp N, et al. Lengthening of the human mandible
by gradual distraction. Plast Reconstr Surg. 1992;89:1-8.
3. Denny AD, Talisman R, Hanson PR, Recinos RF. Mandibular distraction
osteogenesis in very young patients to correct airway obstruction. Plast
Reconstr Surg. 2001;108:302-311.
4. Sarnat BG. Growth pattern of the mandible: some reflections. Am J Orthod
Dentofacial Orthop. 1986;90:221-233.
5. Chung MT, Levi B, Hyun JS, et al. Pierre Robin sequence and Treacher
Collins hypoplastic mandible comparison using three-dimensional
morphometric analysis. J Craniofac Surg. 2012;23(7 suppl 1):1959-1963.
6. Printzlau A, Andersen M. Pierre Robin sequence in Denmark: a retrospective
population-based epidemiological study. Cleft Palate Craniofac J.
2004;41(1):47-52.
7. Cohen MM Jr. Robin sequences and complexes: causal heterogeneity and
pathogenetic/phenotypic variability. Am J Med Genet. 1999; 84(4):311-315.
8. Mackay DR. Controversies in the diagnosis and management of the Robin
sequence. J Craniofac Surg. 2011;22(2):415-420.
9. Dudkiewicz Z, Sekuła E, Nielepiec-Jałosińska A. Gastroesophageal reflux in
Pierre Robin sequence: early surgical treatment. Cleft Palate Craniofac J.
2000;37(2):205-208.
10. Meyer AC, Lidsky ME, Sampson DE, et al. Airway interventions in children
with Pierre Robin sequence. Otolaryngol Head Neck Surg. 2008;138:782.
11. Tahiri Y, Greathouse ST, Tholpady SS, et al. Mandibular distraction
osteogenesis in low-weight neonates with robin sequence: is it safe? Plast
Reconstr Surg. 2015;136(5):1037-1044.
12. Kohan E, Hazany S, Roostaeian J, et al. Economic advantages to a distraction
decision tree model for management of neonatal upper airway obstruction.
Plast Reconstr Surg. 2010;126(5):1652-1664.
13. Runyan CM, Uribe-Rivera A, Karlea A, et al. Cost analysis of mandibular
distraction versus tracheostomy in neonates with Pierre Robin sequence.
Otolaryngol Head Neck Surg. 2014;151(5):811-818.
14. Murage KP, Tholpady SS, Friel M, et al. Outcomes analysis of mandibular
distraction osteogenesis for the treatment of Pierre Robin sequence. Plast
Reconstr Surg. 2013;132(2):419-421.

15. Vecchione L, Smith DM, Losee JE. Neonatal mandibular molding: a novel
method of treating congenital open bite. Plast Reconstr Surg.
2010;125(2):648-651.

43
CHAPTERMandibular Setback
Haithem M. Elhadi Babiker and Deepak G. Krishnan
DEFINITION
■ Surgical correction of maxillofacial skeletal deformities dates back to the late
19th century.
■ Numerous techniques have been described for repositioning of the maxilla and
mandible through various osteotomies.
■ The bilateral sagittal split osteotomy (BSSO) is the most common surgical
procedure for correction of mandibular deformities.
■ It was first described by Obwegeser in 1957.1
■ The technique was modified by Dalpont in 19612 and further refined by
Epker in 1977.3
■ The BSSO setback is a procedure used for correction of mandibular
prognathism and asymmetries through a series of connected osteotomies that
posteriorly reposition the mandible.4
ANATOMY
■ The mandible is a U-shaped bone forming the lower jaw. It is the only
movable bone of the skull, articulating with the temporal bones at the
temporomandibular joints.
■ It consists of a horizontal horseshoe-shaped body and two broad and oblong
rami projecting upward. The alveolar processes of the mandible house and
support the mandibular teeth.
■ The inferior alveolar nerve enters the mandibular foramen on the medial
surface of the ramus near its center. It then extends downward and forward
within the body of the mandible; it exits at the mental foramen, located on the
external surface midway between the alveolar process and the lower border, in

the interval between the premolar teeth.
■ The anteromedial margin of the mandibular foramen is guarded by an upward
tonguelike projection, the lingula. Along its course, the inferior alveolar nerve
innervates the mandibular teeth and terminates as the mental nerve, which
supplies sensation to the skin and mucous membrane of the lower lip and chin.
■ The muscles of mastication directly attach to the surface of the mandible. The
masseter and medial pterygoid muscles attach to the lateral and medial surfaces
of the ramus.
■ These two muscles form the pterygomassetric sling, which straddles the
mandibular ramus.
■ The lingual nerve, before reaching the tongue, comes in close contact with the
inner surface of the alveolar border of the mandible in close proximity to the
mandibular third molar.
PATHOGENESIS AND NATURAL HISTORY
■ Mandibular prognathism is a condition in which the mandible is positioned
anterior to the maxilla, referred to as class III malocclusion.
■ In the NHANES study (1989–1994), 0.3% of the US population was reported
to have mandibular prognathism severe enough to require orthodontic-surgical
treatment.5
■ About 14% of youth (less than 18 years of age) in the United States have a
class III malocclusion. Roughly a quarter of these patients have isolated
mandibular prognathism, whereas the remaining three-quarters have a
combination of maxillary deficiency, in addition to mandibular protrusion.
■ Mandibular prognathism causes aesthetic concerns, as well as chewing and
speaking difficulties, prompting patients to seek surgical treatment at a younger
age.
■ In cases of severe mandibular prognathism, bimaxillary surgery is the
preferred method of treatment (BSSO setback combined with maxillary
advancement). This is because excessive mandibular setback may result in
obstructive sleep apnea and is also subject to higher rates of relapse.
PATIENT HISTORY AND PHYSICAL FINDINGS
■ Patients usually present during the teenage years.
■ The main complaints are difficulty with chewing and speech, and the aesthetic
concerns of a large mandible. Often, the malocclusion also presents as an open
bite.

■ Patients are usually first seen by an orthodontist and eventually referred to a
maxillofacial surgeon when ready for surgery.
■ Orthodontic treatment is usually undertaken for approximately a year and
serves to align the teeth within the dental arches and corrects any dental
compensation.
■ Surgery is undertaken when the patient reaches skeletal maturity and there is
proof of growth cessation (girls 16–18 years, boys 18–20 years).
■ Preoperative workup includes obtaining
■ Dental models
■ Cephalometric analysis
■ Face bow transfer to record the relationship of the jaws to the skull base
■ Model surgery to fabricate the surgical splints
■ In the case of single-jaw surgery, a single splint is fabricated to help position
the mandible.
■ In the case of double-jaw surgery (LeFort I advancement combined with
BSSO setback) for severe class III malocclusion, two splints are made: an
intermediate splint used intraoperatively to position the maxilla in its final
position and a final splint to position the mandible.
■ If third molar teeth are present, they may be extracted 6 months prior to
surgery.
IMAGING
■ Lateral cephalometric radiographs are obtained for cephalometric analysis.
■ Panoramic radiographs are obtained to determine the presence and location of
mandibular third molar teeth and also level of the inferior alveolar canal.
■ A CT scan with 3D images is obtained and can be used for virtual surgical
planning (VSP) in lieu of traditional model surgery.
DIFFERENTIAL DIAGNOSIS
■ Class III skeletal relationship can be secondary to mandibular prognathism,
maxillary hypoplasia, or a combination of both.
■ Accurate diagnosis is important to determine the appropriate surgery.
■ The diagnosis is confirmed by detailed clinical evaluation combined with
cephalometric analysis. Often, a midface deficiency is wrongly diagnosed as
mandibular prognathism, whereas in reality upon cephalometric investigation,
the mandibular position may be normal.
■ Acromegaly and pituitary hyperactivity should be suspected in mandibular

prognathism that presents later in life, and appropriate workup should be
undertaken.
■ Unilateral hyperplasia of the mandible can cause an asymmetric prognathism
and malocclusion. A neoplasm of the mandibular condyle should be ruled out
in these cases. Unilateral condylar hyperplasia is an idiopathic rare condition
that can also cause an asymmetric mandibular prognathism.
NONOPERATIVE MANAGEMENT
■ Mild class III malocclusion can sometimes be treated with orthodontic
management alone.
■ True skeletal class III relationship can only be treated by surgical intervention.
SURGICAL MANAGEMENT
■ The BSSO setback procedure is usually performed during the teenage years
after skeletal maturity.
■ The main objective of the operation is to correct mandibular prognathism by
cutting the mandible and repositioning it posteriorly to meet the maxilla in a
normal class I relationship.
■ The main steps of the procedure are as follows:
■ Make bilateral intraoral incisions to expose the posterior aspect of the
mandible.
■ Perform bilateral sagittal split osteotomies of the mandible (FIG 1).
■ Position the mandible into a class I relationship using an occlusal splint.
■ Use wires to perform maxillomandibular fixation.
■ Remove any bony interference between the two cut segments of the
mandible.
■ Establish a proper position of the condyles in the fossae bilaterally.
■ Rigidly fixate the mandible in its new position.

FIG 1 • The BSSO procedure includes a medial ramus
osteotomy, an anterior ramus horizontal osteotomy, and
a vertical osteotomy.
Preoperative Planning
■ The risks, benefits, and complications are discussed with the patient prior to
surgery. Discussing the risk of damage to the inferior alveolar nerve is
mandatory.
■ The mandibular third molar teeth are preferably extracted 6 months prior to the
surgery to allow adequate time for healing.
■ If they have not been extracted previously, they may be removed during the
procedure.6
■ The occlusal splints are tested on the patient preoperatively to ensure adequate
fit.
■ Preoperative photos are obtained for documentation.
Positioning
■ The patient is positioned supine with the arms tucked in.

■ They are intubated nasally, and the endotracheal tube is sutured to the nasal
septum and secured appropriately to the forehead (FIG 2).
Approach
■ Surgery is performed through an intraoral approach.
FIG 2 • The patient is positioned supine and the
endotracheal tube is sutured to the nasal septum and
then secured to the forehead.
T E C H N I Q U E S
■ Exposure
■ Clean the oral cavity with chlorhexidine or an equivalent antiseptic mouth
rinse, and place a throat pack.
■ Inject local anesthetic containing a vasoconstrictor to infiltrate the area of
dissection.
■ Insert a bite block on the opposite side to adequately open the mouth.
■ Place two Langenbeck retractors to pull away the cheek.
■ Place a tongue retractor to protect the tongue (TECH FIG 1A).
■ Make a 3-cm incision along the external oblique ridge of the mandible from
midway on the ramus to the level of the second molar tooth (TECH FIG

1B).
■ If the mandibular third molar is present and indicated for removal, the
incision is modified to incorporate the tooth.
■ A sufficient cuff of gingiva (5 mm) is maintained adjacent to the molar
teeth for a relaxed wound closure.
■ Sharp dissection is extended through mucosa, muscle, and periosteum to
raise a full-thickness mucoperiosteal flap, exposing the entire ascending
ramus and posterior body of the mandible (TECH FIG 1C).
■ Care is taken not to dissect the lateral muscular attachments along the
anterior ramus ensuring adequate blood supply to the proximal segment of
the mandible.
■ Expose the inferior border of the mandible in the area of the planned vertical
osteotomy.
■ Keep the periosteum intact to prevent excessive bleeding and herniation of
the buccal fat.
■ Strip enough of the masseter muscle to adequately visualize the planned
vertical osteotomy site (TECH FIG 1D). Keep as much of the masseter as
possible attached to the proximal segment of bone to prevent bony
devascularization. At the anterior extent of the incision, the depressor
anguli oris attaches tenuously to the inferior border of the mandible. This
area must be stripped off sternly to adequately mobilize the mandible after
the osteotomy.
■ Place a notched ramus retractor over the anterior border of the ramus and
strip the lower fibers of the temporalis muscle from the coronoid process. A
curved Kocher clamp is then inserted to retract tissue and expose the entire
border of the ascending ramus (TECH FIG 1E).
■ Dissect the periosteum from the internal oblique ridge to the medial side of
the retromolar area (TECH FIG 1F). Then extend the dissection inferiorly to
the region of the lingula and mandibular canal.
■ A malleable retractor is inserted on the medial aspect of the ramus to
retract and protect the neurovascular bundle (TECH FIG 1G).

(Trang không có chữ)

TECH FIG 1 • A. Exposure is obtained by Langenbeck
retractors to pull away the cheek and a tongue
retractor to protect the tongue. B. An incision is made
along the external oblique ridge halfway up the ramus
to the level of the second molar tooth. Leave enough
gingival cuff to facilitate easy closure. C. Sharp
dissection is undertaken to raise a full-thickness
mucoperiosteal flap to expose the ramus and posterior
body. D. Using a sharp elevator, the masseter muscle
fibers are stripped to expose the planned vertical
osteotomy site. E. A curved Kocher clamp is used to
retract tissue over the ascending ramus. F. The
periosteum is dissected from the internal oblique ridge
to expose the medial ramus. G. A malleable retractor
is used to protect the neurovascular bundle.

■ Osteotomy of the Medial Ramus
■ The medial ramus osteotomy is performed first. This is a horizontal
osteotomy through the medial cortex of the ramus.
■ A short, straight-blade reciprocating saw or a Lindemann bur is used to make
the osteotomy (TECH FIG 2A).
■ The osteotomy should not extend more than 2 cm posteriorly (Hunsuck
modification) and should be low and parallel to the occlusal plane (TECH
FIG 2B).
■ By keeping the medial osteotomy short and low (TECH FIG 2C); the
incidence of a “bad split” is reduced.
■ Ensure that the osteotomy extends to the medullary bone (TECH FIG 2D).
■ The osteotomy is then directed anteriorly, remaining inside the buccal
cortex, into medullary bone, and ends inferiorly, immediately lateral to the
second molar tooth (TECH FIG 2E).
■ The presence of an impacted wisdom tooth may make the osteotomy
difficult. In this case, the osteotomy is carried through the tooth as if it were
bone.
■ Avoid excessive angulation of the saw blade, keeping it parallel to the
osteotomy, so as not to weaken the buccal cortex and cause a fracture.

TECH FIG 2 • A. The medial osteotomy is made with a
reciprocating saw blade. B. Hunsuck modification. The
medial osteotomy should not extend more than 2 cm
posteriorly to avoid a bad split. Horizontal osteotomy
parallel to the occlusal plane (see arrow). C. The
medial osteotomy is short, low, and parallel to the
occlusal plane of the mandibular teeth. D. Ensure that
the osteotomy is into bleeding medullary bone. E. The
medial osteotomy is continued onto the anterior ramus
and ends at the level of the second molar.
■ Mandibular Osteotomy and Split
■ The vertical osteotomy of the mandibular body is then made.
■ Remove the bite block and the curved Kocher clamp to relax the soft tissue

and improve access to the inferior border of the mandible.
■ Place a Channel retractor at the inferior border of the mandible and rotate it
into position to improve visibility of the planned osteotomy site.
■ The assistant may pull on the mandible and rotate it in the opposite
direction to enhance access (TECH FIG 3A).
■ The osteotomy location will depend on the planned buccal extension of the
proximal segment (Dalpont modification).
■ A fissure bur is used to make the vertical osteotomy (TECH FIG 3B).
■ Start the osteotomy at the inferior border and angle it superiorly to join the
anterior osteotomy that was previously completed (TECH FIG 3C).
■ Ensure that the bur penetrates the cortex into bleeding medullary bone.
Take extra care not to injure the neurovascular bundle, which tends to be
situated very close to the buccal cortex in cases of mandibular prognathism
(TECH FIG 3D).
■ Adequately cut the entire inferior border of the mandible and include it in
the osteotomy.
■ After the vertical osteotomy is completed, retractors and bite block are
reinserted in preparation for completion of the mandibular split.
■ A thin 10-mm rigid osteotome is used with a mallet to tap along the entire
length of the osteotomy to confirm completeness of the cortical cuts (TECH
FIG 3E).
■ Twisting of the osteotome should produce movement between the
segments including the inferior border (TECH FIG 3F).
■ To split the mandible, a large, 10-mm osteotome is placed into the osteotomy
near the second molar tooth and a smith (sagittal split spreader) forceps is
placed near the inferior border.
■ By simultaneous twisting and spreading, the two segments are slowly split
under direct vision (TECH FIG 3G).
■ If the split does not start spontaneously, stop and redefine all osteotomies.
■ As the split starts, be certain that the neurovascular bundle is visualized and
remains with the distal segment (TECH FIG 3H).
■ If the neurovascular bundle is still attached to the proximal segment, use
blunt forceps to gently tease it free (TECH FIG 3I).
■ If the split results in transection of the inferior alveolar nerve,
microneurosurgical repair is performed prior to proceeding further.
■ Ensure that the inferior border splits with the proximal segment (TECH FIG

3J), so as to avoid a “bad split.”
■ The mandible should be well supported during the splitting process to avoid
damage to the temporomandibular joint.
■ A curved Kocher clamp is applied to the distal part of the proximal segment
and used as a handle to apply force in all directions to ensure complete
separation of the two segments.
■ The same steps are repeated on the contralateral side with sagittal splitting of
the ramus.

E D

TECH FIG 3 • A. The bite block is removed and the
assistant pulls the mandible laterally, away from the
operator, to enhance access to make the vertical
osteotomy. B. A bur is used to make the vertical
osteotomy. C. Bur completing the vertical osteotomy
and joining it with the anterior ramus osteotomy. D.
Avoid injuring the neurovascular bundle when making
the vertical cut. E. Use a rigid osteotome to complete
the cuts. F. Before completing the split, twist the
osteotome inside the osteotomy. Some separation of
the segments should be seen indicating that the cuts
are complete. G. Simultaneous twisting and spreading
to complete the split. H. Split completed. Notice how
the nerve is not visualized within the proximal
segment and remains with the distal segment. I.

Neurovascular bundle being teased free from the
proximal segment. J. Inferior border completely cut
and remains with the proximal segment.
■ Occlusal Correction and Maxillomandibular
Fixation
■ If there are impacted mandibular third molars, they are removed at this point
using dental elevators.
■ The wisdom tooth will be located within the distal segment and is usually
cut while performing the anterior osteotomy.
■ Avoid fracturing the lingual cortex of the distal segment while removing
the tooth.
■ Using a sharp periosteal elevator, strip any remaining pterygomassetric sling
at the inferior border of the distal segment.
■ This allows free movement of the distal segment and facilitate placement
onto the occlusal splint.
■ Similarly, strip the attachment of the medial pterygoid muscle from the
medial aspect of the proximal segment.
■ This maneuver prevents interference when positioning the distal segment
posteriorly and allows for proper seating of the condyle in the glenoid
fossa.
■ Use a large bur to smooth the contact areas between the two bony segments;
this will ensure proper apposition and rigid fixation.
■ Mobilize the distal segment with digital pressure to ensure that the two
segments move freely.
■ Using 26-gauge wire loops, wire the two jaws together into occlusion using
the prefabricated occlusal splint (TECH FIG 4).

TECH FIG 4 • Occlusal splint used as a guide for
maxillomandibular fixation.
■ Removal of Bony Interference
■ Setting the mandible posteriorly will result in overlap between the proximal
and distal segments.
■ This amount of overlap has to be removed for proper apposition between
the two segments in preparation for rigid fixation.
■ Position the proximal segment with a hemostat or wire positioner with the
condyles properly seated.
■ Mark the proximal segment for the amount of bony overlap that needs to be
removed (TECH FIG 5A).
■ The bony overlap should coincide with the planned setback (plus the width
of the osteotomy cut). Protect the neurovascular bundle during removal the
bony overlap with a saw or rongeur (TECH FIG 5B).
■ Remove enough bone to facilitate optimal bone contact between the distal
and proximal segments.
■ Check the lingual plate of the distal segment to determine the need for
removal of further bony interferences.

TECH FIG 5 • A. Marking the proximal segment for the
amount of bony overlap indicated for removal. B. Bony
overlap removed with a saw.
■ Condylar Positioning and Rigid Fixation
■ Using a wire instrument or a fine curved hemostat applied to the most distal
edge of the proximal segment, digital pressure is applied extraorally at the
angle of the mandible to seat the condyle in the glenoid fossa.
■ Enough pressure is applied to seat the condyle into its preoperative centric
relation (TECH FIG 6A).
■ The inferior borders of the proximal and distal segments are lined up so
that there is no palpable step in the final position.
■ A bone clamp is used to hold the two segments together in that position in
preparation for rigid fixation.
■ Rigid fixation is achieved by three or four bicortical screws placed
transcutaneously.
■ A lateral neck stab incision is made just below the inferior border of the
mandible at the level of the gonial notch.
■ A hemostat is then used to bluntly dissect through the stab incision.
■ The trocar is introduced through the neck incision to gain access
intraorally.
■ Use two fingers intraorally to guide the trocar to pierce the periosteum and
reach the bone (TECH FIG 6B–E).
■ Remove the pin and place the cheek retractor to improve visualization.

■ The drill is introduced through the trocar and used to drill through both
proximal and distal segments (TECH FIG 6F).
■ The screw location is determined by areas of best bony contact, away from
the neurovascular bundle.
■ Screws should be placed as far apart as possible to improve stability.
■ They are placed either in a straight line across the superior border or in a
triangular fashion with one screw placed at the inferior border (TECH FIG
6G).
■ After each hole is drilled, the trocar is maintained in position, the hole is
measured, and the screw is placed accurately through the trocar and gently
tightened (TECH FIG 6H).
■ While tightening the screw, ensure that the screw is engaging the distal
segment. If the two segments are able to be pushed apart, the screw should be
removed and a new hole drilled.
■ Ensure that the screws do not compress the bone segments, which may result
in displacement of the condyle resulting in relapse (TECH FIG 6I).
■ The same steps are repeated on the contralateral side to fixate the bony
segments.
■ An alternative to screws is to use a plate with monocortical screws to secure
the two segments together.

TECH FIG 6 • A. A wire instrument is used to seat the
condyle while simultaneously applying external digital
pressure. The bone clamp is then tightened to hold

the two segments together in preparation for rigid
fixation. B. Stab incision in the neck at the level of the
gonial notch. C. Blunt dissection using a hemostat
through the stab incision. D. The trocar is inserted
through the incision. E. Trocar gaining access
intraorally using two fingers as a guide. F. Drill
introduced through the trocar. G. Screw configuration.
H. Keep the trocar absolutely still after drilling the hole
and then place the screw. I. Positional screws are
placed to engage both segments without displacing
the condyle from the glenoid fossa.
■ Completion
■ Remove maxillomandibular fixation and determine the occlusion.
■ The mandible is opened and closed multiple times to check that the
occlusion is symmetric, stable, and reproducible, as planned.
■ If the occlusion is not correct, do not be tempted to “manipulate” the
mandible into occlusion with elastics or wires. Rather, remove the fixation
and repeat the fixation steps as above, ensuring that the condyles are
passively seated within the glenoid fossa.
■ The wounds are then thoroughly irrigated and closed with continuous,
watertight 3-0 chromic.
■ The skin stab incisions are approximated with 5-0 nylon sutures.
■ The mouth is irrigated and suctioned and the throat pack is removed.
■ Place interdental elastics to secure the occlusion. The elastics are placed in a
class III fashion to reinforce the setback movement.
PEARLS AND PITFALLS
Physical
findings
■ Class III skeletal relationship can be due to mandibular prognathism,
maxillary hypoplasia, or a combination of both. Accurate diagnosis is
critical to determine the appropriate surgery to correct the deformity.

■ Mandibular setbacks in general reduce airway space at the level of the
base of tongue. This can create obstructive sleep apnea.
Technique
■ Leaving an insufficient cuff of gingiva when making the incision will
lead to difficulty suturing and possible wound dehiscence.
■ Improper handling of the tissue during dissection may lead to
perforation of the periosteum, herniation of buccal fat, hemorrhage,
and excessive postoperative swelling.
■ Making the medial ramus osteotomy too far posteriorly may lead to a
bad split. Keep the medial osteotomy short and low, closer to the
occlusal plane of the mandibular teeth.
■ Ensure that all the osteotomies are deep enough into bleeding
medullary bone.
■ The anterior ramus osteotomy should be precise to avoid weakening of
the buccal cortex resulting in fracture of the proximal segment.
■ When making the vertical osteotomy, be certain to completely cut the
inferior border of the mandible to avoid a bad split.
■ Be careful not to cut too deep in the area of the neurovascular bundle.
■ When performing the split, the two segments should separate easily;
the inferior border of the mandible splits and stays with the proximal
segment. If the mandible is not splitting with ease, stop and redefine
the osteotomies.
■ If a bad split occurs, complete the splitting process as planned, and
fixate the fractured fragments similar to a mandible fracture.
■ Ensure that all bony interferences have been removed.
■ Choose the location of the skin stab incisions carefully to avoid
struggles with screw fixation. This step can be very frustrating if the
trocar is not kept absolutely still after drilling the holes. Redrilling the
holes multiple times may weaken the bone and jeopardize the fixation.
■ Appropriate positioning of the condyle is the most critical step of the
procedure.
■ Immediately after removal of the maxillomandibular fixation, the
occlusion should be exactly as planned. Do not accept an incorrect
occlusion. There is no better time to correct this problem than at this
stage, in the operating room.
POSTOPERATIVE CARE
■ The patient is generally extubated in the operating room and taken to the
recovery room breathing spontaneously. If there are any airway concerns, the
patient may be taken to the ICU while still intubated.

■ If any airway need arises, the interarch elastics may be removed and replaced
later when the patient is stable.
■ The patient is maintained on a soft diet for 6 weeks.
■ The elastics and splint are removed in 2 weeks and guiding elastics placed.
OUTCOMES
■ Relapse after the BSSO setback depends on the magnitude of the setback,
especially in growing individuals. Relapse rates reported in the literature vary
widely, with a range of 7% to 50%.
■ Cessation of lower jaw growth in individuals with true mandibular excess may
occur later than it does in individuals with normal occlusion. For this reason,
surgery is best delayed until confirmation of growth cessation (comparison of
lateral cephalograms obtained 6 months apart).
COMPLICATIONS
■ An unfavorable bad split is not an uncommon complication, with an incidence
of up to 23%.
■ A bad split could be a fracture of the buccal/lingual plate, or a more serious
situation in which the condyle remains with the distal segment.
■ If this occurs, an additional osteotomy is required to free the condyle (FIG
3).
■ Occurrence of a bad split should be recognized intraoperatively and
additional rigid fixation may be needed.
■ Injury to the inferior alveolar nerve may occur while making the osteotomies
or while placing the screws. The reported incidence varies greatly in the
literature, but patients seem to adapt well to the sensory deficit in the long
term.
■ Lingual nerve injury is a rare complication. It occurs during the subperiosteal
dissection along the medial ramus, or during bicortical screw fixation. Avoid
using very long screws (more than 15 mm) that extend beyond the lingual
cortex.
■ Injury to the facial nerve can occur but is a very rare complication.

FIG 3 • A bad split can occur with fracture of the buccal
cortex or higher near the condyle, resulting in a third
segment.
■ Significant bleeding is rarely encountered. Potential sources are the facial
artery and the retromandibular vein. It is prevented by careful surgical
technique and protection of the soft tissue.
■ Wound dehiscence and/or infection are rare complications and are most often
related to poor oral hygiene.
REFERENCES
1. Trauner R, Obwegeser H. The surgical correction of mandibular prognathism
and retrognathia with consideration of genioplasty. Oral Surg. 1957;10:787-
792.
2. Dalpont G. Retromolar osteotomy for the correction of prognathism. J Oral
Surg. 1961;19:42-47.
3. Epker BN. Modifications in the sagittal split osteotomy of the mandible. J
Oral Surg. 1977;35:157-159.
4. New GB, Erich JB. The surgical correction of mandibular prognathism. Am J

Surg. 1941;53:2-12.
5. Profit WR, Fields HW, Murray LJ. Prevalence of malocclusion and
orthodontic treatment needed in the united states: estimates from the
NHANES-III survey. Int J Adult Orthodon Orthognath Surg. 1998;13:97-107.
6. Doucet JC, Morrison AD, Davis BR, et al. The presence of mandibular third
molars during sagittal split osteotomies does not increase the risk of
complications. J Oral Maxillofac Surg. 2012;70:2153-2163.

44
CHAPTEROsseous Genioplasty
Mark E. Walker and Derek M. Steinbacher
DEFINITION
■ Osseous genioplasty is an operative technique wherein the surgeon performs
an osteotomy proximal to the mental prominence allowing for the repositioning
of the chin to improve facial harmony.
■ Mobilizing this segment enables the surgeon to address the complete spectrum
of chin deformities including asymmetry, as well as vertical and sagittal
deficiency, and excess.
■ Size, shape, and position of the chin can enhance or detract from normal facial
harmony and symmetry.
■ Chin appearance influences social perceptions of masculinity and femininity.
ANATOMY
■ Anterior labial vestibule of the lower lip is the outermost layer forming the
labiogingival sulcus.
■ Deep to the labiogingival mucosa, the two bellies and median raphe of the
mentalis muscle insert onto and cover the chin.
■ Mentalis muscle is the sole elevator of the lower lip and chin providing major
vertical support.
■ Mental nerve courses inferiorly (4.5 ± 1.9 mm) and anteriorly (5.0 ± 1.8 mm)
within the canal prior to exiting at the mental foramen (FIG 1).

FIG 1 • Mental nerve courses inferiorly (4.5 ± 1.9 mm)
and anteriorly (5.0 ± 1.8 mm) within the canal prior to
exiting at the mental foramen.
■ Osteotomy is designed inferior to this path to avoid damage to the mental
nerve.
■ Submental posterior insertion of the genioglossus muscle is responsible for
blood supply to the bone flap following osteotomy.
PATHOGENESIS
■ Chin asymmetry and/or malposition can be congenital or traumatic in etiology.
■ Malocclusion and maxillomandibular discrepancy can contribute to chin
malposition.
NATURAL HISTORY
■ In the setting of an open bite, progressive worsening of retrognathia, often
perceived as microgenia, should be investigated for possible
temporomandibular joint resorptive processes, such as idiopathic condylar

resorption.
PATIENT HISTORY AND PHYSICAL FINDINGS
■ Inquire about any history of dentofacial trauma or prior maxillofacial surgery.
■ Assess patient for maxillomandibular discrepancy or obvious dentofacial
abnormalities.
■ Simple visual inspection of the vertical and sagittal position can identify
microgenia, macrogenia, and chin asymmetry.
■ Microgenia, or small chin, is defined as some combination of vertical and
sagittal deficiency (FIG 2A).
■ Macrogenia, or large chin, is defined as some combination of vertical and
sagittal excess (FIG 2B).
■ Asymmetry assessed on frontal view can present with vertical and/or
rotational components (FIG 2C).
■ Ideal chin projection is described in relation to the lips, nose, and midface.
■ Cephalometrics is a powerful tool to generate objective descriptors of chin
position.
■ Distance between soft tissue nasion to soft tissue chin (2 mm)
■ Depth of the labiomental fold (4 mm)
■ Cervicomental angle (acute vs obtuse)
■ Ricketts S-line
• Line that connects the soft tissue nasion with the menton, the distance from
which measures 2 mm at the upper lip prominence and 4 mm at the lower
lip prominence1 (FIG 3A).
■ Riedel plane
• Line that connects but does not cross the most prominent portion of the
upper and lower lips and connects with the soft tissue menton2 (FIG 3B).

FIG 2 • A. Vertical and sagittal microgenia. B. Vertical
and sagittal macrogenia. C. Frontal asymmetry
secondary to unilateral vertical microgenia and rotation.
■ Facial convexity angle
• On lateral view, this is the angle defined by the pogonion position in relation