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.

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