For the purposes of this article, lengthening of the mandible is subdivided into vertical lengthening of the ramus as in patients with hemifacial microsomia and horizontal lengthening of the mandibular body as in patients with Pierre Robin syndrome. Unfortunately, many of the patients that present for treatment of mandibular deformities often have a combination of both vertical ramal deficiencies and horizontal body deficiencies. One of the cases presented includes an intrarch distraction of the body of the mandible illustrating how complex are some patients with skeletal discrepancies. The design of commercially available distractors may not satisfy the needs of an individual patient. This issue is addressed in greater detail elsewhere in this issue. Depending on the age of the patient and the complexity of the movement, a single vector or a multivector distractor may be needed. In very young patients or in individuals with complex movements, an external distractor may be necessary. As with orthognathic surgery, lengthening of the vertical aspect of the mandibular ramus is technically more difficult than lengthening the body of the mandible to correct sagittal deficiencies.
Indications
A number of syndromic patients may present for care either at a pediatric age where airway issues prompt intervention, or later when conventional osteotomies may not give the best results. These can include but are not limited to hemifacial microsomia (types I–III), Treacher Collins syndrome, Pierre Robin syndrome, and Stickler’s syndrome. Intervention in a pediatric patient may obviate the need for a tracheostomy or allow removal of the tracheostomy (see later). In some cases, patients with severe mandibular deficiency have or are on the borderline of having obstructive sleep apnea.
There is a number of nonsyndromic patients, however, who can benefit from distraction osteogenesis. Advancement of the mandible greater than 7 mm becomes increasingly more unstable with traditional osteotomies. Large advancements of the mandible are a relative indication, but when technical difficulties with a thin ramus or relapse after a previous sagittal split are accompanied with a large movement, then distraction is a reasonable alternative. A less commonly seen indication is a patient with unusual mandibular anatomy that makes doing a traditional mandibular osteotomy difficult (see later). Another relative indication for advancement by distraction is a patient with temporomandibular joint (TMJ) symptoms, especially when they need a large advancement. The concept is that distraction provides a gradual lengthening of mandible and may decrease forces on the TMJ.
Vertical lengthening of the ramus
Even though distraction osteogenesis vertically to augment the mandibular ramus has been reported, there are still many variables involved in the diagnosis and treatment planning to solve all the growth and consequent asymmetry problems using the technique. The most common use of vertical distraction of the ramus is for types I and II hemifacial microsomia patients (see later). Distraction during growth, although challenging, can address some of the soft tissue and hard tissue issues that these patients have. Prediction of the growth of the opposite side and vector control, however, remains difficult. In addition, when lengthening the ramus against an intact joint, the pterygomasseteric sling is stretched. This creates a vertical force on the condylar head against the glenoid fossa compressing the intracapsular structures. The ultimate consequence may be unpredictable resorption, remodeling, or adaptation of the TMJ. These types of pressures can cause the cartilage surfaces to be flattened, putting pressure on the synovial spaces. Histologic changes occur in the subchondral bone, where there is a reparative phase with vertical condylar loss and possible damage of the articular tissues. Most authors who distract the vertical ramus during growth suggest that the patient may need a secondary surgery when growth is complete because of some of these concerns.
Vertical lengthening of the ramus
Even though distraction osteogenesis vertically to augment the mandibular ramus has been reported, there are still many variables involved in the diagnosis and treatment planning to solve all the growth and consequent asymmetry problems using the technique. The most common use of vertical distraction of the ramus is for types I and II hemifacial microsomia patients (see later). Distraction during growth, although challenging, can address some of the soft tissue and hard tissue issues that these patients have. Prediction of the growth of the opposite side and vector control, however, remains difficult. In addition, when lengthening the ramus against an intact joint, the pterygomasseteric sling is stretched. This creates a vertical force on the condylar head against the glenoid fossa compressing the intracapsular structures. The ultimate consequence may be unpredictable resorption, remodeling, or adaptation of the TMJ. These types of pressures can cause the cartilage surfaces to be flattened, putting pressure on the synovial spaces. Histologic changes occur in the subchondral bone, where there is a reparative phase with vertical condylar loss and possible damage of the articular tissues. Most authors who distract the vertical ramus during growth suggest that the patient may need a secondary surgery when growth is complete because of some of these concerns.
Horizontal lengthening of the body
Horizontal lengthening of the body of the mandible may be used in pediatric patients where airway is an issue. In these patients, an inverted “L” osteotomy is usually done with either an internal distractor with an extraoral port, or an extraoral distractor. In nongrowing adults, the distractor can exit intraorally, as in the case shown later. Relapse with mandibular advancement by a sagittal split osteotomy is well known. Less relapse with distraction is speculative because there are no controlled studies of advancement with traditional osteotomies versus distraction. What is not disputed is that distraction does allow large advancements not possible with traditional osteotomies without additional bone grafts.
Ankylosis of the temporomandibular joint
Ankylosis of the TMJ especially during or before growth is completed presents several challenges to the clinician. Here there may be both deficiencies in the vertical portion of the ramus and the horizontal portion of the body. In addition, there may be compensatory changes in the maxilla ( Fig. 1 ).
For lengthening the ramus in TMJ ankylosed patients the surgical procedure is performed in two stages. The first step is the ramus and body lengthening, which allows the clinician a predictable mandibular ramus vertical augmentation, and muscle lengthening. The second surgical step is planned once the consolidation process is completed, and consists of freeing the TMJ ankylosis by a gap arthroplasty. Following this protocol, the clinician has better control of the two distracted segments. This avoids pressure against the new surgically created joint, and allows active muscle physiotherapy after releasing the joint.
Cases
Case 1: vertical deficiency of the ramus with a concomitant anteroposterior deficiency
A 10-year-old girl with type 2A hemifacial microsomia presents with progressive asymmetry of her maxilla and mandible to the left ( Fig. 2 ). She was taken to surgery, where a horizontal line was scribed on the left ramus superior to the site of the third molar. A single vector internal distractor was temporarily placed intraorally with an external port. An anteroinferior vector was chosen to anticipate growth of the mandible on the opposite side while lengthening the ramus ( Fig. 3 ). The distractor was removed and a near complete osteotomy was made. The distractor was replaced and the osteotomy was completed. She had a 5-day latency period followed by a twice-a-day rhythm to achieve 1 mm of distraction per day. She was distracted for 15 days to a slightly overcorrected position ( Fig. 4 ). Frontal symmetry was achieved; however, the lower midline was approximately 2 mm to the right of maxillary midline. At 1 year, symmetry is still good, but the left side is not as full as the right ( Fig. 5 A, B). Occlusally, she is class I, but from the submental vertex photograph, she is less prominent on her left side ( Fig. 5 C, D). Although distraction during growth can help an asymmetry, often these patients need secondary osteotomies when growth is complete.
Case 2: horizontal deficiency of the mandible with unusual anatomy
A 17-year-old boy was referred for distraction osteogenesis after a failed attempt at completing a bilateral sagittal split osteotomy advancement ( Fig. 6 ). The original surgeon commented that the ascending ramus was very thin and that there was an unplanned fracture of the proximal segment on one side. The segments were then fixed in place to allow healing. A three-dimensional CT was obtained and from that a stereolithographic model was made ( Fig. 7 ). They confirmed that rami on both sides were very thin. Four months after the first surgery, an osteotomy was planned anterior to the esthetic unit of the angle, bileveled on the medial aspect of the ramus. The distractors were prebent on the model and the primary vector was chosen to parallel the maxillary occlusal plane. ( Fig. 8 ). This slightly upward primary vector was chosen to account for the inferior pull of the suprahyoid muscular (intrinsic vectors). A 5-day latency was chosen with a twice-a-day rhythm to achieve 1 mm per day for 10 days. Consolidation time was 3 months from the time of surgery. A lateral cephalogram confirms the desired advancement ( Fig. 9 ). The distractors were removed at 3 months. At this point orthodontic management commenced to achieve ideal interdigitation of the occlusion ( Fig. 10 ).
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