Distraction Osteogenesis of the Maxilla Treatment & Management

Devices available for distraction can be subdivided into internal and external devices.

• Internal devices are applied under soft tissue cover, with a small rod for distraction protruding through the skin. They are best used for larger bones and require a second stage for their removal. The distractors are placed with anchoring plates on each side of the osteotomy. External devices are located outside the skin, and the bone is held with transcutaneous pins.
• External devices can be applied to smaller bones and removed without a second stage. A skull-anchored distractor, which attaches to a tooth-borne appliance called the rigid external distraction system, can advance the mid face in many directions.

An external distractor is shown below.

Procedure

• Patients require general anesthesia before the distraction device is inserted. Lidocaine with epinephrine 1:100,000 is injected to ensure hemostasis.
• The maxilla can be exposed by using various methods. Usually a Caldwell-Luc exposure is adequate.
• To ensure an adequate amount of mucosa for closure, attention is paid to making the incision superiorly, at least 1 cm above the gum line. After the infraorbital nerve is identified and the skin flap is adequately raised, the osteotomies can be made in the appropriate position.
• In patients with maxillary retrusion and severe exorbitism, a Le Fort III osteotomy may be necessary. In patients with severe sleep apnea, a Le Fort I osteotomy is used to advance the maxilla. In patients with a complex facial fracture, no osteotomy may be necessary if the bone is already mobilized.
• The distraction device is inserted before the osteotomies are completed. A test with application of the distraction device is necessary to ensure that they are functioning.

Combined mandible and maxillary distraction

• In cases in which the mandible and maxilla are to be concomitantly distracted, attention to detail is crucial.
• When the surgeon performs the mandible corticotomy, a maxillary osteotomy can be performed as well.
• The jaws can be wired into intermaxillary fixation, or elastics can be placed during the latency period.

Endoscopic-assisted osteotomies: An endoscopic technique may decrease morbidity of midface distraction.

Immediate postoperative period

• After the procedure, all patients must be observed overnight in a monitored hospital bed.
• The postoperative antibiotic course varies from 7-10 days.
• Pain should subside during the first week.

Latency period

• The latency period is the time delayed before the distraction phase. This period varies widely among surgeons, although most recommend about 4-7 days.
• If the latency period is too long, the patient may have premature fusion of the bones. Children are especially susceptible to premature fusion because of their higher metabolic rates.
• A short latency period may predispose to fibrous union of the 2 distracted bones, inadequate osteogenesis, and decreased callous volume. Early distraction is theorized to disrupt new capillary formation by not allowing the capillaries to mature enough to withstand the distraction forces.
• Several studies have demonstrated no differences in distraction between immediate distraction and latencies of 1, 2, or 3 weeks. The differences may be related to the increased blood supply in the facial skeleton compared with that in the extremities. The craniofacial skeleton is largely formed by intramembranous ossification versus endochondral ossification in the extremities.

Distraction course

• The distraction period varies. According to some of Ilazarov's studies in long bones, the bone should ideally be continually distracted. Patients with a fractionated distraction schedule have less soft tissue injury and increased preservation of blood supply than those distracted once daily. However, most surgeons apply distraction once or twice a day because of convenience.
• The recommended distraction is about 1 mm a day. Distraction that is too aggressive can lead to fibrous union. Distraction that is too slow can lead to early fusion of the bones.

Consolidation period

• The consolidation period is the period of bone remodeling. It should be about twice the length of the distraction phase. The device remains in place, now as a fixation device. Consolidation generally takes approximately 10 weeks to develop.
• The consolidation phase differs in the face compared with long bones in terms of the functional load that exists in this state, differences in bone healing throughout the facial skeleton, and the complex morphology of the distraction chamber.
• Decreased stability of bone segments may lead to the formation of cartilage, then to delayed bony formation or possibly fibrous union. On the contrary, stability of the 2 bone segments directly leads to bony remodeling after 10 weeks of stabilization.

See the Postoperative details section regarding bone stabilization and consolidation. After all of the hardware is removed, follow-up is necessary to ascertain how the patient's distracted area appears in the context of the normal growth of the surrounding tissue. If the patient underwent distraction because of airway compromise, close follow-up with a pediatric otolaryngologist is warranted until the patient's breathing problems resolve.

In one review, 3278 cases were described in surveys sent out to craniofacial surgeons. The results revealed that procedures performed by experienced surgeons resulted in fewer complications than procedures performed by inexperienced surgeons.

Reported complications include the following:

• Velopharyngeal insufficiency

  • Guyette et al examined changes in speech after maxillary distraction osteogenesis.^[5] Although 16.7% of patients had increased hypernasality, 67% had an improvement in overall articulation at 1-year follow-up. The authors concluded that the risk of velopharyngeal insufficiency is similar to that of traditional Le Fort I advancement.
  • Harada examined 6 patients with a facial cleft and its effect on velopharyngeal function. They found no change in the hypernasality rating of patients who underwent distraction of less than 15 mm.^[6]
• Device failure
• Premature fusion of the segments undergoing distraction
• Noncompliance
• Device extrusion
• Wound infection
• Relapse of maxilla in patients
• Possible interference of tooth buds
• Fracture of transport segment
• Fracture of anchorage segment
• Undesirable transport vector

Overall, if the patient can tolerate the distractor, his or her prognosis is good, and a long-lasting result can be expected. However, Krimmel and associates examined cephalometrics postdistraction in patients aged 12-31 years.^[7] They found that distraction was stable at 1 year postprocedure, but further growth in the adolescent facies lead to a decrease in SNA and avascular necrosis of bone (ANB) with a subsequent increase in facial concavity. Similar results were seen by Harada in children with maxillary external distraction.^[6]

Compared with traditional midface advancement with osteotomies and harvesting of bone grafts, distraction in the mid face has decreased intraoperative morbidity and postoperative midface regression. Traditional methods have been associated with a number of complications, including a skeletal relapse rate of 50-60%. Wong and Padwa reported no relapse in 5 patients after 2 years.^[8] A study in adult sheep showed minimal relapse in the 3-month postoperative period and none in the 6- to 12-month postoperative periods. The amount of facial growth at other areas in children and adolescents may lead to residual facial concavities as the patients facial structure matures. Distraction is a relatively minor surgical procedure compared with traditional methods, and it can preserve the integrity of the nerves and the vascular supply.^[9]

A recent study by Iannetti et al compared traditional Le Fort III osteotomies with distraction osteogenesis.^[10] Based on clinical examination and cephalometrics, patients who underwent distraction osteogenesis had farther projection, and distraction osteogenesis was deemed the method of choice for severe midface retrusion.

Future approaches to distraction osteogenesis of the maxilla may involve the following devices or techniques: implantable devices made of bioresorbable materials, multivectorial internal devices, advancement of the mid face without osteotomies (this was performed in an animal study, in which it prevented the morbidity and postoperative sequelae induced with an osteotomy), minimally invasive placement by means of endoscopic techniques, computer-assisted distraction with automated or motorized devices (to improve and quicken distraction techniques), and flexible distraction rods that allow for concurrent occlusal adaptation.

Rapid maxillary expansion remains an area of study.^[11] Koudstaal and associates found that rapid expansion lead to tip of segments in a cadaver model. This was especially seen in tooth-borne devices over bone-borne devices. Rapid expansion may lead the way for further advances in distraction osteogenesis and improving the rate of expansion.