Distraction Osteogenesis of the Maxilla

Synonyms and related keywords: distraction osteogenesis of the maxilla, bone deformities, reconstructive surgery, Crouzon syndrome, Crouzon's syndrome, Pfeiffer syndrome, Pfeiffer's syndrome, Apert syndrome, Apert's syndrome, maxillary distraction, midface distraction, bony distraction
Distraction osteogenesis is a surgical technique for reconstruction of bony deformities. Increased amounts of both bone and soft tissue are created as a result of the gradual displacement of surgically created bony fractures. Because distraction techniques generate new bone, the morbidity of harvesting bone from other sites is obviatedIn terms of techniques, traditional advancement of the mid face with osteotomies and harvesting of bone grafts are associated with high rates of midface regression and morbidity. Distraction in the mid face decreases intraoperative morbidity and rates of postoperative midface regression. Both of these factors have led to an increase in the popularity of midface distraction, demonstrated in a survey of craniofacial surgeons, who reported that the mid face was the site of distraction in 28% of their cases.
History of the Procedure: Osteogenic distraction is the result of the evolution of techniques for bone fixation, skeletal traction, and osteotomy. Osteogenic distraction was first used in orthopedics to lengthen bones after planned osteotomies. However, the complication rate remained high and the technique was not understood until Gavriel Ilizarov, a Russian orthopedic surgeon, performed detailed studies in 1952. Working in a rural clinic in Siberia, Ilizarov did not have the requisite equipment for surgeons used at that time. Therefore, he performed studies by using his own equipment and procedures, which proved to be more effective than contemporary procedures, as evidenced by modern day use of his methods.
Distraction of the maxilla was first performed by expanding the midpalatal suture in monkeys in 1965. The first human application of maxillary distraction in craniofacial surgery was a mandible distraction in 1989. Case reports of its application in maxillary distraction were published in 1992.
Pathophysiology: The principle of distraction osteogenesis is based on new bone formation that develops when tension forces are applied. This new bone formation is a result of membranous ossification.
The viability of bone cells (osteocytes and osteoblasts) is crucial in distraction osteogenesis. Bone viability can be enhanced by limiting damage to the cortex by making distinct cuts. Bone viability can also be enhanced by preserving the blood supply to the bone, which is necessary for its growth, by leaving adequate soft tissue coverage. Endothelial cells may stimulate angiogenesis and play an important role as well.
Distraction histogenesis is a term that describes the gradual increase in soft tissue volume in response to the stress forces applied with bony distraction. Traditional midface techniques provide immediate bony correction but do not allow for compensatory growth of the soft tissues. As a result of scarring and memory, the soft tissue often contracts to its preoperative state. This is thought to be the main reason for the high rate of relapse of midface insufficiency after the use of traditional techniques. In contrast, distraction techniques create a gradual increase in the amount of soft tissue by preventing its contraction.
Indications for distraction osteogenesis of the maxilla are craniofacial anomalies, facial clefts, severe sleep apnea, hemifacial microsomia, a deficient alveolar ridge, and complex trauma.
Craniofacial anomalies account for most indications for maxillary distraction. Distraction may improve aesthetic contouring of the face, resolve sleep apnea, and improve orthognathics. Distraction can be applied to a wide variety of anomalies with maxillary deficiency; Crouzon syndrome and Pfeiffer syndrome account for most of the reported cases. Advancement of the lower maxilla, as in a Le Fort I osteotomy, or complete midfacial advancement, as in a Le Fort III procedure, can be accomplished. Distraction cannot only achieve the aesthet
goals of realignment but also apnea resolves, obviating tracheostomy.
Patients with facial clefting often have maxillary hypoplasia. Even after cleft repair and orthodontic treatment, severe maxillary deficiency may persist. These patients traditionally undergo repair with Le Fort I osteotomy advancement with internal fixation. This approach often fails because of palatal scarring, soft tissue memory, and scar formation. External distraction leads to slow expansion of the surrounding tissues, allowing the body to accommodate the new position of the maxilla. Krimmel et al found that external distraction is superior to traditional techniques in patients who have facial clefting with maxillary hypoplasia (Krimmel, 2001).
Sleep apnea in select adults with a deficiency in their upper airway dimension may be an indication for distraction.
Hemifacial microsomia may respond to a combination of maxillomandibular distraction. Satoh et al found that distraction osteogenesis is a safe and effective method for reducing the use of orthodontic appliances to 7-14 years (Satoh, 2002).
A deficient alveolar ridge is another indication for maxillary distraction. A deficiency of the alveolar ridge may be the result of circumstances, such as traumatic avulsion of mandibular incisor teeth or a congenital deformity. Expansion of the alveolar housing creates a site for the placement of a dental implant. This may improve ridge esthetics for a pontic, or replacement, artificial tooth or teeth that are mounted on a fixed or removable dental appliance, and it may expand the alveolus to allow for orthodontic tooth movement.
Distraction may also be indicated in cases of complex, high-impact midface fractures, especially for the delayed repair of bony fractures of the mid face.

Contraindications: As long as the bone where the distraction device is placed is adequate, the procedure has few contraindications. Young patients must be selected carefully because of their fragile bones and because the amount of bone available for device placement may be inadequate. In infants, numerous studies have demonstrated successful results with the careful selection of infants, with no untoward effects. The surgeon must preoperatively confirm that the strength of the transport and anchorage segments is adequate to withstand forces of mobilization and transport.
Skeletal deformities resulting from bone disease are not a contraindication, as long as enough bone for distraction is available.
Last, the patient's participation is as important as the procedure itself. A noncompliant patient can cause any distraction procedure to fail.
Imaging Studies:
• Patients undergoing distraction require a photographic assessment throughout the distraction to assess their progress.
o Necessary radiographic studies include cephalography, mandibular panoramic (Panorex) imaging, and CT.
o Not all surgeons recommend 3-dimensional reconstructive scanning.
• Several important relationships must be considered before distraction of the mid face is preformed (see Image 1).
o Quantifying the degree of exorbitism is especially important in syndromic patients.
o Important relationships include the maxillary plane and the occlusal plane angle.
o Assessing the anteroposterior deficiency in the mid face in relation to the remaining facial structures
TREATMENT
Preoperative details:
• Devices available for distraction can be subdivided into internal and external devices (see Image 2).
o 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.
o 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.
Intraoperative details:
• Procedure
o Patients require general anesthesia before the distraction device is inserted. Lidocaine with epinephrine 1:100,000 is injected to ensure hemostasis.
o The maxilla can be exposed by using various methods. Usually a Caldwell-Luc exposure is adequate.
o 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.
o 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.
o 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
o In cases in which the mandible and maxilla are to be concomitantly distracted, attention to detail is crucial.
o When the surgeon performs the mandible corticotomy, a maxillary osteotomy can be performed as well.
o 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.
Postoperative details:
• Immediate postoperative period
o After the procedure, all patients must be observed overnight in a monitored hospital bed.
o The postoperative antibiotic course varies from 7-10 days.
o Pain should subside during the first week.
• Latency period
o The latency period is the time delayed before the distraction phase. This period varies widely among surgeons, although most recommend about 4-7 days.
o 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.
o 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.
o 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
o 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.
o 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
o 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.
o 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.
o 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.
Follow-up care: See above 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

Posted by: happie01Posts: 48 :: 10-12-2006 :: | Reply to this Message