Background
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 obviated. [1, 2]
In 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.
Views of a person with Apert syndrome are below.
Frontal view of a patient with Apert syndrome. Note the classic stigmata of exophthalmos, hypoplastic maxilla, saddle-nose deformity, and craniofacial dysostosis.
Lateral view of a patient with Apert syndrome. Note the orbital exorbitism and maxillary deficiency.
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
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. [3] Distraction cannot only achieve the aesthetic 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. [4, 5, 6]
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. [7]
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 aesthetics 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.
Relevant Anatomy
The maxilla (see the image below) has several roles. It houses the teeth, forms the roof of the oral cavity, forms the floor of and contributes to the lateral wall and roof of the nasal cavity, houses the maxillary sinus, and contributes to the inferior rim and floor of the orbit. Two maxillary bones are joined in the midline to form the middle third of the face.
In the midline of the anterior surface of the maxilla is found a prominence, called the anterior nasal spine, with a lateral concave rim, called the nasal notch, that forms the floor of the piriform aperture. Inferiorly, the alveolar process of the maxilla houses the teeth, including central incisors, lateral incisors, canines, 2 premolars, and 3 molars in adults. The tooth roots form vertical, wavelike eminences in the anterior face of the maxilla; the canine root is the most prominent. The canine root forms a vertical ridge, termed the canine eminence, in the anterior face of the maxilla. The shallow fossae medial and lateral to the canine eminence are called the incisive fossa and the canine fossa, respectively.
For more information about the relevant anatomy, see Facial Bone Anatomy.
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.
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Frontal view of a patient with Apert syndrome. Note the classic stigmata of exophthalmos, hypoplastic maxilla, saddle-nose deformity, and craniofacial dysostosis.
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Lateral view of a patient with Apert syndrome. Note the orbital exorbitism and maxillary deficiency.
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Lateral postoperative view of a patient with Apert syndrome and an external distractor in place. Note the improvement in the midface projection.
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Lateral preoperative view of a patient with Crouzon syndrome. Note the obvious characteristics of mandibular prognathism, small maxilla, exophthalmos, and parrot-beaked nose.
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Lateral preoperative cephalogram demonstrates midface regression despite the use of the traditional approach of osteotomy and immediate advancement.
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Lateral postoperative view of a patient with Crouzon syndrome and an external distractor in place. Note advancement of the maxilla and correction of mandibular prognathism.
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Lateral view demonstrates grossly evident maxillary hypoplasia in a patient with Pfeiffer syndrome.
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Frontal view of a patient with Pfeiffer syndrome and maxillary retrusion severe enough to require a tracheotomy.
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Lateral postoperative view of a patient with Pfeiffer syndrome and an internal distractor. Note evidence of midface improvement. Decannulation was performed several weeks later.
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Three-dimensional reconstructed CT scan demonstrates preoperative maxillary deficiency.
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Three-dimensional reconstructed CT scan demonstrates preoperative maxillary deficiency.
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Postoperative reconstructed 3-dimensional CT scan in the same patient as in Images 10-11 depicts improved skeletal balance with advancement of the mid face.
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Postoperative reconstructed 3-dimensional CT scan in the same patient as in Images 10-12 depicts improved skeletal balance with advancement of the mid face.
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Left maxilla.
