Distraction osteogenesis (DO) is a surgical technique for reconstruction of bony deformities. It involves making osteotomies in the bone and gradually displacing the two bony segments apart. This results in new bone formation that fills the gap and stretches the overlying soft tissue envelope. DO was first used in orthopedics to lengthen long bones. The technique was not well understood until Ilizarov, a Russian orthopedic surgeon, laid down its foundation in 1952 through his work in rural Siberia. Distraction of the maxilla was first performed in monkeys in 1965 by expanding the midpalatal suture. The first application of DO in the craniofacial region was a mandible distraction reported by McCarthy and colleagues in 1992. Since then, application of DO to the craniofacial skeleton has increased exponentially. Traditionally, maxillary hypoplasia has been treated by Le Fort I osteotomy but today DO at the Le Fort I level has become the workhorse for managing maxillary retrusion in difficult cases because of soft tissue limitations and large advancements.
Indications for maxillary distraction osteogenesis
There are a variety of indications for maxillary distraction. The majority of cases are patients who have craniofacial deformities. Those who have maxillary deficiency include patients who have Apert’s, Crouzon’s, or Pfeiffer’s syndrome and maxillary cleft lip and palate, to name a few. DO can improve their facial esthetics and in those who have airway issues resolve them by increasing the size of the airway. Patients who have facial clefts usually have severe maxillary hypoplasia. Although they may undergo a traditional Le Fort I osteotomy with bone grafting, there is a variable amount of relapse as a result of palatal scarring and soft tissue resistance. Obstructive sleep apnea commonly is seen in many of the children who have craniofacial syndromes. They and select adults who have deficiency in their upper airway dimension can benefit from DO. Patients who have hemifacial microsomia are the second most common congenital craniofacial malformation after cleft lip and palate. They may need a combination of maxillomandibular distraction. Deficient maxillary alveolar ridge secondary to traumatic avulsion of teeth and their accompany bone segments can be treated by distraction as can patients who have facial deformities secondary to incompletely managed complex midfacial fractures.
Contraindications for maxillary distraction osteogenesis
The only true contraindication is a noncompliant patient. As long as there is adequate bone for placement of the distraction device, there is no contraindication. Younger patients are a relative contraindication due to their bone being quantitatively and qualitatively insufficient for the device placement.
Contraindications for maxillary distraction osteogenesis
The only true contraindication is a noncompliant patient. As long as there is adequate bone for placement of the distraction device, there is no contraindication. Younger patients are a relative contraindication due to their bone being quantitatively and qualitatively insufficient for the device placement.
Advantages of maxillary distraction osteogenesis
The underlying physiology of DO is that bone grows when stretched. This new bone formation is a result of membranous ossification. There are three phases of DO: latency, activation, and consolidation. DO also causes a gradual increase of the soft tissue volume because of stretch forces applied with bony distraction, termed distraction histiogenesis . (See Chapter one for a more in-depth discussion of DO and histiogenesis.) Increase in the soft tissue through distraction histiogenesis is believed an advantage of DO over traditional midface advancement techniques. Traditional midface advancement osteotomies cause immediate bony correction but do not allow for gradual compensatory soft tissue changes. As a result, scarring and memory in the soft tissue occur in the preoperative period. These negative soft tissue forces on the advanced bone segments are the main reason for relapse after traditional midface advancement surgeries. From a stability point, a traditional Le Fort I osteotomy is limited as to how much advancement can be achieved. Many surgeons consider 10 to 15 mm to be the maximum advancement attainable. Relapse of a Le Fort I osteotomy in the range of 4% to 40% has been reported by several investigators. In contrast, the more gradual stretching of the soft tissue seen with distraction is believed to prevent bone relapse. This is important especially when large advancements are needed, such as in the many individuals who have midface hypoplasia caused by cleft lip and palate. In many instances, the class III skeletal relation is so severe a compromise is chosen where the maxilla is advanced and the mandible is set back. With DO, the amount of advancement is unlimited obviating a bilateral sagittal split osteotomy setback ( Fig. 1 ). With large maxillary advancements, a bone graft harvested from a secondary site is used to increase stability. With distraction, however, the need for a bone graft is eliminated. DO at the Le Fort I level can be performed as a same-day procedure especially when using an external distractor. It also eliminates the need for blood transfusion or permanent hardware.
In summary, there are five significant advantages to DO: large advancements; low relapse rates resulting from simultaneous soft tissue expansion; decreased operative time and, hence, morbidity; the ability to vary the height of the osteotomy when internal bone devices, such as bone plates, are not needed; and decreased incidence of velopharyngeal insufficiency in cleft patients.
Disadvantages of distraction osteogenesis
There are several disadvantages of DO when used to correct skeletal discrepancies. It is technically demanding and imprecise compared with orthognathic surgery. Its imprecise nature is primarily a problem of vector control. When orthognathic surgery is executed, segments of bones and their accompanying soft tissue are precisely translated in space as dictated by model surgery and splints. With distraction, segments are moved more slowly but are influenced by the attached tissues (secondary vectors) during the movement. Additionally, even when distractors are prebent on stereolithographic models, application of them in an operating room is less precise than with model surgery. Significant patient compliance is required and many office visits are necessary, which increases overall treatment time. Finally, the procedure is more expensive as a result of the cost of the individual distractors.
Vectors for maxillary distraction osteogenesis
There are primarily three vectors: anterior-posterior—severe class III skeletal malocclusion due to maxillary hypoplasia, as in cleft patients and majority of dentofacial deformities; vertical—anterior open bite cases mainly in combination with the anteroposterior deficiency seen in syndromic patients; and horizontal or transverse discrepancy with narrow maxilla leading to V-shaped palate and teeth crowding. Finally, there may be a combination of all of the deficiencies. The same distraction devices can be used to achieve maxillary advancement and vertical height, whereas transverse widening of the maxilla is achieved by a separate device applied to the palate. Currently, there are no devices to achieve correction of a skeletal problem in all three dimensions.
Types of distractors
There are two types of distractors based on anchorage for the anteroposterior and vertical advancement of maxilla: internal and external devices. (See the article by Van Sickels and Reddy elsewhere in this issue for a more in-depth discussion of the types of distractors.)
Internal distractors
Internal distractors are submerged under the soft tissue with a small rod for distraction protruding through the oral cavity or through the skin ( Fig. 2 ). The device is placed with anchoring plates on either side of the osteotomy. They are best used for larger bones and require a second-stage surgery for their removal. There also are modular types of devices, which are custom made. The advantages of internal distractors are better patient acceptance, direct adaptation to bone reducing the distance from the callus to the activating axial screw, and better wound management.
