Craniofacial Distraction Osteogenesis Treatment & Management

Although opinion differs regarding the timing of intervention and the type of device to use in distraction osteogenesis (DO), careful preoperative planning and proper case selection are critical to a successful outcome. Initially, acquire all of the necessary preoperative data and analyze data to precisely define existing deformities. Then, identify the various subunits of the craniofacial skeleton that need mobilization and repositioning to determine the nature of the desired osteotomies and the desired vector of displacement to be applied to the osteotomized segment(s) during the distraction phase. Consider both the magnitude and direction of the distraction vector prior to device selection, osteotomy design, and device placement.

Preoperative considerations for mandibular distraction include (1) the preexisting shape of the lower jaw (eg, ramus height, body length, gonial angle), (2) its position relative to the maxilla and cranial base, (3) the presence of asymmetry and mandibular and occlusal plane angles, and (4) the occlusion (eg, anteroposterior relationships, transverse relationships, open bite deformities).

Considerations during planning for procedures involving the midface include (1) the degree of exorbitism, (2) the presence of anteroposterior deficiency within the midfacial bony structures and their position relative to the cranial base (SNA) and the mandible (ANB), (3) the vertical midfacial deficiency or elongation, (4) the maxillary plane and occlusal plane angles, and (5) the occlusal relationships described above.

Selection of the proper distraction device is another important consideration prior to surgery. ^[12] In general, 2 basic devices are available: internal and external.

• Internal devices

  • For the most part, internal devices are buried (with both the fixation components and the distraction mechanism) under soft tissue cover. A small rod extrudes through skin or mucosa, which allows turning of the distraction mechanism. Internal devices are suitable in large bones and have the advantage of being less obtrusive and visible during the distraction and consolidation phase. Their point of application is closer to the point of distraction resistance; and, therefore, internal devices carry a mechanical advantage.

  • However, applying internal devices to small bone segments in the younger patient is technically difficult. Furthermore, early editions of internal devices required a second major surgical procedure to remove them following the consolidation phase. Newer models are being designed whereby the transport mechanism is removed through small incisions following disengagement from the fixation components, which are left in situ.

• External devices: These have the distraction mechanism located outside the skin or mucosa and attach to the bone segments by either transcutaneous pins or wires. External devices tend to have greater flexibility in their range of movement and allow alteration of the distraction vector during the distraction phase. They can be applied to smaller bone segments, and removal is relatively easy. They are cumbersome and visible when in situ, however, and depending on the application, can produce significant soft tissue scars at the pin tracts.

The planning phase requires careful cooperation between surgeon and orthodontist if skeletal movements affect dentition. At the initial surgery, appropriate bone cuts are performed and the distraction appliances are secured.

Use of the distraction technique requires the same operative exposure as conventional craniofacial surgery. Recent studies, however, are looking at less-invasive surgery using endoscopic techniques to complement DO. Completion of the osteotomies is performed as per the preoperative plan. However, prior to complete mobilization of the segments, the distraction appliance is secured to either end of the osteotomy in the predetermined direction of the distraction vector. After loosening the segments, a test distraction should be performed to ensure that the appliances are working and that the bone segments are sufficiently mobilized. The appliances are then returned to the neutral position.

Depending on the procedure, patients generally require a 1- to 5-day postsurgical in-hospital course. Place patients on prophylactic antibiotics and allow a suitable waiting period or latency phase to elapse prior to commencing the distraction phase. During the distraction phase, frequently see patients in the office to ensure that they are advancing the devices. (Periodic plain radiography is useful for this purpose.) After distraction, allow consolidation to occur and subsequently remove the distraction devices.

A number of problems can arise with the distraction process (eg, patient noncompliance, device failure, premature fusion of the segments undergoing distraction). ^[13] These problems necessitate a repeat surgical procedure to reosteotomize the bone segments. Infection at the distraction site may impair the osteogenesis process. During the consolidation phase, nonunion or delayed union results if micromovement across the regenerate occurs. Excessive scarring is also possible, particularly when using external devices. Finally, a relative lack of control in repositioning the bone segments exists compared with conventional surgery, which leads to a less-than-ideal final position.

Distraction osteogenesis (DO) holds great potential for various osseous defects that can be encountered within the craniofacial skeleton. ^[14] Numerous advantages seem to be emerging with the technique. The initial osteotomy procedure is less invasive and does not carry the attendant limitations and complications that may be associated with conventional bony mobilization and repositioning. Furthermore, the potential for substantially larger movements and greater postoperative stability exists. Surgical intervention is possible in the very young patient and, apparently, much earlier than with standard craniofacial technique.

DO, however, does not correct underlying growth disturbances in craniofacial patients. DO does not reduce the need for orthodontic intervention, and it carries the disadvantage of requiring a second procedure to remove the distraction appliances. As experience with DO accumulates, this technique is becoming established as an essential tool in the craniofacial surgeon's armamentarium. The indications in which it is the standard of care are slowly being defined.

Several new developments are on the horizon in the field of craniofacial DO. A successful combination of endoscopic techniques to create osteotomies and insert distraction devices will move distraction into the field of minimally invasive surgery. New work using bioresorbable materials may lead to the implementation of devices that do not require a second surgical procedure to remove them and following resorption leave no trace that they had ever been inserted. In addition, use of microprocessors and miniature motorized distraction devices may provide the ability to insert submerged appliances capable of auto-distraction according to preprogrammed data.