Distraction Osteogenesis Treatment & Management

Regardless of which facial skeletal element is undergoing distraction, the treatment can be divided broadly into the following phases:

• Presurgical phase
• Operative phase
• Lag phase
• Distraction phase
• Consolidation phase
• Retention phase

Presurgical phase

This phase involves radiographic studies to determine the feasibility of placement of the distraction device, whether an internal or external device is more appropriate, and the vector (direction, amplitude) of the distraction. Anticipated trajectory depends directly on the distraction vector, which can be vertical, horizontal, or oblique. Multiplanar devices even allow manipulation of the vector during the distraction phase. When possible, 3-D electronic or manufactured models help to visualize the placement of the device and simulate the distraction process. Involvement of the orthodontist is essential during this phase. Presurgical orthodontic preparation assists the skeletal distraction by providing an occlusal guide. See the image below.

Operative phase

Osteotomies used with distraction are well described with the conventional reconstructive approaches and need only be modified to accommodate the specific device. While the exact details may vary with the procedure, the following are guidelines:

• Mandibular distraction

  • Adequate mandibular bone stock must be available for the osteotomy and placement of the device.
  • Numerous factors should be considered when deciding between an internal versus external device. External devices allow for more predictable, multidirectional control of the distraction, which cannot be achieved with the currently available internal devices.^[9] However, external devices require multiple skin incisions that may lead to significant facial scarring. For many children and their families, the application of sequential distraction-vectors with a series of internal devices is preferable to the risk of permanent external scars.
  • The approach, either intraoral or extraoral, depends upon the degree of bony and soft-tissue exposure required for placement of the device and the allowable maxillary-mandibular opening.
  • The placement and direction of the device dictates the distraction vector. The osteotomy line does not necessarily need to be perpendicular to the distraction vector but should be placed to avoid injury to the inferior alveolar nerve and the developing dentition. In addition, avoidance of such injury can be facilitated by an incomplete osteotomy with subsequent separation occurring during the distraction phase. See the image below. Intraoperative photographs of distractor placement.
  • Temporarily fixing the distractor into position before making the osteotomy can simplify distractor placement. Positioning the device after the osteotomy can be difficult because of the mobility of the proximal segment.
  • Employ standard principles of a sagittal split osteotomy when lengthening the mandibular body. Preserve the nerve by using a reciprocating saw for the buccal corticotomy and “green-stick” fracturing the lingual cortex with an osteotome. Complete mobilization is not always necessary, since the distraction device completes the osteotomy. Warn the patient and family of the discomfort the patient will feel until the fracture is completed.
  • Prior to closure, test the device and clearly mark for the family the direction (clockwise or counterclockwise) of the driver used to turn the device.
• Midfacial and frontofacial distraction

  • The use of external devices (head frame and/or helmet) typically requires the presurgical placement of a palatal appliance to guide the horizontal distraction vector.^[10]
  • Completely mobilize the midface with conventional approaches and osteotomies.
  • Avoid dental root disruption during the stages of primary or mixed dentition by modifying the typical Le Fort I osteotomy. Place the horizontal cut more cephalad, near the level of the inferior orbital foramen.
  • Midfacial advancements at the Le Fort I level with currently available internal devices are limited because of the difficulty in appropriately orienting the devices in the limited space. The fixation of the device may also injure the developing dentition. External multidirectional devices are preferred as they allow more control over the distraction process.
  • Midfacial advancement at the Le Fort III level^[11] and frontofacial advancements can be approached with either internal or external devices, depending on the circumstances. Place the internal devices at the level of the body and arch of the zygoma. External devices require a palatal appliance and additional traction wires at the zygoma, nasal root, and supraorbital regions.

Lag phase

Before proceeding with distraction, a period of 5-7 days after the operation must elapse. This latency phase allows for initial osteotomy healing. In patients younger than 4-5 y, the latency period may be significantly shortened or omitted altogether to prevent early consolidation.

Distraction phase

The process of distraction is activated when bone segments are gradually pulled apart using either an internal or external device. Three variables must be set: the rate of distraction, the rhythm or frequency of distraction, and the total time of distraction. The rate of distraction is typically 1.0 mm/d.^[12] Some advocate up to 2.0 mm/d in younger children to avoid early consolidation and a slower rate of 0.25-0.5 mm/d in older patients. This can be accomplished either once a day or divided throughout the day, determining the rhythm or frequency of distraction. While the distraction rate is 1.0 mm/d, ideally maintain the tissues under constant tension by dividing the total daily rate of distraction into smaller increments throughout the day to favor histogenesis.

The total time of the distraction phase is customized to the severity of the deformity and the patient’s demographics. There can be a discrepancy between the anticipated bone length and the total time of distraction. External devices that use pins to transmit the forces frequently bend, and the distance at the site of the distracting mechanism rarely equals the distance of the gap at the osteotomy sites. In hemifacial microsomia, for example, the position of the menton, distance from the lateral canthus to the commissure, and the mandibular cant should serve as clinical guidelines.

Consolidation phase

Once the desired correction is achieved with the distraction phase, allow mineralization of the immature bone to occur. Lock the distracting appliance into place to maintain stability until the newly formed bone has sufficient strength. The length of this phase varies depending on the circumstances. In general, 6-8 weeks is considered adequate. A guideline used by some centers is 2 days of consolidation to every day of distraction.

Retention phase

Remove the device and maintain stability, typically with the assistance of orthodontic appliances. In children with hemifacial microsomia, this step may require occlusal splints to guide the maxilla into position when the leveling of the mandibular cant creates a posterior open bite. In children with midfacial deformity, retention may require a face mask with elastic traction for a period of time.

Complications specific to the distraction process include the following:

• Device mechanism failure
• Injury to the developing tooth follicles (eg, maxillary and mandibular osteotomies)
• Injury to various branches of the facial or trigeminal nerves (eg, the inferior alveolar nerve with mandibular distraction)
• Pin site infection with external devices or semiburied devices
• Nonunion and premature fusion
• Complications specific to the osteotomy
• Psychosocial issues related to the recovery (length of treatment time and patient's physical appearance with distraction device)

With increasing clinical experience, the long-term outcome and the specific role of distraction osteogenesis are better defined today. Clearly, distraction can generate bone with the capacity for remodeling and adaptation to functional loads. However, distraction osteogenesis is likely incapable of restoring the normal development of a once dysplastic pattern of craniofacial growth. Distraction techniques allow the surgeon to intervene earlier in childhood to restore the facial form and function, but the extent to which it eliminates subsequent conventional procedures remains uncertain. See the image below.

As with conventional orthognathic surgery, distraction osteogenesis of the craniofacial skeleton should be considered one of the many tools in the armamentarium of a surgeon. Compared to orthopedic lengthening and rotations of long bones, craniofacial distraction is highly complex. Challenges include carefully placed osteotomies to mobilize facial elements and the multidirectional vectors of distraction. The last 5 years have seen exciting advances in computer-assisted surgery. Newly designed software can simulate osteotomies and planned distraction in difficult, asymmetric cases. Cone beam CT scanners, which provide excellent bony resolution at a fraction of the radiation, are now available for intraoperative CT imaging and postoperative follow-up.

The extent to which distraction osteogenesis will replace conventional approaches depends largely on technical innovations that will allow for implantable multidirectional devices that can be easily activated and controlled remotely with minimal incisions.