If mandibular advancement is necessary in the growing child, it is best to use distraction osteogenesis. The amount of mandibular advancement is rarely symmetric, especially in Hemifacial microsomia patients. However, it is generally necessary to perform bilateral distraction.
The approach depends on the age of the child, the severity of the deformity and the part of the mandible in which the distraction is going to be performed.
Occasionally and especially if there has been previous facial incisions made an external approach is chosen.
Distractors can be placed free-hand without any guides, but may produce unpredictable results. This section will therefore describe a more predictable approach using computer-assisted planning.
Planning is carried out in virtual reality on a 3D-CT scan using appropriate software. An estimate can then be made of the amount of distraction required and the bone stock available. This is helpful in deciding which distractor to use.
Internal distractors are generally preferred and the one shown here has the activation rod exiting into the oral cavity. An alternative is for the distractor to face the opposite direction and for the activation rod to exit skin behind the mandible.
The virtual distractors are selected and placed on the left and right mandibular bodies. The virtual osteotomies are marked and completed.
The distractors are virtually activated. If the movement is not satisfactory, the virtual distractor positions can be adjusted until the desired vector is achieved.
A physical model of the mandible is produced using stereolithography. The distractors are adapted to the mandible in the planned positions.
Guides are constructed which allow the accurate positioning of the distractors and the osteotomies. Intraoperative navigation can achieve a similar result.
Consequently the distractors and the distraction vector should be exactly as planned.
4. Osteotomy and distractor placement
Marking of the osteotomy lines
The surgical guides are positioned and stabilized with one screw. The holes for the distractor screws are drilled and the osteotomy lines marked on the bone.
The guides are then removed.
The osteotomies are completed through the outer cortex. Fine osteotomes are then used to complete the osteotomies avoiding the area of the inferior dental nerve. Twisting an osteotome in the osteotomy is performed to assure complete mobilization.
Placement of the distractors
The distractors are then placed using the predrilled screw holes.
The distractor is activated to ensure that it is working properly and is then deactivated (returned to starting position).
After a suitable latency period, the ramus is distracted at a rate of 1.0 mm per day.
Weekly review of the patient is valuable until such time as the required distraction has been achieved.
After reaching the desired distraction the device is left in place to retain the distraction and to allow for bone consolidation.
It is valuable to check that distraction is progressing well periodically with radiographs. It is also useful to slightly overcorrect the deformity -- the younger the patient the more this should be done.
Consolidation will take approximately 8 weeks and the regeneration of bone into the distraction gap can also be verified with radiographs. When sufficient bone is present in the gap, the distractors are removed.
Precise positioning of the occlusion can be carried out using fixed orthodontic appliances and intermaxillary elastics.
This radiograph shows the bone healing after the removal of the distractors.
These x-rays show the lateral views of the face before and…
…after mandibular advancement by distraction.
6. Aftercare following distraction osteogenesis
Apply ice packs (may be effective in a short term to minimize edema).
The sterile dressing placed over the skin incisions is maintained for a minimum of 48 hours. Thereafter routine wound care should be instituted around the activation rod.
Antibiotic prophylaxis is continued for 1-5 days depending on the nature, complexity, and duration of the surgical procedure.
Patients with intraoral wounds must be instructed in appropriate oral hygiene procedures. A small soft toothbrush with toothpaste should be used. Antiseptic rinses can be used in the early postoperative period. If a Waterpik is used, care should be taken not to direct the jet stream directly over intraoral incisions to prevent wound dehiscence in the early postoperative phase.
Early post-operative x-rays are obtained to verify correct device placement. Additional postoperative imaging is performed as needed.
Remove sutures from skin after approximately 5 days if nonresorbable sutures have been used.
Regular follow up examinations to monitor healing and the postoperative occlusion are required.
Avoid sun exposure and tanning to skin incisions for several months.