Arthroplasty and distraction osteogenesis

Here we will describe a procedure where the ankylosis is first removed and the remaining mandibular ramus contoured before the distraction osteogenesis.

However, the procedure can also be performed in a different sequence where the distraction osteogenesis is performed prior to the removal of the ankylosis and contouring of the remaining mandibular ramus. The ankylolsis is resected at the time of removing the distractor.

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 virtually using a 3D-CT scan and appropriate software. Planning should include the resection of any existing ankylosis, recontouring the ramus stump, and positioning of the osteotomy and distraction device.

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.

The greater the resection, the smaller will be the mandibular ramus and the greater will be the distraction distance required. This is problematic because there is less space available for an internal distractor. This can be solved by the use of either an external distractor or an internal distractor that employs an external activation rod. External pin distraction has the disadvantage of leaving unsightly facial scars.

The virtual distractor is selected and placed on the mandibular ramus. A horizontal osteotomy is marked above the lingula. The virtual osteotomy is completed and the distractor virtually activated. If the movement is not satisfactory, the virtual distractor position can be adjusted until the desired vector is achieved.

The photo to the left shows the intraoperative placement of the distractor.

A guide can be fabricated which allows the accurate positioning of the distractor and the osteotomy. Intraoperative navigation can achieve a similar result.

A preauricular approach is used to gain access to the entire ankylosed temporomandibular joint.

A submandibular approach is used for the insertion of the distraction device.

The preplanned osteotomes are performed. Care should be taken not to injure the internal maxillary artery and the inferior alveolar neurovascular bundle.

A round contour is given to the superior border of the ramus stump using a burr.

Lining of the glenoid fossa with the temporalis muscle may not be mandatory since formation of scar tissue in the glenoid fossa and physical therapy may prevent re-ankylosis. If re-ankylosis occurs this can be addressed with gap arthroplasty or alloplastic joint prosthesis.

The surgical guide is positioned and stabilized with one screw. The holes for the distractor screws are drilled and the osteotomy line marked on the bone.

The guide is removed and the osteotomy completed. Care should be taken not to injure the internal maxillary artery and the inferior alveolar neurovascular bundle.

The distractor is placed and stabilized in the preplanned position using screws in the previously made screw holes.

The distractor is activated to ensure that it is working properly and is then deactivated (returned to starting position).

The wounds are then closed with a dressing applied to the external port.

After a suitable latency period, the ramus is distracted at a rate of 1.0 mm per day.

Physical therapy and mandibular mobilization should be encouraged early in the postoperative period.

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.

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 distraction device is removed.

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.