Occasionally the zygomatic arch and glenoid fossa are present but abnormally positioned. If the position is not acceptable (eg, if the glenoid fossa is placed far too medially) the alternatives are either to reconstruct the arch and fossa with rib grafts or to osteotomize the arch and fossa and move it into a new position.
The ideal position of the arch and glenoid fossa on the affected side should be determined by mirror imaging the normal side using CT planning software. In the image, the ideal position is shown in orange.
The arch and glenoid fossa can be virtually osteotomized and repositioned (green) as close as possible to the ideal mirrored image (orange).
An osteotomy guide can be constructed which allows the accurate positioning of the osteotomies and repositioning of the osteotomized segment. Intraoperative navigation can also be used for this purpose.
Careful assessment of planar CT images especially in the coronal plane is essential to check the bone thickness prior to performing the osteotomies.
This enables exposure of the temporo- mandibular joint area, including the:
mastoid bone posteriorly
body of the zygomatic bone anteriorly
lateral orbital rim
Osteotomies are performed as dictated by the planning.
The anterior ostotomy is made sagittaly at the junction between the arch and the body of the zygomatic bone.
Posteriorly two osteotomies are needed. One is made vertically at the root of the zygoma just anterior to the external auditory meatus. The second osteotomy is made extra-cranially horizontally above the glenoid fossa and below the middle cranial fossa.
In order to minimize the risk of perforation into the cranial cavity and to avoid injury to the dura of the temporal lobe, it is helpful to carry out this procedure with a piezoelectric saw. Care is still required, but in theory the piezoelectric saw should not damage soft tissues.
5. Positioning and fixation
Once osteotomized, the zygomatic arch and the fossa are mobilized gently and moved into the predetermined position. A surgical guide constructed from the planned virtual model may help with the repositioning or navigation may be used. In the new position the mobilized complex may be stabilized, generally with screws.
6. Soft tissue cover
It is important to ensure that the bony construct especially of the glenoid fossa is covered with soft tissue to prevent TMJ ankylosis. This can either be carried out during this procedure or at the time of mandibular condyle construction.
The best material to cover the fossa with is fascia. Sometimes temporal fascia is available and can be turned over the construct as a pedicle flap. Sometimes it needs to be used as a free graft. In the absence of suitable local tissue (and muscle should be avoided because it does have the potential to ossify) fascia lata can be harvested from the lateral aspect of the thigh.
7. General wound care
Apply ice packs (may be effective in a short term to minimize edema).
The sterile dressing placed over the incisions is maintained for a minimum of 48 hours. Thereafter routine wound care should be instituted.
Antibiotic prophylaxis is continued for 1-5 days depending on the nature, complexity, and duration of the surgical procedure.
Remove sutures from skin after approximately 5 days if nonresorbable sutures have been used.
Regular follow up examinations to monitor healing are required.
Avoid sun exposure and tanning to skin incisions for several months.