CAS: Mandibular reconstruction

In surgical procedures where bone plates must be pre-adapted, 3D models or patient specific implants (PSI) are prepared to aid in plate adaptation. To facilitate the correct positioning of the bone plate, intraoperative navigation is often used during the surgery, followed by intraoperative imaging at the end of the procedure for quality control.

• Introduction to CAS: Asymmetry correction
• OR setup
• Cone beam vs. fan beam
• Preparation for intraoperative navigation

Planning is carried out in virtual reality on a 3D-CT scan using appropriate software.

In this case a right mandibular resection spanning from the condyle across the symphysis to the left mandibular body (red segment) will be performed.

A virtual mandibular resection is made and a resection guide is prepared using stereo lithography.

A virtual reconstruction of the mandible is performed using a virtual standard fibula template or a 3D-CT scan of the patient's fibula.

Either of the patient's fibulae can be used for a given defect. The choice of side is dependent on the vascular supply to the lower leg as determined by preoperative examinations and recipient vessels in the neck.

A cutting guide for the fibular harvesting, which also serves as a cutting guide for the wedge ostectomies needed to shape the harvested flap, is prepared using 3D printing.

A 3D-model of the virtually reconstructed mandible is prepared and a mandibular reconstruction plate is adapted to a near perfect fit. Alternatively the reconstruction plate is custom made by laser sintering, laser melting, or milling, without using standard bone plates.

The resection guide is placed onto the mandible, fixed with a screw and the osteotomy carried out.

If possible, the mandibular nerve is liberated and spared, like in this case of bisphosphonates osteonecrosis of the mandible (BONJ).

The diseased segment is liberated by subperiosteal dissection and removed. If possible, care is taken to conserve the articular disk.

The fibula free flap is harvested in a standard fashion using the pre-fabricated cutting guide.

The pre-fabricated cutting guide is then used to perform wedge osteotomies of the fibula. Use of Piezoelectric osteotomes facilitates the preservation of the vascular bundle and minimized damage to the periosteal blood supply.

The prebent mandibular reconstruction plate serves as a template for positioning the osteotomized fibula.

While care is taken to protect the vascular bundle, the osteotomized fibula is secured to the plate with monocortical locking screws.

The reconstruction plate is then secured to the native mandible with at least 3 bicortical locking screws.

The detailed procedure for the revascularization is outside the scope of this surgery reference.

However, in short the procedure consists of the following steps:

• Appropriate recipient vessels are selected in the neck and dissected so as to be available for anastomosis
• The recipient and the donor vessels adventitia are cleaned under a microscope
• Appropriate vessel geometry is assured and the vessels are placed into a microvascular clamp and anastomosis carried out using 9-0 nylon sutures
• Vascularization is restored after both arterial and venous anastomoses are completed

A postoperative 3D-CT scan is made to check the results of the reconstruction. The precision of the osteotomies facilitates bone healing especially in compromised pathologies like the BONJ or in patients that will receive adjuvant radiation treatment.