Computer-assisted surgical planning for craniofacial microsomia

Distraction osteogenesis

The location of the osteotomies is critical when planning for distraction osteogenesis. It is critical to assess the quality of the bone and determine the location of the inferior alveolar nerve. Ideally, the osteotomy is designed superior to the foramen where the inferior alveolar nerve enters the mandible. The orientation of the cut should be perpendicular to the direction of distraction. There should be enough bone on either side of the osteotomy to hold screws and to distract the mandible in the appropriate orientation. The goal may be to lengthen the mandible in an anterior-posterior orientation, superior-inferior orientation, or both. Once the ideal location and orientation of the osteotomies is determined, cutting guides can be manufactured that have a higher degree of interaction with the mandible, allowing precise placement of the osteotomy on the patient’s mandible. This sometimes requires wider periosteal undermining than would normally be done during the procedure. Sterile models of the mandible can also be produced on which the cutting guide can be placed to determine the adequacy of the fit and assist with locating the guide on the patient.

The thickness of the bone as well as avoidance of teeth and nerves are also critical factors that can be determined when planning the operation virtually and can inform screw placement and the location/orientation of osteotomy.

Virtually planning the placement of the osteotomies and distractors allows the advance determination of the vector and distance of activation.

Orthognathic surgery

CaSP for orthognathic surgery in patients with hemifacial microsomia has similar advantages to its use with distraction osteogenesis. Osteotomies on the maxilla can be designed to avoid tooth roots and locate screw placement in robust and stable bone.

The movement of the Le Fort segment can be completely controlled by custom plates. The use of predictive screw holes withing the cutting guides, combined with custom plates, dictates translation and rotation in all three planes and axis. This computer- and hardware-controlled accuracy facilitates accurate intraoperative placement of the maxilla, which in turn, usually determines mandible placement. Although the plates determine the final location of the maxilla, dental splints can be used to confirm appropriate movement of the segment.

Mandibular osteotomies can also be designed to avoid injury to the inferior alveolar nerve. This is more relevant depending on which osteotomies, other than a sagittal split, are used, such as an inverted L osteotomy. Custom cutting guides can be used and custom plates manufactured that secure the predetermined movement.

With traditional orthognathic surgery, movement of the genioplasty is determined using two-dimensional cephalograms. This is usually insufficient in patients with hemifacial microsomia in 3D rotation and translation is required. CaSP can facilitate the planning and accurate execution of these complex movements and determine areas where bone may need to be contoured to optimize the facial framework.

Finally, bone grafts to the maxilla, mandible, and chin can all be designed by use of custom guides and shaping templates to improve stability and streamline the construction of accurately shaped bone grafts.