Intraoperative guidance in maxillofacial and craniofacial surgery.

The authors' experiences with intraoperative computer assisted guidance in interventions in oromaxillofacial and craniofacial surgery are reported. The guidance system SPOCS (Surgical Planning and Orientation Computer Systems, Aesculap, Germany) consists of an infrared light emitting system of diodes and camera, an imaging workstation and assorted freehand instruments. The software is an updated version of the well-known Viewing Wand software (ISG Technologies, Canada). In tests on phantoms, the system proved a mean accuracy of less than 1.5 mm. Within the last 15 clinical tests, the system has achieved an accuracy better than 3 mm which, at the moment, the authors estimate to be sufficient to proceed with its clinical evaluation. Using bone screws to register the patient's position, an accuracy in the range of less than 2 mm in relation to bony reference points has been achieved. By visualizing the tip of the instrument in real time, this technique allows surgical interventions, even in anatomically complicated situations, without endangering vital neighbouring structures. The 'offset' function of the software, by which the surgeon can elongate the tip of the instrument virtually, allows the surgeon to analyse structures before they are penetrated by the instrument as in a 'look ahead' operation. The authors expect computer assisted simulation and guidance systems to improve surgical quality and reduce the risks associated with surgical interventions.