Bone segment navigation

Use the bone segment navigation fails bones are standing out in a computer-assisted surgery in the correct position and fixed by osteosynthesis. The bone segment navigation was first realized in the oral and maxillo- facial surgery. Bone segments can be congenital or fail due to an accident. Such misalignments can in the mouth, jaw and facial area have influence on the aesthetics and the function of the organs; are the bony confines of the orbit walls affected, then it may come to the double vision, the temporomandibular joint is affected, then it may cause a malfunction of the tooth row conclusion, the entire skull roof is affected in terms of craniosynostosis, increased intracranial pressure may result.

Importance of surgical planning and simulation

The cutting of the bone and re- assembly in the correct position is referred to as osteotomy. Thus, the bone actually being in the correct position after the operation, such an osteotomy is planned in advance of surgery and simulated. This simulation is necessary to save operation time. Frequently bone segments are also exposed during surgery not or only to a small part and remain as muscle, fat, and skin covered - an assessment of whether a bone segment is in the correct position intraoperatively so difficult or impossible to meet - this circumstance underlines the need for preoperative surgical planning and simulation on an exposed bone model.

Tool for surgical planning and simulation

Osteotomy as part of orthognathic surgery are usually planned based on plaster models of jaws in an articulator. Osteotomy at the non- tooth-bearing bony skull can be scheduled to stereolithography models. These physical models have to cut up for the surgery simulation and then re-assembled. New since the 90s is also the possibility to simulate osteotomies at a computer directly on preoperative CT or MRI image data set; which saves the high cost of model creation and the elaborate work of Zersägens and Neuzusammensetzens of physical models. The first system that allows such an operation simulation, the Laboratory Unit for Computer Assisted Surgery ( LUCAS ), which has been developed since 1998 at the University of Regensburg, with the support of Carl Zeiss Oberkochen.

Transfer of operational planning to the surgical site

The benefit of surgical planning depends on how well it manages to reproduce the simulation of osteotomy on the patient. Mostly the judgment of the surgeon was crucial for the transfer of the operation planning on the patient. In addition, various head frame have been developed where a bone segment offset was adjusted by mechanical means; such a head frame then the patient had, however, already wear during CT or MRI imaging; aggravating factor was that the head frame of the CT or MRI imaging on the surgical planning to the surgical procedure had to remain unchanged in position - for the patient that was relatively uncomfortable, even impossible in children because of the lack of cooperation.

Surgical Segment Navigator

The first system that allowed a bone segment navigation was the Surgical Segment Navigator (SSN ), which has been developed since 1997 at the University of Regensburg, with the support of Carl Zeiss ( Oberkochen ). The system works kopfrahmenlos and consists of an infrared camera and infrared transmitters that are directly anchored to the skull bone. At least three infrared emitters are attached to the skull cap in order to detect movements of the head as a whole. At least three other infrared transmitters are connected to the bone segment to be placed under a corrective osteotomy. The spatial position of the infrared transmitter - and hence that of the bone segment - is measured by the infrared camera, which principle is the same satellite navigation. The workstation of the Surgical Segment Navigator (SSN ) displays the source and target position of being moved to the bone segment, and also designates the currently measured position of the dissolved, freely movable bone segment. The bone segment is navigated according to the operation simulation by visualizing the actual measured position with the visualization of the target position is placed on the cover.

Indications for bone segment navigation

The bone segment navigation is used for the correction of jaw deformities in the orthognathic surgery, the operative setting of the TMJ condyle, for the reconstruction of the midface and orbital walls.