Bone segment navigation: Difference between revisions

Revision as of 12:17, 14 April 2012

Revision as of 10:34, 23 December 2012

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The osteotomies performed in [[orthognathic surgery]] are classically planned on cast models of the tooth-bearing jaws, fixed in an [[articulator]]. For [[edentulous]] patients, the surgical planning is made by using [[stereolithography|stereolithographic models]]. These tridimensional models are then cut along the planned osteothomy line, slid and fixed in the new position.

Since the 1990’s1990s, modern techniques of presurgical planning were developed – allowing the surgeon to plan and simulate the osteotomy in a virtual environment, based on a preoperative [[computed tomography|CT]] or [[MRI]]; this procedure reduces the costs and the duration of creating, positioning, cutting, repositioning and refixing the cast models for each patient. The first system that allowed such a surgical simulation environment is the [[Laboratory Unit for Computer Assisted Surgery]] (LUCAS), that was developed in 1998 at the [[University of Regensburg| University of Regensburg, Germany]], with the support of the [[Carl Zeiss AG|Carl Zeiss Company]].

== Transferring the preoperative planning to the operating theatre ==

The usefulness of the preoperative planning, no matter how accurate, depends on the accuracy of the reproduction of the simulated [[osteotomy]] in the surgical field. The transfer of the planning was mainly based on the surgeon’ssurgeon's visual skills. Different guiding headframes were further developed to mechanically guide bone fragment repositioning. Such a headframe is attached to the patient’spatient's head, during CT or MRI, and surgery. There are certain difficulties in using this device. First, exact reproducibility of the headframe position on the patient’spatient's head is needed, both during CT or MRI registration, and during surgery. The headframe is relatively uncomfortable to wear, and very difficult or even impossible to use on small children, who can be uncooperative during medical procedures.

[[Image:SSNimOP.jpg|thumb|Using the [[Surgical Segment Navigator|SSN]] in the operating theatre; 1=IR receiver, 2 and 4=IR Reference devices, 3=SSN-Workstation]]

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== Surgical Segment Navigator ==

The first system that allowed a seamless bone segment navigation for preoperative planning was the [[Surgical Segment Navigator]] (SSN), developed in 1997 at the [[University of Regensburg| University of Regensburg, Germany]], with the support of the [[Carl Zeiss AG|Carl Zeiss Company]].<ref>Marmulla R, Niederdellmann H: ''Computer-assisted Bone Segment Navigation'', J Craniomaxillofac Surg 26: 347-359, 1998</ref> This new system does not need any mechanical surgical guides (such as a headframe). It is based on an [[infrared|infrared (IR)]] camera and IR [[transmitters]] attached to the skull. At least three IR transmitters are attached in the [[neurocranium]] area to compensate the movements of the patient’spatient's head. There are three or more IR transmitters are attached to the bones where the osteotomy and bone repositioning is about to be performed onto. The [[Three-dimensional space|3D]] position of each transmitter is measured by the IR camera, using the same principle as in [[satellite navigation]]. The workstation of the [[Surgical Segment Navigator]] (SSN) is constantly visualizing the actual position of the bone fragments, compared with the predetermined position, and also makes real-time spatial determinations of the free-moving bony segments resulting from the osteotomy.

Thus, fragments can be very accurately positioned into the target position, predetermined by surgical simulation.