Bone segment navigation: Difference between revisions

Revision as of 02:29, 29 September 2008

Revision as of 22:25, 26 May 2009

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'''Bone segment navigation''' is a surgical method used in the surgical field in order to obtainfind the correct anatomical position of displaced bone fragments in fractures, allowing a good fixation by [[osteosynthesis]]. It has been developed for the first time in [[Oral and maxillofacial surgery]].

After an accident or injury, a fracture can be produced and the resulting bony fragments can be displaced. In the oral and maxillofacial area, such a discplacement could have a major efect both on facial aesthetics and organ function: a fracture occurring in a bone that delimits the [[orbit (anatomy)|orbit]] can lead to [[diplopia]]; a [[mandibula|mandibular]] fracture can induce significant modifications of the [[occlusion (dentistry)|dental occlusion]]; in the same manner, a skull ([[neurocranium]]) fracture can produce an increased [[intracranial pressure]].

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== What are surgical planning and surgical simulation ==

An [[osteotomy]] is a surgical intervention that consists of cutting through bone and repositioning the resulting fragments in the correct anatomical place. In order toTo insure the optimal repositioning of the bony structures by [[osteotomy]], the intervention can be planned in advance and simulated. The surgical simulation is a key factor in reducing the actual operating time. Often, during this kind of operation, the surgical access to the bone segments is very limited by the presence of the soft tissues: muscles, fat tissue and skin - thus, the correct anatomical repositioning is very difficult to assess, or even impossible. This led to the necessity of a preoperative planning and simulation on models of the bare bony structures.

== Materials and devices needed for preoperative planning and simulation ==

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== 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’s visual skills. Different guiding headframes were further developed, into order tomechanically guide the bone fragmentsfragment repositioning,. by mechanical means; suchSuch a headframe should beis attached to the patient’s head, during CT or MRI, and surgery. There are certain difficulties in using this device: first of. allFirst, exact reproductibilityreproducibility of the headframe position on the patient’s head is needed, both during CT or MRI registration, and during surgery;. theThe headframe is relatively uncomfortable to wear, and very difficult or even impossible to use on small children, thatwho arecan notbe readily cooperatinguncooperative during the 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 [[Zeiss|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, in order to compensate the movements of the patient’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, resultedresulting from the osteotomy.

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

== Indications for the hard tissue segment navigation method ==