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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 displacement could have a major effect both on facial aesthetics and organ function: a fracture occurring in a bone that delimits the [[orbit (anatomy)|orbit]] can lead to [[diplopia]]; a [[Human mandible|mandibula]]r 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]].
In severe congenital malformations of the facial skeleton surgical creation of usually multiple<ref>{{Cite journal|last=Obwegeser|first=HL|date=1969|title=Surgical correction of small or retrodisplaced maxillae. The "dish-face" deformity.|journal=Plast Reconstr Surg|volume=43|issue=4|pages=351–65|doi=10.1097/00006534-196904000-00003|pmid=5776622|s2cid=41856712}}</ref><ref>{{Cite book|title=Craniofacial Surgery 3|lastlast1=Cutting|firstfirst1=C|last2=Grayson|first2=B|last3=Bookstein|first3=F|last4=Kim|first4=H|last5=McCarthy|first5=J|publisher=Monduzzi Editore|year=1991|isbn=9788832300000|editor-last=Caronni|editor-first=EP|___location=Bologna|chapter=The case for multiple cranio-maxillary osteotomies in Crouzon's disease.}}</ref> bone segments is required with precise movement of these segments to produce a more normal face.
== 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. To insure 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. Preoperative planning and simulation on models of the bare bony structures can be done. An alternate strategy is to plan the procedure entirely on a CT scan generated model and output the movement specifications purely numerically.<ref>{{Cite journal|lastlast1=Cutting|firstfirst1=C|last2=Bookstein|first2=F|last3=Grayson|first3=B|last4=Fellingham|first4=L|last5=McCarthy|first5=J|date=1986|title=Three dimensional computer aided design of craniofacial surgical procedures: Optimization & interaction with cephalometric and CT-based models.|journal=Plast. Reconstr. Surg.|volume=77|issue=6|pages=877–87|doi=10.1097/00006534-198606000-00001|pmid=3714886|s2cid=41453653}}</ref>
== Materials and devices needed for preoperative planning and simulation ==
== Surgical Segment Navigator ==
Initial bone fragment positioning efforts using an electro-magnetic system were abandoned due to the need for an environment without ferrous metals.<ref>{{Cite journal|lastlast1=Cutting|firstfirst1=C|last2=Grayson|first2=B|last3=Kim|first3=H|date=1990|title=Precision multi-segment bone positioning using computer aided methods in craniofacial surgical procedures.|journal=Proc. IEEE Eng. Med. Biol. Soc.|volume=12|pages=1926–7}}</ref> In 1991 Taylor at IBM working in collaboration with the craniofacial surgery team at New York University developed a bone fragment tracking system based on an [[Infrared|infrared (IR)]] camera and IR [[transmitters]] attached to the skull.<ref>{{Cite book|title=A Model-Based Optimal Planning and Execution System with Active Sensing and Passive Manipulation for Augmentation of Human Precision in Computer-Integrated Surgery|lastlast1=Taylor|firstfirst1=RH|last2=Cutting|first2=C|last3=Kim|first3=Y|display-authors=etal|work=Proceedings International Symposium on Experimental Robotics.|publisher=Springer-Verlag|year=1991|___location=Toulouse, France}}</ref><ref>{{Cite journal|lastlast1=Taylor|firstfirst1=RH|last2=Paul|first2=H|last3=Cutting|first3=C|display-authors=etal|date=1992|title=Augmentation of Human Precision in Computer Integrated Surgery.|journal=Innovation et Technologie en Biologie et Medicine|volume=13|issue=4|pages=450–68}}</ref> This system was patented by IBM in 1994.<ref>{{Cite book|title=Signaling device and method for monitoring positions in a surgical operation.|lastlast1=Taylor|firstfirst1=R|last2=Kim|first2=Y (inventors)|publisher=United States Patent 5,279,309|year=1994|___location=Ossining, NY}}</ref> At least three IR transmitters are attached in the [[neurocranium]] area 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]]. A computer workstation 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. More recently a similar system, the [[Surgical Segment Navigator]] (SSN), was developed in 1997 at the [[University of Regensburg| University of Regensburg, Germany]], with the support of the [[Carl Zeiss AG|Carl Zeiss Company]].<ref name=":0">Marmulla R, Niederdellmann H: ''Computer-assisted Bone Segment Navigation'', J Craniomaxillofac Surg 26: 347-359, 1998</ref>
== Clinical use of bone segment navigation ==
The first clinical report of the use of this type of system was by Watzinger et al. in 1997<ref>{{Cite journal|lastlast1=Watzinger|firstfirst1=F|last2=Wanschitz|first2=F|last3=Wagner|first3=A|display-authors=etal|date=1997|title=Computer-aided navigation in secondary reconstruction of post-traumatic deformities of the zygoma.|journal=J Craniomaxillofac Surg.|volume=25|issue=4|pages=198–202|doi=10.1016/s1010-5182(97)80076-5|pmid=9268898}}</ref> in the reposition of zygoma fractures using a mirrored image from the normal side as a target. In 1998 the system was reported by Marmulla and Niederdellmann to track LeFort I osteotomy position as well as zygoma fracture repositioning.<ref name=":0" /> In 1998 Cutting et al.<ref>{{Cite journal|lastlast1=Cutting|firstfirst1=C|last2=Grayson|first2=B|last3=McCarthy|first3=J|display-authors=etal|date=1998|title=A virtual reality system for bone fragment positioning in multisegment craniofacial surgical procedures.|journal=Plast Reconstr Surg|volume=102|issue=7|pages=2436–43|doi=10.1097/00006534-199812000-00027|pmid=9858182}}</ref> reported use of the system to track multisegment midface osteotomies in major craniofacial malformations.
== References ==
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