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'''Bone segment navigation''' is a surgical method used to find the anatomical position of displaced bone fragments in fractures, or to position surgically created fragments in craniofacial surgery. Such fragments are later fixed in position by [[osteosynthesis]]. It has been developed for use in [[craniofacial]] and [[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 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]].{{cn|date=January 2022}}
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|last1=Cutting|first1=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.
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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 to mechanically guide bone fragment repositioning. {{citation needed|date=October 2018}}
Such a headframe is attached to the patient'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'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. For this reason headframes have been abandoned in favor of frameless stereotaxy of the mobilized segments with respect to the skull base. Intraoperative registration of the patient's anatomy with the computer model is done such that pre-CT placement of fiducial points is not necessary.{{cn|date=January 2022}}
[[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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