page_title: Bone segment navigation
section_title: Transferring the preoperative planning to the operating theatre
hierarchical_section_title: Bone segment navigation / Transferring the preoperative planning to the operating theatre
caption_attribution_description: Scheme of the SSN principles
context_page_description: 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 can lead to diplopia; a mandibular fracture can induce significant modifications of the dental occlusion; in the same manner, a skull fracture can produce an increased intracranial pressure.
  In severe congenital malformations of the facial skeleton surgical creation of usually multiple bone segments is required with precise movement of these segments to produce a more normal face.
context_section_description: 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.
  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.
caption: Schematic representation of the principle of bone segment navigation; DRF1 and DRF2 = IR
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