title: Occipitocervical Instability After Far-Lateral Transcondylar Surgery: A Biomechanical Analysis.
abstract: After a far-lateral transcondylar approach, patients may maintain neutral alignment in the immediate postoperative period, but severe occipitoatlantal subluxation may occur gradually with cranial settling and possible neurological injury. Previous research is based on assumptions regarding the extent of condylar resection and the change in biomechanics that produces instability.
  
  
  
  To quantify the extent of bone removal during a far-lateral transcondylar approach, determine the changes in range of motion (ROM) and stiffness that occur after condylar resection, and identify the threshold of condylar resection that predicts alterations in occipitocervical biomechanics.
  
  
  
  Nine human cadaveric specimens were biomechanically tested before and after far-lateral transcondylar resection extending into the hypoglossal canal (HC). The extent of condylar resection was quantified using volumetric comparison between pre- and postresection computed tomography scans. ROM and stiffness testing were performed in intact and resected states. The extent of resection that produced alterations in occipitocervical biomechanics was assessed with sensitivity analysis.
  
  
  
  Bone removal during condylar resection into the HC was 15.4%-63.7% (mean 35.7%). Sensitivity analysis demonstrated that changes in biomechanics may occur when just 29% of the occipital condyle was resected (area under the curve 0.80-1.00).
  
  
  
  Changes in occipitocervical biomechanics may be observed if one-third of the occipital condyle is resected. During surgery, the HC may not be a reliable landmark to guide the extent of resection. Patients who undergo condylar resections extending into or beyond the HC require close surveillance for occipitocervical instability.
authors.affiliation: Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, Utah.
authors.forename: Marcus D
authors.initials: MD
authors.lastname: Mazur
authors.affiliation: Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, Utah.
authors.forename: William T
authors.initials: WT
authors.lastname: Couldwell
authors.affiliation: Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, Utah.
authors.forename: Aaron
authors.initials: A
authors.lastname: Cutler
authors.affiliation: Department of Radiology, University of Utah, Salt Lake City, Utah.
authors.forename: Lubdha M
authors.initials: LM
authors.lastname: Shah
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, Utah.
authors.forename: Darrel S
authors.initials: DS
authors.lastname: Brodke
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, Utah.
authors.forename: Kent
authors.initials: K
authors.lastname: Bachus
authors.affiliation: Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, Utah.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Dailey
mesh_terms: D001269:Atlanto-Occipital Joint / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000209:etiology*; D009777:Occipital Bone / Q000000981:diagnostic imaging / Q000601:surgery*; D016059:Range of Motion, Articular; D014057:Tomography, X-Ray Computed
keywords: Biomechanics; Far-lateral; Hypoglossal canal; Instability; Occipital condyle; Occipitocervical junction; Skull base