title: Measurement of a posterior occipitocervical fusion angle.
abstract: METHODS
  A method for evaluating occipitocervical neutral position is described.
  
  
  OBJECTIVE
  To describe and measure a posterior occipitocervical angle (POCA) in normal subjects that can be used to guide contouring of fusion implants to achieve occipitocervical neutral fusion and for use in standardized testing of occipitocervical constructs.
  
  
  BACKGROUND
  The goal of occipitocervical fusion is to fuse the head in an ideal functional position. Several methods of estimating occipitocervical neutral position have been described and tested, yet none has been proven superior. An ideal method would easily and reproducibly aid in evaluating occipitocervical position intraoperatively and potentially aid in the design and testing of implant constructs.
  
  
  METHODS
  Fifteen adult lateral cervical spine radiographs taken in occipitocervical neutral position and interpreted as normal by an experienced radiologist were studied. Analysis consisted of measurement of the POCA. The POCA is defined as the angle formed by the intersection of a line drawn tangential to the posterior aspect of the occipital protuberance and a line determined by the posterior aspect of the facets of the third and fourth cervical vertebrae.
  
  
  RESULTS
  The mean POCA was 109.7 degrees with a SD of 5.7 degrees. Compilation of the data revealed a normal distribution of measurements where 80% of the POCA values were between 101 and 119 degrees.
  
  
  CONCLUSIONS
  POCA is a simple measurement that may be valuable as an intraoperative tool during occipitocervical fusion and may aid the design and testing of fusion implants and their application in the operating room.
authors.affiliation: Department of Orthopaedic Surgery, University of Florida, Shands-Jacksonville, FL 32209, USA.
authors.forename: Ryan U
authors.initials: RU
authors.lastname: Riel
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Lee
authors.forename: John S
authors.initials: JS
authors.lastname: Kirkpatrick
mesh_terms: D000886:Anthropometry / Q000379:methods*; D001175:Arthrography / Q000379:methods*; D001269:Atlanto-Occipital Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000601:surgery; D001270:Cervical Atlas / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000601:surgery; D002574:Cervical Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D006801:Humans; D009777:Occipital Bone / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000601:surgery; D019736:Prostheses and Implants / Q000592:standards; D011474:Prosthesis Design / Q000379:methods; D019919:Prosthesis Implantation / Q000379:methods; D016059:Range of Motion, Articular / Q000502:physiology; D012016:Reference Values; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D021801:Zygapophyseal Joint / Q000033:anatomy & histology / Q000502:physiology