title: Application of the fulcrum axis to estimate the central scapular axis.
abstract: BACKGROUND
  Glenoid resurfacing can be a challenging component of total shoulder arthroplasty when significant glenoid retroversion or deformity is present. The purpose of this study was to determine whether a newly designed glenoid-targeting guide using the parallel relationship between glenoid version and an anatomic fulcrum axis could accurately estimate the central axis of the scapula.
  
  
  METHODS
  Three orthopaedic surgeons used a newly designed glenoid-targeting guide to place a guide pin into 6 normal Sawbones scapulae (Pacific Research Laboratories, Vashon Island, WA, USA), 6 retroverted Sawbones scapulae, 8 cadaveric scapular specimens, and 5 cadaveric shoulder specimens. Angles of deviation from the central scapular axis and from perpendicular to the fulcrum axis were measured.
  
  
  RESULTS
  The mean pin deviation angle from the central scapular axis and the mean fulcrum deviation angle for the normal Sawbones scapulae were 1.7° (SD, 1.2°) and 2.1° (SD, 1.5°), respectively. For altered retroverted Sawbones scapulae, the mean deviation angles were 1.8° (SD, 1.2°) and 2.8° (SD, 1.6°), respectively. The combined mean pin deviation angle and mean fulcrum deviation angle for cadaveric shoulder specimens were 2.8° (SD, 3.3°) and 2.3° (SD, 2.3°), respectively. The surgeons' results did not differ significantly whether using Sawbones models, cadaveric scapular specimens, or cadaveric shoulder specimens.
  
  
  CONCLUSIONS
  A glenoid-targeting guide based on the relationship of the fulcrum axis and glenoid version can be used to accurately estimate the central scapular axis. Such a tool can be accurate and reliable intraoperatively, aiding in glenoid component placement to within 5° of ideal version, irrespective of glenoid deformity.
authors.affiliation: Department of Orthopaedics and Rehabilitation, University of Florida, Gainesville, FL, USA.
authors.forename: Sang V
authors.initials: SV
authors.lastname: Le
authors.affiliation: Department of Orthopaedics and Rehabilitation, University of Florida, Gainesville, FL, USA.
authors.forename: Bryan
authors.initials: B
authors.lastname: Conrad
authors.affiliation: Department of Orthopaedics and Rehabilitation, University of Florida, Gainesville, FL, USA. Electronic address: wrightw@ortho.ufl.edu.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Wright
mesh_terms: D019643:Arthroplasty, Replacement / Q000295:instrumentation / Q000379:methods; D002102:Cadaver; D005471:Fluoroscopy; D006801:Humans; D008953:Models, Anatomic; D012540:Scapula / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery*; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000601:surgery
keywords: Fulcrum axis; glenoid deformity; glenoid version; scapular axis; total shoulder arthroplasty