title: Comparison of glenoid inclination angle using different clinical imaging modalities.
abstract: BACKGROUND
  The β-angle, formed by the intersection of a line on the floor of the supraspinatus fossa and glenoid fossa line, has been described as a reliable measurement tool in the clinical setting to analyze glenoid inclination on the anteroposterior (AP) view of the shoulder. The purpose of this study was to compare the accuracy of the β-angle measurement using different imaging modalities with a validated 3-dimensional (3D) software tool.
  
  
  METHODS
  The β-angle was measured on AP radiographs, unformatted 2-dimensional (2D) computed tomography (CT) scan, and reformatted 2D CT scan in the scapular plane for 51 shoulders of 49 patients undergoing primary total shoulder arthroplasty. Comparison to the glenoid inclination angle calculated by the 3D software was performed.
  
  
  RESULTS
  The β-angle measured on reformatted CT scan was found to be the most accurate measurement method, with a mean difference of 1° (standard deviation [SD], 0.5°) with respect to 3D measurement. On AP radiographs, the β-angle was not as accurate, with a mean difference of 3° (SD, 0.7°; P < .006). The β-angle on unformatted 2D CT scan was not a reliable method to measure glenoid inclination, with a mean difference of 10° (SD, 0.9°; P < .0001).
  
  
  CONCLUSIONS
  The β-angle measured with 2D CT scan formatted in the scapular plane was the most accurate method for measuring glenoid inclination. The β-angle on the AP radiograph is less accurate and reliable. Measurement of the β-angle on an unformatted 2D CT scan is not an acceptable method to determine glenoid inclination.
authors.affiliation: Centre Orthopédique Santy, Hôpital Privé Jean Mermoz, Lyon, France. Electronic address: matthewdaggett@gmail.com.
authors.forename: Matthew
authors.initials: M
authors.lastname: Daggett
authors.affiliation: Centre Orthopédique Santy, Hôpital Privé Jean Mermoz, Lyon, France.
authors.forename: Birgit
authors.initials: B
authors.lastname: Werner
authors.affiliation: Centre Orthopédique Santy, Hôpital Privé Jean Mermoz, Lyon, France.
authors.forename: Marc Olivier
authors.initials: MO
authors.lastname: Gauci
authors.affiliation: Centre Orthopédique Santy, Hôpital Privé Jean Mermoz, Lyon, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Chaoui
authors.affiliation: Centre Orthopédique Santy, Hôpital Privé Jean Mermoz, Lyon, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Walch
mesh_terms: D061165:Glenoid Cavity / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional; D012189:Retrospective Studies; D012540:Scapula; D012785:Shoulder Joint / Q000000981:diagnostic imaging*; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: 3D software; CT scan; Glenoid inclination; measurement method; β-angle