title: The effects of arm elevation on the 3-dimensional acromiohumeral distance: a biplane fluoroscopy study with normative data.
abstract: OBJECTIVE
  Narrowing of the subacromial space has been implicated in several shoulder pathologies. However, the location of the minimum distance points during clinical testing has not been defined. We sought to measure the in vivo minimum distance and location of the minimum distance points on the acromion and proximal humerus during arm elevation.
  
  
  METHODS
  Eight healthy male subjects (mean age, 30 years) underwent a dynamic in vivo biplane fluoroscopy assessment of scaption and forward elevation. For each frame, the 3-dimensional position and orientation of the humerus and scapula were determined, and the acromiohumeral distance (AHD) was measured as the shortest distance between the acromion and proximal humerus.
  
  
  RESULTS
  The minimum AHD was 2.6 ± 0.8 mm during scaption and 1.8 ± 1.2 mm during forward flexion at elevation angles of 83° ± 13° and 97° ± 23°, respectively. The minimum distance point was located on the articular surface of the humeral head from the neutral arm position until 34° ± 8° for scaption and 36° ± 6° for forward flexion. Upon further elevation, the minimum distance point was located within the footprint of the supraspinatus muscle until 72° ± 12° for scaption and 65° ± 8° for forward flexion. At greater elevation angles, the minimum distance points were between the acromion and the proximal humeral shaft, distal from the greater tuberosity.
  
  
  CONCLUSIONS
  The shortest AHD was at approximately 90° of arm elevation. The AHD was no longer measured intra-articularly or within the supraspinatus footprint above approximately 70° of arm elevation.
authors.affiliation: Biomechanics Research Department, Steadman Philippon Research Institute, Vail, CO 81657, USA.
authors.forename: J Erik
authors.initials: JE
authors.lastname: Giphart
authors.forename: Olivier A J
authors.initials: OA
authors.lastname: van der Meijden
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Millett
mesh_terms: D000174:Acromion / Q000000981:diagnostic imaging*; D000328:Adult; D001132:Arm / Q000000981:diagnostic imaging* / Q000503:physiopathology; D001696:Biomechanical Phenomena; D005471:Fluoroscopy / Q000379:methods*; D006801:Humans; D006811:Humerus / Q000000981:diagnostic imaging*; D021621:Imaging, Three-Dimensional; D008297:Male; D016059:Range of Motion, Articular; D012016:Reference Values; D015203:Reproducibility of Results; D017006:Rotator Cuff / Q000000981:diagnostic imaging* / Q000503:physiopathology; D019534:Shoulder Impingement Syndrome / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012785:Shoulder Joint / Q000000981:diagnostic imaging