title: Glenohumeral relationships at different angles of abduction.
abstract: OBJECTIVE
  The objective of this study was to clarify the relationships among anatomical landmarks of the glenohumeral joint at different angles of abduction.
  
  
  METHODS
  Fifteen volunteers (ten men, five women; mean age 29 years) were enrolled in this study. Images of externally and internally rotated positions at 45°, 90°, and 135° of abduction in the plane 30° anterior to the trunk were taken using an open magnetic resonance imaging system. Landmarks including the glenoidal long axis with its center, bicipital groove, center of the head, and humeral shaft axis were determined. Using a line set on the surface of the head in the plane parallel to the humeral axis (including the head center and bicipital groove with its parallel and perpendicular lines), the glenoid location and rotational relationships were investigated in each position.
  
  
  RESULTS
  The average angles of axial rotation were 48° ± 27° at 45º of abduction, 71° ± 20° at 90° of abduction, and 40° ± 27° at 135° of abduction. The trajectories of the glenoid center primarily extended over the anterior portion of the humeral head at 45° of abduction and over the posterior portion at 90° of abduction, while those at 135° of abduction were localized on a small upper portion of the head.
  
  
  CONCLUSIONS
  The glenohumeral relationships demonstrated that arm abduction might influence shoulder function through its effects on the portion of the humeral surface in contact with the glenoid during rotation and the resultant changes in the glenohumeral relationships.
authors.affiliation: Nobuhara Hospital and Institute of Biomechanics, 720 Haze, Issaicho, Tatsunoshi, Hyogo, 679-4017, Japan, inuhiro123@yahoo.co.jp.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Inui
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tanaka
authors.forename: Katsuya
authors.initials: K
authors.lastname: Nobuhara
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D012785:Shoulder Joint / Q000033:anatomy & histology / Q000502:physiology*; D055815:Young Adult