title: Effect of plane of arm elevation on glenohumeral kinematics: a normative biplane fluoroscopy study.
abstract: BACKGROUND
  Understanding glenohumeral motion in normal and pathologic states requires the precise measurement of shoulder kinematics. The effect of the plane of arm elevation on glenohumeral translations and rotations remains largely unknown. The purpose of this study was to measure the three-dimensional glenohumeral translations and rotations during arm elevation in healthy subjects.
  
  
  METHODS
  Eight male subjects performed scaption and forward flexion, and five subjects (three men and two women) performed abduction, inside a dynamic biplane fluoroscopy system. Bone geometries were extracted from computed tomography images and used to determine the three-dimensional position and orientation of the humerus and scapula in individual frames. Descriptive statistics were determined for glenohumeral joint rotations and translations, and linear regressions were performed to calculate the scapulohumeral rhythm ratio.
  
  
  RESULTS
  The scapulohumeral rhythm ratio was 2.0 ± 0.4:1 for abduction, 1.6 ± 0.5:1 for scaption, and 1.1 ± 0.3:1 for forward flexion, with the ratio for forward flexion being significantly lower than that for abduction (p = 0.002). Humeral head excursion was largest in abduction (5.1 ± 1.1 mm) and smallest in scaption (2.4 ± 0.6 mm) (p < 0.001). The direction of translation, as determined by the linear regression slope, was more inferior during abduction (-2.1 ± 1.8 mm/90°) compared with forward flexion (0.1 ± 10.9 mm/90°) (p = 0.024).
  
  
  CONCLUSIONS
  Scapulohumeral rhythm significantly decreased as the plane of arm elevation moved in an anterior arc from abduction to forward flexion. The amount of physiologic glenohumeral excursion varied significantly with the plane of elevation, was smallest for scaption, and showed inconsistent patterns across subjects with the exception of consistent inferior translation during abduction.
authors: Department of BioMedical Engineering, Steadman Philippon Research Institute, 181 West Meadow Drive, Suite 1000, Vail, CO 81657, USA.
authors: J Erik
authors: JE
authors: Giphart
authors: John P
authors: JP
authors: Brunkhorst
authors: Nils H
authors: NH
authors: Horn
authors: Kevin B
authors: KB
authors: Shelburne
authors: Michael R
authors: MR
authors: Torry
authors: Peter J
authors: PJ
authors: Millett
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D005471:Fluoroscopy; D006801:Humans; D021621:Imaging, Three-Dimensional; D016014:Linear Models; D008297:Male; D009068:Movement; D016059:Range of Motion, Articular; D012540:Scapula / Q000000981:diagnostic imaging / Q000502:physiology; D019534:Shoulder Impingement Syndrome / Q000473:pathology / Q000534:rehabilitation; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D014057:Tomography, X-Ray Computed