title: In vivo 3-dimensional analysis of scapular kinematics: comparison of dominant and nondominant shoulders.
abstract: BACKGROUND
  Alterations in scapular motion frequently are seen in association with various shoulder disorders. It is common clinically to compare the pathological shoulder with the contralateral shoulder, in spite of arm dominance, to characterize the disorder. However, there have been few articles that test the underlying assumption that dominant and nondominant shoulders exhibit comparable dynamic kinematics. The purpose of this study was to compare the 3-dimensional (3-D) scapular kinematics of dominant and nondominant shoulders during dynamic scapular plane elevation using 3-D-2-D (2-dimensional) registration techniques.
  
  
  METHODS
  Twelve healthy males with a mean age of 32 years (range, 27-36) were enrolled in this study. Bilateral fluoroscopic images during scapular plane elevation and lowering were taken, and CT-derived 3-D bone models were matched with the silhouette of the bones in the fluoroscopic images using 3-D-2-D registration techniques. Angular values of the scapula and scapulohumeral rhythm were compared between dominant and nondominant shoulders with statistical analysis.
  
  
  RESULTS
  There was a significant difference in upward rotation angles between paired shoulders (P < .001), while significant differences were not found in the other angular values and scapulohumeral rhythm. The dominant scapulae were 10° more downwardly rotated at rest and 4° more upwardly rotated during elevation compared to the nondominant scapulae.
  
  
  CONCLUSIONS
  Scapular motion was not the same between dominant and nondominant arms in healthy subjects. The dominant scapula was rotated further downward at rest and reached greater upward rotation with abduction. These differences should be considered in clinical assessment of shoulder pathology.
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, USA. kmatsuki@med.teikyo-u.ac.jp
authors.forename: Keisuke
authors.initials: K
authors.lastname: Matsuki
authors.forename: Kei O
authors.initials: KO
authors.lastname: Matsuki
authors.forename: Shang
authors.initials: S
authors.lastname: Mu
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Nobuyasu
authors.initials: N
authors.lastname: Ochiai
authors.forename: Takahisa
authors.initials: T
authors.lastname: Sasho
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sugaya
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Toyone
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Wada
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
authors.forename: Scott A
authors.initials: SA
authors.lastname: Banks
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D012399:Rotation; D012540:Scapula / Q000000981:diagnostic imaging / Q000502:physiology*; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D014057:Tomography, X-Ray Computed