In vivo 3-dimensional analysis of scapular kinematics: comparison of dominant and nondominant shoulders Keisuke Matsuki, MD, PhD a,b, *, Kei O. Matsuki, MD a,c , Shang Mu, PhD a , Satoshi Yamaguchi, MD, PhD c , Nobuyasu Ochiai, MD, PhD c , Takahisa Sasho, MD, PhD c , Hiroyuki Sugaya, MD, PhD d , Tomoaki Toyone, MD, PhD b , Yuichi Wada, MD, PhD b , Kazuhisa Takahashi, MD, PhD c , Scott A. Banks, PhD a a Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, USA b Department of Orthopaedic Surgery, Teikyo University Chiba Medical Center, Ichihara, Chiba, Japan c Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, Chiba, Japan d Funabashi Orthopaedic Sports Medicine Center, Funabashi, Chiba, Japan Background: Alterations in scapular motion frequently are seen in association with various shoulder disor- ders. 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 shoul- ders during dynamic scapular plane elevation using 3-De2-D (2-dimensional) registration techniques. Materials and methods: Twelve healthy males with a mean age of 32 years (range, 27e36) 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-De2-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. Discussion/Conclusion: 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. Level of evidence: Basic Science Study. Ó 2011 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Shoulder; scapular kinematics; 3-D kinematics; fluoroscopy; 3-De2-D registration technique hand dominance IRB approval of the study was obtained from the Internal Review Boards of Chiba University Graduate School of Medicine (#766) and the University of Florida (#639-2008). *Reprint requests: Keisuke Matsuki, MD, PhD, Department of Ortho- paedic Surgery, Teikyo University Chiba Medical Center, 3426-3 Anesaki, Ichihara, Chiba 2990111, Japan. E-mail address: kmatsuki@med.teikyo-u.ac.jp (K. Matsuki). J Shoulder Elbow Surg (2011) 20, 659-665 www.elsevier.com/locate/ymse 1058-2746/$ - see front matter Ó 2011 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2010.09.012