Effect of humeral component version on impingement in reverse total shoulder arthroplasty Daniel R. Stephenson, MD a , Joo Han Oh, MD, PhD b,c , Michelle H. McGarry, MS b , George F. Rick Hatch III, MD a , Thay Q. Lee, PhD b, * a University of Southern California Department of Orthopaedic Surgery, Los Angeles, CA, USA b Department of Orthopedic Surgery, Seoul National University College of Medicine, Seoul, Korea c Orthopaedic Biomechanics Laboratory, VA Healthcare System, Long Beach, CA, USA Hypothesis: Reverse shoulder arthroplasty is growing in popularity for patients with deficient rotator cuffs; however, the phenomenon of scapular notching continues to be a concern. This study examined the effects of humeral component version in the Aequalis Reversed Shoulder Prosthesis (Tornier, Edina, MN) on impinge- ment of the humeral prosthesis against the scapula to test the hypothesis that the mechanical contact of the humeral component with the scapular neck is influenced by the version of the humeral component. Materials and methods: Seven shoulders from deceased donors were tested after the Aequalis Reversed Shoulder was implanted. The deltoid, pectoralis major, and latissimus dorsi were loaded based on physiologic cross-sectional area. The degree of internal and external rotation when impingement, subluxation, or dislo- cation occurred was measured at 0  , 30  , and 60  glenohumeral abduction in the scapular plane. Testing was performed with the humeral component placed in 20  of anteversion, neutral version, 20  of retroversion, and 40  of retroversion. Results: Maximum external rotation at 0  abduction was e1   4  at 20  anteversion, 15   3  at neutral, 28   4  at 20  retroversion, and 44   5  at 40  retroversion (P <.05). Maximum internal rotation at 0  abduc- tion was 128   9  at 20  anteversion, 112   9  at neutral, 99   8  at 20  retroversion, and 83   8  at 40  retroversion (P <.05). Maximum external rotation at 30  abduction was 70   6  at 20  anteversion, 84   7  at neutral, 97   6  at 20  retroversion, and 110   5  at 40  retroversion (P < .05). There was no limitation to internal rotation at 30  abduction. No impingement occurred at 60  abduction. Discussion: Version of the humeral component plays a role in range of motion and impingement in reverse total shoulder arthroplasty. Anteversion can significantly decrease the amount of external rotation achievable after reverse total shoulder surgery. Conclusion: Placing the Aequalis Reversed Shoulder humeral component at between 20  and 40  of retroversion more closely restores a functional arc of motion without impingement. Level of evidence: Basic Science Study, Biomechanical Study. Ó 2011 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Reverse total shoulder; humeral version; impingement; scapular notching; range of motion The Delta (Depuy Orthopaedics, Warsaw IN) reverse total shoulder prosthesis was introduced by Grammont in 1985 as a surgical option for patients with severe glenohumeral arthritis and advanced rotator cuff disease. 3,10 As originally *Reprint requests: Thay Q. Lee, PhD, Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System (09/151), 5901 E 7th St, Long Beach, CA 90822. E-mail addresses: tqlee@med.va.gov or tqlee@uci.edu (T.Q. Lee). J Shoulder Elbow Surg (2011) 20, 652-658 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.2010.08.020