Effect of humeral component version on impingement in reverse total shoulder arthroplasty

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 impingement 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 dislocation occurred was measured at 0 degrees, 30 degrees, and 60 degrees glenohumeral abduction in the scapular plane. Testing was performed with the humeral component placed in 20 degrees of anteversion, neutral version, 20 degrees of retroversion, and 40 degrees of retroversion. Results: Maximum external rotation at 0 degrees abduction was -1 degrees +/- 4 degrees at 20 degrees anteversion, 15 degrees +/- 3 degrees at neutral, 28 degrees +/- 4 degrees at 20 degrees retroversion, and 44 degrees +/- 5 degrees at 40 degrees retroversion (P<.05). Maximum internal rotation at 0 degrees abduction was 128 degrees +/- 9 degrees at 20 degrees anteversion, 112 degrees +/- 9 degrees at neutral, 99 degrees +/- 8 degrees at 20 degrees retroversion, and 83 degrees +/- 8 degrees at 40 degrees retroversion (P<.05). Maximum external rotation at 30 degrees abduction was 70 degrees +/- 6 degrees at 20 degrees anteversion, 84 degrees +/- 7 degrees at neutral, 97 degrees +/- 6 degrees at 20 degrees retroversion, and 110 degrees +/- 5 degrees at 40 degrees retroversion (P<.05). There was no limitation to internal rotation at 30 degrees abduction. No impingement occurred at 60 degrees 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 degrees and 40 degrees of retroversion more closely restores a functional arc of motion without impingement.