Superior migration of the humeral head does not significantly affect outcomes at an average of 11 years after total shoulder arthroplasty

Background: Superior migration of the humeral head has been linked with rotator cuff dysfunction and glenoid loosening after total shoulder arthroplasty (TSA). We aimed to determine if superior migration was associated with poor shoulder function following anatomic TSA at long-term follow-up. Methods: In this retrospective cohort study, we reviewed patients undergoing TSA by a single surgeon at an urban, academic institution. To study the effect of superior migration on TSA outcomes, we stratified the cohort by ≥ and <7 mm of acromiohumeral interval (AHI) and compared range of motion and patient reported outcomes (PROs). Clinical variables included preoperative and postoperative forward elevation (FE), internal rotation, external rotation, visual analog scale, American Shoulder and Elbow Surgeons shoulder score, and Simple Shoulder Text score. Radiographic variables included immediate postoperative and long-term follow-up AHI, lateral humeral offset, and glenoid loosening scores. Results: After applying exclusion criteria, 121 TSAs were included. The mean age was 63.9 ± 9.5 years, and 66 surgeries (55%) were in male patients. The mean follow-up for our cohort was 11.2 years (range, 5-26 years). Nine shoulders underwent revision surgery. All range of motion and PROs improved significantly from preoperative to the most recent postoperative follow-up. The mean AHI immediately following surgery was 10.9 ± 4.1 mm, while the mean AHI at most recent follow-up was 8.4 ± 3.5 mm. Glenoid loosening was observed in 29 (23.8%) shoulders at the most recent follow-up appointment. Although AHI correlated weakly with FE (r = 0.252; P = .006), we did not observe a clear threshold of migration which led to degraded function. Importantly, glenoid loosening was not related to AHI at long-term follow-up (P = .631). None of FE, internal rotation, external rotation, visual analog scale, American Shoulder and Elbow Surgeons shoulder score, Simple Shoulder Text, or revisions were significantly different between patients with ≥ and <7 mm of AHI. Conclusion: Our results suggest that anatomic TSA provides durable improvements to pain, function, and PROs despite changes to the AHI.