Teres minor deficiency does not predict clinically inferior external rotation after reverse total shoulder arthroplasty: a 2-year matched cohort study

Background

Current teaching maintains that reverse total shoulder arthroplasty (RTSA) is unlikely to restore external rotation (ER) without a functional posterior rotator cuff, specifically the teres minor (TM). This study compared restoration of ER in TM-deficient (TMD) with TM-intact (TMI) shoulders after RTSA.

Methods

All patients who underwent lateralized RTSA using an onlay prosthesis with no adjunct tendon transfers between January 2014 and July 2020 and with 2-year follow-up were identified. Preoperative imaging review identified patients with TMD, and propensity score matching was used to create a control group of equal size. TMD was divided into three subgroups: 1) atrophy; 2) fracture/malunion/nonunion (proximal humerus); and 3) endoprosthesis. Primary outcome measures were active ER range of motion (ROM) measured at the side, ΔER ROM from baseline, ER strength, and American Shoulder and Elbow Surgeons subscore question, “can you reach back of head.”

Results

Thirty-nine patients with TMD shoulders (atrophy: n = 15; fracture n = 14; endoprosthesis: n = 10) were matched with 39 patients with TMI shoulders. Although TMD was associated with reduced baseline ER ROM (13.6 vs. 28.8; P = .004), the TMD group achieved greater ΔER ROM 2 years after RTSA (24.6 vs. 10.3; P = .014) and demonstrated comparable 2-year ER ROM (38.6 vs. 40.7; P = .484). The TMD group had a higher rate of ER weakness (12% vs. 0%; P = .044) but no difference in ability to reach back of head (unable: 24% vs. 20%; P = .686) or patient-reported functional scores (2-year American Shoulder and Elbow Surgeons: 76.2 vs. 74.8; P = .793).

Conclusion

This study suggests that patients with an insufficient or absent teres minor can achieve satisfactory ER ROM and function after lateralized RTSA similar to their TMI peers. Future study will seek to identify muscle activation patterns of the shoulder girdle that allow TMD patients to overcome this insufficiency to perform activities requiring ER.