Association Between Preoperative Shoulder Strength and Clinical Outcomes After Primary Reverse Total Shoulder Arthroplasty

Introduction: We aimed to determine whether preoperative shoulder strength predicts postoperative values and improvement in strength, range of motion (ROM), and outcome scores after primary reverse total shoulder arthroplasty (rTSA).

Methods: We retrospectively reviewed 264 shoulders with a minimum of 2-year follow-up after primary rTSA. Preoperative external rotation (ER) strength, supraspinatus strength, and abduction strength were analyzed to establish their correlation with postoperative values and improvement in strength, ROM, and outcome scores (Constant score, American Shoulder and Elbow Surgeons Shoulder score, Shoulder Pain and Disability Index, Simple Shoulder Test, and the University of California, Los Angeles score). Multiple linear regression models were used to identify the preoperative shoulder strength measures that most affected postoperative outcomes and improvement in outcomes.

Results: Preoperative measures of shoulder strength were positively correlated with all measures of postoperative shoulder strength, active abduction and elevation, and all outcome scores studied. On multivariate analysis, greater preoperative ER, supraspinatus, and abduction strength were significantly associated with greater corresponding postoperative values (P = 0.009, P = 0.041, and P = 0.008, respectively); however, they were also associated with less respective improvement (P < 0.001 for all) because the weakest patients tended to see the largest improvements. Notably, preoperative values of ER and supraspinatus strength exceeding 17.5 and 20.5 lbs were associated with a decline in their respective values postoperatively, but no limit was identified for ROM or outcome score measures. On multivariate analysis, reduced preoperative abduction strength was markedly associated with greater improvement in 3 of 4 ROM measures and 4 of 5 outcome scores.

Conclusion: Preoperative shoulder strength, especially abduction strength, predicts superior postoperative outcomes and greater improvement in shoulder strength, ROM, and outcome scores after primary rTSA. However, a minority of patients with well-preserved strength may lose strength after surgery, and patients who are weaker preoperatively tend to see larger improvements in postoperative outcomes.

Level of evidence: Ⅳ, prognostic study.