The influence of anatomic total shoulder arthroplasty using a subscapularis tenotomy on shoulder strength.

ABSTRACT

BACKGROUND AND HYPOTHESIS: There is limited evidence describing the influence of total shoulder arthroplasty on strength. The hypothesis was that after total shoulder arthroplasty, strength would improve compared with the preoperative state but remain inferior to that of the nonoperative shoulder. An additional aim was to determine whether strength improvement was associated with improvements in outcome scores and motion. MATERIALS AND METHODS: Thirty-six patients underwent total shoulder arthroplasty, with 31 patients (86%) having 1 year of follow-up for all outcomes. Patient-determined outcomes (Western Ontario Osteoarthritis of the Shoulder score; Disabilities of the Arm, Shoulder and Hand score; Single Assessment Numeric Evaluation rating; and shoulder activity level), range of motion, and strength were assessed. Isometric strength was determined for scaption and external rotation, as well as the liftoff test, belly-press test, and bear-hug test. RESULTS: All strength measures improved, with significant increases in external rotation, the liftoff test, and the bear-hug test, but remained inferior to the nonoperative-side strength. Improved strength in the belly-press test was associated with greater improvement in Single Assessment Numeric Evaluation scores. Improvements in scaption and belly-press testing were associated with improvements in active flexion. Strength improvements in the liftoff test were associated with improved internal rotation in 90° of abduction. Patients with improvements in strength had improvements in their shoulder activity level from baseline to final follow-up, whereas patients without improved strength test findings did not have improved shoulder activity levels. CONCLUSIONS: Total shoulder arthroplasty improved external rotation, liftoff, and bear-hug strength testing. Operative shoulder strength remained inferior to strength of the nonoperative shoulder. Patients with improvements in strength were more likely to have greater improvements in outcome scores and range of motion. Improvements in the shoulder activity level after anatomic total shoulder arthroplasty may be dependent on improvements in strength.