The return of subscapularis strength after shoulder arthroplasty

During shoulder arthroplasty, the subscapularis tendon is released and repaired. Whether subscapularis strength subsequently returns to normal is poorly understood. This study's purpose was to determine whether subscapularis strength returns to normal after shoulder replacement and whether any preoperative factors predict the return of strength postoperatively.

Sixty-four patients underwent unilateral shoulder arthroplasty. Subscapularis strength was compared between the surgical and contralateral (normal) limbs at baseline (preoperatively) and follow-up. In addition, operative arm subscapularis strength recovery was compared with ipsilateral supraspinatus strength recovery. Independent variables were assessed for their effect on subscapularis strength, including sex, age, dominant-side surgery, preoperative strength, preoperative external rotation, subscapularis management technique, and fatty infiltration.

The mean subscapularis strength ratio at 24 months from baseline was 1.19 ± 2.23 (P = .0007). The normal side was significantly stronger than the operative side at all time points (P < .0001). The operative-side subscapularis mean strength ratio was 0.54 ± 0.28 of normal at baseline and 0.70 ± 0.24 at 24 months. Defining normal strength as ±15%, 15% of patients were normal at baseline up to 22% at 24 months. At 24 months, the mean supraspinatus strength ratio from baseline (3.13 ± 6.11) was significantly greater than the subscapularis mean strength ratio (P = .0007). Multivariable regression analysis did not demonstrate any correlation (P > .05) between the independent variables studied and final subscapularis strength.

Although significant strength improvement from baseline was observed at 2 years after shoulder arthroplasty, subscapularis strength returned to normal in only a minority of patients. Potential prognostic variables associated with final subscapularis strength remain elusive.