The minimal clinically important difference for function and strength in patients undergoing reverse shoulder arthroplasty

Abstract

Hypothesis: Despite a statistically significant improvement in functional scores after receiving a reverse shoulder arthroplasty (RSA) in a cuff-deficient shoulder, not all patients perceive a minimal clinically important difference (MCID) in every functional domain of the score.

Methods: This was a prospective longitudinal study including 60 consecutive patients with a cuff-deficient shoulder treated with a RSA. The Constant score was recorded before surgery and at a 1-year follow-up assessment. At the 1-year follow-up, all patients also filled out a 15-item anchor questionnaire to assess their perception of change in their overall function, forward elevation, lateral rotation, internal rotation, and strength to determine the MCID.

Results: The mean Constant score was 30.1 (standard deviation, 10.7) before surgery and was 58.4 (standard deviation, 16.2) at the 1-year follow-up, with statistically significant improvement (P < .001). A statistically significant improvement was found in the domains of forward elevation (P < .001), lateral rotation (P < .001), and strength (P < .001) except for internal rotation (P = .15). The MCID for overall function, forward elevation, lateral rotation, internal rotation, and strength in the Constant score increased by 8, 6, 2, 2, and 11.5 points, respectively; only 46.7%, 20%, 50%, 45.8%, and 33.3% of the patients, respectively, exceeded the MCID on each domain after surgery.

Conclusions: A statistically significant improvement in the Constant score is expected after receiving an RSA in a cuff-deficient shoulder, but a considerable number of patients do not reach the MCID in the function and strength domains. A small improvement in rotation is perceived to be beneficial by patients, whereas large improvements in forward elevation are required for the improvement to be perceived to be beneficial.

Keywords: Reverse shoulder arthroplasty; cuff-deficient shoulder; minimal clinically important changes; outcome.