Quantifying success after total shoulder arthroplasty: the minimal clinically important difference

BACKGROUND: Knowledge of the minimal clinically important difference (MCID) for different shoulder outcome metrics and range of motion after total shoulder arthroplasty (TSA) can be useful to establish a minimum threshold of improvement that defines successful treatment. This study quantifies how MCID varies with different prosthesis types, patient age, gender, and length of follow-up after TSA.

METHODS: A total of 466 anatomic TSA (aTSA) and reverse TSA (rTSA) with 2-year minimum follow-up were performed by 13 shoulder surgeons. The MCID for the American Shoulder and Elbow Surgeons, Constant, University of California Los Angeles Shoulder Rating Scale, Simple Shoulder Test, Shoulder Pain and Disability Index, global shoulder function, and visual analog scale for pain scores, as well as active abduction, forward flexion, and external rotation, were calculated for different prosthesis types and patient cohorts using an anchor-based method.

RESULTS: The anchor-based MCID results were American Shoulder and Elbow Surgeons = 13.6 ± 2.3, Constant score = 5.7 ± 1.9, University of California Los Angeles Shoulder Rating Scale = 8.7 ± 0.6, Simple Shoulder Test score = 1.5 ± 0.3, Shoulder Pain and Disability Index score = 20.6 ± 2.6, global shoulder function = 1.4 ± 0.3, pain visual analog scale  = 1.6 ± 0.3, active abduction = 7° ± 4°, active forward flexion = 12° ± 4°, and active external rotation = 3° ± 2°. Female gender and rTSA were associated with lower MCID values compared with male gender and aTSA patients.

CONCLUSION: The minimum improvement necessary for patients to achieve a result they believe is clinically meaningful after aTSA and rTSA is nominal and was achieved by at least 80% of the patients. Future endeavors should investigate the influence of different anchor questions on the MCID calculation.