Minimally Important Differences and Change Across Time in Patients Treated Surgically and Non-Surgically for Full-Thickness Rotator Cuff Tears

OBJECTIVES: The minimally important difference (MID) is the smallest change in an outcome measure that is perceived by patients as beneficial. The MIDs for the ASES and WORC scores have not been established in a homogenous population of patients with rotator cuff tears. The objective of the present study was to establish the MIDs for patients with known cuff tears who were treated both surgically and non-surgically, and to compare the MIDs over time. METHODS: We included 209 subjects with known full-thickness rotator cuff tears who were followed prospectively for two years. The WORC and ASES scores were collected at baseline, 4, 8, 16, 32, and 48 weeks, 1 year and 2 years. At the final follow-up point patients filled out an end-of-study form which included questions regarding change in their condition after treatment. RESULTS: For those that indicated being minimally better, the change from baseline for the ASES score was -20.57 (-2.94 to -38.20) and for the WORC was 418.60 (70.39 to 766.81); both indicated improvement in outcomes. When converted to the percentage change score the WORC change represented 19.93%. The plots of these new MID values for the ASES and WORC indicate that not only does the operative group improve more than the non-operative group but it does so to an extent that is greater than the MID. The non-operative group also improved across time, but the magnitude did not exceed the MID for either the WORC or the ASES. CONCLUSION: We found that the ASES and the WORC MIDs in patients with rotator cuff tears is different from that previously reported, and that the operative group change was greater than the non-operative group change. This information will directly improve our ability to: (1) Determine when patients with RCTs are changing in a meaningful manner; (2) Accurately power clinical studies using these outcome measures; (3) Make more informed choices of treatments in these patients. This is the first study to report MIDs for the ASES and WORC in a population of patients with strictly rotator cuff disease and to explore their changes relative to MIDs across time.