Establishing minimally important differences for the American Shoulder and Elbow Surgeons score and the Western Ontario Rotator Cuff Index in patients with full-thickness rotator cuff tears.

BACKGROUND: The American Shoulder and Elbow Surgeons (ASES) score and the Western Ontario Rotator Cuff Index (WORC) are frequently used measures in clinical research for patients with rotator cuff tears (RCTs). The minimally important differences (MIDs) for these measures have not been established in patients with RCTs. The purpose of this study was to establish the MIDs for patients with known RCTs treated both surgically or nonsurgically.

METHODS: We included 222 subjects with full-thickness RCTs. The WORC and ASES were collected at baseline and at 4, 8, 16, 32, 48, and 64 weeks, as was an end of study form with questions about change in the condition after treatment. We calculated anchor-based and distribution-based MIDs. We used regression modeling to determine change in MIDs as predicted by several variables.

RESULTS: For the anchor-based method, we found an MID of 21.9 for the ASES and -282.6 for the WORC. When using the distribution-based method of ½ and ⅓ the standard deviation, we arrived at an MID of 26.9 and 17.9 points for the ASES and -588.7 and -392.5 points for the WORC. No variables predicted MID changes.

CONCLUSION: This is the first study to report MIDs for the ASES and WORC in a population of patients with only full-thickness RCTs. This information will directly improve our ability to determine when patients with RCTs are changing in a meaningful manner and accurately power clinical studies using these outcome measures.