Determination and comparison of the smallest detectable change (SDC) and the minimal important change (MIC) of four-shoulder patient-reported outcome measures (PROMs)

BACKGROUND There is a need for better interpretation of orthopedic treatment effects. Patient-reported outcome measures (PROMs) are already commonly used for patient evaluation. PROMs can be used to determine treatment effects in research as well as in clinical settings by calculating change scores, with pre- and post-treatment evaluation. The smallest detectable change (SDC) and minimal important change (MIC) are two important benchmarks for interpreting these change scores. The purpose was to determine the SDC and the MIC for four commonly used shoulder-related PROMs: Simple Shoulder Test (SST), Disabilities of the Arm, Shoulder and Hand (DASH and QuickDASH), and the Oxford Shoulder Score (OSS). METHODS A cohort of 164 consecutive patients with shoulder problems visiting an orthopedic outpatient clinic completed the SST, DASH, and the OSS at their first visit and 6 months after operative or non-operative treatment. The SDC was calculated with a test re-test protocol (0-2 weeks). For the MIC, change scores (0-6 months of evaluation) were calculated in seven subgroups of patients, according to an additional self-administered ranking of change over time (anchor-based mean change technique). The MIC is defined as the average score of the 'slightly improved' group according to the anchor. The QuickDASH was computed from the DASH. RESULTS The SDC of the SST was 2.8, DASH 16.3, QuickDASH 17.1, and OSS 6.0. The MIC change score for the SST was 2.2, DASH 12.4, QuickDASH 13.4, and OSS 6.0. CONCLUSION This study shows that on an individual patient-based level, when taking into account SDC and MIC, the change score should exceed 2.8 points for the SST, 16.3 points for the DASH, 17.1 points for the QuickDASH, and 6.0 points for the OSS to have a clinically relevant change on a PROM, which is not due to measurement error.