Background: This study was performed to determine the minimal clinically important difference (MCID) of Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function (PF) computer adaptive test (CAT) for patients with thumb carpometacarpal (CMC) arthritis. Methods: This study retrospectively analyzed data from 152 adults receiving surgical and nonsurgical care for unilateral thumb CMC arthritis at a single institution between January 2016 and January 2018. Patients completed PROMIS PF v1.2/2.0 CAT at each visit. At follow-up, patients also completed two 6-item anchor questions assessing the degree of perceived improvement. Statistical testing analyzed the ability of the clinical anchor to discriminate levels of improvement. An anchor-based MCID estimate was calculated as the mean PROMIS PF change score in the mild improvement group. The anchor-based MCID value was examined for the influence of patient age, initial and final PROMIS scores, and follow-up interval. A distribution-based MCID value was calculated incorporating the standard error of measurement and effect size. Results: The change in PROMIS PF scores was significantly different between encounters where patients reported no change, mild improvement, and much improvement. The anchor-based MCID estimate for PROMIS PF was 3.9 (95% confidence interval, 3.3-4.7). Individual MCID values were weakly correlated with the final absolute PROMIS PF score but did not correlate with patient age, time between visits, or the initial absolute PROMIS PF score. The distribution-based MCID value was 3.5 (95% confidence interval, 3.1-3.9). Conclusions: The estimated range of MCID values for PROMIS PF is 3.5 to 3.9 points in patients treated for thumb CMC arthritis.
Keywords: MCID; PROMIS; anatomy; arthritis; diagnosis; minimal difference; thumb.