Clinical cut-offs for hip- and knee arthroplasty outcome - minimal clinically important improvement (MCII) and patient acceptable symptom state (PASS) of patient-reported outcome measures (PROM).

Purpose: Clinical cut-offs like minimum clinically important improvement (MCII) and patient acceptable symptom state (PASS) increase the interpretability of patient reported outcome measures (PROMs), but cut-off estimates vary considerably, clouding a clear definition of a successful surgical outcome. We report estimates of MCII and PASS following hip- and knee arthroplasty using multiple methods and compare the different estimation methods.

Methods: Elective hip or knee arthroplasty patients who underwent the regular pre- and postoperative assessments 2014-2018 were included. The generic EQ-5D-5L and either the Hip or Knee disability/injury and Osteoarthritis Outcome Score (HOOS/KOOS) were used. MCII and PASS were estimated based on multiple estimation techniques.

Results: Distributions were skewed, with up to 95% being acceptable according to anchor questions. MCII estimates for HOOS/KOOS Pain ranged 21-60/10-47, with fewest in-sample misclassifications for the lowest cut-offs, provided by the 75th percentile approach. PASS estimates for HOOS/KOOS Pain ranged 84-93/78-91, for EQ-5D Index/EQ-VAS 0.87-0.92/66-79 (for hip), and 0.79-0.88/66-76 (for knee), with fewest misclassifications for the 75th percentile approach (hip) and Pythagoras approach (knee). The 75th percentile approach was the approach most often giving MCII estimates below the minimal detectable change (MDC).

Conclusions: We report new one-year estimates of MCII and PASS of HOOS, KOOS and EQ-5D subscales following hip- and knee arthroplasty. Estimates varied considerably when using different anchors and estimation techniques. Overall, the 75th percentile approach had fewest misclassifications, and had the lowest thresholds for the MCII estimations, but which were often below the MDC.