Minimal important change and minimum clinically important difference values of the KOOS-12 after total knee arthroplasty.

PURPOSE The minimal important change (minimal amount of change vs. baseline that a patient recognizes as a clinical change) and minimum clinically important difference (smallest difference between two measurements that are deemed important by patients) are important values to evaluate the clinical relevance of changes over time and differences between groups. This study aims to establish these values for the KOOS-12 at 1 year postoperatively. METHODS KOOS-12 scores were calculated from the full-length KOOS completed by patients undergoing primary TKA preoperatively and at 1 year follow up. Minimal important change (MIC) values were estimated using the anchor-based predictive modeling approach and adjustment for the large proportion of improved patients in the study cohort was performed. The MCID was defined as the difference in the mean change in the KOOS-12 between the 'no improvement' and 'little improvement' groups. RESULTS A total of 352 patients (161 male:191 female) with an overall mean age of 67.9 years (standard deviation (SD) 8.2) and a mean body mass index of 31.4 kg/m2 (SD 6.3) were included: 97.1% of patients reported an important improvement, 1.1% reported being about the same and 1.7% reported being importantly worse. The MIC improvement values were 11.5 for Pain, 13.7 for Function, 5.5 for Quality of Life (QoL) and 14.9 for the total KOOS-12 score. MCID values were 13.5 for Pain, 15.2 for Function, 8.0 for QoL and 11.1 for the total KOOS-12 score. CONCLUSION MIC of 14.9 and MCID of 11.1 established in this study can assist clinicians and researchers in the interpretation of within-group changes (MIC) and differences between groups (MCID) at 1 year after TKA.