Evaluation of the “Minimal Clinically Important Difference” (MCID) of the KOOS, KSS and SF‐12 scores after open‐wedge high tibial osteotomy

PURPOSE: Defining a Minimal Clinically Important Difference (MCID) value for Patient-Reported Outcome Measures (PROMs) is crucial for determining the effectiveness of a procedure and calculating the sample size for trial planning. The purpose of this study was to determine the MCID of several PROMs (Knee injury and Osteoarthritis Outcome Score (KOOS), Knee Society Score (KSS) and the SF-12) in patients who underwent medial opening-wedge High-Tibial Osteotomy (owHTO) with Patient-Specific Cutting Guides (PSCGs), using anchor-based methods. METHODS: Patients undergoing isolated medial owHTO with PSCGs between January 2013 and January 2017 were enrolled in this single-center, prospective, observational study. Three outcome scores were collected pre-operatively and at the 2 years follow-up evaluation: KOOS, KSS and SF-12. The MCIDs were calculated using anchor-based method: at 2 years postoperatively: "Compared with before surgery, how would you rate operated joint now?" The responses were recorded using a five-point scale. Patients who answered "about the same" or "somewhat worse" were classified into the no change group, while those who answered "somewhat better" were classified into the minimal change group. A receiver operating characteristic (ROC) curve was used to define the cutoff point that best discriminated between the minimal change and no change groups for each PROMs RESULTS: 196 patients were included, 75 (somewhat better) and 24 patients (about the same and somewhat worse) were, respectively, assigned to the "no change" and "minimal change" groups. There was no significant difference between the two groups in terms of baseline characteristics and postoperative complications. At 24 months follow-up all the PROMs (KOOS, KSS and SF-12) were significantly better for the "minimal change" group compared to the "no change" group. MCID was 15.4 for KOOS pain, 15.1 for KOOS symptoms, 17 for KOOS ADL, 11.2 for KOOS sports/recreation, 16.5 for KOOS QQL, 3 for KSS symptoms, 5.6 for KSS activity, 7.2 for SF-12 physical component and 6.3 for PCS mental component. CONCLUSION: This study determined the MCIDs of common used PROMs in patients undergoing owHTO. LEVEL OF EVIDENCE: Prospective Cohort Study, Level II.