Predictors affecting the achievement of the minimum clinically important difference following total knee arthroplasty

Introduction: The aim of our study was to (a) establish the minimum clinically important difference (MCID) for the New Knee Society Score (NKSS) and its subcomponents following primary total knee arthroplasty (TKA) in the Indian population and (b) study the predictors associated with achieving MCID following TKA. Methods: We retrospectively reviewed all patients undergoing primary TKA. The NKSS was filled by the patient preoperatively, the day before, and at 1 year ± 1 month from TKA. The NKSS has 5 main components: Objective Knee Score (OKS), Symptoms Score, Function Knee Score (FKS), Satisfaction Score, and Expectation Score. MCID was calculated using the distribution method. Univariate and multivariate regression analyses were performed to identify predictors of achieving MCID. Results: The MCID for the Symptom Score was 2.5, with 88.2% achieving it. Higher Satisfaction Score post-TKA was a significant ( B = 0.37, P < 0.01) predictor for achieving MCID for the Symptom score. The MCID for OKS was 7.1, with 93.4% achieving it. Higher preoperative flexion ( B = 0.05, P < 0.01) and lower body mass index ( B = −0.20, P = 0.01) were significant predictors of achieving MCID for OKS. The MCID for FKS was 6.8, with 81.1% achieving it. Lower age ( B = −0.42, P < 0.01), higher Satisfaction Score post-TKA ( B = 0.99, P < 0.01), and higher preoperative flexion ( B = 0.13, P < 0.01) were significant predictors of achieving the MCID for FKS. Conclusion: The MCID for the Symptom score, OKS, and FKS was 2.5, 7.1, and 6.8 in the Indian population 1 year post-TKA, with 88.2%, 93.4%, and 81.1% achieving the MCID for these scores, respectively. Interestingly, post-TKA satisfaction was associated with the likelihood of achieving MCID only for the symptom and function score, but not for the OKS. Higher preoperative flexion was an important predictor of achieving MCID for both objective and functional scores post primary TKA. Researchers can use these MCID values specific for the Indian population to understand the clinical validity of changes in outcome scores after TKA.