Minimal Clinically Importance Difference and Substantial Clinical Benefit in Total Knee Arthroplasty: Delayed Achievers and Maintaining Improvement.

INTRODUCTION

Improvement in Knee injury Osteoarthritis Outcome Survey, Joint Replacement (KOOS, JR) scores is commonly used as a marker of patient satisfaction following total knee arthroplasty (TKA). The purpose of this study was to determine predictors of patients who had delayed achievement of satisfied KOOS, JR scores following TKA and those who did not maintain their score despite achieving an early high score.

METHODS

We conducted an observational cohort study using our institutional registry comprising patient-reported outcomes collected pre- and postoperatively at 3-, 6-, 12-, and 24-month intervals following TKA. The primary outcome was the achievement of minimal clinically important difference (MCID) and substantial clinical benefit (SCB) in KOOS, JR scores at 24 months. Multivariate logistic regressions were performed to determine the likelihood of delayed achievement of MCID/SCB and not maintaining early achievement of MCID/SCB.

RESULTS

Among the 664 patients included in the study, 72.4% of patients achieved early MCID (i.e., 12 months), and 9.9% had a delayed achievement (i.e., 24 months). With the SCB benchmark, 63.1% of patients achieved early SCB and 13.0% achieved delayed SCB. There were 11.0 and 8.4% of patients who did not maintain MCID and SCB after early achievement, respectively. Patients who had delayed MCID achievement had lower (P = 0.005) baseline stiffness scores (52.3 ± 20.0) compared to patients who did not achieve MCID (61.3 ± 21.4). Adjusted analyses did not identify significant predictors related to patient characteristics or baseline survey responses of the likelihood of delayed MCID/SCB achievement or maintenance of early MCID/SCB at 24 months.

CONCLUSIONS

The majority of patients achieve MCID or SCB within 12 months of TKA. Poorer preoperative knee health, especially related to stiffness, may be a driver of eventual achievement for patients who have unsatisfactory patient-reported outcome scores immediately after surgery.