Knee injury and osteoarthritis outcome score and knee society score for the minimal clinically important differences after cruciate-retaining total knee arthroplasty: Two-year follow up.

BACKGROUND

This study investigated changes in the Knee Injury and Osteoarthritis Outcome Score (KOOS), 2011 Knee Society Score (KSS), and minimal clinically important differences (MCIDs) of these scores preoperatively to 2 years after total knee arthroplasty (TKA).

METHODS

This single-center retrospective study included 168 patients who underwent primary cruciate-retaining (CR) TKA using the subvastus approach. The KOOS and KSS were assessed preoperatively and during the 3-month, 6-month, 1-year, and 2-year follow ups. The MCIDs of the KOOS and KSS were calculated using distribution-based methods with standard deviation.

RESULTS

All patient-reported outcome measures improved considerably from preoperatively to 3 months postoperatively. KOOS pain and symptom scores considerably improved at approximately 2 years postoperatively, with KOOS activities of daily living (ADL) and sports/recreation subscale scores showing rapid improvement within 3 months, followed by smaller gains. MCID thresholds for KOOS subscales were as follows: pain, 14.3-15.3; symptoms, 14.1-15.6; ADL, 15.2-16.0; sport/recreation, 11.7-11.8; and quality of life, 13.6-14.4. KSS objective knee indicators and satisfaction improved considerably approximately 2 years postoperatively; however, scores on the expectation and functional activity subscales did not improve after 1 year. MCID thresholds for KSS subscales were as follows: objective knee indicators, 4.6-4.7; satisfaction, 4.9-5.0; expectation, 2.4; and functional activities, 12.0-12.3.

CONCLUSIONS

Improvements in the KSS objective knee indicators and KOOS subjective pain and symptom scores were similar over the 2-year follow up. These findings may help better understand the expected outcomes of CR-type TKA, especially in severe osteoarthritis cases, thereby informing patient counseling.