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.