Knee Injury and Osteoarthritis Outcome Score has higher responsiveness and lower ceiling effect than Knee Society Function Score after total knee arthroplasty.

PURPOSE: To compare the following subjective scoring instruments: the Knee Society Function (KS-F) Score and Knee Injury and Osteoarthritis Outcome Score (KOOS) in patients who underwent total knee arthroplasty (TKA) by assessing standard metrics related to the utility of each instrument, including responsiveness, ceiling effect, and distribution of scores.
METHODS: Patients undergoing TKA for osteoarthritis (n = 82) were evaluated pre-operatively and post-operatively at a median time of 1 year (range 0.7-3.6 years) using the KS-F score and KOOS. Responsiveness, the ability of a tool to measure change over time, was evaluated by computing the standardized response mean. Ceiling effects were determined by calculating the percentage of patients who attained the best-possible score.
RESULTS: The KOOS scale had higher standardized response mean than KS-F scale in the majority of subsections (except sports and recreation). The KOOS had a lower ceiling effect in the majority of subsections (except pain) and was significantly lower on the symptoms and quality of life subscales (both p < 0.05). Scores were not normally distributed for either KS-F or KOOS scales.
CONCLUSIONS: Since the KOOS scale had a higher responsiveness and a lower ceiling effect, it appears to be a superior outcome tool versus the KS-F scale when evaluating the outcomes of TKA patients. LEVEL OF EVIDENCE: Diagnostic Study, Level I.