A Comparison Study of KOOS-PS and KOOS Function and Sport Scores

BACKGROUND: The KOOS-PS represents a shortened version of the Knee Injury and Osteoarthritis Outcome Score (KOOS) Function and Sport scales. Previous investigations have not evaluated the KOOS-PS against performance measures or self-report measures composed of items that assess a broad spectrum of ability levels. OBJECTIVE: The purpose of this study was to compare the construct validity of the KOOS Function and Sport subscales with a shorter version of the measure (KOOS-PS). METHODS: Using a cross-sectional, observational design, consecutive consenting patients diagnosed with knee osteoarthritis were recruited at an assessment center visit to determine need for conservative or surgical management. Participants completed the Lower Extremity Functional Scale (LEFS), KOOS, Timed "Up & Go" Test, and Six-Minute Walk Test. A single function-sport score (KOOS FunSportsum) and the KOOS-PS were abstracted from the KOOS. Pearson correlation coefficients were compared between the reference standards' scores (performance measures and LEFS) and KOOS scores. KOOS-PSraw scores were compared with KOOS-PSRasch scores. RESULTS: Three hundred seventy-seven patients with a mean age of 64.4 years (SD=10.5) participated. The correlation between performance reference standard and KOOS-PSRasch scores was significantly lower than with KOOS FunSportsum scores (mean difference in r=.08 [95% confidence interval=.03, .11], z=4.45, P1<.001). A similar finding was observed with the LEFS comparison. LIMITATIONS: The study sample did not consist of many patients with mild or severe functional status limitations. CONCLUSIONS: For patients with knee osteoarthritis, the KOOS-PS appears too restricted in item content to provide a comprehensive estimate of lower extremity functional status level relative to the KOOS Function and Sport subscales. Pursuit of a computer-adapted test may be a productive direction for future inquiry.