Patient-Reported Measures of Physical Function in Knee Osteoarthritis

Knee osteoarthritis is a common cause of an array of functional limitations in older adults, and the accurate assessment of such limitations is critical for practicing clinicians and scientists. Patient-reported measures are a valuable resource to track the type and severity of limitation, although the psychometric performance of each instrument should be thoroughly evaluated before adoption. This article reviews the validity, reliability, sensitivity to change, and responsiveness of 3 patient-reported measures of physical function: the Western Ontario and McMaster Universities Osteoarthritis Index, the Knee Injury and Osteoarthritis Outcome Score, and the Patient Reported Outcomes Measurement Information System Physical Function scale.

Key points

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The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) physical function subscale is a well-validated and reliable patient-reported measure, although it is questionable if the constructs of physical function and pain are separately evaluated.
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The Knee Injury and Osteoarthritis Outcome Score (KOOS) Function in Sport and Recreation subscale is a well-validated measure of physical function, although floor effects are present for people with moderate to severe functional limitation.
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The Patient Reported Outcomes Measurement Information System (PROMIS) Physical Function measure is a newer measurement instrument, and preliminary studies show high test-retest reliability and no floor or ceiling effects among people with osteoarthritis (OA).