Many articles have addressed knee pain as a result of osteoarthritis (OA) in both the younger and older adult population. Various measures including radiographs (X-rays), MRI, CT scan and synovial fluid analysis have been employed to diagnose and deduce severity of knee pain secondary to osteoarthritis.
Additionally, self-measurement tests have been used in order to measure physical function and pain in individuals with OA. Of these pencil and paper measures, the one most commonly used in research is the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). It was originally devised to evaluate three dimensions of OA symptoms including pain, stiffness and physical function of the hip and knee.1 While the WOMAC has demonstrated good reliability2 and validity3, another measure to be considered in conjunction with the WOMAC is the Knee injury and Osteoarthritis Outcome Score (KOOS).4
There is an increased interest in the early treatment of OA to reverse or at least slow down the disease process. Because OA develops over decades, it is prudent to examine patients who are younger and more active early in the disease process.
To meet this need, the KOOS was developed as an extension of the WOMAC for younger and/or more active patients with knee injury and/or knee osteoarthritis.5 Studies have shown the KOOS to be more sensitive and responsive than the WOMAC in younger or more active patients,4,6 thereby lending greater reliability to identifying early symptoms and functional deficits as a result of developing OA.
The KOOS is 42-item, self-administered and assesses five outcomes: pain, symptoms, activities of daily living, sport and recreation function, and knee-related quality of life. Several questions contained in the KOOS were obtained from the WOMAC and include pain questions, which are in the "Pain" subscale of the KOOS. The WOMAC stiffness questions are included in the subscale "Other Disease-Specific Symptoms" and the WOMAC subscale "Function" is equivalent to the KOOS subscale "ADL." The KOOS takes about 10 minutes to complete. Complete directions and scoring of the questionnaire can be found at www.koos.nu.
The KOOS has been validated in several different populations having surgical procedures due to knee complaints. It has been tested and validated in individuals who have undergone knee total arthroplasty,7 and in others who have undergone surgical reconstruction of the ACL.4 Convergent and divergent construct validity was determined by comparison to the SF-36 and to the Lysholm knee scoring scale. Reliability of the KOOS was analyzed in a study examining the usefulness of the KOOS in assessing the condition of individuals after undergoing treatment for focal cartilage lesions.8
In this study, the Cronbach's alpha of the KOOS subcategories and total score ranged from 0.74 to 0.96. The overall ICC of the KOOS was 0.97 while the subscales ranged from 0.87 to 0.95. Spearman's rank correlations between the subscales of the KOOS and representative subscales of the SF-36, Lysholm and EQ-5D were high to moderate, ranging from 0.43 to 0.70.
In terms of responsiveness, a moderate to large effect size ranging from 0.70 to 1.32 and the standardized response mean 0.61 to 0.87 was seen. Roos and Lohmander found that the effect sizes following surgical procedures vary both with regard to the procedure performed and the specific KOOS subscale. In general, the subscale QOL was the most responsive, followed by the subscale "Pain." The highest effect sizes observed were obtained after total knee replacement.5
The KOOS's five patient-relevant dimensions are scored separately: Pain (nine items); Symptoms (seven items); ADL Function (17 items); Sport and Recreation Function (five items); and Quality of Life (four items). A Likert scale is used, all items have five possible answer options scored from 0 (no problems) to 4 (extreme problems), and each of the five scores is calculated as the sum of the items included. Scores are transformed to a 0-100 scale, with 0 representing extreme knee problems and 100 representing no knee problems as common. Scores between 0 and 100 represent the percentage of total possible score achieved.5
Why use the KOOS as opposed to the WOMAC? One advantage as stated by the authors is that the KOOS assesses certain domains that the WOMAC and other quality-of-life instruments do not, such as sport and recreation function and knee-related quality of life. Additionally, the KOOS has a greater responsiveness compared to other more generic instruments such as the WOMAC and the SF-36.4-6 Another strength of the KOOS is it includes questions from the WOMAC in various subscales, thereby allowing for comparisons across studies.
The KOOS has demonstrated high test-retest reproducibility (ICC >0.75) and includes the WOMAC Osteoarthritis Index in its complete and original format, thereby allowing comparisons to other studies that use the WOMAC in elderly individuals with knee OA. If you are looking for a measurement tool for younger individuals who may develop or have OA as a result of injuries (e.g. ACL tears, cartilage damage) or surgeries, the KOOS may be the right instrument for you.
References are available at www.advanceweb.com/PT or by request.
Dr. Lewis is a consulting clinical specialist for Professional Sportscare and Rehab and co-owner of The Center of Evidence. She lectures exclusively for GREAT Seminars and Books Inc. Her Website address is www.greatseminarsandbooks.com. She is also editor-in-chief of Topics in Geriatric Rehabilitation (www.topicsingeriatric
rehabilitation.com) and an adjunct professor at George Washington University department of geriatrics, College of Medicine. Dr. Shaw is associate professor for the School of Physical Therapy at Rueckert-Hartman College for Health Professions, Regis University, Denver, CO.