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Discriminative Ability of Functional Measures in Knee Osteoarthritis Patients Classified Based on Radiographic Severity

LEVEL OF EVIDENCE: 3B SUMMARY Background. Determining the discriminative ability of functional outcome measures among patients of knee osteoarthritis (OA) with different severity degrees of radiographic signs can be valuable for clinicians and researchers to classify the functional limitations in these patients before starting their rehabilitation. Objective. To determine the discriminative ability of patient-reported outcome measures (PROMs) and performance-based ones in knee OA patients classified based on radiographic severity. Methods. Based-on the Kellgren-Lawrence (KL) grading scale, 130 knee OA patients were classified into 65 patients with mild (a KL grade ≤ 2) and 65 patients with moderate-to-severe (a KL grade ≥ 3) radiographic sign. PROMs and performance-based outcome measures in knee OA patients were assessed by Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire as well as Timed-up and go test (TUG), Functional Reach Test (FRT), and step test, respectively. The discriminative ability of these measures was determined by calculation of sensitivity, specificity, area under the Receiver Operating Characteristic curve, likelihood ratios, and predictive values. Results. Our results showed that all subscales of the KOOS except for the sport/recreation and all performance-based outcome measures have good ability to discriminate between the two groups of knee OA. Also, the ADL subscale of KOOS and step test have good ability in accurate identification of mild grade of knee OA patients. The symptoms subscale of KOOS and TUG test have the best ability in correctly identifying moderate-to-severe grade of knee OA. Conclusions. Our findings provide evidence for the good discriminative ability of functional measures in patients of knee OA classified based on radiographic severity.