How should worsening in osteoarthritis be defined? Development and initial validation of preliminary criteria for clinical worsening in knee and hip osteoarthritis.

OBJECTIVES: There is a need to define and validate measures of clinical worsening in knee and hip osteoarthritis (OA). The objectives of this exploratory project were: (i) to characterize worsening criteria in knee and hip OA using psychometric methods; (ii) to estimate their sensitivity and specificity; and (iii) to validate and compare these criteria with worsening criteria previously described in the literature. METHOD: An Expert Group reached consensus on 10 sets of worsening criteria to be tested in observational data sets of patients with knee or hip OA who received multimodal conservative treatment. These sets included 219 patients (derivation cohort) and 296 patients (validation cohort). We estimated minimal clinically important worsening (MCIW) values for pain, function, stiffness, and patient global assessment, and tested candidate worsening criteria in the derivation cohort. Finally, using patient judgement, we examined the sensitivity and specificity of literature-based as well as candidate worsening criteria in the validation cohort. RESULTS: Literature-based worsening criteria were found to have high specificity (range 60-92%) but low sensitivity (range 22-59%). Two out of 10 candidate worsening criteria constructed by the Expert Group showed an acceptable combination of sensitivity and specificity in the derivation cohort, which was confirmed in the validation cohort (ranging from 54% to 65% and 67% to 74%, respectively). CONCLUSIONS: This is the first study to describe symptomatic worsening criteria based on expert consensus after examining the performance of candidate criteria derived from the literature applied to data in an observational study. The newly proposed worsening criteria show an acceptable combination of sensitivity and specificity.

Responsiveness of four patient-reported outcome measures to assess physical function in patients with knee osteoarthritis.

OBJECTIVES: The aim of this study was to evaluate the responsiveness of four patient-reported outcome measures (PROMs) to measure change in physical function simultaneously in patients with knee osteoarthritis (OA) following currently recommended COSMIN (COnsensus-based Standards for the selection of health status Measurement INstruments) standards. METHOD: Patients with knee OA receiving conservative treatment following a stepped care approach were invited to complete a set of questionnaires at baseline and 3 months. Questionnaires included four widely used measures of physical function: the Knee Injury and Osteoarthritis Outcome Score Physical Function Short Form (KOOS-PS), the Lequesne algofunctional index (LAI), the Lower Extremity Functional Scale (LEFS), and the Western Ontario and McMaster University Osteoarthritis Index Physical Function subscale (WOMAC-PF). Responsiveness of physical function was investigated according to the COSMIN standards by testing 15 a priori defined hypotheses. Responsiveness was considered positive if > 75% of the hypotheses could be confirmed. RESULTS: A total of 161 patients participated [61% female, mean (sd) age 59 (9) years and body mass index 29.7 (5.0) kg/m2]. Baseline values of the four PROMs were, mean (sd): KOOS-PS 53.6 (16.8), LAI 11.0 (4.0), LEFS 40.6 (14.1), and WOMAC-PF 51.8 (19.4). We could confirm 12 out of 15 predefined hypotheses (80%) about expected correlations for the WOMAC-PF whereas for the KOOS-PS, LAI, and LEFS < 75% hypotheses could be confirmed (73, 67, and 73%. respectively). CONCLUSIONS: Our results suggest that the WOMAC-PF is able to detect changes over time in physical function and therefore should be the measure of first choice in clinical trials evaluating the effectiveness of an intervention on physical function in knee OA patients.