A systematic review of estimates of the minimally clinically important difference and patient acceptable symptom state of the western ontario and mcmaster universities osteoarthritis index in patients who underwent total hip and total knee replacement

Abstract

Purpose: Patient reported outcome measures (PROMs) are increasingly used in clinical research to measure the effectiveness of treatments and in clinical care to monitor patient care. However, interpreting such measures can pose a challenge. The minimum clinically important difference (MCID) is defined according to the patient’s perspective of what change is important. MCIDs are defined using anchor-based methods (linking change in the outcome to an external anchor accounting for the patient’s perspective), or distribution methods which define different statistical parameters to assess clinical significance. A complementary concept to MCID is the patient acceptable symptom state (PASS) which has been defined as the highest level of symptoms beyond which patients consider themselves well. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is a commonly used PROM in osteoarthritis (OA). It has demonstrated reliability, validity and responsiveness in patients with OA. A number of empirical studies have been conducted to estimate the MCID and PASS of the WOMAC in patients with OA. Earlier work suggested there was wide variation in values across studies in rheumatology. Our objective was to systematically review the evidence regarding reported MCID and PASS estimates in pain and function measured using the WOMAC in patients who underwent primary total knee replacement (TKR) and primary total hip replacement (THR). Methods: We searched five electronic databases from inception until August 2018: Medline, Embase, Cinahl, Cochrane and Lilacs. Two reviewers independently screened titles, followed by abstracts, and then full-text papers using a priori inclusion/exclusion criteria. Papers were eligible if they included: 1) adults with OA of the hip or knee undergoing primary THR or TKR and 2) MCID or PASS estimates for WOMAC pain and function. Papers were excluded if the MCID/PASS was not determined for TKR and THR separately. Data were extracted by two independent reviewers. When a third reviewer compared the two extractions, minimal inconsistencies were found and were rectified through discussion. The Interpretability box of the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) checklist was completed for all studies with two additional questions to facilitate interpretation of scores. All reported values for MCID/PASS were converted to 0-100 scores (0=best and 100=worst). Results: The five database searches yielded 9322 results. After duplications were removed, 4804 citations remained for preliminary screening. 309 full text articles were assessed for eligibility. A total of 13 studies including data from seven countries were included (10 studies with TKR and 9 with THR. Five studies reported on five or more (of 7) Cosmin criteria while eight studies reported on four or fewer items. There was variation across studies in baseline WOMAC scores, follow-up time frames and wording of anchors. MCID for TKR: Nine studies used anchor-based methods to determine MCIDs for TKR. The MCID for WOMAC pain calculated using the mean change method was 13.3 in one study conducted in Holland and ranged from 22.6-29.9 in studies conducted in Spain. Using the ROC method, the MCIDs ranged from 20.5-36.0. The MCID for WOMAC function calculated using the mean change method was 1.8 in one study and ranged from 17.67-33.5 in studies conducted in Spain. Using the ROC method, the MCIDs ranged from 22.8-33.0. Two studies reported on distribution methods. The MCID calculated using 0.5 standard deviations from the mean difference in WOMAC scores was 9.4 (summary score) in one study and 10.6 for pain and 10.0 for function in another study. MCID for THR: Nine cohort studies included patients undergoing THR. The MCID for WOMAC pain calculated using the mean change method was 8.3 in one study and ranged from 24.55 to 29.26 in studies conducted in Spain. Using the ROC method, the MCID was 41 in one study. For function, the MCID, using the mean change method ranged from 20.8-26.54. Using the ROC method, one study calculated the MCID as 34. Using distribution methods (0.5 standard deviations from the mean difference in scores), MCIDs were 10.5 for pain and 9.7 for function. PASS: PASS cut-offs varied with reported cut-offs for TKR ranging from 25.0-28.6 for pain and 32.3-36.7 for function, and cut-offs for THR from 15.0-30.6 for pain and 28.0-42.0 for function. Conclusions: Findings highlight the variation in methodological approaches to determining MCIDs and PASS, variation in approaches within methods (e.g. different wording of anchor questions) and variation in patient sample characteristics (baseline WOMAC scores) used to determine values. Although the WOMAC is a commonly used measure for a single condition, this variability results in a range of values reported for MCID and PASS across studies.