Objective performance tests assess aspects of function not captured by self-report in knee osteoarthritis

Abstract

Purpose: Knee osteoarthritis (OA) may lead to substantial functional limitation, which can be assessed objectively with validated performance tests or using self-report data. The relationships between the findings of objective performance tests and self-report measures of functional status have received little investigation. We sought to determine whether the performance tests are independent of one another, whether they capture different information from self-report measures of function, and whether they are influenced by features of chronic pain including anxiety and depression, neuropathic pain, widespread pain, and pain catastrophizing. Methods: We used baseline data from participants enrolled in the ORBIT Registry (Osteoarthritis Registry of Biomarker and Imaging Trajectories). At study entry, participants were 40+ years old and had evidence of both symptomatic and radiographic knee OA (Kellgren-Lawrence grade 2-3) in at least one knee. Self-reported pain of the most bothersome knee (index knee) was ascertained using the Knee Injury and Osteoarthritis Outcome Score (KOOS) Pain scale and functional status with the KOOS ADL scale (0-100, 100 best). Subjects completed the five-item Mental Health Index (MHI-5, a measure of anxiety and depressive symptoms), the Neuropathic Pain Scale (NPS), a widespread pain index (WPI; sum of 23 possible musculoskeletal pain locations), and the Pain Catastrophizing Scale (PCS). Performance testing included the 40-meter fast paced walk (40m Walk), Timed-Up-and-Go (TUG), timed single leg balance test (SLB), and 30-second sit-to-stand (30s STS) tests. We used Pearson correlation coefficients to examine linear associations among the four performance tests and the associations between each performance test and the self-report measures of pain, functional status and chronic pain features. We further investigated the associations between performance tests and self-reported knee pain and function with adjustment for MHI-5, WPI, PCS and NPS using partial correlations. Results: We assessed 78 subjects with mean age 63.1 (SD 10.0), mean body mass index (BMI) 30.2 (SD 5.4), 69% female. The mean (SD) values for the performance tests included: 40m Walk 27.9 (5.6) seconds, TUG 9.1 (2.2) seconds, SLB 21.8 (19.7) seconds, and 30s STS 11.7 (4.5) stands. The individual performance measures had modest correlations with one another (Pearson r ranging from 0.33 to 0.74). The highest correlation (r = 0.74) was between TUG and 40m Walk, indicating that just 50% of the variability in TUG was explained by variability in 40m Walk. ORBIT participants had an average KOOS ADL score of 66.1 (18.2) and KOOS Pain of 74.6 (19.8). The correlations between performance tests and KOOS Pain, KOOS ADL, PCS, NPS, WPI and MHI-5 are shown in the Table. None of the correlations exceeded 0.40. Correlations were weakest for the associations between widespread pain and MHI-5 scores and the performance tests (all ≤ 0.23). Partial correlations between KOOS ADL scores and the performance tests were 28-64% lower than the crude correlations, adjusting for PCS, NPS, widespread pain and MHI-5 (Table).Table 1Pearson correlation coefficients for associations between performance tests and self-report measures of pain, function and chronic pain features40 Meter WalkTimed Up and GoTimed Single Leg Balance30-Second Sit to StandKOOS Pain-0.25-0.260.290.40KOOS ADL-0.33-0.290.400.40Pain Catastrophizing0.340.26-0.19-0.24Neuropathic Pain Scale0.320.20-0.24-0.23Widespread Pain0.15-0.08-0.23-0.18Mental Health Index-0.10-0.050.170.03Partial correlations adjusting for pain catastrophizing, NPS, widespread pain, MHI-5KOOS Pain-0.15-0.240.280.30KOOS ADL-0.12-0.200.290.25 Open table in a new tab Conclusions: 40m Walk, TUG, SLB and 30s STS each assess different aspects of functional capacity in knee OA patients. Self-reported functional status in persons with knee OA has weak to modest correlations with objective measures of functional status, which are further attenuated with adjustment for pain catastrophizing, neuropathic symptoms, widespread pain and anxiety and depression. These data suggest that objective performance tests capture elements of physical functional status in persons with knee OA that are not assessed well by frequently used self-report measures of functional status. Objective performance tests are not influenced strongly by other features of chronic pain such as catastrophizing, neuropathic pain symptoms, widespread pain or depression and anxiety. These data point to the importance of adding objective measures to the assessment of functional status in OA trials.