Functional limitations, sedentary time and light physical activity on 24-month clinical outcomes in patients with knee osteoarthritis

Abstract

Purpose: Physical activity is well-established as a strong predictor for achieving general health benefits. Despite growing support for increased physical activity prescription in persons with knee osteoarthritis, informed recommendations for reducing sedentary time has received disproportionate attention. The objective of the present study was to quantify the relative contribution of reduced sedentary behaviour (SB) and increased light physical activity (LPA) on clinical knee osteoarthritis progression, in the presence or absence of functional limitations. Methods: Data were extracted from the Osteoarthritis Initiative Accelerometer sub-cohort dataset on 995 participants that had valid wear time data (greater than or equal to 4 days) at baseline (OAI 48-month visit), a Kellgren-Lawrence Grade (KLG) greater than or equal to 2 in one or both knees, and complete self-report measures of pain, joint stiffness and physical function at baseline and 24-month follow-up (OAI 72-month visit). The effect of functional limitation, reduced sedentary time, and increased light physical activity on 24-month clinical worsening was analyzed using multivariate linear models. Sedentary time and light physical activity were categorized into tertiles, and functional limitation was defined as walking <1.2m/sec during a 20-meter walk. The effect of functional limitation and physical activity were estimated in separate models for each tertile that defined clinical worsening using the pain, stiffness and physical function subdomains of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Analyses were adjusted for potential confounders including age, sex, body mass index (BMI), disease severity and previous history of knee injury. Beta coefficients and 95% confidence intervals (CI) were derived for each tertile compared with the reference group (most time spent in sedentary time or least time spent in light activity). Positive and negative beta values correspond to increases (or worsening), and decreases (or improvements), in WOMAC pain, stiffness and physical function, respectively. Results: Approximately 1 in 4 participants (n=295) had functional limitations at baseline. For full description of participant demographics refer to Table 1.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Individuals in the highest tertile of sedentary behaviour had on average 90 minutes less per day of light activity and spent 190 more minutes per day being sedentary compared to the lowest tertile. In participants that did not demonstrate functional limitations at baseline, low time spent in sedentary behaviour and high time spent in light physical activity were associated with improvements in pain (SB adjusted β: -0.74; LPA adjusted β: -3.57) and physical function (SB adjusted β: -1.00; LPA adjusted β: -3.06). However, in participants that did demonstrate functional limitations at baseline, low time spent in sedentary behaviour (adjusted β: -3.82) and high time spent in light activity (adjusted β: -3.14) had the largest average improvements in joint stiffness. Only a moderate amount of time spent in light activity had the largest average improvements in pain (adjusted β: -1.69), yet worse physical function scores (adjusted β: 3.34). Contrary to expectations, the lowest tertile of time spent in sedentary behaviour had an average worsening physical function score of 1.81 (adjusted β), compared to the highest tertile. For changes in 24-month WOMAC subdomain scores between tertiles of sedentary behaviour and functional limitation, refer to Figure 1. Conclusions: Reduced sedentary time compared to increased light physical activity did not demonstrate proportionate effects on long-term clinical outcomes at 24-months. These data propose that the balance between reduced sedentary time, and increased light activity time be considered when prescribing physical activity, and that these recommendations may differ for individuals already demonstrating functional limitations.