Sit-to-stand Performance As A Proxy For K-l Grade Scores In Knee Osteoarthritis-Serial Mediation Analysis

PURPOSE: Knee osteoarthritis (KOA) is the most common form of arthritis worldwide. While Kellgren-Lawrence (K-L) grade scores are the primary tool for assessing disease severity via radiography, there is a need for cost-effective measures to reliably track changes in KOA. The sit-to-stand (STS) test measures, primarily engages the hip and knee joints and associated musculature and measures changes in physical capacity. Decreased STS performance correlates with increased pain and lower levels of moderate-to-vigorous physical activity (MVPA) that consequently can impact health-related quality of life. The purpose of this study was to investigate the potential STS test as a proxy for K-L scores and its reflection of patients' social and behavioral health outcomes. METHODS: Data were analyzed from the Osteoarthritis Initiative (OAI) including information from years 6 and 8 of the ongoing study where consistent variables were available. Worsening knee OA (independent variable) was quantified by assessing the change in K-L grade scores over the two-year period denoted by > = 1 KL grade change. Change-score mediators included pain levels measured by the WOMAC scale, MVPA was assessed via accelerometry, and the outcome measure was HR-QOL evaluated using the SF-12 scale. A serial mediation model was used as an approach to explain how an independent variable sequentially influences a dependent variable through multiple, ordered mediators. RESULTS: The total change serial mediation model revealed that worsening OA status predicted poorer STS performance (β = .34, p < .001), increased pain (β = .10, p < .001), decreased MVPA (β = -0.12, p = .02), and lowered HR-QOL (β = -0.12, p < .001). The entire indirect pathway was statistically significant (β = -0.56, 95%CI [−0.815 to -0.325]), while the direct pathway was not significant (β = -0.01,95% CI [−0.258,0.284]), indicating a total mediation effect. CONCLUSION: The sit-to-stand score is a quick and economically feasible assessment tool for subjects with KOA that can provide insights into an individual's pain levels, MVPA, and overall health-related quality of life. Investigations are warranted to identify how increasing MVPA, especially through resistance training, may improve STS performance and potentially improve patients HR-QOL.