Association of physical activity with loss of knee joint space width over two years: a compositional data analysis in the Osteoarthritis Initiative

Abstract

There is continued debate as to how engaging in physical activity (PA), including moderate-to-vigorous PA (MVPA), light PA (LPA), and sedentary time (SED), affects one's risk for knee osteoarthritis (OA). Traditional regression methods do not account for the codependence of these categories of PA, whereby when one category increases, the others must decrease. Thus, we used compositional data analysis (CoDA) to examine time spent in each category of PA, or PA composition, and its association with loss of knee joint space width (JSW), a common indicator of knee OA progression. We performed a secondary analysis of data from a subset of participants in the Osteoarthritis Initiative. These participants had minute-by-minute activity data collected over 7 days at baseline; we then categorized each minute as MVPA, LPA, or SED. Our exposure, PA composition, represented min/day spent in each category. Our outcome, medial JSW loss, was the difference in medial tibiofemoral JSW from baseline to 2years later. We employed CoDA, using an isometric log-ratio transformation, to examine the association of PA composition with medial JSW loss over 2years, adjusting for potential confounders. We included 969 participants (age: 64.5 years, 56% female, body mass index [BMI]: 28.8kg/m2). Mean PA composition was: MVPA 9.1min/day, LPA 278min/day, SED 690min/day. Per adjusted regression models, higher MVPA was not associated with greater medial JSW loss (β=-0.0005, P=0.97), nor was LPA (β=0.06, P=0.27) or SED (β=-0.06, P=0.21). Using CoDA, PA composition was not associated with medial JSW loss over 2years.