Obesity, a state of excess adiposity, is a major risk factor for knee osteoarthritis (OA). Prior studies of obesity and knee OA have mostly defined obesity using anthropometric measures, such as body weight or body mass index (BMI). However, these measurements reflect the composite of fat, muscle and bone mass and are not exclusive measures of adiposity. Thus, it is not clear whether the effects of BMI, typically interpreted as effects of obesity, are truly due to excess adiposity rather than to overall loading due to the combined weight of body mass.
Misra et al. undertook this study to examine the longitudinal association of body composition categories based on fat and muscle mass with the risk of incident knee OA.
The researchers included participants from the Multicenter Osteoarthritis Study, a longitudinal cohort of individuals with or at risk of knee OA. Based on body composition (i.e., fat and muscle mass) from whole-body dual X-ray absorptiometry, subjects were categorized as obese nonsarcopenic (obese), sarcopenic obese, sarcopenic nonobese (sarcopenic) or nonsarcopenic nonobese (the referent category). They examined the relationship of baseline body composition categories with the risk of incident radiographic OA at 60 months using binomial regression with robust variance estimation, adjusting for potential confounders.