It is already well established that obesity is a risk factor for the incidence and progression of osteoarthritis (OA). Joint-adjacent subcutaneous fat (SCF) has recently been investigated as an independent OA risk factor. Findings thus far suggest that greater levels of joint-adjacent SCF are associated with prevalence and progression of knee degenerative changes. Understanding the impact of fat changes on adjacent knee joint tissue would therefore provide novel insights on the effect of localized adipose tissue on OA pathogenesis. A manuscript published recently by Joseph et al. in Osteoarthritis and Cartilage, went on to evaluate whether longitudinal changes in body weight have an impact on changes in joint-adjacent SCF and cartilage thickness over 4 years, and whether an association exists between changes in joint-adjacent SCF and knee cartilage thickness.
The study analysed data collected from participants enrolled in the Osteoarthritis Initiative (OAI), a multi-centre, longitudinal OA study sponsored by the US National Institutes of Health (NIH). Following approval by the local institutional review boards of all participating centres, the study analysed MRI and radiographic knee images of 399 individuals (aged 45–79 years at enrolment), performed at baseline and after 4 years, to quantify joint-adjacent SCF and cartilage thickness. Based on their weight gain over 4 years, participants were classified into three weight change groups: individuals with >10% weight gain (n=100), individuals with >10% weight loss (n=100), and individuals <3% weight change (controls, n=199). Using linear regression models, authors evaluated (1) associations between weight change group and changes in both knee SCF and cartilage thickness, and (2) associations between changes in knee SCF and cartilage thickness. Analyses were adjusted for age, sex, baseline body mass index (BMI), and tibial diameter.
Findings showed that weight loss was associated with decreases in joint-adjacent SCF, but not with changes in cartilage thickness. Instead, changes in cartilage thickness were directly associated with changes in joint-adjacent SCF, in a BMI-independent manner. In particular, increases in joint-adjacent SCF were associated with decreased cartilage thickness, something that may be attributed to localized inflammatory factors.
This work was the first to focus on longitudinal changes in joint-adjacent SCF, and to demonstrate that increases in joint-adjacent SCF are associated with decreases in cartilage thickness. Although, the findings are based on the retrospective analysis of the OAI data, which does not allow for conclusions on causal associations, one potential clinical implication of this study is that reduction of SCF around the knee could slow cartilage thickness loss.