Associations between total and regional fat-to-muscle mass ratio with the risk of osteoarthritis: Mediating role of systemic immune-inflammation index

Background While obesity is an established risk factor for osteoarthritis (OA), the differential impacts of regional body composition is not well understood. This study aimed to examine the associations of whole-body and region-specific (arms, legs, and trunk) fat-to-muscle mass ratio (FMR) with OA prevalence, as well as the mediating effects of systemic inflammation in this relationship. Methods Data from adults aged ≥40 years were collected from the 1999–2006 & 2011–2018 cycles of National Health and Nutrition Examination Survey. Total and region-specific FMR was assessed using dual-energy X-ray absorptiometry, with OA status determined by self-report. Logistic regression was used to analyze the associations between total or regional FMR and OA prevalence. Mediation analysis was conducted to determine the mediating effect of the systemic immune-inflammation index (SII). Results Among the 9,504 participants included, 953 (10.63%) had OA. The odds ratio (95% confidence intervals) for OA by arm, leg, trunk and total FMR were 1.122 (1.082–1.163), 1.156 (1.101–1.213), 1.142 (1.094–1.192), and 1.194 (1.131–1.260), respectively. Compared to the lowest quartile, the highest quartile of arm, leg, trunk, and total FMR had 75.4%, 115.7%, 113.6%, and 161.3% increased risk of OA, respectively. Restricted cubic spline curves indicated a linear relationship between leg, trunk and total FMR with OA. The discriminatory performances of FMR measures were modest (area under the curve 0.635–0.656). SII mediated 2.4%–2.6% of the association between FMR and OA. Conclusion A higher FMR in all body regions is associated with a higher risk of OA, which is partially mediated by systemic inflammation.