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

Among 9,504 participants, 10.63% had osteoarthritis, and higher fat-to-muscle mass ratio (FMR) in all body regions was associated with increased OA risk.

• 953 of 9,504 participants (10.63%) had OA
• Data were drawn from adults aged ≥40 years from the 1999-2006 and 2011-2018 cycles of the National Health and Nutrition Examination Survey (NHANES)
• OA status was determined by self-report
• Total and region-specific FMR was assessed using dual-energy X-ray absorptiometry (DXA)

Each unit increase in arm, leg, trunk, and total FMR was independently associated with increased odds of osteoarthritis.

• Odds ratio for OA per unit increase in arm FMR: 1.122 (95% CI: 1.082–1.163)
• Odds ratio for OA per unit increase in leg FMR: 1.156 (95% CI: 1.101–1.213)
• Odds ratio for OA per unit increase in trunk FMR: 1.142 (95% CI: 1.094–1.192)
• Odds ratio for OA per unit increase in total FMR: 1.194 (95% CI: 1.131–1.260)
• Associations were analyzed using logistic regression

Participants in the highest quartile of FMR had substantially greater OA risk compared to those in the lowest quartile across all body regions.

• Highest vs. lowest quartile of arm FMR: 75.4% increased risk of OA
• Highest vs. lowest quartile of leg FMR: 115.7% increased risk of OA
• Highest vs. lowest quartile of trunk FMR: 113.6% increased risk of OA
• Highest vs. lowest quartile of total FMR: 161.3% increased risk of OA

Restricted cubic spline analysis indicated a linear relationship between leg, trunk, and total FMR with OA prevalence.

• Restricted cubic spline curves were used to characterize the dose-response relationship between FMR measures and OA
• A linear relationship was observed for leg, trunk, and total FMR with OA
• The nature of the relationship for arm FMR was not specified as linear in the abstract

The discriminatory performance of FMR measures for osteoarthritis was modest across all body regions.

• Area under the curve (AUC) values ranged from 0.635 to 0.656 across arm, leg, trunk, and total FMR measures
• These values indicate modest but limited ability of FMR to discriminate OA cases from non-cases

The systemic immune-inflammation index (SII) partially mediated the association between FMR and osteoarthritis.

• SII mediated 2.4%–2.6% of the association between FMR measures and OA
• Mediation analysis was conducted to determine the mediating role of SII
• The mediation proportion was consistent across different regional FMR measures
• The findings indicate that systemic inflammation explains only a small portion of the FMR–OA relationship