Association of Thigh Intramuscular Fat Infiltration With Incident Knee and Hip Osteoarthritis: A Longitudinal Cohort Study

OBJECTIVE: Intramuscular fat infiltration (IMFI) in the thigh is linked to metabolic inflammation and muscle dysfunction, which could contribute to osteoarthritis development. However, no longitudinal studies have examined the associations between thigh IMFI and incident knee and hip osteoarthritis. METHODS: We conducted a cohort study using UK Biobank data, including participants with baseline IMFI in thigh muscle assessed by magnetic resonance imaging and no history of knee or hip osteoarthritis. A total of 24,224 and 24,221 participants were included in analyses of IMFI of anterior and posterior thigh muscle with knee osteoarthritis, respectively, whereas 24,767 and 24,764 were included in analyses of IMFI of anterior and posterior thigh muscle for hip osteoarthritis, respectively. Cox Proportional-hazard models were used to estimate hazard ratios (HRs) for incident clinically diagnosed knee or hip osteoarthritis, adjusting for potential confounders. RESULTS: During a mean follow-up of 4.9 years, 472 participants developed knee osteoarthritis, and 387 developed hip osteoarthritis. IMFI in the anterior thigh was significantly associated with incident knee osteoarthritis, with adjusted HRs of 1.78 (95% confidence interval [CI] 1.19-2.65), 2.00 (95% CI 1.34-2.99), and 2.34 (95% CI 1.53-3.59) across the second to fourth quartiles, respectively (P for trend <0.01). Both anterior and posterior thigh IMFI were significantly associated with hip osteoarthritis (P for both trends <0.01). Dose-response relationships were observed in restricted spline models. The interaction and subgroup analyses support that the effect of IMFI is independent of body mass index and sex. CONCLUSION: Elevated thigh IMFI is significantly associated with increased incidence of both knee and hip osteoarthritis. Interventions targeting IMFI reduction may help prevent osteoarthritis and mitigate its impact.