Does fat mass contribute to knee osteoarthritis risk beyond weight itself? Data from the Multicenter Osteoarthritis...

We examined the extent to which fat mass may contribute to the risk of incident radiographic knee osteoarthritis (ROA) beyond body weight alone.

Participants from the Multicenter Osteoarthritis (MOST) Study with DXA body composition and no ROA in ≥1 knee at baseline were included. Incident ROA (KL grade ≥2 or knee replacement) was assessed at 7 years. We created sex-specific weight categories (<70,70-79.9,80-89.9, ≥90 kg in females, <90,90-99.9, ≥100 kg in males), computed % fat mass quartiles, and then evaluated the relation between quartiles (lowest as referent) to risk of ROA in each weight category. We then scaled and standardized % fat mass in a combined model to assess the overall relationship between relative fat mass and ROA risk.

We included 1611 individuals (60% female, mean age 61.7 years, BMI 29.6 kg/m², 2646 knees). Incident ROA developed in 27.6% of knees after 7 years. In females only, risk for ROA increased in those with the highest % fat mass relative to lowest in their weight category (Q4 vs Q1, RR 1.29, 95% CI 1.02, 1.64). Spline analyses identified a J- or U-shaped pattern of % fat mass on incident ROA in females and males, with predicted probabilities only differing by 10-20% across the fat mass percentiles.

A higher relative fat mass did not influence increased risk of incident ROA in males, but there was a potential threshold effect in females. Overall, total body mass (weight) appears to be driving risk for ROA rather than a distinct influence of relative fat mass.