BACKGROUND:Patients with hip and knee osteoarthritis (OA) have high bone mineral density (BMD) and high BMI. If the same accounts for patients with foot or ankle OA is unknown. METHODS:We measured BMD and femoral neck (FN) width by dual-energy X-ray absorptiometry in 42 women and 19 men with idiopathic OA in the foot or ankle, and in 99 women and 82 men as controls. RESULTS:Women with OA had significant higher BMI than controls. Women with OA had higher BMI-adjusted BMD (p<0.01) and smaller BMI-adjusted FN width (p<0.01) than controls. Men with OA had higher BMI adjusted-BMD (p<0.05) and smaller BMI-adjusted FN width (p<0.01) than controls. CONCLUSION:Patients with OA in the foot or ankle have higher BMD and smaller bone size than being expected by their BMI. This phenotype may provide unfavourable forces across the joint and is hypothetically important for development of OA.