Correlates of subchondral BMD: a cross-sectional study.

Subchondral bone is hypothesized to be important in the development and progression of osteoarthritis (OA); however, little is known about the determinants of subchondral bone. This study describes the relationship between tibial subchondral BMD (sBMD) and anthropometric, lifestyle, and structural measures in 740 randomly selected subjects (mean age, 62 yr; range, 50-80 yr; 52% women). We measured medial tibial sBMD by DXA at two regions of interest (ROIs). We also assessed anthropometrics, vitamin D, steps per day by pedometer, joint space narrowing (JSN) and osteophytes (by X-ray), cartilage defects, cartilage volume, and bone marrow lesions (BML; by MRI), and hip and spine BMD (by DXA). sBMD using ROI 1 was negatively associated with age and female sex and positively associated with BMI. In multivariable analysis, sBMD was positively correlated with steps per day (r = 0.08, p = 0.025), tibial osteophytes (r = 0.08, p = 0.028), JSN (r = 0.11, p < 0.01), cartilage defects (r = 0.16, p < 0.01), cartilage volume (r = 0.12, p = 0.01), BMLs (r = 0.17, p = 0.013 [tibial]; r = 0.16, p = 0.018 [femoral]), and hip and spine BMD (r = 0.36, p < 0.01 and r = 0.38, p < 0.01, respectively). Similar associations were observed using ROI 2, with vitamin D also associated with sBMD (r = 0.10, p < 0.01). In conclusion, this study identified a large number of factors associated with sBMD, of which the most novel is cartilage defects. Longitudinal studies are required to address causality.