Objectives To investigate cross-sectional and longitudinal associations between systemic bone mineral density (BMD), subchondral BMD (sBMD) and knee cartilage thickness in older adults with or without radiographic osteoarthritis (ROA).

Methods A prospective cohort of 158 randomly selected subjects (mean 63 years, 48% women) including 69 non-ROA and 89 ROA subjects were studied at baseline and 2.7 years later. Knee cartilage thickness was semi-automatically determined from T1-weighted fat-suppressed MRI. Knee cartilage volume was measured from MRI. Systemic BMD and sBMD were measured by dual-energy X-ray absorptiometry (DXA).

Results Cross-sectionally, total body, total hip, spine BMD and/or lateral tibial sBMD were significantly and positively associated with femoral, lateral tibial and/or patellar cartilage thickness in subjects with ROA after adjustment for potential confounders. Longitudinally, a high total body BMD was associated with an increase in femoral cartilage thickness (β: 0.33 mm/g/cm², 95% CI 0.13 to 0.53); a high spine BMD was associated with increases in femoral and lateral tibial cartilage thickness (β: 0.25 mm/g/cm², 95% CI 0.10 to 0.41; and β: 0.18 mm/g/cm², 95% CI: 0.01 to 0.34, respectively) and a high medial tibial sBMD was associated with an increase in medial tibial cartilage thickness (β: 0.45 mm/g/cm², 95% CI 0.02 to 0.89) in subjects with ROA. In contrast, there were no significant associations between baseline systemic BMD, sBMD and cartilage volume loss, nor were there associations between BMD and cartilage thickness in subjects without ROA.

Conclusions Both systemic and subchondral BMD are positively associated with increased cartilage thickness in subjects with ROA, suggesting BMD may play a protective role against cartilage loss in knee OA.