Association between knee cartilage volume and bone mineral density in older adults without osteoarthritis

Objectives. Studies have suggested an inverse association between osteoarthritis (OA) and osteoporosis, based on the presence of osteophytes rather than joint space narrowing (JSN), an indirect measure of joint cartilage. We conducted a cross-sectional study to determine the relationship between knee cartilage volume, a direct measure of joint cartilage, and bone mineral density (BMD) in an adult population. Methods. 86 adults aged 55.1+/-10.4 years (50% females) had total BMD and bone mineral content (BMC) measured using dual X-ray absorptiometry. Site-specific BMD was performed on men in the study. Tibial and patella cartilage volumes were determined by processing images acquired in the sagittal plane using T-1-weighted fat saturation magnetic resonance on an independent work station. Results. Tibial knee cartilage volume was positively associated with total body BMD in both men and women after adjusting for age, BMI, tibial bone area and physical activity. In men, tibial cartilage volume was positively associated with proximal femur BMD, but not lumbar spine BMD. No relationship was seen between patellar cartilage volume and BMD at any region. Conclusions. We have shown a positive association between tibial cartilage volume and total BMD in men and women, but no such association with patellar cartilage volume. The mechanism for this is unclear but may represent a common environmental or genetic component. This study also highlights the need to examine the osteophyte and joint cartilage separately when investigating factors affecting the joint in health and disease since each feature is likely to reflect different aspects of the pathogenic process in OA.