Is greater lumbar vertebral BMD associated with more disk degeneration? A study using µCT and discography.

It is well documented that osteoarthritis is associated with greater BMD in peripheral extremities. Yet the relationship between vertebral BMD and disk degeneration (DD) remains controversial in the lumbar spine, which may be due largely to the inadequacies of BMD and DD measures. Aiming to clarify the association between vertebral BMD and adjacent DD, we studied 137 cadaveric lumbar vertebrae and 209 corresponding intervertebral disks from the spines of 48 white men aged 21 to 64 years. DD was evaluated using discography. The vertebrae were scanned using a micro-computed tomography (µCT) system to obtain volumetric BMD for the whole vertebra, the vertebral body, the vertebral body excluding osteophytes, and the vertebral body excluding osteophytes and endplates. A random effects model was used to examine the association between the different definitions of vertebral BMD and adjacent DD. No significant association was found between the BMD of the whole vertebra and adjacent DD. However, when the posterior elements were excluded, there was a significant association between greater vertebral body BMD and more severe degeneration in the disk cranial to the vertebra. This association remained after further excluding osteophytes and endplates from the vertebral body BMD measurements. Also, a trend of greater BMD of the vertebral body associated with more adjacent DD was evident. These results clarify the association between vertebral BMD and DD and specifically indicate that it is higher BMD of the vertebral body, not the entire vertebra, that is associated with more severe adjacent DD. This association may be obscured by the posterior elements and is not confounded by osteophytes and endplate sclerosis.