BONE-MINERAL DENSITY AND BONE TURNOVER IN SPINAL OSTEOARTHROSIS

Objectives-To determine whether there was a generalised increase in bo ne mineral density (BMD) in spinal osteoarthrosis (OA), and to determi ne the mechanism of this possible protection against osteoporosis as a ssessed by biochemical markers of bone turnover. Methods-We studied 37 5 women (ages 50 to 85) from a population based group. Spinal OA was d efined from radiographs as the presence of degenerative changes affect ing intervertebral or facet joints. BMD of the lumbar spine (LS), femo ral neck (FN) and total body (TB) was measured by dual energy x ray ab sorptiometry (Lunar DPX). Bone turnover rates were estimated from meas urement of biochemical markers of bone formation and resorption (urine deoxypyridinoline (Dpyr) and serum bone specific alkaline phosphatase (BAP)). Results-BMD at each site was greater in the women with spinal OA (mean increase in LS-BMD 7.9%, 95% confidence interval (CI) 1.0 to 15.1; TB-BMD 8.4%, 95% CI 1.9 to 9.7; FN-BMD 6.4%, 95% CI 0.3 to 12.6 ). Twenty four hour urinary excretion of Dpyr, corrected for TB bone m ineral content,, and serum BAP were 19% lower in the women with spinal OA (95% CI for Dpyr 4.3 to 31.9%; for BAP 6.3 to 32.0%). Conclusions- Spinal OA is associated with a generalised increase in BMD and a decre ased rate of bone turnover. This suggests that the protective effect o f spinal OA against osteoporosis may be mediated by decreased bone tur nover.