Degenerative changes at the lumbar spine--implications for bone mineral density measurement in elderly women

Degenerative changes of the lumbar spine may lead to misinterpretation of bone mineral density (BMD) measurements and cause underdiagnosis of osteoporosis. This longitudinal study of 1,044 women, 75 years at inclusion and followed for 10 years, shows that identification of apparent degenerative changes on the dual energy X-ray absorptiometry (DXA) scan can increase the proportion diagnosed.

In the elderly, degenerative manifestations in the lumbar spine may result in falsely elevated BMD values, consequently missing a large proportion of those with osteoporosis. Our aim was to determine the distribution and impact of degenerative changes on lumbar spine DXA over time and its clinical implications.

Participants were 1,044 women from the population-based Osteoporosis Risk Assessment cohort. All women were 75 years old at invitation and followed up after 5 years (n=715) and 10 years (n=382). Degenerative changes were evaluated visually on the DXA image for each vertebra L1 to L4 (intraobserver precision kappa values of 0.66-0.70).

At baseline, apparent degenerative changes were more frequent in the inferior segments of the lumbar spine [5% (L1), 15% (L2), 26% (L3), and 36% (L4)] and increased over time. At 10 years, the prevalences were 20% (L1), 39% (L2), 59% (L3), 72% (L4), resulting in a significant increase in overall BMD. In women without apparent degenerative changes, BMD remained stable between 75 and 85 rather than an expected bone loss. At baseline, 37% had osteoporosis (BMD<-2.5) at L1-L4; exclusion of women with apparent degenerative changes increased this proportion to 47%. Using L1-L2, which was less prone to degenerative changes, 46% of women were classified as osteoporotic regardless of degenerative changes.

Degenerative changes were very common in elderly women, accelerated disproportionately over time, were increasingly frequent from vertebrae L1 to L4, and had significant impact on diagnosing osteoporosis. This suggests that routine reporting of spine BMD at L1-L2 would add valuable information for reassessment and monitoring.