Bone mineral density (BMD) in the lumbar vertebra was measured by dual energy X-ray absorptiometry (DXA) for diagnosis of spinal osteoporosis. Generally, osteoporosis begins with cortical and trabecular bone loss, and some authors have described the importance of trabecular bone loss in the diagnosis of spinal osteoporosis. Estimated bone mineral content (EBMC) expresses the lowest bone mineral content per square centimeter in the trabecular bone.
We studied EBMC in the os calcis by single energy X-ray absorptiometry (SXA) and BMD in the third lumbar vertebra by DXA. The results were as follows.
1) A phantom, and both EBMC and BMD in the left and right os calcis of a male volunteer were measured by SXA. EBMC was significantly correlated with BMD, and was usually lower than BMD. EBMC and BMD on the X-ray side tended to be higher than those on the opposite side.
2) EBMC and BMD of the os calcis of nine men and eight women with chronic renal failure and diabetes mellitus were measured. EMBC of the os calcis was significantly correlated with BMD, EBMC and BMD in women were lower than those in the men.
3) EBMC of the os calcis in SXA and BMD of the third lumbar vertebra in DXA were measured in 30 female volunteers. Age, weight, height and EBMC of the os calcis were significantly correlated with BMD of the third lumbar vertebra.
EBMC of the os calcis and BMD of the third lumbar vertebra tended to be lower in older subjects. Both of them tended to be higher in heavier subjects and in taller subjects. EBMC of the os calcis and BMD of the third lumbar vertebra in subjects who exercised regularly were significantly higher than those in subjects who did not.
In conclusion, EBMC of the os calcis may indicate trabecular bone mineral content, the loss of which may reflect osteoporosis.