Osteoporosis and normality: how to express the bone mineral content of lumbar vertebrae

Bone mineral content of the 2nd, 3rd, and 4th lumbar vertebrae (lumbar BMC) was measured in 70 normal women (aged 19-88 years) and 72 post-menopausal women (aged 58-89 years) with primary osteoporosis using dual-photon (153Gd) absorptiometry. The inter-individual variation of lumbar BMC was 26.7% in normal women. This figure could be reduced to 13.9%, if lumbar BMC was normalized to age (or years after the menopause), body height, body weight, and vertebral size according to multiple regression analysis. The reduction thus obtained of the inter-individual variation in normal post-menopausal women was statistically insignificant, however, and it appeared that other variables were of importance as the lumbar BMC of older women. Mean lumbar BMC of the osteoporotic women was 41% lower than that of normal pre-menopausal women. The separation between normal and osteoporotic individuals became less clear, if lumbar BMC was normalized as mentioned. The data suggest that spinal osteoporosis is predominantly a condition of normal small old women with diminutive vertebrae and early menopause. It is recommended that lumbar BMC is expressed as the total mineral mass of the bones measured, the normal range being BMC of health pre-menopausal women. Normalization to age, body height, body weight, and vertebral size seems rather speculative.