Bone density variation within lumbar vertebrae in apparently normal women.

Using dual energy x-ray absorptiometry, lumbar bone mineral density was measured in 236 consecutive nonathletic white women of ages 36-85 years, who had been referred for evaluation of possible osteoporosis. Of these, 141 women had an average lumbar density of 100 +/- 15% of age, race, sex and weight matched normal adults. These apparently normal women were analyzed for the distribution of bone density values between lumbar vertebrae L2, L3 and L4. The difference between the highest and lowest lumbar vertebral density was determined, and expressed as a percent. Distribution of the density differences in this population was log-normal. A density difference of over 25% was found in 11% of the population, and its occurrence was age dependent. In the age group below 46 years, none exceeded the 25% difference value; in those over 75 years, 40% exceeded the 25% difference. For age groups between 46 and 75, the fraction of the population exceeding a 25% density difference increased linearly. A description of lumbar vertebral density values should include a statement of variation between the vertebrae.