Bone density in the iliac crest.

An analysis of variance of the volumetric density of trabecular bone (Vv), expressed in percentage of the total bone volume was carried out to determine the quantitative degree to which inter-individual and intra-individual differences in bone composition contribute to sampling variation of Vv values. Samples were obtained from the iliac crest of ten deceased males (aged 46 to 73) without clinical signs of bone disease. A total of 800 separate duplicate values for Vv were obtained. The average values for Vv within the area of interest ranged from 13.9 to 28.2 with a mean of 21.4. The analysis of variance, based on 160 values, showed that inter- and intra- individual differences in bone composition contributed in about equal parts to the total variance. The standard deviation for intra-individual differences(si) was 4.4 and the standard deviation for inter-individual differences (sp) 4.2. Total standard deviation (s) for all measurements was 5.9 and the standard deviation for duplicate measurements (sd) was 0.7. These data indicate that Vv is subject to much variation in a single individual because of inadequate sampling and not the measuring procedure. At present the procedure is most valuable in large groups of individuals. Consideration of the relative contributions of various factors to sampling variation is essential to proper planning and interpretation of bone histomorphometry.