Trabecular architecture in iliac crest bone biopsies: infra-individual variability in structural parameters and changes with age.

A histomorphometric study was conducted on bilateral iliac crest samples obtained at autopsy from 27 subjects who had died suddenly. Six parameters related to cancellous bone structure were measured: bone volume (BV/TV), surface density (BS/TV), surface/volume ratio (BS/BV), trabecular thickness (Tb.Th.), trabecular number (Tb.N), and trabecular separation (Tb.Sp). There were no significant differences between right and left sides in the mean values for each parameter. However, when subjects were considered individually, there was a substantial difference in the majority of cases for all parameters. The intra-individual variation (IIV) was calculated for each subject as the percentage deviation from the mean for the two sides. There was a wide range in IIV (0.05-30.27%) with a mean value of approximately 11.5% for each parameter. In males the mean IIV ranged from 9 to 11% and from 14 to 16% in females. The IIV in BV/TV was positively correlated with age. Data generated on a subsample of 15 males were used to predict patient group sizes required to detect minimum significant differences in studies involving repeat biopsies. Sample sizes of 32, 16, and 8 patients would be required for relative increments in BV/TV of 29, 36, and 46%, respectively, to be statistically significant. Tb.Sp increased significantly with age but there was no significant change in Tb.Th. This supports the view that bone loss with aging occurs primarily through a mechanism involving complete disappearance of individual trabecular plates.