Age-related changes in cancellous bone structure. A two-dimensional study in the transiliac and iliac crest biopsy sites.

In 94 pairs of large sections of normal iliac bone (53 men, 41 women, aged 20-80 years) we confirmed trabecular bone area (B.Ar) and the mean number of trabeculae per mm (Tb.N) to decline with age, in areas representative of the transiliac (TI) and iliac crest (IC) biopsy in both sexes, whereas mean trabecular width (Tb.Wi) did not decrease. Our data also confirm that disappearance of entire elements is the main event in age-related loss of trabecular bone. In addition, our study demonstrated that Tb.Wi is lower in women than in men in the IC site, and a preferential loss of the thinner trabeculae could be seen in this group. Up to 50 years, Tb.N was found higher in women in both sites. B.Ar and Tb.Wi values are markedly higher in the TI site (+/- 15%); Tb.N values were similar. Measured and calculated Tb.Wi values show systematic differences. In a pilot study in 14 IC biopsies with widely diverging B.Ar values, we tested the validity of several equations currently used for derived parameters in the structural analysis of cancellous bone sections. The equation for mean trabecular number passed the test, whereas the validity of the equations for mean trabecular separation and Tb.Wi appeared limited. We found anisotropy of iliac bone to increase as B.Ar decreases.