The macroscopic architectural properties of vertebral trabecular bone and their relation to whole vertebral failure loads.

Abstract

Trabecular architecture and compressive failure properties of human and beagle vertebrae were investigated in a series of three studies. The first study used a regional bone mineral density technique (rBMD) to determine the average bone density in eighteen cylindrical volumes from female vertebral bodies ex vivo (n = 20, T7 to L4). Correlations between vertebral failure properties (in static or fatigue uniaxial compression) and any individual region of bone density explained up to 50% of the variance. All-subsets regressions that combined regions of density explained up to 89% of the variance. Vertebral static and fatigue characteristics were predicted by different combinations of regional density. Predictive models using regions of density that declined least with age were more strongly related with the failure properties than regions of maximum decline. In the second study, detailed trabecular architectural parameters were determined in nine regions within the L2 vertebral centrum from twenty sham operated adult female beagles. Vertebrae L3 and L4 were mechanically tested in either static of fatigue uniaxial compression. Relationships between static failure properties and architectural parameters in any single region explained up to 48% of the variance. All-subsets regressions that combined architectural parameters in the nine regions of the vertebra explained up to 59% of the variance. Failure properties of whole vertebrae in the beagle were better characterized by a combination of bone volume, trabecular number, and connectivity. The third study used sixty adult female beagles that were sham operated (SH, n = 20), ovariohysterectomized (OV, n = 20), or ovariohysterectomized/calcitonin treated (CA, n = 20). Five animals per group were sacrificed at 2, 4, 6, or 12 months post-surgery. Vertebrae (T9, T10, L3, and L4) were tested in static and fatigue uniaxial compression. Detailed trabecular architecture was determined in nine regions within L2 vertebrae. Vertebral mechanical properties were significantly different (p $<$ 0.05) between groups (SH $>$ OV $>$ CT). Vertebral architecture parameters were significantly different (p $<$ 0.01) only between CA and the other treatment groups. Ovariectomy and ovariectomy/calcitonin treatment has limited usefulness to evaluate adaptive responses on architectural and mechanical properties of vertebrae in the beagle.