The mechanical behavior of normal and osteoporotic canine femora before and after hemiarthroplasty.

Nutritional secondary hyperparathyroidism (NSH) was induced in adult beagle dogs through nutritional control by feeding them a diet containing high phosphorus (1.2%) and low calcium (0.12%). A control group was fed a diet containing 0.42% phosphorus and 0.54% calcium. An osteoporotic condition was produced by NSH, which was verified with histologic, histomorphometric, and biochemical analyses. A significant increase in i-PTH level was measured at both ten and 20 weeks after initiation of the diet in experimental animals when compared with control animals. A 25% reduction in volume fraction cancellous bone and increased osteoclastic activity was found in histologic sections from the femoral heads of the NSH animals when compared with control animals. No abnormally large osteoid seam was found in the cancellous bone of the experimental animals. The results of energy dispersive radiographic analysis and bone ash analysis revealed no significant differences in calcium-to-phosphorus or mineral-to-matrix ratios between the two groups. The results of in vitro mechanical testing indicated significant differences in the strain state for the NSH and control animal femora, with the highest strains being observed in the calcar region of the NSH femora. The presence of a Co-Cr-Mo alloy femoral head prosthesis was found to alter the strain distribution significantly in both the control and NSH femora.