THE MECHANICAL STRENGTH OF BONE IN DIFFERENT RAT MODELS OF EXPERIMENTAL OSTEOPOROSIS

In order to discover good parameters for experimental osteoporosis, we measured the failure load of the femoral neck and the bending strengt h of the tibia in orchidectomized (ORC) (20 rats for 4 weeks), ovariec tomized (OVX) (28 rats for 6 weeks), and immobilized (IMM) (33 rats fo r 3 weeks) rats. Each of these operations led to a significant decreas e in trabecular bone volume when compared with corresponding controls (p < 0.001). The ash weight of femurs was significantly decreased in O RC (p < 0.05) and IMM (p < 0.001) rats, but not in OVX rats. Growth of the femur was somewhat slower in ORC (p < 0.05) and IMM rats (p < 0.0 5), but not in OVX animals. All three osteoporosis models showed signi ficant decreases in the maximal load of the femoral neck (ORC: 23.9%, p < 0.001; OVX: 15.8%, p < 0.001; IMM: 27.7%, p < 0.001), as well as i n energy absorption (ORC: 43.9%, p < 0.001; OVX: 28.3%, p < 0.001; LMM : 45.3%, p < 0.001). In tibia orchidectomy reduced maximal strength an d energy absorption significantly (10%, p < 0.01; 27.8%, p < 0.01), bu t ovariectomy decreased only maximal load (8.7%,p < 0.01) and immobili zation only energy absorption (18.0%, p < 0.01). Our results suggest t hat the mechanical strength of the femoral neck is a sensitive indicat or of bone loss in all three osteoporosis models.