Material properties of bone from the femoral neck and calcar femorale of patients with osteoporosis or osteoarthritis.

Patients with osteoarthritis (OA) rarely fracture the neck of the femur whereas this is common in patients with osteoporosis (OP). The reasons for this are not clear. In this study, cores of trabecular bone and thin slices of bone from the calcar were obtained from the femoral neck of patients with OA or OP following hip arthroplasty and a normal group post mortem. The mechanical properties, densities and material composition were measured. The aim was to determine whether differences in these properties could explain why osteoarthritic patients did not suffer from fractured neck of femur. No difference was found in the density or stiffness of the calcar between the groups, though there appeared to be a small increase in mineralization in the OA bone compared with the OP. However, there was a 72% increase in the volume of trabecular bone in the OA group compared with a loss of about 20% in the OP group. This increased apparent density of the OA trabecular bone resulted in a greater stiffness, yield strength and energy absorbed to yield, whereas the same properties of OP bone were not significantly lower than normal. These marked changes in the OA bone could result in a redistribution of stresses due to loads caused by falling, thereby absorbing the energy of impact and preventing the formation of a fracture surface.