The menopause-related expansion of the proximal femoral marrow cavity is thought to have implications for the long-term cohesion of hip prostheses. This theory would be further strengthened if there was evidence to show that the expansion of the proximal femur marrow cavity takes place after the occurrence of a femoral neck fracture, which, it is often recommended, should be fixed with a hip prosthesis. But till now, the temporal relationship between those two osteoporotic-related changes has not been checked carefully. The objective of the current study was to examine the temporal relationship between the marrow cavity expansion of the proximal femur and the biomechanical deterioration of the femoral neck in a rat model. To do so, a cross-sectional study with multiple time points was carried out on 6-month old Sprague-Dawley rats, which were ovariectomized or sham-operated (as controls). The biomechanical properties of the femur neck and geometrical parameters of the femur shaft were evaluated at 0, 3, 6, 9, 12, 15, 18, and 21 weeks postoperatively, with special reference to the timescale of the observed changes. We found that the maximum load of the femoral neck in ovariectomized rats could bear decreased significantly compared, to that of controls, at 9 weeks postoperatively (p=0.03), while the marrow cavity of the proximal femur in ovariectomized rats turned out to be significantly enlarged at 15 weeks postoperatively (p=0.04). Conclusion: Our result demonstrated that the osteoporosis-related marrow-enlarged posterior led to the collapse of femoral neck strength. If the change in postmenopausal women is analogous to that in ovariectomized rats, the menopause-related marrow cavity expansion would be a risk factor for the longevity of hip prostheses.
