An age-related medullary expansion can have implications for the long-term fixation of hip prostheses

Background Diaphyseal bone loss occurs mainly at the endosteal surface in the medullary cavity. Since the menopause is followed by an increase in bone loss, the size of the medullary cavity should theoretically increase during the postmenopausal period. If so, this might affect the long-term fixation of hip prostheses.Patients and methods This 19-year prospective study evaluated bone loss and geometrical changes in 112 women, all premenopausal at baseline. Bone mineral density (BMD) and skeletal geometry, with special reference to the size of the medullary cavity, were estimated every other year by single-photon absorptiometry at the cortical site of the distal radius.Results After menopause, a decrease of 1.7 (95% Cl 1.6–1.8)% occurred in the BMD every year, while an increase of 0.9 (0.8–1.0)% in the medullary width (endosteal width) too place every year. The annual change in BMD was inversely correlated with the annual change in the medullary width (r = −0.5, p < 0.001). The quartile of women with the largest BMD loss had a greater medullary expansion than the quartile of women with the least BMD loss (p < 0.001).Interpretation If the age-related expansion of the radial medullary cavity is a general phenomenon, this may have implications for the long-term fixation of hip prostheses.