Cancellous bone changes in hip osteoarthritis: a short-term longitudinal study using fractal signature analysis.

OBJECTIVE: To quantify changes to the trabecular structure in the femoral heads of patients with hip osteoarthritis (OA). METHODS: Patients with OA (n=14; F=7), mean (standard deviation age) 50.6 (10.1) years, had macroradiographs at approximately x4 magnification at baseline and 18 months later using a standardized protocol. Following digitization, computerized measurement was obtained of minimum hip joint space width and fractal signature analysis (FSA) measured longitudinal changes separately in the principal compressive (vertical) and horizontal trabeculae at the region of interest within the centre of the head. RESULTS: The patient group had mean annual rate of joint space narrowing of 0.14+/-0.36 mm/yr. FSA detected no significant changes in horizontal trabeculae, whereas the larger principal compressive (vertical) trabeculae (0.96 mm to 1.02 mm) increased significantly in thickness and the fine to medium trabeculae (0.18 mm to 0.54 mm) decreased significantly in number. CONCLUSION: The increased thickness of the larger trabeculae within the compressive structural element of the femoral head is a response to the increase in stress associated with an overall loss of trabeculae in this region, suggesting the presence of an osteoporosis within the femoral head in OA patients.