Changes in Bone Microarchitecture and Bone Mineral Density following Experimental Osteonecrosis of the Hip in Rabbits

BACKGROUND: Osteonecrosis of the femoral head is a common disorder which can lead to hip joint destruction usually necessitating total hip replacement. METHODS: Quantitative micro-computed tomography, digital radiography and histology were used to characterize changes in bone microarchitecture and bone mineral density during the repair of the osteonecrotic femoral head as well as during the development of secondary osteoarthritis in the ipsilateral acetabulum. Osteonecrosis was induced surgically in 17 adult, male rabbits and the contralateral side was used as control. RESULTS: At 4 weeks no changes in microarchitecture in the femoral head nor in the acetabulum were found. At 6 months the repair process led to an increase in bone mass in the trabecular region of the femoral head. However, a decrease in volumetric bone mineral density and an increase in apparent porosity were seen in the compact subchondral and cortical region of the osteonecrotic femoral head. At 6 months the subchondral bone of the osteoarthritic ipsilateral acetabulum was thicker, but had a lower volumetric bone mineral density and a higher apparent porosity. CONCLUSION: Resorption of necrotic compact bone may weaken the structural properties of the femoral head. Moreover, remodeling and resorption of subchondral bone may play a critical role in the disease process of osteoarthritis.