[Changes in bone micro-architecture and bone mineral density following experimental osteonecrosis of femoral head by local injection of ethanol in canines].

OBJECTIVE: To measure the changes of bone mineral density and bone micro-architecture of the femoral head that harvested from the three-foot bearing ethanol destroyed canine model for osteonecrosis of femoral head, and discuss the influences of local injection of ethanol and biomechanical loading to the structural properties of the femoral head.

METHODS: Twenty-four Beagles were divided randomly into four-foot bearing canines and three-foot bearing canines. One fore-limb was fixed randomly in three-foot bearing canines. Osteonecrosis was induced in all experimental animals by local injection of 5 mL pure ethanol into one side of the femoral head. The hind limbs injected with NS were acted as control group, that of three-foot canines injected with ethanol were acted as three-foot canine group, and that of four-foot canines injected with ethanol were acted as four-foot canine group. The contralateral femoral head was injected into equal amount of NS. Animals were sacrificed at the time intervals of 1, 3, 6, and 12 weeks after the injection of ethanol. Quantitative microcomputed tomography was used to characterize changes in bone micro-architecture and bone mineral density of femoral head.

RESULTS: The clear three-dimensional model of trabecular bone of necrotic femoral head were obtained. There were no significant differences among 3 groups according to the time line by 1 week after ethanol injection(P > 0.05). At 3 weeks after injection of ethanol, in three-foot canine group and four-foot canine group, the volume of BMC, BMD, BVF, and BS/BV increased gradually as the distance to the drilling canal increased. There were significant differences between 3 regions (P < 0.05). At 6 weeks, in three-foot canine group and four-foot canine group, the volume of BMC, BMD,BVF, and Tb.N of region I and II decreased significantly compared with region III (P < 0.05). At 12 weeks, there are no differences among 3 groups (P > 0.05). There were significant decreases in BMD values, BVF, BS/BV, Tb.N, Tb.Sp and Tb.Th after the injection of pure ethanol. And, the changes were more and more obvious by the time line. These changes were differentiable at 3 weeks after injection of ethanol, and became obvious at 6 weeks. These changes were more obvious at the part that near the injection canal. The changes in three-foot canine group were more obvious than that in four-foot canine group.

CONCLUSION: Resorption of necrotic compact bone trabecular may weaken the structural properties of the femoral head. Moreover, remodeling and repairing process of necrotic bone trabecular may be hampered by constant biomechanical loading that presented in three-foot bearing canines, and thereby further weaken the structural properties of the femoral head. Biomechanical loading may be one of the critical reasons that lead to the collapse of femoral head.