Experimental Study Of Injectable Hydroxyapatite Cement For The Augmentation Of Mechanical Properties In The Osteoporotic Femoral Intertrochanteric Area

ObjectiveTo determine the feasibility of carbonated hydroxyapatite (CHA) cement injected into the intertrochanteric region of cadaveric femur and its effect on the mechanical properties. Elucidate the degradation and the osteogenic response of CHA cement injected into the intertrochanteric region of rats with experimentally induced osteoporosis. Even the potential side effects of it was studied.MethodsBiomechanical evaluation of of CHA cement injected into the intertrochanteric region: Six pairs of cadaver femurs were mechanically tested in a single-limb stance configuration. From each pair, one femur was augmented in intertrochanteric region with CHA cement, with the contralateral femur serving as a control. In a load to failure test, the compression rigidity and the fracture load were recorded and calculated. The differences between the ehnanced femurs and the native controls were detected.Osteoporotic animal model: Eighty female mature Sprague-Dawley rats were weight matched before ovariectomy (Ovx) or Sham surgery (Sham). Rats were euthanized at 3 and 6 monthes after surgery, and had received fluorochrome bone markers at 10 and 3 days prior to euthanasia. All rats were also scanned for bone mineral parameters by DEXA before euthanasia. Proximal femurs were used for bone histomorphometry.Osteogenic response of CHA cement in osteoporotic bone: CHA cement wasinjected into the intertrochanteric region of rats with experimentally induced osteoporosis. Specimens of proximal femur were retrieved at 1, 3,7 days and 1, 3, 6 monthes after injection. The degradation and the osteogenic response of CHA cement were evaluated histomorphologically in nondecalcified section. At the same time, the integration of CHA cement and osteoporotic bone was observed under SEM (scanning electron microscope).Possible side effects of CHA cement injection into the intertrochanteric region: The potential pathological changes in the femoral heads were evaluated in decalcified section and TEM (transmission electron microscopy). The possible occurrence of fat embolus in pulmonary and brain tissues were monitored in section with osmic acid staining.ResultsBiomechanical evaluation of of CHA cement injected into the intertrochanteric region: Volumes of 18 - 25 ml of cement (mean, 21.2ml) could be injected into each femur. Compression rigidity has significance different in the groups. Compression strength was increased by 24% after CHA cement was injected into the intertrochanteric region. The peak fracture load was significantly higher in the groups injected with CHA cement than the contral group (P<0.01).Qsteoporotic animal model: Mineral density was significantly higher in the Sham rats relative to Ovx animals. Ovariectomy reduced trabecular number and thickness, and increased trabecular separation. The structure of the remaining trabeculae was dramatically changed. Cortical thickness in Ovx rats was reduced because of the high endocortical resorption, which, in addition to cancellous bone resorption, resulted in fewer endocortico-trabecular connections.Osteogenic response of CHA cement in osteoporotic bone: There was significant bone conduction of CHA cement in the intertrochanteric region of these osteoporotic rats. There were more osteoblast and osteoclast in the CHA...