| BackgroudsEarly operative intervention was believed as the most effective way to treat osteonecrosis of the femoral head(ONFH) in early stage. There are many operative methods to treat early stage ONFH, which have their own merits and demerits. There is no consensus on which method is easy performed and has good performance in medium and long time follow up. Owning to strut on subchondral bone of necrotic femoral head, ONFH treated with vascularized bone-grafting often has a better clinical outcome. But, when performing with vascularized bone-grafting intervention, the operative procedures are often complicated and the patients subjected usually need long time immobilization. Therefore, there is an urgent need to develop new methods to treat early stage ONFH.This study tried to advance porous tantalum rod produced by American Zimmer Company in several aspects including replacing raw materials, advancing porous structure configuration and fabricating technique, which designed and fabricated regular and bionic trabecular porous titanium alloy rods by electron beam melting(EBM) and selective laser melting(SLM) technique respectively and investigated the interventional effects of these two type rods on early stage ONFH in sheep. These rods may overcome the disadvantage of unsatisfied clinical outcome of porous tantalum rods in long time follow up, providing a new therapeutic method for early stage ONFH. ObjectivesThe aims of this study are investigating the effectiveness of establishing animal model of ONFH on Small Tail Han Sheep induced by local liquid nitrogen cryo-insult, examining the probability of fabricating bionic trabecular porous titanium alloy rods by SLE technique, and observing the therapeutic effects of aforementioned two types porous titanium alloy rods on sheep ONFH. Methods16 adult female Small Tail Han Sheep was adopted, and unilateral ONFH of each animal was induced using a liquid nitrogen therapeutic equipment and cryo-insult probe designed and produced by ourselves. Imaging and histological examinations of insulted femoral heads were performed 1, 2, 3 and 6 months postoperatively, which were compared with those of normal femoral heads and then analyzed statistically.8 paired femurs of adult female Small Tail Han Sheep were performed with computed tomography(CT) scan, and then the data of Digital Imaging and Communications in Medicine(DICOM) format was acquired and imported in Materialise’s Interactive Medical Image Control System(MIMICS) 16.0 software. The sheep femurs were reconstructed three-dimensionally and the parameters of them were measured. The obtained femoral parameters were analyzed and used for size design of porous titanium alloy rods. Open-cell structure of repeating dodecahedrons was designed in UG NX 7.0 software and used in design of regular trabecular rods, which were finally printed using EBM equipment. A human femoral head of adult male was adopted and performed with micro computed tomography(micro-CT) scan. In MIMICS 16.0 software, bionic trabecular reconstructed three-dimensionally using acquired data was eroded and smoothed, and then was used for the design of bionic trabecular rods, which were finally printed using SLM technique. The printed rods were then eroded in acid solution and cleaned with ultrasonic washer. 4 rods of each type were performed with micro-CT scan, and then the parameters of pore configuration were measured after three-dimensional reconstruction in MIMICS 16.0 software, which were compared with their 3D model statistically.Another 27 adult female Small Tail Han Sheep were induced ONFH using aforementioned methods, and treated with decompression alone, decompression combined with regular trabecular rod insertion, and decompression combined with bionic trabecular rod insertion respectively 1 month after cryo-insult. 3 months and 6 months after operative intervention, general condition and specimen observation, imaging and histological examination, and mechanical test were performed, which were used for evaluation of effectiveness of aforementioned three interventional methods.Two type human porous titanium alloy rods were designed and processed using procedures mentioned above, and implanted in human femoral models simulatively. The shape and size of human rods were verified. ResultsAfter inducing ONFH, X-ray examination and CT scan of insulted femoral heads showed obvious necrotic changes including low density belt and local sclerosis and so on, which were similar with those of human early stage ONFH. Histological examination showed necrotic changes in early time, which included abundant empty lacunae, decreased hematopoietic cells and destroyed adipose tissue in medullary. Later, both necrotic and repairing changes were observed in histological examination, which included fractured trabecula, increased fibroblasts and newborn vascular, and so on. The bone volume to total volume and mean trabecular thickness were decreased during the entire observational phase in micro-CT scan, whereas the mean trabecular number was increased in later time. One femoral head and 3 femoral heads became flatten 3 months and 6 months after the operation respectively.The pore interconnectivity of both regular trabecular rods and bionic trabecular rods were 100%, which were the same with their models. Whereas the mean porosity and average pore diameter of two type rods were below their models respectively. The complicated bionic trabecular porous titanium alloy rods could be fabricated using SLE technique. The 3D model decorating and reprocessing of the bionic trabecular rod could improve its porous characteristic.There was a slow repairing process in drill track of the intervened femoral head, which was still evident 6 months after the decompression. 3 months after the insertion, a moderate condition of bone ingrowth was observed in both two type rods. Bone ingrowth was mainly located in periphery of regular trabecular rods, whereas in all position of bionic trabecular rods. 6 months after the insertion, there were still some areas that had no bone ingrowth in regular trabecular rods. The maximum loads of femoral heads intervened with both two type rods were higher than those of femoral heads performed with decompression in mechanical test. Femoral heads intervened with bionic trabecular rods had larger maximum loads than those with regular trabecular rods. ConclusionONFH can be successfully induced by liquid nitrogen cryo-insult in Small Tail Han Sheep using our advanced method. Bionic trabecular porous titanium alloy can be processed using SLE technique with 3D model decorating and later reprocessing. Both regular trabecular rods and bionic trabecular rods have therapeutic effects on early stage ONFH in sheep, whereas bionic rods have better outcome. Both type of human rods are located legitimately in human femoral models, which are suitable for next clinical trial. |
PDF Full Text Request