| The femoral neck fracture is very common fracture in clinic. It accounts for 3.6% of all fractures. Because of the specialty of the anatomic structure and biomechanics, it would be injured easily when the fracture took place. This not only affected the fracture healing but also would produce ischemic necrosis of femoral head easily. It is reported that femoral neck fracture nonunion is 20% and femoral head ischemic necrosis is 30%. It is a diffcult problem in orthopaedics because it's rate of nonunion and avascular necrosis is highly. With the development of tissue engineering, it provide a new way to treat femoral neck fracture. The purpose of this study was to treat the femoral neck fracture using cannulated screw and BMP release system and combining the principle of tissue engineering with the technique of internal fixation. Then to evaluate the possibility of treating femoral neck fracture with the method and provide experimental basis in clinical application.Objective1. Correct the finite element model of cannulated screw fixated femoral neck fracture and provide rational mechanics vertification of cannulated screw.2. Preparation and related study of injectable BMP release system.3. To investigate the biocompatiblity and ectopic osteoinduction of rhBMP-2/PLGA microsphere/FS by cell culture in vitro and ectopic osteoinduction in vivo.4. To treat the femoral neck fracture using cannulated screw and BMP release system in animal, to evaluate the possibility of treating femoral neck fracture and provide experimental basis in clinical application.Materials and Methods1. To establish three dimension model of cannulated screw fixation femoral neck fracture. The stress of hollow screws internal-fixed are calculated using finite element analysis software ANSYS 9.0.2. The rhBMP-2/PLGA microspheres was prepared using W/OAV solvent evaporation method, rhBMP-2 loaded PLGA microsphere were incorporated in fibrin glue, estabilish injectable BMP release system.3. RhBMP-2/PLGA microsphere and rhBMP-2/PLGA microsphere/FS were add to medium, cell differentiation was detected by ALP kit. Composite were implanted into muscle pouches of rat so as to observe ectopic bone formation histilogically.4. 18 mongeral were used in this study, they were operated into experimental models of femoral neck displace fracture. control side was fixed using cannulated screw, experiment side was fixed with cannulated screw and injectable BMP release system. At 4, 8, 12 weeks 6 animals were sacrificed each time. Results were revealed in histology, radiography, scintimetry and gross observation.Results1. The results showed that new cannulated screw could satified the strength of femoral neck fracture. According to computation, ceiling value of open pore diametral is 2.0mm.2. The results showed that when prepared under the optimal condictions, the Diameter of PLGA microsophere was 53.2±2.1μm,the load density of rhBMP-2 was(5.12±1.32)%s. In 42 days, about rhBMP-2(76.75%) was released from FSPM system, which was lower than that from PM (91.75%).3. The results indicated that rhBMP-2/PLGA microsphere/FS could enhance significantly differentiation of canine bone mesenchymal stem cells and possesses more powerful effectiveness of inducing ectopic osteogenesis.4. The fracture line was vague at four weeks with osseointegration conjoined the fracture. when it was eight weeks after the operation, the fracture line almost disappeared. It was healed completely after twelve weeks. Observed from cross-section of the femoral neck, the healing of the fracture in experimental side was better than that of the control side. At 4 and 8 weeks, the post-operative uptake ratios (head: shaft) of experimental side was significant greater than that of control side (P<0.01). There was the same result of observation in histology.Conclusion1. Modified cannulated screw could provide full mechanics strength to fix femoral neck fracture.2. RhBMP-2/PLGA microsphere/FS has satisfactory slow-release effect and syringeability. It not only degrade partial acid enviroment but also maintain the biological effect of higher density.3. RhBMP-2/PLGA/FS composite is biocompatible,nontoxic and could significantly enhance the differentiation of bone mesenchymal stem cells. It possess more powerful effectiveness of inducing ectopic osteogenesis.4. The cannulated screw combined with BMP we used in the experiment is effective and feasible, it may not only provide strong internal fixation but also infuse growth factor into site of fracture. It would accelerate the reconstructing of the vascular supply to the femoral head after the fracture and promote the restoration of bone.
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