| Background:The treatment methods of fracture currently are plates and screws system, tension band, intramedullary nail and gypsum/plywood and so on, what have become a worldwide recognized mainstream, at the same time, they have certain limitations in the field of large-scale emergencies, such as complex to use, high demand to the operation environment and conditions, not good enough for reduction and fixation, inconvenience to be viewed and handled in the surface of limbs, and general fixed method cannot be suitable for the massive casualty and rapid treatment in battlefield and natural disaster situation. Therefore, there is a very important and urgent subject to develop a rapid, massive, convenient and minimal invasion internal fracture-fixing system.Objective:Designed and manufactured a medical nail shotting system, which is suitable for metaphysis and intra-articular, to achieve the purpose of rapid, simple and effective fracture fixation, and evaluate the effectiveness of fracture fixation. Research on in vivo degradation of the magnesium alloys, and explore the feasibility of absorbable nail.Methods:1.Design and manufacture of nail gun:on the basis of the early manual nail gun (authorized patent 200820079268.9), we made the Electric and pneumatic nail gun and applied for five inventions and new practical patent.2. In vitro biomechanical of the nail and the system of fracture fixation:use the nail gun to shoot rough and smooth nails into the swine thighbones and fastened to biomechanics machine MTS858 to explore the pull out strength of the nails, then made the pig metaphysis fracture model and using medical system nail gun fracture internal fixation to put the magnesium alloy and titanium alloy material of straddle nail respectively at 45°and 90°angles to fracture area. Using biomechanics machine MTS858 for the treatment of fractures of the tensile strength and torsional strength were research and compared.3. Magnesium alloy materials implanted in vivo:we implanted the surface micro-arc oxidation treatment of AZ31 magnesium alloy pin and PLGA pin into rabbit femoral condyle, and in 6 time points, mean 1 week,4 weeks,12 weeks and 24 weeks.36 weeks and 48 weeks, with the method of comparison of two kinds of material degradation, by using Micro-CT scan images and numerical data we delved into the degradation of magnesium alloy and new bone formation around the material.Results:In vitro mechanical test results showed that the maximum pull out strength of the agnail group was (307.474±17.396) N, maximum pull out strength of the smooth group was (136.139±11.862) N, which had significant statistical difference (P<0.01); The tensile strength of the straddle nail of the same material type by different angles had no obvious difference:tensile strength of magnesium alloy nail 45°fixed was (319.319±37.445)N and 90° fixed was (346.372±38.434)N; the tensile strength of tanium alloy nail 45° fixed was (353.676±27.210)N and 90° fixed was (363.329±21.894)N. The tensile strength of the different material type by the same angle also had no obvious difference:the tensile strength of tainum alloy 90°fixed and magnesium alloy 90° fixed were (363.329±21.894)N and the tensile strength of tainum alloy 45°fixed and magnesium alloy 45° fixed were (353.676±27.210)N and (319.319±37.445)N. The straddle nail of the same material type on the fracture fixed with fracture line into different angles (45° and 90°) showed that the 45° group twist 10° the torque needed significantly greater than 90° group (P<0.05); Fixing with the fracture line into the same angle screws of different material, magnesium alloy and titanium alloy side fracture fixation, which showed that titanium alloy specimens of materials needed for 10° torsion was bigger than the magnesium alloy materials (P<0.05). In vivo animal experiment results showed that the samples had a slowly and inconspicuously decreasing rate of degradation in the early stage, the decreased rate of PLGA accelerated at week 4-12, and the decreased rate of AZ31 accelerated at week 12-24 and continued degradation until the end of the 48-week experiment and the content of magnesium decreased as the implant degraded but the density of the material showed almost no change. Micro-CT also showed increasing amounts of new bone around the alloy during the experiment, and as the magnesium degraded, both the number of bones and the density of new bone increased. The data of Micro-CT showed the decrease of magnesium volume, magnesium mineral density, mean’magnesium thickness’, BS/BV, Tb.Sp, and the increase of magnesium surface area/ magnesium volume, BVF, Tb.Th, Tb.N. TMD, and prove the positive effect of magnesium on osteogenesis. From the maximum inner diameter of the new bone loop and the diameter of the pin in the same position, magnesium alloy was not capable of creating sufficient bridges between the bones and biomaterials when there were preexisting gaps.Conclusions:Internal fixation nail with surface agnail will greatly increase the fixed strength firmly; Tensile strength had no significant correlation with nail internal fixation materials and incoming angle; 45° torsional strength was higher than 90°; Torsion strength of titanium alloy material was higher than that of magnesium alloy; Regarding the degradation of the magnesium alloy and PLGA in vivo, the rate was slow in the early stage, and then increased with time. The PLGA degrade faster but was then overtaken by AZ31 at week 12. During the degradation, the density of the magnesium had almost no change. Finally, despite incomplete contact between the pin and new bone around the pin, the magnesium alloy was not capable of creating sufficient bridges between the bones and biomaterials when there were preexisting gaps. Lastly, Micro-CT is useful for providing non-traumatic, in vivo, quantitative, precise data, and is ideal for exploring the degradation of implants. |
