| Objective: At present, the"killer turn"of tibia side in the posterior cruciate ligament renconstruction is one of the important factor for affecting the results of operation, the scholars through the unremitting efforts made a lot of effective ways to solve this problem. But very few scholars are concerned about "acute angle effect" of femoral side in the posterior cruciate ligament reconstruction with hamstring tendons, and how to reduce the "acute effect." This paper advances a combine fixation technique, the application of extracortical fixation method to fixed graft in femoral side, the bone tunnel is closed with absorbable interference screw , can be firmly fixed grafts and reduce injury of the graft which is "acute angle effect" to exist in the edge of the femoral tunnel; Another technology is bone-tunnle technique, by increasing the angle between the bone tunnel and intercondylar fossa of femur side wall and processing polished the edges of bone tunnel, to reduce the friction between graft and bone tunnel edge, thereby reducing " acute angle effect. " This paper tests in animal models to explore the feasibility and biomechanical properties of these two kinds of approach for reduced "acute angle effects", to guide further clinical research.Methods: The experimental studied of randomized controlled trials. Selected 80 fresh pig knees at -20℃for frozen, and thawed 12 hours before the test at room temperature. Removed the muscle and soft tissue, removal of the proximal tibia, completely. Femur specimens assigned to eight different research groups randomly, each with 10 specimens. Application of pig flexor tendon as a free graft ligaments to simulated the hamstring tendon. Graftes were placed in storage under -20℃when them takened down, immediately. All grafts thawed 12 hours before the test at room temperature, and rinsed with physiological saline to keep moist in the preparation and mechanical tests , to knited into a graft with diameter of 8mm for reconstruction posterior cruciate ligament. The load was 352N to pull graft, the direction was 15°angle with median sagittal plane (the approximate load of the physiological state and direction), and was 90°angle with coronary plane roughly. Part I: a) To completed the extracortical fixation with EndoButton; to completed the interference screw fixation with interference screw with diameter of 8mm and the fixation location of interference screw was front-upward and rear-inferior of bone tunnel, respectively; To completed the combine fixation with a interference screw less than 1mm diameter of bone tunnel and combined with EndoButton, applicationed of pressure-sensitive film in the above-mentioned each group to measured the pressure between the edge of bone tunnel and graftes to evaluate the wear of the graft. The greater pressure value was, the greater wear and tear was; b) for the biomechanical testing, useing the CSS-44020 Biomechanical machine to compared of yield load (the load for the graft was deformation with extend apparently) of extracortical fixation technique groups, interference screw fixation technique groups and combine fixation technique groups, to indicated the strength of fixation. art II: Based on the first branch of research, reconstructed posterior cruciate ligament with the combine fixation , to established the bone tunnel with the angle of 80°,90°and 100°between the tunnel and intercondylar fossa of femur side wall, and to grinded the bone tunnel edges, useing the pressure-sensitive film calculated pressure to evaluated wear and tear of load for graft was same as the first part. In this experiment, an analysis of variance with two-sample mean comparison t test and the Student Newman-Keuls multiple range test was used for the statistical analysis of multiple comparisons of data. In order to prove whether the combine fixation and bone-tunnel techniques could reduced the "acute angle effect", and combine fixation technique could provided enough strength for the graft fixed.Results: All samples were not damaged and no fracture of femoral condyle, graft without break, interference screw and EndoButton were not damaged. The first part showed that the pressure(F=32.37,P<0.01) and yield load(F = 9.47, P<0.01) of each group were statistically significant differences with extracortical fixation group, front-upward interference screw fixation group, rear-inferior interference screw fixation group, and combine fixation group respectively. To make further pairwise comparison of Q tests: the pressure values of combine fixation group (3.28±0.22 Mpa) was less than interference screw group and less than extracortical fixation group (4.28±0.28 Mpa), while the value of rear-inferior interference screw fixation group (3.22±0.13 Mpa) was less than the front-upward interference screw fixation group (3.49±0.27 Mpa). The yield load of combine fixation group (470±55N) was greater than compared with the extracortical group (387±22 N) and the interference screw fixation group (439±29 N, 418±19 N). The second part showed that the pressure values of the bone tunnel with the angle of 80°,90°and 100°between the tunnel and intercondylar fossa of femur side wall in each group was statistically significant difference (F = 18.20, P <0.01). To make further comparison of Q tests: the pressure values of 100°group (3.55±0.21 Mpa) significantly less than the other two groups, while the pressure values of 90°group (3.81±0.19 Mpa) was less than 80°group (4.12±0.21 Mpa). Also, the value of the edge of bone tunnel grinded group and without grinded group were statistically significant difference (t = 2.89, P = 0.0097). The pressure values of grinded group (3.29±0.19 Mpa) was significantly lower than the grinded group (3.55±0.21 Mpa).Conclusion: To reconstructed posterior cruciate ligament using the combine fixation technique with small interference screw combined extracortical fixation and the bone tunnel technique with to increase the angle between the bone tunnel and intercondylar fossa of femur side wall and polished the edge of the bone tunnel, could reduced the " acute angle effects"of the femur side, and combine fixation could more strength than simply extracortical fixation and simple interference screw fixation.
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