Biomechanical Study On The Fixation Effect Of Circular External Fixators With Different Configurations For Oblique Fractures Of Long Bones

Objective: To compare the biomechanical fixation effect of circular external fixators with different configurations for oblique fractures of long bones,and to explore what kind of external fixation configuration is able to control the micro motion of fracture end within the scope of the ideal,thus to provide theoretical basis for clinic.Methods: 15 polyethylene plastic rods with the same batch were selected,They were randomly divided into groups A-E,and each group consists of three polyethylene plastic rods,The model of oblique fracture in the middle of tibia was simulated.The five sets of models were fixed with external fixator of four rings,and the difference was the connection between PE rod and external fixator: Group A(A1,A2,A3):2.0mm diameter kirschner wires were placed vertically in each ring plane,after pulling,the wires were fixed to the appropriate position on the ring by the grooved fixed bolts,tensile tension was 1200 N,and the bolt torque was 14 Nm.Group B(B1,B2,B3):In each ring plane,the 2.0mm diameter olive pins were placed vertically,and after pulling,the wires were fixed to the appropriate position on the ring by the grooved fixed bolts,tensile tension was 1200 N,and the bolt torque was 14 Nm.Group C(C1,C2,C3): 5.0mm diameter half pins were placed vertically in each ring plane,which were fixed to the appropriate position of the ring by half pin bolts,and the bolt torque was 14 Nm.Group D(D1,D2,D3)In each ring plane,the 2.0mm diameter olive pins were placed vertically,and after pulling,the wires were fixed to the appropriate position on the ring by the grooved fixed bolts,tensile tension was 1200 N,and the bolt torque was 14 Nm,at the distal end and proximal end of the fracture line,a single cortical fixed half pin was inserted into the PE rod,which were fixed to the appropriate position of the ring by half pin bolts and connection pieces,Group E(E1,E2 and E3): In each ring plane,the 2.0mm diameter olive pins were placed vertically,and after pulling,the wires were fixed to the appropriate position on the ring by the grooved fixed bolts,tensile tension was 1200 N,and the bolt torque was 14 Nm,at the distal end and proximal end of the fracture line,an olive pin was inserted into the PE rod,which was fixed to the appropriate position of the ring by the grooved fixed bolts and connection pieces after pulling.The axial compression and torsion experiments were performed on the five sets of models respectively.Measured the end displacement under different loads and the Angle of breaking end of different torque by computer software,calculated the axial stiffness and torsional stiffness,The measured data were analyzed by SPSS 22.0 statistical software,and the biomechanical differences of the fixation effects of five different external fixators on the fracture end of oblique fracture were compared.Results: 1.In axial compression test,under the axial load of 200N?400N?600N?800N,the overall median difference between the five groups was statistically significant(P<0.01).Then,when the axial load was 800 N,the displacement of fracture ends between each group were compared,and the results showed that the differences between the groups were statistically significant(P<0.005).The order of displacement under 800 N axial loads,from small to large was: group E,group D,group C,group B,group A,That is to say,in the 5 kinds of configuration,the group that inserted olive pin at the distal end and proximal end of the fracture end provided maximum axial stiffness,and the group that simple using kirschner wires provided minimal axial stiffness.2.In torsion load test,under the torsional load of 4Nm,7Nm and 10 Nm,the overall mean difference between the five groups was statistically significant(P<0.01).Then,when the torsion load was 10 Nm,the torsion angles between each group were compared,and the results showed that the differences between the groups were statistically significant(P<0.05).The order of torsion angle under 10 Nm torsion loads,from small to large was: group C,group E,group D,group B,group A,That is to say,in the 5 kinds of configuration,the group that simple inserted half pins provided maximum Torsional stiffness,and the group that simple using kirschner wires provided minimal Torsional stiffness.Conclusion: 1.As to the axial stiffness,the order from large to small are as follows: The group that inserted olive pin at the distal end and proximal end of the fracture end after fixed the pulled olive pins on the rings,The group that inserted single cortical fixed half pin at the distal end and proximal end of the fracture end after fixed the pulled olive pins on the rings,The group that simple inserted half pins,The group that simple using olive wires,The group that simple using kirschner wires.2.According to the torsional stiffness,the order from large to small are as follows: The group that simple inserted half pins,The group that inserted olive pin at the distal end and proximal end of the fracture end after fixed the pulled olive pins on the rings,The group that inserted single cortical fixed half pin at the distal end and proximal end of the fracture end after fixed the olive pins on the rings,The group that simple using olive wires,The group that simple using kirschner wires.3.The configuration which inserted olive pin at the distal end and proximal end of the fracture end after fixed the pulled olive pins on the rings can directly pressurize the fracture end and obtain the maximum axial stiffness and strong torsional stiffness;The configuration that simple inserted half pins can obtain the maximum torsional stiffness through the rigid fixed characteristic of the half pins.