Biomechanical Study Of The Improved External Flxator Which Treated Open Diaphyseal Fracture Of Extremities

Abjective:Unilateral axial dynamic fixator is widely used in open diaphyseal fracture of extremities,and has achieved good results.But,its stability is relatively weak,and it may produce shearing force whith is harmfull to fracture healing during elastic fixation.We designed and improved the components of the unilateral axial dynamic fixator, and hope to improve its stability and the efficiency during elastic fixation. The purpose of this study is to checkout the biomechanic property of the improved unilateral axial dynamic fixator by mechanical test,and to provide the theoretial basis to clinic application of the improved external fixator. Method:The improved fixator and common fixator are install to tibia.The biomechanical test of different fixation be compared to this frame at different loading level in test machine.The specimen we select are fresh freeze focile of cattle instand of embalmed human tibia.twenty 4.1.A3 simulated fracture has been done according to the AO/ASIF classification.The specimen are randomly devided into 4 groups as follows:A1 improved fixator with neutral position(that is parallel screw); A2 improved fixator with non-neutral position(that is non-parallel screw); B1 common fixator with neutral position; B2 common fixator with non-neutral position. Then each model was loaded cyclically at standard vertical and torsional loading rates on the biomechanical test machine.The data were recorded and laid in SPSS 11.5 respectively. Statistical analysis was done with methods of Paired-Samples T Test. Rezult:In the vertical loading test, the displacement enlarged with the load increasing,when the displacement is 2mm,the loading of every group is that 309.78±3.86N in group A1, 300.10±5.92N in group A2,257.30±3.08N in group B1,158.68±4.46N in group B2. following the statistical results of Paired-Samples T Test, the null hypothesis was accepted, according to 0.05 size,there is significent difference amang the 4 groups. In the torsional test,the torsional angle augmentated with the increasing of torsional moment,when turning to 3Nm,the torsional angle of every group is 1.96±0.08°,2.04±0.05°,2.25±0.07°,3.04±0.10°. following the statistical results of Paired-Samples T Test,there is no significent difference between group A1 and A2, there is significent difference between group A1,A2 and group B1,B2,and there is significent difference between group B1 and group B2. Conclusion:1.The biomechanical test data indicate that the improved fixator have a superior anti-compression stiffness stability and anti-torsion biomechanical properties than common fixator. It can provide adequate excellent stability during early period of fracture healing.2.Improve fixator always install in the neutral position,that is,the fixator body is aligned with the long axis of the bone.Theorotically,it improves the efficency of elastic fixation during late period of fracture healing.3. Improve fixator is especially for the treatment of open diaphyseal fracture of extremitie.