| Objective: With the progress of people's understanding of thoracic trauma and the development of internal fixation technology and material science,a various of new internal fixations have been applied in the clinical work gradually.A variety kinds of internal fixations can be used for rib fixation surgery,and the most commonly are plates.Pure titanium rib plate and titanium nickel memory alloy connector have been used in clinical internal fixation,and both of them have achieved satisfactory effects.There are many characteristics of internal fixation evaluating,such as the reliability of internal fixation,the compatibility of the organization,the simplicity of the operation method and the cost.Orthopedical biomechanics is an important branch field of biomechanics.It combines law of mechanics such as the mechanics of Newton's three law and the law of conservation of energy principle with the anatomical and physiological characteristics of bone,joint and soft tissue of human,guides people to understand the biomechanical characteristics of bone and joint,provides the scientific basis of internal fixation and clinical application guidance by testing and assessing the parameters and indexes of internal fixations.A biomechanical test is necessary before one internal fixation being used in clinical work.Among the literature at home and abroad,the biomechanical tests of spine,limbs and pelvic are numerous,but there are few literature about internal fixation biomechanical tests of rib.This experiment by artificially creating rib internal fixation model for biomechanical test,selecting classical options of biomechanical test such as the three point bending test,the torsion test and the fatigue test,comparing and analyzing the data,comparing the biomechanical characteristics of pure titanium rib plate and titanium nickel memory alloy connector,makes up data gaps,gets evaluations combined with clinical,provides a scientific basis for the clinical application of two types of internal fixation of rib.Methods: 6 male corpses of adult were obtained from the anatomy teaching and research department of Hebei Medical University,the whole ribs of both left and right,were taken out form each corpse's 5th-8th ribs,a total of 48.All the ribs without the characteristics of deformity,trauma,tumors and other pathological changes.All of the soft tissue attached to the ribs were removed,rib fracture model created,the midaxillary line corresponds to the ribs were marked,every rib was cut off from the marker by a saw.The 48 ribs were randomly grouped in five biomechanical tests: non-destructive three point bending tests,non-destructive torsion tests,destructive three point bending tests,destructive torsion tests and fatigue tests.The destructive three point bending tests were the continuation of the non-destructive three point bending tests and the destructive torsion tests were the continuation of non-destructive torsion test loading.Each test was divided into pure titanium rib plate group and titanium nickel memory alloy connector group.Test data obtained by the sensor transmitted to the computer and application software for statistical analysis of the data.Results:1 The non-destructive three point bending tests and destructive three point bending tests: when the center of force displacement was less than 6mm,the load of two groups were increasing with the increasing of the force displacement;when the center of force displacement was more than 6mm,the two fixations became elastic yield.When the displacement was 8mm,the man-made fracture gap increased significantly,when the displacement was 10 mm,two groups of implants were found by claw loose,fall off,but at the end of the experiment,two groups of specimens were without fresh fractures or implants off completely.There was no significant statistical difference between the two groups by load when the displacement was 2mm,4mm.When the displacement was 6mm,8mm and 10 mm,there was a significant statistical difference,the pure titanium rib plate required much more load value at 6mm and 10 mm.The yield strength of both groups appeared at the displacement of 6mm: the pure titanium rib plate was 161.6N,the titanium nickel memory alloy connector was 143.2N.Both the values were bigger than the average load of rib fracture 87 N.Either the pure titanium rib plate or the titanium nickel memory alloy connector can provide reliable fixation for rib.2 The non-destructive torsion tests and destructive torsion tests: when the torsion angle was less than 25°,the torque of two groups were increasing with the increasing of the torsion angle;when the torsion angle was more than 25°,The torque of two groups were decreasing with the increasing of the torsion angle,the two fixations became elastic yield.There was no significant statistical difference between the two groups by torque when the degree was 5,10,15and25.Only when the torsion angle came to 20° and 30°,a significant statistical difference appeared.Curve trend were similar between them.The difference of the ability of anti-torsion was not found significantly between the two groups.The yield torsion torque of both groups appeared at the degree of 25°: the pure titanium rib plate was 356.3N·cm,the titanium nickel memory alloy connector was 351.2N·cm.The elastic yield state appeared,two groups of implants were found by man-made fracture gap increased significantly,claw loose,fall off,but at the end of the experiment,two groups of specimens were without fresh fractures or implants off completely.3 Fatigue tests: After 50000 cycles,stiffness values of the two groups values were both decreased,but significant difference of each group's stiffness value was not found before and after fatigue tests.But the stiffness value's change ratio of the titanium nickel memory alloy connector group was higher than that of the pure titanium rib plate group,with a significant difference statistically.Conclusions:1 The pure titanium rib plate and titanium nickel memory alloy connector can provide solid and reliable fixation for ribs,the anti-bending ability of the pure titanium rib plate is better than that of the titanium nickel memory alloy connector.2 About the anti-torsion capacity,there is no significant difference between the pure titanium rib plate and the titanium nickel memory alloy connector,either of their destructive power to the ribs is tiny.3 The anti-fatigue of the pure titanium rib plate is better than that of the titanium nickel memory alloy connector. |
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