Investigation Of The Tension Loss Of Ilizarov Fixation Wires Impacted By Different Wire Fixations And Torques

Objective: In 1950 s,Ilizarovinvented the ring external fixation which requires a certain degree of stability to maintain a relatively stable position of the bone segment s.The stability is determined by the tension in wires.After fixed on the ring,tension will need to be maintained by the fixed torque and wire fixation.The change of tension after tighten bolts,remove tension device and axial compression load of 800 N is recorded,to compare the difference of hole bolt,groove bolt,hole bolt + washer,groove bolt +washer four different types of wire fixation,the difference of torque of 10 Nm,15Nm,20 Nm,on the ability of maintenance of wires.Methods: 7 polyethylene bars of the same texture and appearance with diameter of 30 mm,length of 176 mm wereselected to instead of proximal diaphysis of tibial transverse fracture,and were randomly divided into A,B,C,D,E,F,G seven groups.Two homogeneous 180 mm stainless steel ring wereconnected by 3 identical 240 mm threaded rods,the distribution of threaded rodswas uniform and make the two ring parallel,the distancewas 100 mm.The tension sensor was installed inside the upper ring,and ensure the connection site and ring at the same level.The sensor was connected with the signal conversion and transmission device.The lower ring was connected to the base with a distance of 100 mm.The PE bar was sheathed on assembled external fixator,the ring was close to the proximal end of the 50 mm of PE bar,and the PE barwas arranged at the center of two rings and was perpendicular to rings.Two 2.0mm wires were drilled to PE bar,on each plane of rings,two wires in the horizontal plane was vertical,perpendicular to the PE bar.In group A,the hole bolt(type I)was used,and group B was made of groove bolt(type II).Group C was made of the hole bolt + washer(type III),and group D was made of grooved bolt +washer(type IV).Fixed torques through torque wrench were given 15 Nm.Group E,group F,group G used the groove bolt(type II),which is most commonly used clinically,fixed torque were 10 Nm,15Nm,20 Nmrespectively.Tensions of wires wereapplied to 1275 N by tension device.Wires of same ring were tensioned Simultaneously.Tension values after tighten the bolts,remove the tension device,were recorded.After that,the axial compressive load of 800 N of A-G seven groups mechanical modelswerepositioned on the electronic universal testing machine.Each model was tested 3 times.The experimental data were analyzed by SPSS22.0 software,and the variance analysis(ANOVA)was used to compare among groups.Results: 1.In the experiment of different wire fixations,tension of group A,B,C,D,when tightened bolts,were respectively 1234.7�4.3N,1236.9�10.6N,1243.5� 11.1N,1247.8 �7.0N;when removed tension device,were 1097.3� 28.2N,1117.6� 6.7N,1190.1�11.8N,1194.3�11.0N;afterapplied axial compression load of 800 N,tension values were 836.7 �8.4N,895.3�7.2N,1001�8.2N,1055.2�6.7N.By analysis of variance(ANOVA)for data analysis,group A,B,C,the D had no significant difference when tighten the bolts,four kinds of bolts had no significant difference;when removed tension device,there was no statistically significant differences between the two groups of AB,eitherdid groupsof CD,but between the group AB and CD,it had significant difference,values of tension of group AB were lower than that ofgroup CD.After loading the axial compression load,the value of the four groups were statistically significant,group D was higher than the group C higher than group B and group A.2.In the experiment of different bolt torques,tensions of groups E,F,G,when tightened the bolts were 1251.8�5.6N,1234.8�3.2N,1211.5�27.7N;when removedtension device,tension values were 1008�6.6N,1120.9� 9.0N,1128.4�8.6N;after axial compression load,tension values were 812.7�7.7N,931.3 �5.9N,942 �35.0N.Variance analysis(ANOVA)was used to analyze the data.When tightened the bolts,there was no statistical difference between the groups,three torques has no obvious difference;after the removal of tension device,no statistically significant difference between groups FG,tension of group E was lower than that of group FG;when applied the axial compression load,no statistically significant difference was found between group F G,tension of group E was lower than that of group E G.Conclusion: By the method of experimental biomechanics,conclusion was as following:When the application of tension and tightened the bolts,there was no significant differences between the four types of bolts,and the three kinds of bolt torque.When removed the tension device,thetension loss of the group ofcombination of hole bolt and washer,was less than the groups without the use of washer.The loss of tension of high torque group was less than that of groups of low torque.After of axial compression load of 800 N,therearesignificant differences between the four types of wire fixations.The combination of groove bolt and washer had the best ability to maintain the tension,followed by the combination of the hole bolt andwasher and the groove bolt.