Mechanical Analysis Of Patellar Transverse Fracture Fixed By Compression Bone Needle Wire Tension Band

Objective:Through finite element analysis and mechanical test of artificial patella model,the fixation effect of compression bone wire tension band,Kirschner wire tension band and hollow nail wire tension band on transverse fracture of patella was compared.Methods:Finite element analysis(FEA):The CT data of a healthy young male volunteer were selected to establish the transverse fracture model of patella,and then the finite element models were established using three different fixation methods:Kirchner wire tension band,hollow nail wire tension band and compression bone wire tension band.Ansys17.0 software was used to simulate the force state of patella at 300 and 60° knee flexion,and the total displacement of patella,fracture space and pressure of broken end of the three finite element models were compared.Artificial patella model test:18 artificial patella models were selected and randomly divided into 3 groups(n=6),and the transverse fracture model of patella was made by 3D printing guide plate.Kirschner wire tension band(Kirschner wire group),hollow nail wire tension band(hollow nail group)and pressure bone wire tension band(pressure bone group)were respectively used to fix.The models were fixed on the mechanical test machine to simulate the stress state of the knee joint under 60° flexion,and the cyclic load test was carried out.The space increment of the broken end of the fracture was recorded after 1,50 and 100 times of loading during the cyclic test.Models that do not meet the failure criteria in the cycle test are then subjected to extreme load testing to record the peak tension when the patella is re-fractured or internal fixation is broken.The gap increment in cyclic test and the tensile peak in ultimate load test of the three groups of models were compared.Results:In the finite element analysis,the total displacement of patella,fracture space and fracture end pressure of the Kirschner wire tension band model were the largest in the three models under different angles.Compared with the Kirschner wire tension band model,under 800N load at 30° and 60° directions,the total displacement of the tension band model of the compression bone-wire wire decreases by 16.8%and 17.4%,and the total displacement of the tension band model of the hollow nails wire decreases by 17.5%and 9.4%,respectively.In terms of fracture space,the fracture space in the compression bone-wire tension band model was reduced by 28.8%and 26.5%,respectively,and that in the hollow nail wire tension band model was reduced by 27.5%and 15.4%,respectively.Under 800N load at 30° and 60°directions,the fracture end pressures of Kirschner wire tension band model were 16.334MPa and 33.778MPa,respectively.The tension band models of hollow nail wire were 12.821MPa and 27.356MPa,respectively.The tension band models of bone needle wire were 11.837MPa and 22.027MPa,respectively.In the cyclic test of artificial patella model,the mean displacement of fracture end space of patella model in hollow nail group and pressure bone needle group was 0.033±0.039mm and 0.132±0.132mm,respectively,which was significantly lower than that in Kirschner wire group(2.425±0.307mm).There were significant differences between the Kirschner wire group and the hollow nail group and the pressure needle group(P<0.01),but no significant differences between the hollow nail group and the pressure needle group(P>0.05).In the ultimate load test,the average peak tension of the hollow nail group and the pressure pin group was 3373.04±100.75N and 2435.05±121.51N,respectively.The average peak tensile value of the pressure pin was lower than that of the hollow pin group,and the difference between the two groups was statistically significant(P<0.01).Conclusion:As a new technique for fixing transverse fracture of patella,the compression bone needle wire tension band can meet the biomechanical requirements,and the fixing effect is better than the traditional Kirschner wire tension band.The stability performance of fracture fixation can reach the common clinical hollow nail wire tension band,which is an effective fixation method to replace the Kirschner wire tension band to fix transverse fracture of patella.