Biomechanical Analysis Of F-type Screw Configuration Combined With Off-axis Screw In The Fixation Of Pauwels Type Ⅲ Femoral Neck Fracture

Objective:To explore the biomechanical properties of F-type screw configuration combined with off-axis screw in the fixation of Pauwels type III femoral neck fracture,and compare it with the inverted triangle screw configuration and the F-type screw configuration,so as to provide a biomechanical basis for improving the treatment of Pauwels type III femoral neck fracture.Methods:Twenty artificial adult femoral models were sawed off at the middle of the femoral neck according to the Pauwels angle of 70 to make Pauwels type III femoral neck fracture model.The models were randomly divided into five groups for internal fixation.Group A: inverted triangle screw group,Group B: F-type screw group,Group C: F-type double transverse tension screw group.Two screws parallel to the femoral neck were off-axis inserted in the direction perpendicular to the fracture line on the F-type basis,and Group D: the screws parallel to the femoral neck at the proximal end were off-axis inserted on the F-type basis,and Group E:the distal screws parallel to the femoral neck in the F-type screws were off-axis inserted.Placing the fixed model in the pressure testing machine,and performing pressure testing to obtain load-displacement data of each group of models in a bearing range of 700N;Subsequently,the model was placed on a torsion testing machine,and the torques of the fractured ends were measured when the model was twisted by 2,4 and 6 degrees,Finally,the pressure was continuously applied on the pressure testing machine,so that the model was damaged and the internal fixation failed,and record the ultimate load of each model.SPSS26.0 software was used for statistical analysis of the experimental data.The difference was considered to be statistically significant when it was P<0.05.Graph Pad Prism 9 software is used to draw statistical pictures.Results:In the pressure test,the displacement values of fracture end were recorded when the pressure was applied to 300 N,500N and 700 N N.The results show that the displacement values(300 n-0.12 0.04 mm,500 n-0.53 0.09 mm,700 n-0.95 0.11 mm)of the F-type double transverse drawing screw group(fitting curve Y=0.002113X-0.5004)are smaller than those of the other four groups under the same pressure,and the differences are statistically significant(P<0.05).In the torsion experiment,the torque of this configuration at the fracture end of each rotation angle(2-4.13 0.33 N.m,4-6.18 0.39 N.m,6-8.75 0.29 N.m)is greater than the other four groups,and the data difference is statistically significant(P < 0.05).In the ultimate load experiment,the ultimate load value(2376.5±163.69N)is larger than the other four groups,and it is 1.7times that of the inverted triangle screw group and 1.3 times that of the Ftype screw group,and the data difference is statistically significant(P <0.05).Conclusion:In this experiment,we made some improvements on the configuration of F-type cannulated compression screw for fixation of Pauwels III type femoral neck fracture.In combination with the transverse tension and compression characteristics of the off-axis screw perpendicular to the fracture line,we placed two screws of F-type screw parallel to the femoral neck perpendicular to the fracture line to resist the large shear stress at the fracture end.The experimental results showed that this configuration had biomechanical advantages in compression resistance and anti-rotation.