Finite Element Analysis Of Comminuted Fracture Of Femur Shaft Fixed With Oblique Locking Plate

Purpose: The bridging plate association with locking screw is the widespread used internal fixation in comminuted fracture of femoral shaft. As far as possible on the premise of satisfactory reduction of fracture end reset treated with closed reduction and internal fixation technology has reached consensus. After closed reduction in clinical practice, however, because of inadequate exposure it is difficult to adjust the plate position, there will be into a fixed angle between the middle route of the bone plate and long axis of the femoral. The purpose of our study is to compare and evaluate the effect by using three-dimensional finite element analysis to simulation comminuted fracture of frmur fixed with oblique locking plate, and study the risk of the oblique bone plate fixed femoral comminuted fracture. We hope to provide theoretical basis for clinical treatment.Methods: Using 64-slice CT to scan a healthy human’s femur to obtain DICOM data. And then we import the DICOM data to the Mimics medical modeling software for 3D reconstruction, and at the same time set up the femoral comminuted fracture model. Using the software of Pro/E Wildfire 5.0 to design the locking plate model based on the femoral anatomic locking plate. Import the model STL file of locking plate to Mimics to simulate internal fixation surgery under different deflection angles respectively on the femur comminuted fracture models. On the basis of the location of the proximal screw, we divide it into two groups: bone plant oblique forward and oblique backward. Each group on the basis of the distance of proximal and distal screw with surface of the femur is divided into 2mm, 4mm, 6mm, 8mm, 10 mm five subgroups respectively, and there are 11 groups combing the upright plate. We use the software of 3-matic and Mimics to perform the mesh division and material assignment, to stimulate load and constraints of double-feet loading by using the various internal fixation model. And then we observe the change of equivalent stress of implants and displacement in the end of fracture among the groups.Results: For each subgroup under the same load and constraints, with the incline of the plate the stress peak value increased in no.1,no.5 and no.6 screw-femur interface.(1)In the forward-oblique 2 group and forward-oblique 4 group has arisen concentration of stress in no.1,no.5 and no.6 screw-femur interface, the stress is more than the yield strength of bone. In the forward-oblique 6 group has arisen concentration of stress in no.5 and no.6 screw-femur interface, the stress is more than the yield strength of bone.(2) In the backward-oblique 2 group and backward-oblique4 group and backward-oblique 6 group has arisen concentration of stress in no.1,no.5 and no.6 screw-femur interface, the stress is more than the yield strength of bone. In the backward-oblique 8 group has arisen concentration of stress in no.5 and no.6 screwfemur interface, the stress is more than the yield strength of bone.(3) In each subgroup, the peak stress and strain of locking plate and screw are located in the end of no.3 screw and less than the strength of titanium alloy.(4) In the forward-oblique groups, the more incline of the plate, the more axial displacement in the end of femur.(5) In the backoblique groups, the more incline of the plate, the less axial displacement and more shear displacement in the end of fracture.Conclusion: Two feet stand in the situation of forward-oblique locking plate,the distance between ends screw and surface of the femur are less than or equal to 6mm, the two most distal screw will lost stability when the bone broken. The distance between ends screw and surface of the femur are less than or equal to 4mm, the two most distal screw and the most proximal screw will lost stability when the bone broken. Two feet stand in the situation of backward-oblique locking plate,the distance between ends screw and surface of the femur are less than or equal to 8mm, the two most distal screw will lost stability when the bone broken, the distance between ends screw and surface of the femur are less than or equal to 6mm, the two most distal screw and the most proximal screw will lost stability when the bone broken. Oblique locking plate will lead to double instability in the axial and shear direction. It is remind us that when we use the MIPO technique in deal with femur comminuted fracture that the distance between ends screw and surface of the femur should greater than 6mm when the plate forward-oblique or greater than 8mm when the plate forward-oblique. Or the internal fixation could be failed when patient doing functional exercise in postoperation.