Three-dimensional Finite Element Analysis On Locking Plate Internal Fixation Combined With Bone Grafting For Fixing Three-part Proximal Humeral Fracture

Objective:By using finite element analysis technology to compare the biomechanical stability of simple locking plate internal fixation and locking plate internal fixation with bone grafting in the treatment of Three parts proximal humerus fracture with different size of bone defect in humeral head and calculate the stress and distribution characteristics of the proximal humerus and locking plate,providing theoretical basis for the clinical treatment of fractures in the area.Methods:The CT raw data of normal proximal humerus was processed by medical image processing software.Establish the three-part proximal humerus fracture model,bone defect model and proximal humerus locking plate model by the 3D modeling software.These models was then assembled based on the principles of AO treatment,for Group A:locking plate internal fixation combined with bone grafting treatment group,Group B:The bone defect was 1cm~3,treated with simple locking plate internal fixation group.Group C:The bone defect was 2cm~3,treated with simple locking plate internal fixation group.Tetrahedral meshing was performed on the assembly models of group A,B and C by using the finite element preprocessing software Hyper Mesh.At last the final model was analyzed by finite element analysis software Abaqus to compare the biomechanical stability and stresses.Results:Under these two loading conditions:1.For the model of proximal humeral:In group A maximum stress were 15.29 MPa and 58.10 MPa,the maximal displacement were 0.017mm and 0.210 mm;In group B the proximal humeral maximum stress were 15.68 MPa and 62.23 MPa,the maximal displacement were 0.019mm and 0.225 mm;In group C the proximal humeral maximum stress were 43.23 MPa and 95.41 MPa,the maximal displacement were 0.030mm and 0.466 mm.2.For the model of internal fixation:In group A maximum stress were 33.32MPa and 177.6MPa,and the maximum displacement were0.014mm and 0.166mm;In group B the maximum stress were 43.41MPa and 181.3MPa,and the maximum displacement were 0.015mm and0.176mm;In group C the maximum stress were 80.72MPa and 282.7MPa,and the maximum displacement were 0.023mm and 0.311mm.There were no significant differences in the maximum stress and displacement of humerus and internal fixation between group A and group B,while the maximum stress of humerus in group C was significantly greater than that in group A and group B.In addition,when the axial load was increased,the maximum stress on humerus in group C reached 95.41MPa,exceeding the yield strength 95MPa of cortical bone and there was a risk of secondary fracture.Conclusion:1.When the size of the bone defect in humerus head is about 1cm~3or less,there is no significant difference in biomechanics between the simple locking plate internal fixation and the locking plate internalfixation combined with bone grafting in the treatment of the proximal humerus fracture,and both are relatively stable,so there is no need to do bone grafting.2.When the defect in humerus head is 1-2cm~3,the maximum stress of humerus would increasing with the increment of defect,internalfixation with bone grafting in the treatment of proximal humeral fracture of three parts has better biomechanical stability,but the real needs ofbone grafting should be considered with actual defect size and location,economic conditions and the risk of bone graft in patients.3.When the size of defect in humerus head reaches 2cm~3or above,locking plate internal fixation combined with bone grafting issignificantly safer and has better biomechanical stability than locking plate internal fixation alone in the treatment of three-part fractures of the proximal humerus.