The Biomechanical Finite Element Analysis Of Proximal Femur After Internal Fixation Of Femoral Neck Fracture With Bone Defect

The first part:The biomechanical finite element analysis of a normal proximal femur.Objective The research of the proximal femur has been a popular and diffcult subject all the time because of its complicated three-dimensional structure, anatomic structure and stress environment. This experiment investigated the stress state of the femoral neck and femoral head, and analysed the proximal femur from the perspective of engineering mechanics.Methods We got DICOM data of a normal femur from the result of a volunteer's thin layer CT scanning. Then imported the data to Mimics, built the femur model and imported it to ABAQUS. After setting corresponding load and constraint, we analysed the stress state of the femoral neck. Then built a cantilever beam model by simplifying the femur model, and analysed the same stress state.Results We built the finite element femur model successfully, and analysed the stress state of the proximal femur which belonged to a person in stationary state. It turned out that the stresses concentrated on the superior and inferior femoral neck. The stress analysis of the femoral neck vertical section showed the stresses concentrated on the bone cortex. The stresses of the femoral head concentrated on its superior lateral quadrant.Conclusion This experiment proved that the superior femoral neck bore the tensile stress, and the inferior femoral neck bore the compressive stress. The proximal femur is similar to a 'cantilever beam' structure. The stresses of femoral head mostly focused on its superior lateral quadrant.The second part:The biomechanical finite element analysis of proximal femur after internal fixation of femoral neck fracture with posterior-inferior bone defectObjective The proximal femur is a typical'cantilever beam'structure. From the perspective of engineering mechanics, the mechanical property variation of the beam effects the bearing capacity and stability of the whole cantilever beam. Studies showed bone defect took place mostly in the posterior -inferior aspect of the femoral neck. We discussed whether the bone defect in the posterior -inferior aspect of the femoral neck would effect the stability of the postoperative proximal femur by finite element analysis experiment.Methods We got DICOM data of a normal femur from the result of a volunteer's thin layer CT scanning. Then imported the data to Mimics and simulated osteotomy, then built a model of a Pauwell 70°femoral neck fracture with posterior -inferior bone defect. Assembled the model with 3 hollow screws, then imported it to ABAQUS. After setting corresponding load and constraint, we analysed and coMPared the stress states of the proximal femur.Results As the enlargement of the bone defect, the 2 screws in the superior femoral neck bore increasing tensile stress, and the inferior femoral neck bore increasing compressive stress. Both the two increasing stresses focused on the fracture site. Meanwhile, the stress distribution area of the femoral head moved to lateral aspect, from the main to non-main bearing area, and a high pressure area formed in the original non-main bearing area.Conclusion The bone defect in posterior-inferior femoral neck fracture site changed the stress state of the end and the internal fixation, and effected their stabilities. Meanwhile, the stress state of the femoral head has changed. Its stress distribution area moved from its superior lateral quadrant to lateral aspect.The third part:The biomechanical finite element analysis of proximal femur after internal fixation of femoral neck fracture with lateral-superior bone defectObjective A large majority of young patients with femoral neck fractures present after high-energy trauma. It's very difficult to cure these fractures because of its complications such as osteonecrosis of the femoral head and nonunion which effect the patients'quality of life seriously. However, the effects of bone defect at the fracture site on postoperative femoral neck have gained insufficient attention. Some clinical studies showed bone defect presented a lot in lateral-superior femoral neck. We researched how the lateral-superior bone defect effect the stress state of postoperative femoral neck by finite element analysis.Methods We got DICOM data of a normal femur from the result of a volunteer's thin layer CT scanning. Then imported the data to Mimics and simulated osteotomy, then built a model of a Pauwell 70° femoral neck fracture with lateral-superior bone defect. Assembled the model with 3 hollow screws, then imported it to ABAQUS. After setting corresponding load and constraint, we analysed the stress state of the proximal femur.Results As the enlargement of the bone defect, the 2 screws in the superior femoral neck bore invariable tensile stress value and range, and the inferior femoral neck bore invariable compressive stress value and range too. The stress distribution area of the femoral head was still in superior lateral quadrant, its maximum stress value and stress range haven't changed obviously.Conclusion Bone defect at lateral-superior fracture site cut off the tensile stress of the superior beam which could be replaced by 2 annulated compression screws in the superior femoral neck on condition that the femoral head was not osteoporotic and there was no sliding between it and the screw thread, and the stress distribution of the femoral head and femoral neck remained mostly unchanged. When there was sliding between the femoral head and the screw thread, the stress distribution area moved from its superior lateral quadrant to lateral aspect.The fourth part:The biomechanical finite element analysis of proximal femur after internal fixation of femoral neck fracture with neck shorteningObjective Clinical observations showed that neck shortening present commonly after the internal fixation of femoral neck fracture Wei Jie etc. had made a retrospective study of 137 femoral neck fracture patients'data. They found that the rate of ONFH in neck shortening cases was much more higher than in normal cases. However, there has no mechanics experiment could support aforesaid clinical research. This experiment researched how the neck shortening effect the stress state of postoperative proximal femur by finite element analysis.Methods We got DICOM data of a normal femur from the result of a volunteer's thin layer CT scanning. Then imported the data to Mimics and simulated osteotomy, then built a model of a Pauwell 70°femoral neck fracture and a model of a Pauwell 70° femoral neck fracture with lcm neck shortening. Assembled the models with 3 hollow screws respectively, then imported them to ABAQUS. After setting corresponding load and constraint, we analysed the stress states of the proximal femur.Results When the postoperative femoral neck was shortened by lcm, the maximum tensile stress value that the 2 screws in the superior femoral neck bore changed from 15.7MPa to 12.4MPa, and the maximum compressive stress value that the inferior femoral neck bore changed from 20.2MPa to 17.8MPa. Meanwhile, the stress distribution area of the femoral head moved from its superior lateral quadrant to right above it. The maximum stress value that the non-main bearing area bore changed from 10.6MPa to 17.2MPa.Conclusion The neck shortening decreased the eccentricity of the proximal femur, the maximum tensile stress value that the 2 screws in the superior femoral neck bore, and the maximum compressive stress value that the inferior femoral neck bore. It hasn't changed the stability of the internal fixation and postoperative fracture site. Meanwhile, the stress distribution area of the femoral head moved from its superior lateral quadrant to right above it.