Finite Element Study On Calcium Phosphate Ceramic Screw Implanting After Extracting Dynamic Hip Screw

As the ageing of the population become more and more serious,the healthy problems of the elderly are gradually concerned by the community.The intertrochanter fractures commonly occur on hips in clinic,especially in aged human with osteoporsis.For internal fixations,the dynamical hip screws(DHS)have been mostly used in stable intertrochanter fractures,the DHS was thought as a more effective and safer implant in treating intertrochanter fractures.however,it was also a problem when the patient recovered and the screw taken out,it would leave a hole and change the structure of the femur,concentrating the stress around the hole and rasing the incidence of refracture.our objective is to investigate the validity of improving the femur's mechanical characteristics by implanting calcium phosphate ceramic screws after removing dynamic hip screw(DHS).The 3-D finite element model of the normal femur was built based on the CT scanning of a health male volunteer which is without hip disorders examinated by X-ray.Then the models of femur with and without DHS were constructed.Calcium Phosphate Ceramic screws with porosity of 80%,50%,30%,and apparent elastic model of 0.1GPa,1.0GPa,1.5GPa respectively,were compared in the model by recording Von Mises stress distribution and maximum stress when the joint was maximally loaded in a gait cycle.and collect the Von Mises stress distribution and maximum stress.According to the result,we found that the Von Mises in normal femoral shaft was uniform.The stress concentration was not significant and the maximum stress was observed in femoral head and.The stress concentration occurred in the femur with DHS and the maximum stress was observed in the distal femur around the screw hole.By comparing several different Calcium Phosphate ceramic screws,when the porosity was 50% and the apparent elastic modulus was 1GPa,the stress distribution of model was similar to the normal femur model.The other screws showed varying degrees of stress concentration.Finally we draw the conclusion,1 Using CT images to establish finite element models is quickly and efficiently.it is much easier to build a highly geometry similar model of a material with given properties,and the models can obtain the result which is hard to get in practice.Researchers can use the same model for simulating in different experimental conditions repeatedly2 Comparing several models above,The stress concentration occurred in the femur without DHS and the maximum stress was observed in the distal femur around the screw hole,and raised the incidence of refracture.3 The stress distribution were different among our models,by comparing several different Calcium Phosphate ceramic screws,when the porosity was 50% and the apparent elastic modulus was 1GPa,the stress distribution of model was similar to the normal femur model.And the stress will help the bones to reconstruct,The other screws showed varying degrees of stress concentration,and the stress distribution is occurred around the screw holes,and the stress is far more than the normal femur model,4 Using the finite element analysis to learn the mechanical property is effect and workable.it will simulate extremely complicated models and can obtain the result which is hard to get in practice,associated with three dimension reconstruction and design software,finite element models may be compresed with bones,ligaments,and the properties of every kind of tissues were applied to attain more convinced results.