Objective To set up a three-dimensional finite element model (FEM) to investigate biomechanics of point contact locking plate (PC-LP) fixating femoral shaft fractures. Methods One intact fresh adult cadaveric femur was scanned by CT at 1 mm interval. Then, the data of CT were utilized to establish three-dimensional FEM by using software Mimics and PRO/E and simulate the different clini-cal loading conditions. The changes of theoretical stress of femur and PC-LP were analyzed under flexion, axial compression and torsion loads. Results (1) Under four-point bending load, the distribution of femur stress was in uniformity, with the largest stress of the PC-LP focused on the edge. (2) Under axial compression load of 250 N, the largest stress of the femur was focused on the screw holes on beth distal ends, with the largest stress of the PC-LP focused on the middle screw holes. (3) Under the torsion load cused on the middlepart and the middle screw holes. Conclusions Under the four-point bending, ax-ial compression and torsion loads, the distribution of femur stress is in uniformity, when the largest stress of the PC-LP focuses on edge or the middle screw holes, while that of the PC-LP on two screw holes of proximal or distal ends.

Mature femur bone, through the process of bone remodeling, renews itself and adapts to mechanical load. In this study, a biomechanical model involving strain and other variable parameters was developed for bone remodeling and used to simulate the removal of bone mass and bone regeneration in the disuse and overload condition. The results exhibit that elastic modulus in bone lateral portion is decreasing and porosity is increasing for acquiring equilibrium strain. The conclusion of simulation for reality femur model is more accurate than what is obtained from simplified model or from only one volume element. These indicate the significance of acquiring scientific data to the development of consummate simulation model.
Adaptation, Physiological ; physiology ; Bone Remodeling ; physiology ; Computer Simulation ; Elasticity ; Femur ; diagnostic imaging ; physiology ; Finite Element Analysis ; Humans ; Models, Biological ; Porosity ; Stress, Mechanical ; Time Factors ; Tomography, X-Ray Computed ; Weight-Bearing

To solve the problem of aseptic loosening of hip joint prosthesis after THR (total hip replacement) and to meet the requirement of individual endoprosthesis for rapid automatic design and manufacture, a new method is presented. According to the anatomical shape of the patient's femoral marrow cavity and the replacement requirement, the hip joint prosthesis is designed via the combination of medical CT technique, computer aided design and finite element analysis. During analysis of the endoprosthesis, the 3-D finite element model of the femur is structured by finite element software ANSYS, the near true femoral material parameters are gained, the quantitative description of femoral material's anisotropy and inhomogeneity is realized by self-developed specific software in the 3-D finite element model of femur. Contact analyses of the customized hip endoprosthesis--femur system are simulated by ANSYS, stress, strain and their distribution are analyzed and contrasted before and after-operation under the action of physiological load in the system. It is feasible to checkout the rationality of the design by comparing the stress distribution in the femur with the situation before replacement, the extent of stress-shielding caused by the replacement is determined quantificationally. The results reveal that the method is more reasonable and reliable and can provide basic means for optimizing the design of custom-made hip prostheses and for evaluating the long-term stability of endoprosthesis after operation.
Arthroplasty, Replacement, Hip ; adverse effects ; Computer-Aided Design ; Finite Element Analysis ; Hip Prosthesis ; Humans ; Prosthesis Design ; methods ; Prosthesis Failure ; Risk Factors ; Stress, Mechanical ; Weight-Bearing