ABSTRACT
OBJECTIVE: To investigate possible causes of micromotion in distal femoral prosthesis. METHODS: Based on the assumption that the femur and prosthesis were considered as concentric cylinders with completely bonded interface, a theoretical model simulating the interfacial stress transfer was established. The distributions of the interfacial shear and radial stresses with the changing of z were obtained through mathematics and mechanics deducing. RESULTS: The maximum interfacial shear stress occurred at the position of z=0, namely, the cross section of the femur neck. The interfacial shear stress sharply decreased with the increasing of z and came to nearly zero at the range of z> 0.1 m. While the interfacial radial stress increased with the increasing of z,at the range of z >0.05 m it was constant and reached the maximum. CONCLUSION: The micromotion in distal prosthesis is caused by the interfacial radial stress.
Subject(s)
Femur/physiopathology , Hip Prosthesis/adverse effects , Joint Instability/etiology , Models, Theoretical , Stress, Mechanical , Biomechanical Phenomena , Femur/anatomy & histology , Femur/surgery , Humans , Joint Instability/physiopathology , Motion , Prosthesis Design , Shear StrengthABSTRACT
OBJECTIVE: To investigate the stress distribution and fracture mechanism of proximal femur under impact loads. METHODS: The image data of one male's femur were collected by the Lightspeed multi-lay spiral computed tomography. A 3D finite element model of the femur was established by employing the finite element software ANSYS, which mainly concentrated on the effects of the directions of the impact loads arising from intense movements and the parenchyma on the hip joint as well as those of the femur material properties on the distribution of the Mises equivalent stress in the femur after impact. RESULTS: The numerical results about the effects of the angle sigma of the impact loads to the anterior direction and the angle gamma of the impact loads to the femur shaft on the bone fracture were given. The angle sigma had larger effect on the stress distribution than the angle gamma, which mainly represented the fracture of the upper femur including the femoral neck fracture when the posterolateral femur was impacted. This result was consistent with the clinical one. The parenchyma on the hip joint has relatively large relaxation effect on the impact loads. CONCLUSIONS: A 3D finite element analysis model of the femoral hip joint under dynamic loads is successfully established by using the impact dynamic theory.
