FEM analysis of bone-implant system by using videodensitometric measurements

Finite element method is the best means to obtain meaningful results in bone implant system biomechanics. Since mechanical characteristics of bone change from person to person and, in the same person, they vary over the time, we have chosen to construct individual models, in terms of geometrical and mechanical characteristics, by means of X-ray images analysis. Our aim is to improve surgery planning and to evaluate patient follow-up. The application of the proposed procedure is illustrated throug the construction of a bidimensional FEM model concerning a patient who underwent surgery for the implant of a total hip prosthesis with a six years follow-up. The paper shows that even a bidimensional individual model can give reliable clinical indication

FEM analysis of bone-implant system by using videodensitometric measurements

Finite element method is the best means to obtain meaningful results in bone implant system biomechanics. Since mechanical characteristics of bone change from person to person and, in the same person, they vary over the time, we have chosen to construct individual models, in terms of geometrical and mechanical characteristics, by means of X-ray images analysis. Our aim is to improve surgery planning and to evaluate patient follow-up. The application of the proposed procedure is illustrated throug the construction of a bidimensional FEM model concerning a patient who underwent surgery for the implant of a total hip prosthesis with a six years follow-up. The paper shows that even a bidimensional individual model can give reliable clinical indications

A finite element model for the wear analysis of polyethylene inserts in total knee joints

In the present work, a wear evaluation of the UHMWPE tibial insert of a total knee joint is attempted based on a simple wear model. A user subroutine has been written and integrated into a commercial finite element program to allow for a structural-kinematic model of the joint. The kinematic model simulates the relative angular velocity and linear movements between tibia and femur during walking. The input data consist of internal-external rotation and flexion-extension angle as taken from the literature. In the simulation, the femoral and tibial components are compressed vertically under gait loads, while at different orientations as determined by the kinematic model. A stress history of each element during the gait cycle is determined. The calculation of the product between the contact pressure and the node relative velocity, as given by the kinematic model, is then used for a qualitative determination of wear map

Analisi strutturale-cinematica di artroprotesi di ginocchio mediante modelli FEM parametrici

This work represents a first investigation into a possible new approach for the design optimization of knee prostheses. The integration of a user subroutine into a commercial finite element program allowed for a structural-kinematic model of the joint. The subroutine reproduces the kinematics of the joint as described by an anatomical model. Starting from the geometry of a commercial prosthesis, different finite element models were designed. The models differ for the degree of conformity of the contact. The analysis showed a reduction of the maximum compressive stress by 15% as compared to the commercial prosthesis. At higher degrees of conformity, the compliance of the surface does not allow for a correct joint kinematics. Results obtained for the size and location of the contact area as the flexion angle increases were found to agree substantially with the experimental data of a previous wor