[Theoretical analysis of changes in femoral stresses after total hip arthroplasty]

Changes in bone stress in the proximal femur following implantation can be estimated with the use of composite beam theory. The aim of this study was to construct the mathematical analytical models for predicting the degree of stress shielding and to test the validity of the predictions using finite element simulation. To define the periprosthetic bone stress values, the proximal femur was divided into eleven equidistant cross sections, then each section was divided into four quadrants corresponding to the anterior, posterior, medial and lateral aspects of the femur. Bone stress values were calculated by both mathematical analytical models and finite element analysis, then linear regression analyses produced slopes and R-values that show numerical and finite element results corresponding well to intact femur and both the types of fixation with/without cement. And the results also showed that femoral bone stress shielding by both the prostheses occurred in most periprosthetic zones. The most serious regions occurred in the proximal medial quadrant. This study has succeeded in creating the mathematical analytical models to predict the bone, cement and prostheses stress values, and thus can help us to evaluate the mechanical behavior of total hip replacement, to further understand the distinction between different fixation, and to make advances in implant design, surgical technique and long-term results.