Theoretical Analysis Of Changes In Femoral Stresses After Total Hip Arthroplasty And Relationships With Relevant Clinical Factors

Background: Femoral bone remodeling following cemented total hip arthroplasty has long been observed radiographically. A detailed, histologic, and histomorphometric analysis of autopsy specimens from patients who previously had cemented total hip arthroplasty has helped to elucidate the skeletal response to components. Mechanical events tended to predominate the early mode of destabilization of femoral components with debonding at the metal-cement interface and fracture in the cement. Clinical and experimental evidence suggest that periprosthetic bone loss following total hip arhroplasty is caused by stress-shielding. Bone adapts and remodels in response to applied stress patterns in accordance with Wolff's law, which states that a bone develops a structure most suited to resisted the factors acting upon it. Areas of bone experiencing high stress will response by increasing bone mass, and areas under lower stress will response by decreasing bone mass. It has been shown in in vitro studies that the loading pattern of the proximal femur is rather complex and the etiology of periprosthetic bone loss in multifactorial such as flexible distal stem, stem stiffness, thicknessof cement mantle, various offset and anteversion.Objective: To construct a mathematical theoretical analyses models to evaluate the methanical behavior of cemented and cementless total hip arthroplasty which have results in an improved understanding of the interaction between implant and alsoresults in improvement in implant design, surgical technique and long-term results. Methods: Changes in bone stress in the proximal femur following implantation can be estimated with use of composite beam theory. The aim of this study was to construct the mathematical analytical models to predict 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 whether the numerical and finite element results corresponded well for intact femur and both type fixation with or without cement. Then using the former mathematical analytical models to analysis the typical metaphyseal and diaphyseal sections for each fixation and to find out the difference of stress distribution by different fixation with or without cement, various offset, various anteversion and various cement mantle thickness.Results: Linear regression analyses produced slopes and R-values that shownumerical and finite element results corresponded well for intact femur and both type fixation with or without cement. The mathematical analytical modes has been proved successful and it also be used to improved study many clinical related factors such as fixation type, various offset and anteversion , various cement mantle thickness. And the results also showed femoral bone stress shielding by the both prostheses occurs in most periprosthetic zones. The most serious regions occurred in the proximal medial quadrant. And the stress-shielding value was higher in cementless prosthesis than cemented one.The variations in implant anteversion and offset lead to changes in the loading of the proximal femur, and causing critical conditions to both bone and cement. Stess on the anterior and posterior aspects were more markedly affected by adjusting the anteversion angle from staright to 30 degrees than medial and lateral aspects. Therewas a highly significant correlation between stress on the side toward which the prosthetic neck was oriented and the extent of neck version. In metaphyseal section, the bone and cement stress were nonlinear raised by increasing offset. But in diaphyseal section, during offset from 30mm to 55mm, the stress of bone and cement de...