Comparative analysis of stress-strain state of mathematical models for an individual endoprosthesis and allocomposite endoprosthesis in case of replacement of long bone defects

Abstract

Background. Replacement of post-resection defects of long bones in case of a tumor process is always an urgent problem of orthopedics. Among the wide variety of materials and methods for reconstruction of post-resection defects of long bones, the most common are individual, modular arthroplasty and bioreconstructive interventions. To study the mechanical properties of the structures we have chosen, various types of post-resection femoral bone defect replacement were simulated using the finite element method. The purpose was to compare the data on stress-strain states in mathematical models “allocomposite endoprosthesis” and “individual endoprosthesis” of the proximal femur. Material and methods. Mathematical models of the femur with the formation of a post-resection proximal defect replaced by a segmental bone allograft in combination with an individual endoprosthesis have been created. The model is presented in two versions, with the formation of transverse and step-cut osteotomy. Each model was examined separately with cement and cementless attachment in the area of the endoprosthesis stem. For comparison, we chose a model with complete replacement of the proximal end of the femur with an individual endoprosthesis without bone grafting. Results. Femur step-cut osteotomy can significantly reduce the level of stress in the osteotomy area. This is due to the fact that performing the step-cut osteotomy allows the bone fragments to provide resistance to shearing movement. The use of bone cement can significantly reduce the level of stress around the stem of the endoprosthesis in both variants of femoral osteotomy (transverse and step-cut). This is due to the fact that bone cement, which has an elastic modulus at an intermediate value between titanium and bone tissue, forms a layer between them, performs a damper function, that smoothes the difference in deformation values of the metal and bone tissue, thereby reducing the level of stress in them. Arthroplasty without performing bone grafting leads to increased stresses in the bone tissue due to the presence of a rigid support on the cortical bone endoprosthesis in the diaphysis along the line of its resection. Conclusions. Performing step-cut osteotomy of the femur reduces the level of mechanical stresses in the osteotomy area by half compared to models with transverse osteotomy, which is of particular importance in the early postoperative stages. The use of bone cement for fixing the stem of the endoprosthesis can also significantly reduce the level of stress in all variants of the studied models, due to the formation of a damping layer between the metal and the bone tissue. The level of stress in models without bone grafting does not depend on the use of bone cement, but is determined by the presence of a rigid support of the endoprosthesis on the cortical bone along the line of its resection.