Development of a hybrid finite element model for individual simulation of intertrochanteric osteotomies

Intertrochanteric osteotomies of the proximal femur are used to improve the anatomy and function of the hip joint in a number of orthopaedic diseases. To investigate the geometrical and biomechanical aspects of pre-operative planning we created a set of programs to automatically per-form a simulatio n of intertrochanteric osteotomies on a three-dimensional finite element mo del of the human proximal femur based on computed tomography (CT) data and using uniform brick-shaped elements. To eliminate artefacts resulting from the rough surface of the brick elements, the femoral head was represented b y a tetrahedron-based head that included a cartilage layer and a subchondra l cortical zone. Applicability of the procedure was tested by performing a parametric study using a model created from CT scans taken in vivo, by appl ying individually calculated force conditions for the one-leg stance situat ion. We found a large influence of osteotomy angle on the observed stress i n the femoral head cartilage, especially in a situation with insufficient c ontainment of the femoral head. The model presented here is a biomechanical tool to simulate intertrochanteric osteotomies patient-specifically for a better understanding of the effects of such operations in the individual ca se. The open design of the described programs allows future interfacing wit h surgical navigation and robot systems. (C) 2001 IPEM. Published by Elsevi er Science Ltd. All rights reserved.