Optimisation of femoral osteotomies around the knee using the finite element method

Abstract

Introduction
Osteoarthritis (OA) is a prevalent joint disease affecting 7% of the global population in 2020. Lower limb malalignment emerges as a significant contributor to OA, presenting as varus or valgus misalignment. This deviation induces unicompartmental pathology, leading to the wear and tear of the protective cartilage. Surgical interventions, including osteotomies, are essential in managing unicompartmental knee OA. During osteotomies, hinge fractures are a common complication. This paper focuses on optimizing open wedge osteotomies, specifically exploring complications in medial open wedge distal femoral osteotomy (DFO) using finite element models. And investigates the viability of the medial open wedge DFO compared to the lateral open wedge DFO.
Method
The research employed a systematic approach to investigate ways to avoid hinge fractures in Distal Femoral Osteotomy (DFO). Finite Element Modelling (FEM) served as the cornerstone of our methodology, providing a numerical solution. The process involved the creation of finite element models from CT scans through the subdivision of femoral geometry. The automated generation of these models was facilitated by a combination of 3-matic, Mimics, and Abaqus. Using Python scripting in these different programs, a workflow for model creation and parameter variation was created. The lateral open wedge DFO model, serving as the baseline, underwent systematic alterations to explorethe impact of hinge size, osteotomy gap angle, and other variables. The creation of finite element models involved several key steps, including geometry creation, mesh generation, addition of material properties, and the application of boundary and loading conditions. Material properties were assigned based on a simplified isotropic model derived from Hounsfield units. Extra attention was given to automate the process of model generation to ensure efficiency and reproducibility.
Results
Six distinct models were created with a comprehensive analysis of their attributes and shortcomings. The study finds that the medial open wedge DFO does not induce hinge tension. Comparative analyses in both opening and loading stages reveal nuanced stress and strain differences with the lateral open wedge DFO. No clear conclusion can be given as to the viability of the medial open wedge DFO compared to the lateral open wedge DFO. In-depth exploration indicates that smaller hinges are favourable for osteotomy gap opening, while larger hinges (10mm and above) contribute to stability during loading. Minimal impact on stress concentration is observed for osteotomy gap angle variations. The study explores the effectiveness of drill holes in stress relief, highlighting precision challenges.
Discussion
Acknowledging inherent limitations such as partial volume effects and assumptions about material properties. The study suggests promising avenues for future research. Recommendations for future research include in vivo experiments, exploration of XFEM and fracture mechanics, and further refinement of modelling techniques. This study provides nuanced insights into hinge fractures during open wedge DFO, guiding future research and bridging the gap between finite element modelling and
clinical realities.