Simulation-Based Design of Orthopedic Trauma Implants

A computer-aided simulation model is developed to aid in the design and optimization of orthopaedic trauma implants. The developed model uses digital imaging, computer-aided solid modeling, and finite element methods in order to study the effects of various geometric parameters of fixation devices in orthopedic surgery practice. The results of the present simulation model would lead to the determination of the optimum implant design that provides the best match with the geometry of the human femur — reducing the risk of over-stressing bone tissue during implant insertion. The effectiveness of the presented simulation model is demonstrated through the design of intramedullary (IM) nails used in treating femoral shaft fractures. CT scans were taken of forty intact human femora. A technique was developed in order to digitally reconstruct the scans into 3D solid models using image segmentation, surface simplification, and smoothing methods while maintaining accurate representation of the original scans. Each resulting surface model is characterized by a network of nearly equilateral triangles of approximately the same size allowing for quality finite element meshing. Femoral lengths, curvature, shaft diameters, and location of maximum curvature were then quantified. An average geometric model was then generated for the investigated sample by averaging corresponding nodal coordinates in each femur model. Using the average model, a length-standardized function representing the curvature of the medullary canal was derived to create a geometrically optimized IM nail for the entire sample. “Virtual surgery” simulating the insertion process was then performed using finite element methods in order to validate the proposed optimal IM nail design. The results of both the optimum nail and a current nail were compared using the femur having the highest curvature in the sample. The present study shows that the developed simulation model leads to a nail design that reduces the insertion-induced stress within the femur to an acceptable level compared to current nails.