3d-printed sacral reconstruction prosthesis from multiscale topology optimization: A comprehensive numerical...

Sacral chordoma, an invasive tumor, necessitates surgical removal of the tumor and the affected region of the sacrum, disrupting the spinopelvic connection. Conventional reconstruction methods, relying on rod and screw systems, often face challenges such as rod failure, sub-optimal stability, and limited osseointegration. This study proposes a novel design for a porous-based sacral reconstruction prosthesis. The design framework involves a two-step topology optimization (TO) process. The first TO step is utilized to obtain the external shape of a patient-specific prosthesis, while the second TO step determines varied density fields. These fields are later integrated with graded Gyroid structures to generate the porous-based sacral prosthesis. Finite element simulations reveal several benefits of the newly developed device. Firstly, considering only solid-based TO tends to result in a highly rigid spinal movement, which may not be entirely favorable. However, the porous-based technique allows for a wider design space, enabling the sacral device's stiffness to be more comprehensively engineered. Secondly, with porous integration, the prosthesis shows potential for promoting bone integration over time, thereby providing further biological fixation and improving long-term structural stability. Thirdly, the porous-based prosthesis outperforms conventional methods such as four-rod reconstruction (FRR) and four-rod plus anterior column reconstruction (FRACR) by reducing maximum von Mises stress in the instruments by approximately 50-80 %. In summary, this study demonstrates how a two-step TO framework can create a superior sacral prosthesis, enhancing its mechanical performance and impact on spinopelvic stability. This suggests potential improvement for similar orthopedic devices in the future.