Pipeline for Specimen Specific Bone-Ligament-Cartilage Finite Element Models

Specimen-specific finite element (SS-FE) models are becoming more common as their use enables the elucidation of the effects of individual anatomy. However, despite their increased prevalence, they remain laborious to produce. The goal of this study was to develop a method to automatically generate SS-FE models that are representative of the bones, ligaments, and cartilage so that anatomical variation can be represented in models of experimental scenarios. Bones from a template model were morphed to the bone surfaces taken from CT data using an adapted morphing process. Elastic registration was used to map a template FE mesh onto target surfaces taken from CT data. The way this mesh was mapped was used to inform the morphing of the insertions sites of ligaments and cartilage (soft-tissues). In this way, the soft-tissue insertions were also morphed. Ligament wrapping around bony surfaces was added to allow for physiologic mid-substance loading. Cartilage thickness was addressed by checking for penetration between cartilage pairs. Material properties and contact definitions were transferred from the template model to the SSFE model. Using this methodology, an existing lower extremity finite element model, including 30 bones, 113 ligaments, and 35 cartilage pairs, was morphed to three lower extremities of varying anatomy: a 5 percentile right female lower extremity, a 95 percentile left male lower extremity, and a 50 percentile right male lower extremity. Morphing for each of the specimens took three to four hours. This process from CT to SS-FE model has the potential to leverage the strengths of parametric computation simulation in concert with experimental test setups to a degree not previously achieved.