Improvements and Validation of THUMS Upper Extremity : Refinements of the Elbow Joint for Improved Biofidelity

Abstract: Introduction One out of five reported motor vehicle collision injuries occur to the upper extremities. Certain parts of The Total HUman Model for Safety (THUMS) lack validation against experimental data, including the elbow. The aim of this project is to refine and validate the elbow joint of THUMS, with focus on anatomical response of the elbow during axial impact applied to the wrist. Methods Internal contacts in the elbow were modified and new contacts assigned between bones and ligaments of the elbow. The posterior part of the radial- and ulnar collateral ligaments, and joint capsule was implemented to the model. Elasticmodulus of the cortical bones of the elbow was increased as well as the shell thickness of the humeral cortical bone. The updated model was validated against an experiment where an axial load was applied to the wrist of a female cadaver. The experimental resultant force in the wrist was then compared with the wrist force obtained from the simulations. Results The correlation between the experimental and simulation resultant wrist force for the updated model resulted in a CORA score of 0.882. This gave a 6.7% higher CORA score compared with the original model. Hourglass energy was reduced from 63.52% of internal energy to 0.78%. Energy ratio and contact energies indicated that the simulation was stable. Discussion Movement of elbow bones was assessed to be more anatomically correct, by accounting for the posterior ligament and elbow capsule support. The contact peak force in the humerus was lower and occurred earlier in the simulation in the updated model compared to the original. This is believed to be due to the reduced gap between the elbow bones after increasing the shell thickness of the humeral cortical bone. The model setup resembled the experiment in a good manner. Conclusion The upper extremity of THUMS was refined for improved biofidelity, with focus on the anatomical response of the elbow joint under an axial impact. However, further model improvements are suggested as well as extended validated against other experimental impact results.