Finite Element Analysis of the scaphoid in a falling onto outstretched hand scenario

Author: Liem Luong

Luong, Liem, 2021 Finite Element Analysis of the scaphoid in a falling onto outstretched hand scenario, Flinders University, College of Science and Engineering

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Plain radiographs are the first imaging technique used to determine the presence of a scaphoid fracture. Due to the alignment of the fracture orientation and radiograph plane, scaphoid fractures can be missed. There are no current methods to determine the orientation of scaphoid fractures prior to an x-ray. Previous analysis of the wrist and scaphoid have not measured the stress and strain distributions on the scaphoid and investigated the influence of simulating wrist ligaments on finite element solutions. To investigate the stress and strain distributions on the scaphoid, 8 finite element models of the scaphoid from CT data from Brown University created in MATLAB were analysed in a falling onto outstretched hand with radial deviation scenario using FEBio. To investigate the influence of ligaments on FE analysis of the scaphoid, ligament attachment sites are mapped onto the scaphoid using a statistical model, iterative closest point algorithms and knnsearches and small tensile forces are applied at the mapped locations. In all simulations, the most significant stresses and strain occurred on the dorsal edge of the scaphoid. When comparing simulations between models with and without ligaments, the addition of ligaments was found to decrease the minimum stress and strains in unsmoothed models by 13.04% and 11.02%, and 11.4% and 14.8% in smoothed models. When comparing the influence of smoothing the mesh, there is a significant decrease in stress and strain distributions in both ligament and no ligament simulations. Due to the lack of scaphoid specific patient information, the same force was applied to all scaphoids, therefore the numerical stress and strain distributions are difficult to analyse, however, the stress and strain patters are similar to common fracture patterns where the most significant stress and strains are on the dorsal side of the scaphoid. Although there is a significant numerical increase in minimum stress and strain due to ligament simulation, there is no or little statistical significance in the changes therefore, the effect of ligament simulation was found to be insignificant overall. In the smoothing process of the meshes, there is an increase in volume of each model, which is likely to be the cause of observed decrease in stress and strain, however, further analysis is required. Future work on simulations of stress and strain simulations on the scaphoid will require the better assumptions and application of the ligament and falling force vectors.

Keywords: Finite Element Analysis, scaphoid, scaphoid fracture, fall, statistical model

Subject: Engineering thesis

Thesis type: Masters
Completed: 2021
School: College of Science and Engineering
Supervisor: Dr. Rami Al-Dirini