Finite Element Simulation and Analysis of the behavior under load of a human shoulder
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This document details a finite element analysis study of human shoulder behavior under load, specifically for a violinist's routine. The study aims to improve tendon and ligament modeling while optimizing computational resources, and it presents various methodologies for mesh generation and interface modeling. Results indicate effective simulation of stress distribution at tendon insertions and ligaments, leading to recommendations for future research on simplified muscle models applicable across different disciplines.
Finite Element Simulation and Analysis of the behavior under load of a human shoulder
- 1. Finite element simulation and analysis of the behaviour under load of a human shoulder Manuel Islán, Emilio Lechosa, Fernando Blaya, Roberto D'Amato, Juan Antonio Juanes and Enrique Soriano
- 2. 1. Background Based on the finite element model (FEM) done to study the behavior of the glenohumeral joint under different postures that represent the routine of a violinist (1), is done this study improving the analysis by improving tendon insertion on bones and adding ligaments and cartilage to the model as well. (1) Manuel Islán, «Linear approximationof thebehavior of therotatorcuffunder fatigue conditions. Violinist case study», Jounal of Mecicalsystem, pp 1, 2017
- 3. 2. Objetives Characterizing behavior of a human shoulder using finite element analysis techniques, main aims are: • Improve tendon insertion for a better effort application on bones. • Cartilage behavior definition • Ligament behavior definition
- 4. 3. Methodology (1), solid reconstruction Starting from a cloud of points, obtained from a resonance, the reconstruction of the bones and muscles involved in the joint is done by using Geomagic Design X software. This tool is able to generate surfaces supported on the points of the cloud, and so, generate a 3D surface representing the solid.
- 5. 4. Methodology (2) solid reconstruction These solid representing bones and muscles are used to model the joint. In this model can be measured distances, positions, angles and so on, needed to define ligaments, tendons or muscles positions.
- 6. 5. Methodology (3) mesh generation. To create the mesh used on FEM, different element type has been used for different components on the joint. • Bones: 3D tetrahedral elements, 10 nodes. • Muscles: 3D tetrahedral elements, 10 nodes. • Tendons: 3D tetrahedral elements, 10 nodes. • Ligaments: 1D linear beam elements, 2 nodes. • Ligaments insertion. Rigid elements. • Cartilage: gap elements, 2 nodes.
- 7. 6. Methodology (4) tendon interface There are two main way to solve interface between tendon and muscle. • Contact modeling at interface area. ü In this case there is no join between bone mesh and tendon mesh, but an algorithm that simulate behavior when contact exist between two parts. ü This method needs more computing resources to get solved, is a iterative procedure and so, more time is needed. ü Meshes can be done independently one from the other. • Node merging at interface area. ü In this case both mesh, bone and tendon meshes, share same node at the interface area between them. ü Requires less resoruces to get solve, is faster and “cheaper” ü Meshes must be done dependently one to the other.
- 8. 7. Methodology (5) tendon interface The method used in this study is the node merging technique. Following images show the nodes located on the humerus head, where the area correspond to the tendon insertion, and nodes on the tendon where is inserted in the humerus. Both nodes distributions are coincident in 3D coordinates, so merging implies that same node belongs to humerus and tendon, and so, effort transmission between parts is done in a better way.
- 9. 8. Methodology (6) ligament modeling Ligaments are modeled as linear beam, 1D, elements between two nodes on the model. These elements are characterized by section and material properties. In the image, superior, middle and lower glenohumeral ligaments are shown. Inserting these ligaments (2) directly onto one node of the bones would imply certain stress concentrations on those nodes. In order to avoid this, rigid elements (3) have been modeled, at the end of the ligaments, to distribute efforts on that area properly.
- 10. 9. Methodology (6) glenohumeral capsule modeling Glenohumeral capsule is considered as a ligament distribution joining humerus head and scapula. It has been modeled following same criteria that ligaments, but in this case several ligaments have been modeled surrounding the humerus head, where the capsule is located. These ligaments that give form to the capsule are considered cylindrical and 3 mm diameter. Can be found in the image in blue color.
- 11. 10. Methodology (7) cartilage modeling Cartilage are modeled as linear gap, 1D, elements between nodes on areas of the joint involved, humerus and scapula These elements are characterized by a stiffness value and a gap distance. They only transmit efforts in their axial direction, and they only transmit this efforts along compression direction They are shown in blue color.
- 12. 11. Analysis, load cases Three different load cases have been considered in the study. As seen on following table, load cases 2 and 3 can be resumed in the image shown. LOAD CASE (LC) LOAD CONDITIONS 1 Gravity applied along negative Z axis (9.841 m/s²) 2 Gravity applied along negative Z axis (9.841 m/s²) + 50 N applied on wirst location along positive Y axis 3 Gravity applied along negative Z axis (9.841 m/s²) + 50 N applied on wirst location along negative Z axis In all three load cases have been fixed the area on the scapula marked on a red discontinuous line.
- 13. 12. Results. Stress distribution As a sample, the stress distribution shown on image represent the first load case. As it can be seen, stress is located on ligaments insertion and tendons. Where it should be.
- 14. 13. Results. Tendon and cartilage area.
- 15. 14. Conclusions This study validates the FEM developed presenting a first qualitative study of the performance of the joint, optimizing computing resources to solve it, and minimizing solving time. • Tendon insertions works properly with node merge technique applied, this imply best performance in solving equations that contact simulation. • Ligaments, and their insertions, modeled as 1D elements, are the best approximation to these areas • Cartilage, modeled as a gap element, shows a correct performance.
- 16. 15. Future investigations On next steps of the study the objective will be simplifying the muscle model to a 1D linear element, this imply considering. • The Young´s modulus of muscle is not linear. • The section of the muscle varies depending on the position the joint is located. Once done, the model could be applied on several disciplines and load cases for this or other human joints, applicable on these, but not only, fields. • Sports practice • Working conditions
- 17. Thank you for your attention