Track 6. Technological innovations in biomedical training and practice Authors: Manuel Islan, Emilio Lechosa Urquijo, Fernando Blaya, Roberto D'Amato, Juan A. Juanes and Enrique Soriano Heras

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