Evaluation of contact definitions in a Finite Element model of the human cervical musculature

Abstract: The human neck is especially vulnerable to severe injuries why it is of interest to gain a better understanding of the injury mechanisms involved. A 3D Finite Element (FE) model including the geometry of the individual neck muscles has been developed at Kungliga Tekniska Högskolan (KTH) and gives the possibility to study the strains inside the muscles. However, in this model the muscles are only hindered to interpenetrate and can glide relative each other with a roughly estimated coefficient of friction. The focus of this thesis has been to modify the FE-model in order to model the connectivity on a physiological basis using methods available in the used FE-software. The main reason for this was to get a more realistic muscle displacement without separations that are present in the current model. The connective tissue surrounding and connecting the muscles was modeled with two principal approaches. The first was based on a combination of FE-contacts where the material properties were contacts. The other approach was based on a new element type called Smoothed Particle Hydrodynamics (SPH) elements in combination with FE-contacts. Both approaches showed that the structural stiffness did not increase significantly, but the strain levels where somewhat elevated. Stability issues arouse with deleted elements and negative element volumes causing the FE‐contact based approach to fail prematurely. The SPH‐based approach had fewest deleted elements and completed the simulation but increased the calculation time with approximately 50 %. It was concluded that the implementation of a connection between the muscles had a relatively low influence on the strains and kinematics of the neck and could be used to avoid muscle separations. The influence on stability of the model was however more evident and the most stable result increased the calculation time significantly.