Evaluation of a combination of continuum and truss finite elements in a model of passive and active muscle tissue.

The numerical method of finite elements (FE) is a powerful tool for analysing stresses and strains in the human body. One area of increasing interest is the skeletal musculature. This study evaluated modelling of skeletal muscle tissue using a combination of passive non-linear, viscoelastic solid elements and active Hill-type truss elements, the super-positioned muscle finite element (SMFE). The performance of the combined materials and elements was evaluated for eccentric motions by simulating a tensile experiment from a published study on a stimulated rabbit muscle including three different strain rates. It was also evaluated for isometric and concentric contractions. The resulting stress-strain curves had the same overall pattern as the experiments, with the main limitation being sensitivity to the active force-length relation. It was concluded that the SMFE could model active and passive muscle tissue at constant rate elongations for strains below failure, as well as isometric and concentric contractions.

Investigation of Conditions that Affect Neck Compression- Flexion Injuries Using Numerical Techniques.

A Finite Element (FE) model of isolated head and neck complex was developed aiming to investigate the mechanisms of injury from axial impacts, in the sagittal plane, and the injury thresholds from experimental studies reported in the literature. The model was validated on a local and a global level, showing a significant correlation with experimental investigations and thereby having the potential to predict both reported injuries and dynamic buckling modes. The frequently reported Hangmans' fracture was predicted to occur at an axial load of about 3.5 kN and at a local injury threshold of 191 MPa in the compact bone of C2. Also, when analyzing an experimentally designed inner roof of a vehicle, the FE model showed that an induced anterior translation of the head reduced both stress and forces of the cervical spine bone. Moreover, the recent FE model suggests that combined compression/flexion may result in less severe injuries compared to pure compression or compression extension.

An experimental head restraint concept for primary prevention of head and neck injuries in frontal collisions.

The Experimental Head Restraint Concept (EHRC), a 'safety belt' for the head, is designed to reduce forces to the head and neck, in frontal car crashes. The EHRC was evaluated experimentally in frontal collision for a crash severity of 11 m/s, and numerically in frontal collision for a crash severity of 11 and 15 m/s. Experimental data obtained from a frontal barrier test (11 m/s) showed a 67% reduction of the HIC value from 411 (without EHRC) to 136 (with EHRC). The same level of reduction was also obtained for the higher speed in the numerical simulation. The moment in the neck was shown in experimental configuration to increase a few percent using the EHRC, but as presented in a numerical analysis, the moment was reduced by stiffening the EHRC. The EHRC clearly has a potential role in the search for primary prevention of neurotrauma injuries in frontal related car crashes. However, there is a strong need for more advanced injury criteria for the neck in order to optimize such complex safety systems.