"HyperMesh finite element modeling and morphing tools have been fundamental to the development of the Wayne State University Brain Injury Model"
– Dr. King H. Yang
Professor of Biomedical Engineering Professor and Bioengineering Center Director, Wayne State University
Biomedical studies of human concussion that relate mechanical input to localized brain tissue deformation, pressure, and stress/strain response are needed to
properly assess brain injury development. A meaningful head injury criterion must identify a threshold below which no loss of function occurs, and a ceiling beyond
which irreversible changes to brain function occur. Such information is crucial to the design of effective head protection systems. Computer models capable of simulating impact events provide significant assistance to researchers in the development of threshold criteria for MTBI. Finite element (FE) based computational models of the human head are now capable of simulating fine anatomic detail and tissue-level characteristics for impacts leading to injury. The Wayne State University
Head Injury Model (WSUHIM) is the most sophisticated of several FE models developed for head injury assessment. Introduced in 1993, WSUHIM has a long history of
development using Altair’s HyperMesh as its exclusive modeling platform.
Method for Modeling Traumatic Brain Injury Data from Football Field Events
NFL players play four preseason, sixteen regular, and additional playoff games each season. Approximately 150 players are diagnosed with apparent or suspected MTBI every year. During 2003-04, a research study identified several confirmed concussion cases gathered from team physicians who treated the injured players. Game videos of the confirmed cases were then used to determine head kinematics, including impact velocity and location.
Laboratory-based reconstructions of the impact events were conducted by using two Hybrid III anthropomorphic test dummy heads wearing exemplar helmets similar to
those worn by the injured players. The two Hybrid III heads were each instrumented with nine linear accelerometers and the heads were attached to Hybrid III necks
instrumented with six-axis load cells. The injured (usually the struck) player was represented as a stationary helmeted head form, while the non-injured (usually
the striking) player was represented by a helmeted head form that moved at the relative velocity derived from the game video (Fig 1).
Using the laboratory-derived head kinematics data, case-by-case FE-based simulations were completed using the Wayne State University Head Injury Model (WSUHIM).
The model has fine anatomic detail of the cranium and brain with more than 300,000 HyperMesh elements (Fig. 2).
The WSUHIM simulates all essential features of a 50th percentile male head, including 15 different material properties for the brain and surrounding tissues. The model includes viscoelastic gray and white brain matter, membranes, ventricles, cranium and facial bones, soft tissues, and slip interface conditions between the brain and dura. The WSUHIM used in this study was modified by Dr. Liying Zhang to improve mesh quality and material definitions. HyperMesh enabled these changes to be made efficiently and accurately. The cranium of the modified FE model was loaded by translational androtational accelerations measured from 24 laboratory head impact reconstructions. “HyperMesh finite element modeling and morphing tools have been fundamental to the development of the Wayne State University Head Injury Model” said Dr. Yang
Simulation Results and Proposed Head Injury Criterion
The FE simulations allowed for predictions of the intracranial pressure distribution and local stress/strain of intracranial mechanical responses for a given input associated with either a concussion or a non-injury event.
For this study, the mechanical response parameters of intracranial pressure and brain shear stress, both predicted by the simulation model, were selected as the most
promising indicators of MTBI. Statistical analyses were completed to assess relationships between injury outcome and head kinematics. The following conclusions
resulted from the simulation study:
- It was concluded that intracranial pressure can serve as a global response indicator for MTBI.
- High translational shear stress concentrations were found to be localized in the upper brain stem and thalamus regions. The induced shear stress may alter brain function leading to mild brain injury.
- Linear regression analyses of the simulation results showed that translational head acceleration had a greater influence on intracranial pressure responses in comparison with rotational acceleration (Fig 3).
- Predicted shear stress response in the upper brainstem was the best injury predictor over other brain response parameters, based on linear logistic regression analyses (Fig 4).
An injury tolerance based on head kinematics was also proposed, applicable to football and across a broad range of activities. Altair HyperMesh played a key role in providing accurate finite element modeling capability for these studies and has been the exclusive mesh modeling tool for the WSUHIM since its inception in 1993.