Development and Validation of a Subject-Specific Finite Element Model for Skull Fracture Assessment

Due to the frequent occurrence of skull fractures from unintended head impacts from kinetic energy weapons, there is an immediate need to develop injury assessment tools for evaluating the risk of skull fracture under the high speed projectile impacts. Skull fracture tolerance has been shown to be dependent on impactor characteristics such as size and shape, as well as subject-specific anatomy. Accurate strain data collected at the fracture location has historically been difficult to measure, which has led to the use of finite element models. Prior research however has used generic finite element (FE) models of the head to determine skull strain and establish FE-based fracture criteria and thus may not be reflective of actual strain in the experimental tests, leading to inaccurate criteria. Additionally, prior FE models have not demonstrated the ability to accurately model fracture patterns. This study reports on two blunt ballistic temporo-parietal head impacts carried out to a post-mortem human subject (PMHS) and the development and validation of a subject-specific FE model. A nine-accelerometer array was mounted to the frontal bone to measure linear and rotational head accelerations. Three rectangular Rosette-style strain gauges were utilized to collect bone strain data surrounding the impact sites. A rigid, flat-faced 38.1 mm diameter projectile with a mass of 0.1 kg was used for all impacts. An accelerometer was mounted to the rear aspect of the projectile for measurement of impactor acceleration and from which impact force was calculated using the projectile mass and applying Newton’s Second Law. A subject-specific finite element head model was developed from the PMHS CT images. Results demonstrated good correlation between experimentally collected strain and accelerometer data to the FE model. The fracture patterns predicted from the model also demonstrated good agreement to fractures observed in the PMHS.