Changing Impact Angles: The Mechanics Involved in Blunt Force Cranial Trauma and Their Importance in Investigating Curb-Stomping Cases

After attending this presentation, attendees will better understand how fracture types can differ as a result of blunt force trauma produced by differing angle strikes. This presentation will impact the forensic science community by providing an experimental model that aids in the understanding of fracture mechanics produced when force is applied to the cranium from differing angles. The majority of studies on the infliction of blunt force trauma to the cranium assess only the initial impact site. This method can therefore result in a loss of essential data relating to the circumstances in which the injury was sustained. The goal of this study was to create an experimental model that would provide a more realistic picture of the damage sustained during a violent attack to aid investigators. Twenty adult pig heads (Sus scrofa domesticus) were placed on a solid base, resting on the mandible. The base could be angled so that the impact angle to the skull could be altered for each strike. Using a drop hammer rig, modified with a replica hammer head (modeled after a 16oz claw hammer), each pig head was struck once over the frontal bone from a height of one meter. A total of five angles were assessed in this preliminary study (0°, 9°, 18°, 27°, and 36°), with each angle tested a minimum of three times. It was not possible to strike the frontal region of the pig head at any angle greater than 36°. To monitor the acceleration, timing, and force of each strike, a piezoelectric accelerometer was attached to the drop hammer, with data recorded at a rate of 10,000 scans per second. Following maceration, the fractures present were compared with previously published images and descriptions, with measurements taken of the width length and depth of each depression fracture. It was noted that a number of mandibles had also fractured when struck using a more direct angle (0°, 9°, and 18°). To establish that this was a result of the impact study, a further set of pig heads were radiographed prior to the strikes. A further radiograph following the impact confirmed that the mandibular fractures had caused a transference of the force through the cranium when struck from above. A total of 22 fractures were observed between the cranium and mandible. Depression fractures (n=10) demonstrated a decrease in size as the angle increased and radiating fractures (n=4) were present on angles from 18°. Mandibular fractures (n=8) were only present up to 18° in this study, with the severity ranging from complete break to partial fractures as the angle increased. It was also noted that the angle of the fracture on the mandible differs as the angles increase. Presented here is a pilot study that exhibits the need to further investigate the issues surrounding violent assaults using blunt force trauma, such as bludgeoning with a hammer; however, an unexpected finding was the secondary trauma inflicted to the mandible as a result of resting on the solid base plate, which mimicked the scenario faced by curb-stomping victims. Although the traditional “biting the curb” posture is not exhibited in this experiment, it provides information on how the transference of force can travel through the skull and exhibit in fractures elsewhere. There are increasing numbers of reports in the media of violent crimes involving blunt force trauma taking place that utilize everyday household objects.2 It has also been highlighted in studies that blunt force trauma to the head is one of the most effective methods of murder, but that the weapons most commonly involved are hands and feet, also referred to as human strength. This study is limited by the small sample size, but has provided information that could direct further research into violent assaults using blunt force trauma. It would be beneficial to repeat the study using a larger sample size, bone substitutes to more directly simulate the cranial biomechanics of a human skull, and by modifying the drop hammer to investigate how increasing the surface area impact will affect the results