When injury causation is in dispute following a pedestrian strike incident, a biomechanical reconstruction of the event is sometimes necessary to confirm or refute eye-witness testimony. In this article, biomechanical expert Carolyne Albert provides an overview of the methodology and type of information that can be determined in these investigations through the lens of an actual incident.
Biomechanical Reconstruction of a Pedestrian Struck by a Vehicle
Injury analysis can provide insight into the movement, positioning, and orientation of a pedestrian at the time the vehicle impact occured. Within the context of a specific crash, biomechanical experts can conduct investigations utilizing information such as diagnosed injuries (as specified in the medical records), anthropometrics of the pedestrian involved, vehicle information including damage, and site evidence to arrive at scientifically supported opinions.
Foundational Principles of Biomechanical Engineering
A properly conducted injury causation analysis is rooted in the application of biomechanical engineering. Biomechanics is the science that deals with the time and space response characteristics of biologic solids, fluids and viscoelastic materials to imposed internal and external forces. In more general terms, biomechanics is the science of how the human body responds to applied external and internal forces. Injuries can result due to specific applied loads. A capable biomechanical expert is able to examine specific injuries and use reverse engineering by applying knowledge of injury mechanics to determine if the pathologic loading was provided within the event in question to cause the injuries claimed.
There are three basic types of loading: tension (pulling), compression (crushing) and shear (sliding). Other modes of loading are combinations of these three basic modes.
Failures of biologic materials (injuries) can occur when the applied loads due the event generate the necessary type and direction of forces that exceed the material’s injury threshold. These forces are typically abnormal, excessive, and often unexpected. In biomechanics, this is sometimes referred to as pathological loading.
The representative incident we will review for this article involves a pedestrian who was struck by a mid-size SUV. Absent video evidence, the parties to the crash were in disagreement over the struck-pedestrian’s position in the roadway and orientation at the time of impact.
The struck-pedestrian claimed that, at impact, he was standing at his mailbox facing south (towards his house), at least 6 feet from the fog line (white line on the edge of the road that delineates the driving lane, also known as edge line).
Pedestrians commonly sustain more severe injuries to the vehicle-impact side of their body. The pedestrian was diagnosed with a left pubic ramus fracture, left-sided facial injuries and right-sided lumbar spine transverse process fractures.
The vehicle, which was traveling east at the time of impact, exhibited damage to the driver’s side grill and hood as well as a spiderweb fracture of the driver’s side lower windshield. Biomechanical analysis of the physical evidence in this case revealed that the injuries were consistent with the vehicle striking the pedestrian on the left side of the body, generating the lateral compression and lateral bending of the pelvis and lumbar spine, respectively, necessary to cause the diagnosed pelvic and spinal fractures.
This contact caused the pedestrian to move on top of the hood of the vehicle, resulting in left head/face impact with the driver’s side windshield. The left-sided facial fractures were comminuted, indicating a high energy impact, which was consistent with the spidering on the windshield that radiated from a central point on the lower driver’s side, indicating a focal impact.
Based on the position and orientation of the pedestrian at the time of impact, we determined that the pedestrian was standing upright, facing north, and near the centerline of the roadway.
Our biomechanical investigation based on the physical evidence, including the diagnosed injury pattern, the vehicle information and resulting damage, and the scene of the incident, determined that the struck-pedestrian was not standing at his mailbox facing south (away from the roadway), as he claimed. Instead, he was standing upright, facing north near the centerline of the road at impact.
BIOMECHANICAL ENGINEERING INVESTIGATIONS
The biomechanical experts at Robson Forensic provide scientific and analytical evaluation of injuries to determine causation. Our experts are engaged when the cause or mechanism of an injury is not known, is not understood, or is in dispute.
Injuries tell a story. Could a fall have occurred as testified? Were the forces great enough to have caused the injuries claimed? Was the known mechanism (direction and type of loading) of injury provided in the event? Is the injury consistent with the physical evidence? The biomechanical engineering experts at Robson Forensic can help address these questions in their forensic investigations.
For more information submit an inquiry or contact the author of this article.
Mechanical Engineer & Biomechanics Expert
Dr. Albert is an expert in mechanical engineering with specific expertise in orthopaedic biomechanics. She has over 15 years of experience in biomedical and materials engineering research. She is an adjunct research professor at Marquette University’s Orthopaedic and Rehabilitation Engineering Center and has a scientific staff appointment at Shriners Hospital in Chicago. Dr. Albert holds a Ph.D. from the University of British Columbia, and her work has been published in the Journal of Biomechanics, Bone, Clinical Biomechanics, and the Journal of Bone and Joint Surgery.