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Read MoreIt’s common that rear-end collisions result in symptoms of whiplash. To determine how these symptoms develop, we must first consider the laws of physics. Newton’s first law of motion states that a body at rest will remain at rest, and a body in motion will remain in motion, unless it is acted upon by an external force. This means that when a vehicle is stationary, the occupant within the vehicle will be at rest or, when the same vehicle is moving, their body will travel at the same speed as the vehicle.
Let’s apply Newton’s first law to an in-line collision scenario where a stationary vehicle is rear-ended by another vehicle. To assess the occupant kinematics within the target vehicle (i.e., the vehicle that gets struck from the rear), collision reconstructionists must break the collision into three distinct phases: pre-impact, engagement, and separation:
The occupant kinematics (i.e. the motion of the occupants inside the target vehicle) changes during each phase of the collision:
Understanding the occupant kinematics, it becomes possible to identify the most common symptoms of whiplash from a rear-end collision.
Head, shoulder, or neck injury symptoms are typical symptoms reported after rear-end collisions. In minor and moderate rear-end impacts, a forensic biomechanical engineer will typically see soft tissue symptoms, primarily in the cervical spine. As the severity of the rear-end collision increases, the risk of injury also increases. In moderate and severe cases, we see the soft tissue neck pain turn into a whiplash diagnosis.
Signs of a whiplash injury from a rear-end collision include headaches, shoulder pain, and/or neck pain. When serious whiplash symptoms from a motor vehicle collision are left untreated, the initial symptoms could develop into chronic symptoms. How long the whiplash symptoms will persist depends on physical therapy interventions, the severity of the collision, and other unique factors that are case and occupant dependent.
Biomechanical engineering analysis applies the concepts of mechanical engineering to biological structures of the human body (such as joints, bones, muscles, tendons, or ligaments). This is a forensic biomechanical engineer’s area of expertise and it helps determine how different parts of a person’s body would respond to the forces resulting from rear-end collisions.
A forensic biomechanical engineer can also assess the severity of the collision, along with other contributing factors, and compare all the evidence to the risks of short-term and long-term whiplash, as well as other reported injuries from a rear-end collision. A forensic biomechanical engineer can also take into account an occupant’s past medical history when assessing these risks.
We would like to thank Karla Cassidy, B.A.Sc., M.A.Sc., P.Eng., for providing insight and expertise that greatly assisted this research.
Karla Cassidy is a Senior Engineer in J.S. Held's Accident Reconstruction Practice. Ms. Cassidy has been an active member in the biomechanics community since 2006 and in the accident reconstruction industry since 2010. Her expertise spans both biomechanical and mechanical engineering. She has been involved in hundreds of cases involving vehicles, pedestrians, motorcycles, farm equipment, and cyclists. Her specialty areas are biomechanics, personal injury, injury probability, seatbelt usage, slip, trip and falls, and determination of occupant position. Ms. Cassidy also conducts collision reconstruction and damage consistency analyses. She is a published author and has provided litigation support.
Karla can be reached at [email protected] or +1 416 977 0009.
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