People whose heads are turned at the time of a rear impact collision risk a much more serious whiplash injury, with potentially chronic symptoms, and a Yale School of Medicine study explains why.
“We believe this is the first study to identify, quantify and determine the mode of cervical spine injury sustained during a rear impact collision when a person in the vehicle has their head turned,” said Manohar Panjabi, a professor in the Departments of Orthopedics and Mechanical Engineering and first author of the study in Spine. “This data may assist clinicians in developing improved diagnostic and treatment protocols.”
Previous clinical studies have found that people sitting in a vehicle with their heads turned at the time of rear-impact sustained more severe injuries and longer lasting symptoms. These studies show that the rotated head posture was the major factor causing more severe chronic symptoms, even when considering the presence of a head restraint and the state of preparedness.
Panjabi and his co-authors performed rear impact simulations with the head turned at the time of impact using six human cervical spine specimens and a sled apparatus. They determined the severity of the neck ligament injuries due to four different impact accelerations ranging from 3.5 to 8 g (force, mass times acceleration). Neck ligament injury was first detected at 5 g and at the C5-C6 spinal level. At higher impact accelerations, the injuries became more severe and spread throughout the neck.
The researchers directly compared their findings with those obtained in their previous study of rear impact with head facing forward at the time of impact.
Rotated head posture at the time of rear impact caused significantly greater neck injury severity and more complex injuries, as compared to facing forward.
They hypothesize that there are more severe and complex injuries for two reasons.
First, there is an initial stretch in the neck ligaments, which is not present when the head is facing forward. During the rear impact, the ligaments are stretched further. This over-stretching of the ligaments can cause ligament tears and spinal instability, leading to neck pain. Second, rear impact with rotated head posture causes three-dimensional head and neck motions, as compared to only two dimensional motions in the head forward posture. These three-dimensional motions cause more complex types of neck injuries.
Co-authors include Paul Ivancic, Travis Maak, Yasuhiro Tominaga, M.D., and Wolfgang Rubin.
From SPINE 31: 420-429
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