Relationships Between Initial Clinical Findings and Accident Mechanisms
By Richard H. Adler
April 13, 1994
A recent study published in Neurology examined the relationship between initial symptoms following a acceleration-deceleration motor vehicle accident (whiplash injury) and certain mechanical features of the accident.
Dr. Matthias Sturzenegger, et al., in Presenting symptoms and signs after whiplash injury: The influence of accident mechanisms, studied the following factors in 137 motor vehicle accident patients:
- Accident Mechanisms
- Position in the car
- Use of seat belts
- Head rest
- Point of contact between head and head restraints
- Damage to seat
- Head position
- State of preparedness of occupant at moment of impact
- Type of collision
- Intensity of post-accident head and neck pain
- Onset delay of post-accident head and neck pain
- Pain in the shoulders, back and anterior neck
- Neurologic dysfunction — cranial nerve, radiculopathy or myelopathic
- The researchers found that three features were of significant influence on the manifestation, severity, and multiplicity of initial symptoms: (1) the state of preparedness for the collision, (2) the type of collision, and (3) the position of the patient’s head at the moment of impact.
Element of Surprise
The state of preparedness proved to be the first significant factor with respect to initial finding. Patients prepared for the impact (28%) had a significantly lower frequency of multiple symptoms and lower intensity of headaches. The authors concluded, based on the results of this study and other research cited in their article, “Since multiple symptoms as well as intensity of headache were associated with a less favorable prognosis and more severe injury, prepared occupants seem to suffer less musculoligamental strain.” The authors surmised, “Reflex tension of the neck and shoulder muscles or pushing the head against the restraint might be preventive measures.” These researchers reference the seminal work done by Severy who experimented with controlled low speed rear-end collisions in dummies and human subjects and noted a pronounced reduction in acceleration forces to the head when the human subject was forewarned. Severy and, now, Dr. Sturzenegger conclude that defensive action taken by a motorist when warned of a imminent collision significantly influences the pattern of whiplash injury.
Type of Collision
The type of collision was the second significant “mechanism” feature affecting initial symptoms. The authors considered four types of collisions, which occurred in decreasing order of frequency: rear-end impact only, frontal impact only, rear-end plus frontal impact, and side impact. The rear-end collision alone, or in combination with subsequent frontal impact, led to a significantly higher frequency of multiple symptoms, especially of neural structure irritation. The authors state:
First, the small cross-sectional area of the neck flexor compared with the neck extensor muscles is the cause of reduced passive and active resistance against extension forces compared with flexion forces. Second, when forward flexion of the neck is produced by acceleration or deceleration, the head is stopped by the chin touching the sternum. With this range of motion occurring, it is often within physiologic limits. However, in extension injuries to the neck, there is no stop to movement until the occiput hits the back where it is far beyond the physiologic limit. When the weak tone of the anterior cervical muscles is overcome, there is nothing to resist the extension movement of the neck except the anterior longitudinal ligament and the annular and capsular fibers.
Position of Head at Impact
The position of the patient’s head at the moment of impact was the “third and most relevant factor” in this study. The authors found:
A rotated head position led not only to severe muscular ligamental strain, but also to a greater risk of damage to cervical nerve roots. Suffering a rear-end collision with the head inclined leads to higher acceleration forces and more severe injury to cervical structures. Rotated or inclined head position was the only accident feature related to injury severity according to our grading system, which is based upon presenting symptoms and signs. The physiologically permitted range of extension is much smaller and reduced by 50% when the neck is rotated. Rupture of the anterior longitudinal ligament is more readily produced in experiments done with cadavers when the head is rotated before an extension strain is applied to the neck.
Research into acceleration-deceleration type injuries has helped to generate an understanding of the residual problems reported by trauma victims with radicular and non-radicular pain complaints. Health care providers who are familiar with, or at least mindful of these studies, can play a critical role in the resolution of their patient’s claim.
At the law firm of Adler Giersch, P.S., we believe doctors, other health care professionals, and experienced counsel form the first line of defense between the victim and debilitating physical injury and financial loss. The medical-legal connection is natural and best serves the interests of the patient-turned-client when both health care and legal communities work together. If we can assist any of your patients, simply have them give us a call. Consultations are without cost.
1 Matthias Sturzenegger, M.D., et al., Presenting symptoms and signs after whiplash injury: The influence of accident mechanisms, Neurology, April 1994, p. 688-693.
2 D. M. Severy, et al., Controlled automobile rear-end collisions, an investigation of related engineering and medical phenomena, Can Serv Med J, 1955, Vol. 11, pp. 727-759.