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What is Whiplash Injury and Can It Occur at Low Speed?

Whiplash is not a diagnosis but rather an attempt at explaining a mechanism of injury in a road traffic accident. It is in fact a musculo-skeletal strain injury to the neck caused by flexion and extension, rotation and lateral flexion movements of the neck as a result of a road traffic accident. Injuries to the neck may occur at low speed, especially when the impact is sudden and unexpected, ie when the neck is relaxed. Similar injuries may be caused when a pedestrian is pushed violently and unexpectedly in the upper back from behind and also during other activities such as contact sport.

The difference between such incidents and for instance a person riding on a bumper car, is that in the bumper car the occupant is expecting the impact and the muscles in the neck are on tension so that very little movement occurs of the head on the shoulders. The problem for the plaintiff from a legal point of view is proving they sustained such an injury since a complaint of pain is subjective. The relative speed of impact (delta V) is directly proportional to the energy transmitted to the occupant. Further, the amount of energy transmitted is increased if the brakes, either the handbrake or footbrake, are applied at the time of impact or if the vehicle dissipates energy by allowing forward momentum when brakes are not applied. This is usually the subject of interpretation by a forensic engineer.

The amount of damage sustained by a car in a bumper to bumper collision is difficult to determine at low speed, as modern bumpers are designed to absorb impact and to spring out again at low speed and therefore an engineer is also required to look at the reinforcer bars behind the bumpers, and the floor of the boot which may reveal damage which is not immediately apparent.

In relation to the occupants of a car which has been hit, from a medical point of view symptoms are more likely to arise if they are not expecting the impact and they have any pre-existing disease of the cervical spine, particularly if it has been previously symptomatic.

Finally, circumstantial evidence may be obtained from the behaviour of the plaintiff after the incident. It is not unusual for no complaint to be made at the time of the impact but rather symptoms develop over the next 24 to 48 hours. Did they visit a hospital or doctor in that time? What was found in examination? Was any specific management undertaken such as x-rays? Was the client referred at any stage for physiotherapy and what were the findings when they were first assessed? What pattern did the symptoms take after they initially developed? A low impact injury would be expected to clear fairly quickly, usually within two to three months and certainly after that time it would not be anticipated that symptoms would continue at any significant level or continue to increase over time.

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