What constitutes a head injury

The debate over cycle helmets is clouded by inconsistencies and misunderstanding of what constitutes a head injury, and especially a brain injury.

Why is it important?
Head trauma. Say the words. Brain injury. Chilling, isn't it? Raises the prospect of 24-hour care, drooling in a hospital bed for the rest of a pitiful and meaningless life.

This is the bogeyman that helmet pushers trail in front of school children to get them to accept the gospel of cycle helmets.

The reality, however, is somewhat different.

Head injuries
Head injuries are defined by different studies in different ways, but for the most part the influential studies (i.e. those with nice big numbers to quote at politicians) define head injuries as any injury above the neck.

This will include cuts to the lower face, broken noses, ear injuries (surprisingly common), cuts, bruises and the like. The British Dental Association wants helmet compulsion to prevent the injuries their members see. Think about that for a moment.

Many of these injuries, then, are not on the area of the head covered by the helmet. In fact, the number of head injuries touted as preventable by the helmet promoters exceeds most estimates of the proportion which do fall within the area covered by the helmet.

Serious cycling injuries are actually quite rare in the West, so little work has been done on accurately quantifying this.

Brain injuries
Just as the vast majority of head injuries are minor cuts, the majority of brain injuries are simple concussions. This is a big secret that helmet promoters never tell you, and that I only found out by accident.

The most serious brain injuries are called diffuse axonal injuries, and are usually caused by very serious collisions - most of which involve cars, of course. So:


 * Helmet promoters are using a scary term (brain injury) to mean a non-scary injury (concussion), to make the injury sound worse, which is if not exactly dishonest (some are doctors, and doctors do use terms in this way) then certainly not in tune with the graphic and simplistic terminology they use elsewhere.
 * Helmet promoters are using estimates of the ability of helmets to prevent non-scary injuries to imply ability to prevent similar proportions of scary injuries, which is at best unproven and at worst dishonest.
 * Helmet promoters use fear of serious injury, usually caused by impact with motor traffic, to sell a device which its own manufacturers' standards show is grossly inadequate for that source of risk. Often they explicitly discuss risks of motor traffic collisions in order to scare parents into making their kids wear helmets, so...
 * Helmet promoters are actively reinforcing risk compensation by overstating the protective benefits of helmets - riding in traffic is not one tiny bit safer with a polystyrene hat on your head.
 * By discussing helmets in the context of motor danger, helmet promoters are making a claim which no helmet manufacturer makes. Most serious or fatal cycling injuries involve forces well beyond the rated capacity of a competition motor racing helmet.
 * Finally and rather disquietingly, there is some emerging evidence that helmets may actually worsen a particular type of injury, rotational injuries, which is most associated with permanently disabling brain injury (which is why cars are now being sold with side curtain airbags).