Cycling head injuries

Proponents of helmet compulsion are fond of quoting very large figures for the numbers, of children especially, head injured while riding.  Of course, a bruised chin is a head injury, and some studies seem to claim that helmets can prevent bruised chins.  In fact, the term head injury is used very loosely - and in some cases deceitfully - by helmet proponents. 

In a presentation by one group of pro-compulsion activists a claim was made that thousands of children suffer permanent disability every year due to cycling head injuries.  The figure quoted meant that every single class in every single secondary school in Britain would have, on average, one child suffer permanent disability as a result of a cycling injury before the age of 16.  In another presentation by the same group they cliaimed that 50 children a year die in cycling accidents and that most of these were due ti head trauma.  Actually the figure for that year was 19 deaths, of which only half were due to head trauma.

So it pays to be a little sceptical about the figures helelmt proponents offer.  But there is more to it than that.

It is very important to be clear here: all injuries to the head, are classed as head injuries - this much is obvious.  And most of them (equally obviously) are not in the least serious.  Equally, all injuries to the brain are brain injuries, but you might not realise that most of these are not serious either.

Surprised?

What is a brain injury?

It has to be one of everybody's worst fears: a brain injury which leaves you a vegetable.  Helmet promoters talk about these kinds of injuries a lot - right before telling you that helmets prevent 88% of brain injuries. 

It's all down to the definition of brain injury.  The most common form of brain injury appears to be concussion.  That's the headache and residual malaise you get when you fall and bang your head.  This is, officially, a traumatic brain injury and when helmet promoters talk about preventing brain injury or traumatic brain injury, this is mostly what they are talking about.  Concussion is very common and rarely causes lasting damage.  It's undesirable of course but not something that inspires dread.  And that, of course, is why helmet promoters refer to brain injury not concussion: the term brain injury conjures up the spectre of permanent disability or worse whereas concussion is one of those things that just happens.

Obviously some brain injuries are more serious than mere concussion, but just think for a minute: is it credible that a couple of centimetres of polystyrene foam could prevent a concussion?  well, yes, it is.  Is it credible that it could prevent brain injury sufficient to cause permanent impairment?  Problematic.

Problematic for two reasons: first, the way helmets work: the foam crushes until it can crush no more.  A large impact will rapidly reach that point, after which no further energy is absorbed.  Indeed, the foam may fracture, in which case the helmet will have absorbed much less energy than designed - polystyrene foam absorbs little energy in brittle fracture. You can verify this for yourself with a bit of packing some time.  It has been stated by Britain's leading helmet tester that the energies car v. cyclists collisions routinely exceed the capacity of Formula 1 racing helmets.

Second, and more controversially, it is now thought that the dominant cause of serious traumatic brain injury is something called diffuse axonal injury, caused by rapid twisting of the head causing the two lobes of the brain to be torn apart.  These rotational injuries have been documented in car crash victims (who form the bulk of seriously brain injured people).  The worst injuries come from side impacts.  That's why side curtain airbags are now becoming common.

So it is quite posisble that the few genuinely scary brain injuries whihc occur

Does cycling cause many head injuries?

But let's not pretend that no injuries happen.  The question is, is cycling unusually likely to cause a head injury?

I analysed Department of Health hospital admissions for children and adults over a period of seven years.  What I found was:

• The proportion of admissions which are for head injury is slightly higher for pedestrians than for cyclists
• This applies to both adults and children
  
• Half of all child head injury admissions are due to trips and falls
• Nearly five times as many child pedestrians as child cyclists are admitted
• Well under half of child cyclist admissions are for head injury
• Well under one third of adult cyclist admissions are for head injury

You can slice and dice the figures a number of ways, but whatever you do the conclusion is much the same: it is extraordinarily hard to find any actual data which suggests that cycling is unusually dangerous, or unusually likely to cause head injury.

Which is, of course, very reassuring for us cyclists!s