For those working on the frontline of trauma care, the findings of a report into the protective effects of helmets in cyclists and motorcyclists published in the Medical Journal of Australia last week come as no surprise.

When an ambulance arrives at an emergency department with a cyclist injured on the road, a clinician needs to first know a few important details. How old is the patient? What are the vital signs? And finally … were they wearing a helmet?

That’s because ambulance officers, doctors and nurses have known for a long time that if a helmet is not being worn at the time a head strikes the road, pavement or cycleway, the chances of severe head injury are much higher.

Now this has been shown in a one-year study I conducted, with two colleagues, of injured cyclists and motorcyclists presenting to seven major trauma centres in Sydney.

The risks of severe head injury were more than five times higher in cyclists not wearing a helmet compared to helmeted ones, and more than three times higher in motorcyclists not wearing a helmet at the time of injury.

Severe head injuries were defined as any with significant brain haemorrhage, complex skull fracture or brain swelling.

Some 70% of such patients end up on a ventilator in intensive care units; many patients with severe head injuries are left with permanent brain damage.

It’s estimated that each new case of severe brain injury costs Australia A$4.5 million.

But it’s the things that can’t be calculated that are perhaps more crippling – the long-term personality changes, the seizures, the post-traumatic adjustment, and the interminable stress on family and carers.

Conflicting studies

Australia is one of the few countries in the world with mandatory helmet laws protecting both motorcyclists and pedal cyclists.

While helmet use in motorbike riders is generally accepted, compulsory helmet laws have been resisted by many experts.

Many argue that helmet use simply deters people from dusting off their two wheelers and pedalling their way to better health.

Using a telephone survey, Professor Chris Rissel from the University of Sydney concluded that cycling rates could increase dramatically if mandatory helmet laws in Sydney were repealed.

In contrast, a recent National Heart Foundation survey showed that overall road safety, road speed and the presence of dedicated bike paths were the main obstacles limiting bicycle use.

Only 17% of respondents identified helmet use as a potential factor.

Turning the tables on rotational injury

Publicised court cases testing Australian helmet laws have even invoked limited autopsy reports hypothesising the effect of helmets imparting “rotational forces” on the brain, causing diffuse axonal injury.

Diffuse axonal injury is widespread (rather than focused) damage to the brain, and is one of the major causes of unconsciousness and persistent vegetative state following head trauma.

The argument here is helmets apparently exacerbate head injury severity by causing the head to twist quickly on impact, thus creating rotational forces on the brain.

There have been no controlled studies in the clinical setting into the association between helmet use and diffuse axonal injury - until now.

We found no reports of diffuse axonal injury in pedal cyclists, helmeted or non-helmeted, and only a marginal increase in such diagnoses in non-helmeted motorcyclists.

Definitely worth helmet hair

This Sydney-based study was the first to place motorcyclists and pedal cyclists side by side and demonstrated that the protective role of helmets in both groups are important - and even better in pedal cyclists.

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These results are within the range reported by a Cochrane Collaboration systematic review on the subject as well as a study of more than 13,000 pedal cyclists in France published in 2012.

Some experts against this type of observational research cite small sample sizes, and flaws inherent in case control studies, such as not being able to take into account factors such as speed and intoxication.

But it is also true that the very same type of observational study designs was the basis on which the association between smoking and lung cancer was first described.

Once you get enough studies pointing in the one direction, the signal becomes harder to refute.

If mandatory helmets are good enough for motorcyclists, they’re certainly good enough for pedal cyclists.

And as more and more people use bicycles to go to work, work up a sweat or just spend time with the kids, they can rest assured that the helmet resting comfortably on their head is doing something much more than simply disrupting their hairdo.