... Skiing is actually safer today than it was decades ago: the total number of injuries per year has gone down 55 per cent since the `70s. But knees have taken the brunt of the accidents that remain. From the `70s to the `90s, the most common knee injury — a sprain of the anterior crucial ligament (ACL) — skyrocketed by 250 per cent. Since then the risk has come back down a bit, but you're still twice as likely to sprain your ACL today as in the early days of the sport. About half of top-ranked skiers have injured their knee ligaments, including Whistler Olympic medallist Ashleigh McIvor and Olympian Julia Murray; a third have done it more than once. And women, thanks to their different physiology, are up to five times more susceptible to these nasty sprains.

When it comes to knees, the basic problem is all the torque from your ski during a twisting fall. Catch an edge and your ski can turn into a torture device that rips your knee apart. And once you've done it, more pain awaits thanks to surgery and a long stretch of physiotherapy. You might find your knee collapses under you when you try to hop or twist, or you lose your balance, for years after injury. Some people never fully recover. ...

... What's interesting is that the type of injury has changed over time, mostly because of equipment. ... With shorter skis, there is less of a "phantom foot" to get tangled up with. With these skis, falling forward with a twist might be a more common way to bust your ACL, though [Robert] Johnson hasn't seen any evidence of this yet. "The back end is still sticking out," he notes. Forward falls are less well understood, but Rick Greenwald, at the Thayer School of Engineering at Dartmouth in New Hampshire, is investigating. Greenwald said Johnson's campaign to prevent backwards twisting falls is great, but "for other falls, like forward twisting falls, we still need to learn about them so we can prevent injury through training or equipment."

Better bindings

What should help in both cases — a forward or backwards fall — is bindings that can better release your foot during a twist. Most bindings only release the heel upwards, while the toe can twist out sideways. If you catch the front tip of your ski, this usually causes the ski to rotate around your heel, creating enough torque to release your toe. In fact, in many forward twisting falls, the bindings do release — although often not in time to prevent an injury. But if you catch an edge near your heel, there's no torque to cause your boot to release; instead, your whole lower leg twists. "We instrumented all kinds of bindings and skied on them to look at times when the load isn't normal. What you'd like is to have a release mode for those settings," says Greenwald, who is working with Solomon on a not-yet-released binding that should help to do this. ...

... Johnson and Greenwald are reserving judgement for now. "People come to me and ask me to endorse their equipment, and I say 'no you haven't proven it,'" says Johnson. "I don't blame them; it's too expensive to prove. It would take years of controlled studies." Things are complicated, adds Greenwald. "Is it the same for adults and kids? The same for men and women? We don't know the answers." Even the phase of a woman's menstrual cycle can change how their knees react, he says. The perfect binding somehow needs to account for all that. And, just as important as releasing during a twist is not releasing at an inconvenient time. "You have to add value, and don't make it any worse than it currently is," says Greenwald.