Oh Knee, Oh My - Ski Mag

Oh Knee, Oh My

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You are skiing. Beneath your shiny nylon ski pants, with their slick Gore-Tex substrate, under the fuzzy sheath of your long underwear, and behind the tough, wrinkled patch of elephantine skin that covers your knee cap, is your knee itself. As you ski, turning left, right, left, right, your knees flex and extend again and again, the rounded, cartilage-covered bottom of your femur's shaft grinding against the slick top of your tibial shaft, gently bathed in a lubricating wash of synovial fluid. You cannot hear it on the hill, but inside your knee, as the bones roll against each other, there is an audible, gristly squish. You go over a small jump, getting a foot or so of air. As you land, your femoral and tibial heads jam together but absorb the shock as they have for years. Between the two slippery, convex surfaces are your medial and lateral menisci, little rings of cartilage that both cushion and distribute the load of your body weight as the two bones are driven against one another. You lean into a turn, driving your shin forward against the stiff cuff of your boot. Preventing the low-friction surface of your tibial head from just squirting out from under your femur are ligaments that attach the two bones to one another. The posterior cruciate ligament prevents your tibia from slipping backward from under your femur; and the anterior cruciate ligament, your ACL, prevents your tibia from sliding forward relative to the femur. You crank out a big, wide turn across the hill, all your weight on your downhill ski, the big quadriceps muscle on the front of your thigh holding your knee in partial flexion, your ACL taut, your thoughts far¿as they should be¿from what is taking place in the dark, moist recesses of your body.

Here's the surprising news, right off the bat: In the first year of the 21st century, you are more likely to completely rip your ACL¿doctors call it a grade-III sprain¿than you were to break your leg back in 1973. Torn ACLs represent 20 percent of all skiing injuries. And things are not getting any better. In fact, they haven't gotten any better in the past 20 years.

What is the likelihood? There's an ACL tear roughly once every 2,100 skier days. It doesn't seem like such bad odds¿a skier who gets out on the slopes 10 days a year is likely to endure one of these injuries only once every 210 years or so¿until you realize that we're all on different schedules. I could be this year, and you could be next, and the guy next to you on the triple could be the one who gets to wait 210 years. Spread across the ski slopes of America, this probability means that somewhere in the vicinity of 24,000 ACLs are ripping every single winter. Given skiers' love of their sport and tolerance for risk, it's not all that surprising that we shrug off the odds and head out to the slopes anyway. But what issurprising is that we know how to reduce the risk of this injury by more than half, and do nothing about it.

WHAT WE KNOW SO FAR
Surprisingly few skiers know that knee injuries can be prevented. In fact, surprisingly few skiers know jack about this most-likely of debilitating injuries. Which is a shame, because an astonishingly large amount is known about this injury.

The first inkling that this epidemic was upon us came from an ongoing study of how skiers manage to hurt themselves, conducted at a Vermont ski area. This research, the only of its kind in the world, is the basis for most of what we know about the ways in which skiers have gotten hurt since 1972, when the study began. The three researchers most closely associated with the study¿Carl Ettlinger, an engineer by training and president of Vermont Ski Safety, a company that manufactures binding-calibration tools and trains ski-shop technicians; Robert Johnson, M.D., professor of musculo-skeletal research at the University of Vermont; and Jasper Shealy, Ph.D., a professor of industrial engineering at the RochesteInstitute of Technology who specializes in ergonomics¿are collectively and individually the foremost experts in the country, and probably the world, on the subject of ski injuries. And the study is undoubtedly the best in the world of its kind. With 28 years of data and details on more than 15,500 injuries, the research is able not only to provide snapshots of which injuries are most common at one time, but identify long-term trends as well.

The study shows that throughout the '70s and most of the '80s, the classic ski injuries¿broken ankles, fractured tibias, and other injuries to the lower leg¿were in significant decline (due to improvements and standardization in boot and binding design and ski-shop practices). But starting around 1980, the rate of a once uncommon injury¿a torn ACL¿increased sharply. In little more than a decade, the frequency of ACL tears among skiers increased threefold.

This sequence of events suggested that the mechanism of injury for skiers' ACLs was quite different from that involved in the classic injuries to the lower leg. After all, the one was increasing at the very same time the other was decreasing. And it suggested that something happened to the skier-equipment equation that reached critical mass in the late '70s. It didn't take long for Ettlinger, Shealy, and Johnson to conclude that stiff, high-backed boots, which went from being rare in the first years of the '70s to being quite common by 1980 and ubiquitous by 1990, were one factor. Simultaneously, enhancements in design, manufacturing, and materials allowed skis to have greater torsional rigidity combined with longitudinal flexibility, improving edge grip and letting them carve as never before while requiring less effort. In the beginning of the '70s, it was not uncommon for skiers to be cruising the hill on wooden skis wearing lace-up boots. By 1980 they were on torsionally stiff metal-and-fiberglass-composite skis and stiff, high-backed boots.

It made intuitive sense that a high-backed boot could be involved in ACL injuries. If the ACL prevents the tibia from sliding forward relative to the femur, then a boot pressing forward on the back of your leg could be placing strain on the ACL. And if skis were turning more easily and readily than ever before, it seemed plausible that they were turning tooeasily and gripping tootenaciously¿allowing the ski (and tibia) to carve acrossthe hill while the skier was still heading downthe hill, giving the knee a good old crank at the same time.

To go from hypothesis to a working model of how the injury takes place, Ettlinger, Shealy, and Johnson studied several videotapes of skiers injuring their ACLs (and also succeeded in verifying the severity of the injury), and by enhancing the images, were able to identify two sets of skier actions that led to serious ACL injury.

The first is fairly straightforward. In what they termed the "Boot Induced" ACL sprain, an off-balance skier lands hard on the tail of his ski after a jump. The tail of the ski, with the skier's full weight on it, acts as a powerful lever, forcing the back of the boot forward against the back of the lower leg, pushing the tibia rapidly forward relative to the femur, and tearing the ACL. This, according to Shealy, accounts for maybe five percent of serious sprains.

The second prominent mechanism is more complex, but essentially involves twisting the tibia relative to the femur while the knee is bent. The researchers call it the "Phantom Foot" mechanism, which refers to the tail of the ski acting as a foot pointing in the wrong direction. Basically, the term refers to losing your balance backward while your skis are still turning. It happens like this: A skier loses control, perhaps only for a moment, and ends up leaning too far back but facing essentially down the hill. At the same time, his downhill ski continues turning, which, with the skier's full weight on it and its fierce edge grip, turns across the hill. This turns the boot, which turns the foot, which turns the lower leg, which stretches the already stretched ACL (the skier is leaning back, butt lower than his knees) past the breaking point. Those who have experienced this injury often report hearing their ACL go with a pronounced pop!

Interestingly, this is a mechanism of injury that can happen before a skier falls, before he even thinks he is out of control. It is, in fact, an injury that can cause a fall. In Phantom Foot injuries, when the ACL snaps, the skier is often still on his skis, thinking he can save himself from falling. Collapse comes when your ligament-deprived knee can suddenly no longer support your weight. Determined competitors have been known to snap the ACL halfway down a racecourse and keep going, not giving way until they cross the finish line.

THE EQUIPMENT FIX
When the magnitude of the ACL epidemic was first clearly laid out in 1989, equipment manufacturers attempted to address it. But until this year, despite the evidence implicating skis and boots, the only ones to experiment with solutions were binding manufacturers. This is not surprising, as bindings had been viewed for decades as safety solutions, and binding manufacturers had been quite successful in reducing the rate of bone breakery.

But it wouldn't prove so with ligament sprains. The first technical feature that was hoped would be effective was upward release at the toe. If forces exerted by high-backed boots were implicated in knee injuries, the thinking went, then a binding that relieved those forces by freeing the boot from the lever of the ski could provide protection. Granted, this was not a new feature. Bindings of one sort or another had offered this mode of release in one form or another since the Hvam binding in the 1940s. But by the late '90s, all six major binding makers were offering models with upward release at the toe. The problem with this, as became apparent with continued research, was that the forces required to tear an ACL¿when the skier was in certain positions¿were far less than those required to keep a skier safely attached to his skis. If you set your binding so that it would release if your ACL was in danger, you wouldn't be able to ski because you'd constantly pop out of the binding in normal use.

The next purported binding solution, offered by Salomon, was the Spheric release system. The company hoped that the Spheric toe unit would provide protection from ACL tears in what the company termed "forward-rolling falls," and trotted out a French doctor to claim this was a significant mechanism for injury. The only documentation to date that this is an actual means of tearing the ACL is reports from skiers that they injured themselves in forward-rolling falls. No such cases have as yet been documented on videotape, according to Shealy, although that does not mean it is not a way to hurt your ACL. But there is so far no evidence that using a Spheric binding will protect you from knee injury. And Spheric does not purport to protect skiers from Phantom Foot ACL injury, which Shealy and Ettlinger feel constitutes the bulk of serious knee sprains.

Despite the role of modern ski boots in ACL injury, boot makers have been largely absent from the ACL fray. But Lange has broken that pattern with its introduction this winter of a new boot, the V 9, which has a releasable cuff that the company hopes will protect skiers in some types of ACL-endangering situations. (For details on the V 9, see "The Boot Route" in the related links above). No other manufacturer has so far marketed a boot that attempts to protect skiers from ACL injury. And no ski manufacturer has introduced a product that addresses the role of torsionally stiff, carve-happy skis in the injury.

Shealy, for one, thinks it's a mistake to look for a "silver bullet" cure via ski modifications. He thinks gear has gone about as t and its fierce edge grip, turns across the hill. This turns the boot, which turns the foot, which turns the lower leg, which stretches the already stretched ACL (the skier is leaning back, butt lower than his knees) past the breaking point. Those who have experienced this injury often report hearing their ACL go with a pronounced pop!

Interestingly, this is a mechanism of injury that can happen before a skier falls, before he even thinks he is out of control. It is, in fact, an injury that can cause a fall. In Phantom Foot injuries, when the ACL snaps, the skier is often still on his skis, thinking he can save himself from falling. Collapse comes when your ligament-deprived knee can suddenly no longer support your weight. Determined competitors have been known to snap the ACL halfway down a racecourse and keep going, not giving way until they cross the finish line.

THE EQUIPMENT FIX
When the magnitude of the ACL epidemic was first clearly laid out in 1989, equipment manufacturers attempted to address it. But until this year, despite the evidence implicating skis and boots, the only ones to experiment with solutions were binding manufacturers. This is not surprising, as bindings had been viewed for decades as safety solutions, and binding manufacturers had been quite successful in reducing the rate of bone breakery.

But it wouldn't prove so with ligament sprains. The first technical feature that was hoped would be effective was upward release at the toe. If forces exerted by high-backed boots were implicated in knee injuries, the thinking went, then a binding that relieved those forces by freeing the boot from the lever of the ski could provide protection. Granted, this was not a new feature. Bindings of one sort or another had offered this mode of release in one form or another since the Hvam binding in the 1940s. But by the late '90s, all six major binding makers were offering models with upward release at the toe. The problem with this, as became apparent with continued research, was that the forces required to tear an ACL¿when the skier was in certain positions¿were far less than those required to keep a skier safely attached to his skis. If you set your binding so that it would release if your ACL was in danger, you wouldn't be able to ski because you'd constantly pop out of the binding in normal use.

The next purported binding solution, offered by Salomon, was the Spheric release system. The company hoped that the Spheric toe unit would provide protection from ACL tears in what the company termed "forward-rolling falls," and trotted out a French doctor to claim this was a significant mechanism for injury. The only documentation to date that this is an actual means of tearing the ACL is reports from skiers that they injured themselves in forward-rolling falls. No such cases have as yet been documented on videotape, according to Shealy, although that does not mean it is not a way to hurt your ACL. But there is so far no evidence that using a Spheric binding will protect you from knee injury. And Spheric does not purport to protect skiers from Phantom Foot ACL injury, which Shealy and Ettlinger feel constitutes the bulk of serious knee sprains.

Despite the role of modern ski boots in ACL injury, boot makers have been largely absent from the ACL fray. But Lange has broken that pattern with its introduction this winter of a new boot, the V 9, which has a releasable cuff that the company hopes will protect skiers in some types of ACL-endangering situations. (For details on the V 9, see "The Boot Route" in the related links above). No other manufacturer has so far marketed a boot that attempts to protect skiers from ACL injury. And no ski manufacturer has introduced a product that addresses the role of torsionally stiff, carve-happy skis in the injury.

Shealy, for one, thinks it's a mistake to look for a "silver bullet" cure via ski modifications. He thinks gear has gone about as far as it's going to go for the time being.

But Ettlinger believes designing a ski that performs well when you're skiing right and protects you from yourself when you're skiing in an unsafe manner is nothing more than a simple engineering problem, and well within the realm of possibility. He has even fashioned a few prototypes himself, the preliminary testing of which has proven that the idea is feasible, he says. These are designs that would perform like any other ski when the skier was well balanced. But if the skier started to lean too far back, say, the ski would progressively lose its carving ability, and start to skid a turn, breaking the sequence of events leading to a Phantom Foot ACL sprain and allowing the skier to recover his balance.

One such design calls for a ski with slight convexity of the base at the tail with slight concavity underfoot. Another would offer progressively decreasing torsional rigidity toward the tail of the ski. In all cases, the goal is to, as Ettlinger says, "tear the carve," or disrupt it gradually as the skier leans further back. Needless to say, in an industry run by passionate enthusiasts who are interested in performance above all else, Ettlinger's ideas have not taken hold. Indeed, it would take a fairly radical change in the concept of what constitutes ski performance in order for a design approach like his to succeed.

According to Shealy, though, what's needed is a paradigm shift of another sort. Because the only thing that's proved effective so far in preventing knee injuries is not hardware, but what Shealy calls "the software"¿changing the way we ski.

THE ONLY THING THAT'S WORKED
When Shealy, Johnson, and Ettlinger were studying the videotapes of how skiers injure their ACLs, they realized it might be possible to help skiers make fewer mistakes. In other words, if you only tear your ACL when you are in very specific situations, why not then teach skiers to avoid those particular situations? And since the Phantom Foot phenomenon appeared to be by far the most common means of severing your ligament, then a method of avoiding that means of injury would cover a lot of ground.

They came up with a training program designed to help skiers learn what kinds of actions, skier errors, and body positions lead to ACL injuries, and then how to avoid those situations. They enlisted ski areas to give the training to ski patrollers and ski instructors, two groups who are on snow a lot and who the ski areas cannot afford to have out of commission with serious knee sprains. In all, 42 areas participated, 22 of which provided training and 20 of which did not, as a control. The results were striking. Over the three years of the study, there was a 62 percent reduction in knee injuries for the group that received the training, while the rate of knee sprains remained unchanged in the control group.

The training program is surprisingly simple: It takes around an hour and involves little more than watching some videos of people injuring their ACLs, and then, under the direction of a group leader, discussing how the injuries occurred and what could have been done to prevent them. The goal is for participants to realize which bad habits and what chain of events combine to bring about Phantom Foot injuries, and then to come up with ways of either breaking the habits or disrupting the sequence that leads to injury.

The crux of the training program is the video, which depicts several knee injuries as they occur and then talks viewers through an analysis of how the injuries occurred. It is impossible to watch the video without consciously assessing your skiing and thinking through how you might avoid injury. The moments of injury depicted look so simple and the mistakes that precipitate them so innocent and familiar,that one can't help but be brought up short. (To purchase the $33 video, fax 802-899-3677 or go to www.vermontskisafety.com.)

And ultimately the advice is so very doable. Keep your hands forward. Don't try to stand up if you s

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