Most ski bindings have not changed in 30 years. When bindings comply with international safety standards, they do a brilliant job of reducing tibia fractures. However, these fractures account for only 3 percent of all skiing injuries, while ACL injuries have risen to 20 percent of skiing injuries. Surprisingly, bindings are not designed to protect the ACL while skiing. Over time, skis have changed in both shape and length—so what is the problem with designing bindings in relation to the ACL?
There are several issues with current ski bindings:
First, capturing both the toe and the heel is a recipe for disaster—with the heel capture being the primary problem. The forces experienced by the leg and then the ACL (which, in part, holds the femur to the tibia) vary widely, depending on hundreds of factors. These include snow conditions, the body of the skier, the length of the tibia, the flexibility of the ski, the flexibility of the boot, the relationship between the ski, foot, and knee… the list goes on. Boot fit and boot buckling also contribute significantly to the transfer of loads between the ski and the tibia.
The ski, acting as a lever, leads to the tibia fracture problem, but it is the length of the tibia itself that affects the ACL problem. When a ski slips sideways, then catches while the heel is captured, the ACL sees abnormally high forces at the top of the tibia, leading to rupture. (Note that while the heel is captured by the snow in skiing, it can also be captured in soccer and football by heel-cleats and in basketball and handball by the high friction between modern athletic footwear soles and the playing surfaces of well-kept gym floors.)
The challenge with ski bindings is to find just the right amount of control—an amount that keeps the skier attached to the ski when desired (retention control) and avoids pre-release, yet releases the boot just before an injury occurs. To do this effectively, the binding design must decouple release forces from retention forces and decouple different kinds of retention forces from other kinds of retention forces.
For racers and steep terrain skiers, releasing at the wrong time is believed to produce as many severe injuries as not releasing—though there is no hard data to support this belief. For recreational skiers, failure to release during a fall is the most frequently stated cause of injury (though skiing injuries that involve “no-release” are evenly distributed across skier-types). Most ACL injuries are incurred before “falling,” so the skier’s report of what happened to their knee is often unreliable.
In the meantime, the ski binding industry continues to make what are called “two-mode bindings,” which release laterally at the toe and vertically at the heel. Some also have a multi-directional toe release. These ACL-unfriendly designs continue to dominate the marketplace — and consequently, fill the orthopaedic surgeon’s office.
As we enter 2018, there are no bindings that attempt to address ACL injury mitigation goals. Despite suggestive marketing names, recent alternative designs have not made a dent in the ACL injury rates. What is needed are ski bindings that release in the presence of certain levels of downward and lateral forces at the heel (mostly) and certain levels of upward and lateral forces at the toe. Most importantly, the retention mechanisms and release controls need to be independently incorporated into the same binding mechanism. Watch for bindings incorporating these design parameters in the 2019 marketplace.
Meanwhile, here are six things you can do to limit your skiing injury exposure this year:
1. Fit your boots snugly, as they transfer the forces to and from the ski — and to the binding for release.
2. Avoid mental errors by skiing without distractions. Leave the phone at home, be in the moment, pay attention, and ski intelligently.
3. Train for the ski season. Focus on flexibility, trunk, core, quad and hamstring strength. The most effective training is proprioception, or balance/awareness/feedback training.
4. Warm up in the morning with yoga, flexibility exercises, hot tubs and hot showers.
5. Tune your skis and your boots to work with your type of skiing. Sharp edges and boots that fit well may matter.
6. Quit early. Ski the best snow and put yourself in a position to really enjoy the outdoors. Pass on the icy, low-visibility conditions.
In skiing, may the Force be with (the vertical) you.
Dr. Kevin R. Stone is an orthopedic surgeon at The Stone Clinic and chairman of the Stone Research Foundation in San Francisco.