Comments: An intriguing, insightful, and highly readable general-level article. The research done by Ettlinger and Johnson is a timeless classic. Be certain to read the peer-reviewed medical-journal article Ettlinger-AJSM-Sep95.shtml. Note that alpine-skiing ACL injuries can occur via various means, including anterior-drawer forcing (boot-induced ACL tear) and twisting (phantom-foot ACL injury). The long skis act as lever arms on the knee, thus raising serious concerns about injuries in general. Bindings cannot protect against anterior-drawer forcing, but they are designed with twisting in mind. However, the problem with twisting is that the binding cannot detect the actual torque at the knee, because this torque is itself a function of the flexion angle of the knee. (This is the prime reason why, in the many years since this article was written, no major improvements in ski bindings have occurred.) Knee injuries can also occur via hyperextension, hyperflexion, and sideways forcing. Bindings provide little or no protection against against these modes of injury. With regards to ACL injuries, modern bindings (including those available 15 years after this article was written) are not much better than those available in the 1980s. Various multi-pivoting designs, including some which appeared promising, seemed to have generated ample advertising rhetoric from equipment manufacturers but have brought very little in terms of tangible benefits for the alpine skier.

Ettlinger et al. describe a variety of means aimed at training the skier to recognize and deal with the precursors to these injuries, and they emphasize the importance of learning to fall correctly. For skiers who use knee bracing, note that anterior-drawer-forcing is something which a knee brace cannot protect against. Twisting is something which a brace can only protect against if connected to the ski boot in a twist-arresting fashion via a special attachment (currently only available for one brace model); such an arrangement ensures timely binding release and is very beneficial for skiers. Such a brace-and-ski-boot-attachment system appears to be the only dependable way to protect against twisting-type ski injuries. (Keep in mind that that phantom-foot ACL injury is not the only way to injure the knee via twisting in alpine skiing.)

Meanwhile, almost any functional brace will protect against sideways forcing and injurious hyperextension; braces with flexion limitations will protect very nicely against hyperflexion. Note, too, that strong leg musculature, trained with an emphasis on endurance, is absolutely essential. Fatigue is especially a concern in the context of trying to pack as many runs as possible into a fixed-price all-day lift ticket. Remember, too, that because alpine skiing tends to be done at considerable speeds, the kinetic-energy-increases-with-speed-squared relationship becomes a serious concern. This means that if you are skiing at ten times the speed at which you would normally walk, your injuries would be 100 times as severe. (An Olympic downhill racer travelling at 100 km/hr and smashing into a solid object would therefore have injuries 625 times as severe as a person walking into a solid object at 4 km/hr.) The kinetic-energy-increases-with-speed-squared relationship is often not apparent to the skier until it is too late. This explains why skiers so often believe that they can recover from a knee-ruinous fall, long after the point of no return. High speeds also mean diminished reaction time. Since injuries occur so quickly, there is no time to think, hence the importance of proper training (e.g. learning to recognize and automatically deal with the precursors to knee injuries, and learning to fall correctly).

Also, remember that any advances in ski-binding technology (and given that we are now well into the 21st century, perhaps electronics will find their way into ski bindings and other ancillary devices) might be accompanied by the revenge effect. In other words, safety improvements often lead to people feeling safer, and therefore they take greater risks. (This phenomenon has already been observed with everything from helmets in a variety of sports to automotive improvements such as anti-lock brakes.) Because safety is a synergy of many factors (including training, behaviour and equipment), safety innovations are most helpful if the user does not develop the expectation that better equipment will bail him/her out of excessive risk-taking. Please note that the terms "Grade III ACL sprain" and "severe ACL sprain" all mean the same thing: a complete tearing of the ACL (or a near-complete tear that should be considered fully-torn from a functional point of view). All ACL injuries are severe injuries, and given the uniquely vulnerable nature of the knee (due to the lever arms of the leg bones, the high dynamic loadings [far greater than the body's static weight], and the near-zero native bony stability), any knee-ligament injury can be expected to bring long-term consequences. This means that an injury which a doctor might describe as "only" a knee sprain would in fact be the most common severe orthopedic injury today.