For those of you who have been wondering what my research colleagues and I have been doing lately, I've attached the abstract below. The full peer reviewed paper is available from ASTM International [www.astm.org.]. It covers a five year study that caps more than 40 years of research into ski binding retention requirements and provides guidelines and strategies to help reduce the risk of serious knee sprains involving the anterior cruciate ligament (ACL). I encourage all those interested in what a Knee-Friendly ski binding of the future might look like to study this paper. I have also attached an abbreviated list of references from that paper. All are accessible through their publishers.
As noted in the abstract below, products and practices that meet ASTM and ISO standards have been effective in reducing lower leg injuries but have not resulted in an abatement in the risk of ACL injury which is still the most common injury sustained by Alpine skiers, with more than 15,000 occurring each year in the US alone. Considering the full spectrum of treatment options, the direct medical cost of skiing related ACL sprains adds up to more than three quarters of a billion dollars a year.
David Dodge of Composite Developments and I formed a joint venture some years ago to develop a practical device for addressing this issue. The collaboration has resulted in three US patents pertaining to ski bindings with several foreign patents pending.
This new technologyprovides the potential for reducing the incidence, and thereby the cost, of ACL sprains by at least half,it also represents a new product in a market in which ski bindings have become a commodity--sugar, salt, Alpine bindings--commodities.
The Release Simulator described in the final phase of the 5 year Retention studyis but one of the devices Dave and I have developed. Our newest device does not replace the conventional binding but acts instead as an Intelligent Platform that isolates the binding from the ski. In principle the device makes use of two reference axes which function in series.
Series as opposed to parallel logic means that conditions required for release must be met for both reference axes at the same time if release is to take place. These features add a new dimension to binding release logic--Position--the position, on a virtual ski of infinite length, of the force that created the load sensed by the skier's leg.
The platform only responds to loads applied in the Zone of ACL Vulnerability--the inside edge of the ski near the tail. Loads in this area have the potential for producing an ACL sprain in a scenario known as the Phantom Foot--believed to be the most common mechanism of ACL injury in skiing.
Torque and load position at release are programmable and are based on ski and skier parameters. An attenuation in the release torque of 50% or more has been shown to be feasible without increasing the risk of inadvertent release.
The platform is well within the width and thickness dimensions of current "lifters" and is symmetrical top and bottom thus eliminating the need for left and right tooling. The internal mechanisms that control release logic are made up of non-precision parts which further reduces tooling costs. Future designs could integrate the function of platform and conventional binding.
If the ski industry is on the brink of developing a new paradigm for release bindings, we believe the process should have its foundation in science.
Dave and I invite your comments. Feel free to pass this on to anyone with an interest in the subject.
Carl F. Ettlinger
|Journal of ASTM International, Vol. 7, No. 6 Paper ID JAI102978 Available online at www.astm.org
Retention Requirements for Alpine Ski Bindings
Releasable ski bindings have helped to reduce the risk of lower leg injury but have not been effective in abating the risk of injury to the knee's anterior cruciate ligament (ACL). The authors theorized that if binding retention requirements were better understood, bindings could be developed that would eliminate excess retention under conditions associated with known mechanisms of injury, while providing an appropriate margin of retention during controlled skiing maneuvers. Currently, release/retention requirements for Alpine bindings are defined simply by a moment (couple). But the moment sensed by a skier's leg at release is dependent on not only the release moment to which the binding has been adjusted but also by where on the ski the load is applied.
During the Winter of 2006-2007, the authors developed the instrumentation, protocols, and methods of data reduction and analysis necessary to express retention requirements of Alpine skiers in terms of load and load position on a virtual ski of infinite length.
During the Winter of 2007-2008, 15 experienced skiers were fitted with a pair of skis in which one ski was equipped with a platform for measuring forces transverse to the long axis of the ski boot in a plane parallel to the bottom of the sole. Each subject in the study performed a series of skiing, recovery, and climbing maneuvers. Video and audio records of those maneuvers were synchronized with the 90 min of recorded data, allowing the data to be classified's by skiing activity and reduced to a force and moment resolved about an axis approximating the skier's tibia. The force was then divided into the moment resulting in the position (lever arm) of the force necessary to produce the moment.
Using current standards, the moment was scaled as a percentage of the recommended release moment (for a Type II skier). Loads applied to the inside edge of the rear body of the ski, an area commonly associated with ACL injuries, were rarely found to be both more than 45 cm from the tibia and more than 40 % of the recommended. The few events in this "zone of ACL vulnerability" were associated with loss of control while skiing backward at low speed.
From these observations, a release simulating platform was developed, which isolated the binding from the ski. The platform sounded an alarm if the moment sensed by the simulator exceeded 50 % of the recommended release moment and the load was applied in the "zone of vulnerability." In more than 120 min of skiing, the alarm never sounded, indicating that no inadvertent release would have taken place if the simulator had been an active release binding. However, subjects were able to initiate the alarm, thus simulating a release, by attempting to twist out of the binding with only the tail end of the ski engaged with the snow surface.
The authors believe that the database and analytical techniques developed in this study may help to optimize the overall release/retention capabilities of future bindings.