INFORMATION FOR ENGINEERS, ORTHOPEDIC SURGEONS, EPIDEMIOLOGISTS AND PHYSIOLOGISTS.
The release decision of an alpine ski-binding is based on the structural thresholds of tibia biomechanics — plus a margin — as indirectly prescribed by the international alpine ski-binding standards, ISO 9462 and ISO 8061 — as well as being based on pre-release thresholds and respective margins. Howell SkiBindings also uniquely provide ACL / MCL / meniscus-friendly skiing — based on extensive biomechanical research. See Part 2 below.
‘Measuring peak-magnitude of applied abduction force along a range of positions on a surrogate test-ski. Testing involves the use of a non-releasing surrogate-binding having zero ramp-angle, a surrogate-metallic 50th-percentile male lower-leg with fixed 90-degree-ankle-flexion. The resultant torsional-torque about the long-axis of the surrogate-metallic-tibia and the resultant abduction-moment at the proximal end of the surrogate-metallic-tibia are measured.
Ski-bindings are force-imparting and force-sensing mechanisms that — when combined together with the length of the boot sole and the positions of the fulcrums that are unique to each binding-design — react to (a) torsional-torque about the long-axis of the tibia through the use of a non-pre-releasing toe-piece; (b) forward bending-moments about the long-axis of the tibia through the use of a non-pre-releasing heel-unit (see footnote-1 for the engineering-definition of 'bending-moment'); (c) strain across the ACL, MCL and meniscus through the use of a special, open-art, non-pre-releasing, lateral-heel release mechanism that is patented to function within the heel-unit of Howell SkiBindings (see Part 2 below).
( Special note — No ski-boot can release ‘laterally’ through the side-lugs of a pivot-turntable. This is why pivot-turntable bindings cause ACL / MCL / meniscus injury. Bindings with ‘diagonal heel release’ cannot read or react to ACL / MCL / meniscus injury loads that combine large ‘abduction-moments’ PLUS ‘downward-heel-weighting’ because ‘diagonal heel release’ formerly-offered by another binding company responds only to abduction-loads plus upward — not downward — loading. Abduction-loading plus upward-loading does not produce strain across the ACL / MCL / meniscus. )
For important information about the retention-function of ski-bindings, see the other sub-tab under Tech Info — 'Retention'. Retention is the 1st functional requirement of a ski-binding.
Part 1 — Tibia-Friendly Release
Technical definition, tibia-friendly release
Ski-bindings limit their holding-force — in conjunction with the position of the fulcrum-points that are stationed between the boot and the ski — by converting potential injury-producing loads (footnote 2) that are applied to the tibia into a release-response.
When engineering a building-structure it's essential to know the strength of concrete, steel, wood and the strength of the other construction materials that form the structure. The same principle applies to ski-bindings: first, we must know the strength of the tibia to mitigate injury to the tibia.
Strength of average male tibia
The 'average' adult male tibia fractures at ~11.3 daNm during slow-torsion and ~25 daNm during slow forward-bending. These average values apply to male skiers who weigh ~170-pounds and who are aged between 20 and 53 years. The full range of tibia fracture-limits in torsion, bending, and combined torsion-bending — as a function of weight, age and gender — are documented in the biomechanical data of Ernst Asang of Munich, Germany [footnotes 3]. For practical use with ski-bindings, Asang's tibia-fracture data is reorganized, biomechanically [footnote 4]. This essay discusses some of Asang's reorganized tibia-fracture data.
Weakest section of the tibia
The tibia is weakest in bending where skiing stresses are also the largest — near the top of the boot. In torsion, the top two-thirds of the tibia are the most vulnerable sections.
No protection of the tibia by muscle activity
Muscle activity cannot add strength to the tibia because skiing injury-loads can occur faster than 'fast-twitch' muscles can be turned-on. Inversely, there is no experimental, epidemiological or observational scientific proof that muscle activity can subtract appreciable strength from the tibia. The failure criteria of the tibia must therefore be based on the most conservative condition — the unprotected tibia.
Role of the ski-boot
The desire for complete "tibia safety in skiing" is impossible since, for example, during some injury-producing events, the boot can be partially constrained by snow — causing an injury-producing load to not flow through the binding. Boot-fit and boot-buckling contribute significantly to the transfer of loads between the ski and the tibia: a binding cannot read or react to loads that are not transmitted to a binding as a consequence of a ‘weak-link’ between the foot / leg / ski-boot. If a boot is buckled too loosely — an injury-producing-load cannot be fully-transferred to the binding. Boots must be buckled snugly.
Factors effecting tibia strength
• Tibia diameter / skier weight — The diameter of a cylinder effects its strength in torsion. In the case of bending loads, strength is effected by the ratio of the diameter to the length. In practice, large variation in the clinical-measurement of tibia-diameters is an uncontrollable problem, even when the measurement is performed by orthopedic surgeons [footnote 5]. Therefore, the measurement of tibia diameter is impractical for selecting ski-binding settings. However, (1) tibia diameter correlates to skier weight — if the skier is not over-weight. A correction for an over-weight condition is determined by the ratio of the skier's height-to-weight. Over-weight corrections — based on height — are found within all of the ski-binding release adjustment charts that are supplied by all of the binding manufacturers. Corrected skier-weight is a practical predictor of tibia strength. Further, however, at the binding manufacturers-level, (2) the application of x-ray-derived or MRI-derived tibia geometry for research — such as learning more about tibia-metrics that relate to the strength of the tibia; or learning more about tibial plateau bone geometry to help predict prospective-risk of ACL-injury — is necessary and essential for the development of new, future, functional-requirements and design-parameters of ski-bindings and other prospective interventions for skiing-safety that do not cause adverse side-effects.
• Age related tibia strength — Children and adolescents under 19-years have soft-weak bones. Females over 40 have the possibility of reduced bone strength. Males over 53 have the possibility of brittle-weak bones. See graph, below. Reasonable exercise and diet (see text, below) can mitigate a large reduction in tibia strength.
• Velocity of loading into tibia — Bones are stronger during 'fast' (dynamic) loading compared with ‘slow’ (quasi-static) loading. The inverse velocity-effect on bone-strength is called 'visco-elasticity'. There can be as much as an ~18% difference in tibia-strength between slow and fast loading. Ski-bindings must function to accommodate the worst-case scenario — slow loading — even though the issues of friction that are found in nearly all mechanical systems become compounded during slow-moving mechanical operations. See graph, below.
• Combined-loading into tibia — Bones are weaker during combined torsion-bending loading when compared with pure-torsional loading. See graph, below.
• Cyclical stress / exercise effecting tibia— As described by Wolfe's Law, bones can become stronger when exposed to repeated cyclical loading. Racers who ski extensively on hard-packed snow and ice can develop stronger tibia's. Astronauts — in the absence of gravitational loading — experience weakened bones.
• Effect of diet on tibia strength — A calcium-rich diet together with vitamin D can mitigate a reduction in bone strength. Excessive phytates (non-soaked beans), meat, salt, oxalates (such as spinach & kale), wheat bran, caffeine (coffee & tea), alcohol and soft drinks are adverse to bone strength [ref: U.S. National Osteoporosis Foundation]. Vitamin K2 appears to be helpful toward bone strength.
• Effect of disease on tibia strength — Certain diseases can reduce bone strength. A doctor should provide medical advice about whether skiing is appropriate during the course of certain diseases.
• Effect of gender on tibia strength — When comparing male tibia strength to female tibia strength, there is no difference in the strength of the same size tibia's — noting of course that the average size of male and female tibia's are different. However, natural calcium depletion in older females can reduce bone strength if calcium is not supplanted (vitamin D is also needed to cause calcium supplements to become effective);
• Effect of previous fracture on tibia strength — Properly healed, a bone has the possibility of becoming stronger than normal (but don't count on it being stronger than normal), and bones that are supplanted with titanium pins can become stronger after bone-fibers grow into the titanium (but here also, don’t count on it being stronger). Bone fractures that are not fully healed can be significantly weaker than normal-strength bones. Skiing should not take place until after a fractured tibia is fully-healed (typically, 10-weeks after proper medical care ... but this time-duration can vary depending many factors that must be assessed by a doctor).
• Other factors effecting tibia-strength — There are other biomechanical and physiological factors that effect tibia strength, but the above factors are the main factors.
Nothing written here should be construed as medical advice: please consult a doctor for medical advice.
Practical reality of ski-binding release-settings on mitigating tibia fracture.
The relationship between an individual's unique physiology and bone strength is significant. Ski binding release settings are 'adjustable' expressly to attempt to accommodate the prime factors that effect tibia strength — but it's impossible to dial-in a binding's release settings to become perfectly aligned with all of the above-noted factors because these factors are difficult to quantify in a 'net result'. This is one of many reasons why 'release settings' should be aligned with a binding's ability to supply 'retention' ( anti-pre-release ) at low release settings (please see 'Retention' sub-section).
Engineering-philosophy differences about ski-binding function & release settings pertaining to tibia integrity.
There are long-running debates between the Germanic and the French approaches toward the interaction between ski-binding function and release settings.
The Germanic approach is to design the binding to supply maximum retention-function. Then, if the retention-function of the binding is performing as defined in the 'Retention / Anti-Pre-Release' section of this website — the binding's setting is adjusted to a biomechanical release threshold.
The French approach is to design the binding to supply maximum multi-directional release. Then, if the release-function of the binding is performing as defined throughout this essay — the binding's setting is adjusted to a skiable retention threshold.
Howell SkiBindings company believes that a binding must functionally-decouple the release-function from the retention-function — as in 2 separate systems. The binding's setting can then be adjusted to a certain 'pre-setting' based on the guidelines of international standard ISO 8061. The pre-setting can then be fine-tuned through the proper use of the 'Self-Release Method' (see below). With Howell SkiBindings, it appears that most skiers can leave the pre-settings — as recommended by ISO 8061 — unchanged.
’Functional Decoupling’ to maximize tibia integrity.
Only Howell SkiBindings are fully-functionally-decoupled between the retention-function and the release-function:
The principles of Axiomatic Design Engineering, formalized as the first new engineering discipline in over 100-years by MIT Engineering Professor, Nam Suh, are utilized robustly in developing new Howell SkiBindings. In this way, release is smooth — only when needed, biomechanically — and retention / anti-pre-release is powerful — always available when performing controlled, aggressive, skiing. Only Howell SkiBindings deploy fully-decoupled Axiomatic Design Engineering technology. Only Howell SkiBindings deliver powerful anti-pre-release / retention / independently of the release-settings. Howell SkiBindings are uniquely the 1st bindings that can be skied at 'chart settings' without pre-release. This is a 1st — a major new breakthrough — within the category of alpine ski bindings.
’Self-Release Method’ Pertaining to tibia integrity. 
Strong, fast, aggressive skiers and racers who need settings higher than the ‘recommended settings’ on the Howell Release Adjustment Chart can use the Self-Release Method to obtain special 'discretionary settings' — only when the method is used correctly. The correct Self-Release Method also helps to (a) assure the settings necessary for strong, fast, aggressive skiers are not grossly overtightened / not too high / as is otherwise typical in the absence of using the Self-Release Method; and (b) — for all levels of skiers — the Self-Release Method helps to assure that there is no ‘gross impediment to release’ (e.g., no stone trapped between the boot sole and boot-binding interface).
First — together with your skis and boots — have Howell SkiBindings mounted and adjusted for proper function by a Certified Howell SkiBinding Technician (you can become one, on-line).
Next, select the proper ‘pre-setting’ from the Howell Release Setting Chart . Adjust the binding’s indicator-settings to the chart-recommended ‘pre-settings’.
Forward-Heel Self-Release Setting:
- Stand on one foot only with the boot firmly buckled as it is buckled during skiing.
- The ski must not be held fixed.
- Release the heel by assertively moving the top of the lower leg forward-and-downward — toward the near-forebody of the ski. Not too fast. Do NOT lunge forward with the opposite leg because this action can rupture the achillies tendon. Hold the back of a turned-around dining-room chair to mitigate falling.
- Readjust the heel setting until release occurs at the ‘comfort threshold’.
- Do not repeat this test more than 4 times with one leg in one session.
Lateral Toe Self-Release Setting:
- Place one ski on its inside edge by moving the knee slightly-inward; place weight on the ball of the foot; then slowly but assertively — cause the toe of the boot to move inward ... toward the ground … to cause full-lateral-toe-release. Fast movement must be avoided because this action does not cause the desired effect that is necessary for proper selection of the binding’s setting.
- Readjust the toe setting until full-release occurs at the ‘comfort threshold’.
- Do not repeat this test more than 4 times with one leg in one session.
Lateral-Heel Self-Release Setting:
• Match the lateral toe setting that is derived by the Self-Release Method onto the lateral heel indicator-setting.
WARNINGS ! Injury can occur during improper use of the process to seek settings that are derived by the Self-Release Method: follow the above process, closely, to avoid injury. During skiing, lowered settings may cause inadvertent pre-release; increased settings may block necessary-release. Self-Release-derived settings are ineffective if the binding is not supplying ‘proper function’ as defined in the Howell SkiBindings Technical Manual. The Self-Release Method is NOT a comprehensive ‘test’ of ski-binding function: this is why Howell SkiBindings company does NOT refer to the ‘Self-Release Method’ as a ‘Self-Release Test’.
Release Measurement for tibia integrity:
A Howell Certified Technician should (optionally, though strongly suggested) measure the release of the complete ski-boot-binding system using measuring instruments — lateral-toe; forward-heel; lateral-heel — as described in the Howell SkiBindings Technical Manual; take appropriate service-action if necessary; record the measurements; preserve each of the recorded measurements on the top-surface of each ski.
We require that all Howell SkiBindings are mounted and serviced by a Howell SkiBindings Certified Technician (you can become one, on-line) — and we recommend that each skier knows their own personal release-settings and knows what constitutes proper ski-binding function in concert together with the release settings. The corollary: high release settings together with bindings that provide poor retention-function — are meaningless release settings. Again, the binding should provide retention that is functionally-decoupled from release: this can only be accomplished with properly designed bindings (e.g., Cubco ski-bindings cranked to DIN 30 (thirty) pre-released excessively because the release-function was adversely cross-linked with the retention-function). Please see the complete in-box instructions that are supplied with Howell SkiBindings for all of the necessary service-information that provides ‘proper’ retention-function independently of the release-setting function.
Howell SkiBindings have been designed to release the ski from the boot laterally at the toe; vertically-downward as well as laterally-outward at the heel — (3 modes) — and to retain the ski to the boot during controlled skiing maneuvers. Despite these features, injury may result from simply falling down or from impact with an object. An appropriately functioning ski binding may not release under all injury-producing circumstances. Skiing, like all athletic endeavors, involves a certain degree of risk that must be recognized and accepted. Additional information about the care and maintenance of Howell SkiBindings can be reviewed in the Howell SkiBindings in-box instructions and through the on-line Howell SkiBindings Help Center.
 This optional Self-Release Method is not part of ISO 8061 or any standards.
 The recommended settings on the Howell Release Adjustment Chart conform to ISO 8061 and conform to related provisions within ISO 9462. Boots must conform to ISO 5355. Howell SkiBindings are not compatible with AT ski boots that have metal inserts for pin-bindings. Howell’s SkiBindings are Grip Sole compatible with the use of the optional Grip Sole AFD’s that are supplied, standard, with each purchase — though all properly set-up Grip Sole boot-binding systems adversely compromise tibial-plateau integrity during forward-release events: caution should be exercised with the use of any Grip Sole set-up with any ski-binding, especially with the use of short-skis.
Testing the release-function of alpine ski-bindings for tibia integrity.
Proper 'testing' (optional, though strongly suggested) of the release-function of the complete ski-boot-binding system must involve the use of properly calibrated release measuring instruments by a certified ski-binding technician. Testing the complete ski-boot-binding system for basic release-function with measuring instruments should take place at least once during every 30-days of skiing — or before the beginning of each ski season — which ever comes first. (( Howell SkiBindings company provides detailed information on how to properly calibrate certain-recommended ski-binding release measuring instruments: the best ski-binding release measuring instruments for ski-ships (and for skiers) are ones that directly-measure torsional-torque, forward-bending-moment, and abduction-boundary. For torsion and bending, we suggest the Vermont Release Calibrator by Vermont Safety Research. For abduction, we suggest the Howell Lateral-Heel Test-Fixture. See ‘Catalog’. ))
Levels of ski-binding testing for tibia integrity.
Release testing ski-bindings can be performed at many levels — skier, retailer, distributor, manufacturer, or independent testing lab. Testing ski-bindings for release — at any level — can focus on demonstration, calibration, or validation. We respectfully encourage ignoring ski-binding test reports that do not involve the use of release measuring instruments (e.g., current SKI magazine ‘binding reviews’ (as of 2019/2020) — and certain popular blogs — contain misleading misrepresentations based on zero measurements: these writings have a reasonable expectation of causing serious injury or worse).
Consumer-level ski-binding 'inspection' for tibia integrity.
Beyond the Self Release Method to fine-tune settings and identify gross impediments to release — skiers should come to know what constitutes proper ski binding function. Howell SkiBindings in-box instructions provide a wealth of information in this way (link under construction).
Retailer-level ski-binding testing for tibia integrity.
At the retailer-level, there are several visual and tactile tests that must be performed; as well as several suggested release-measurement tests — as required by Howell SkiBindings certification / indemnification programs (link under construction). Uniquely, skiers can also become Qualified Mechanics by Howell SkiBindings company. Standards are in-place by the American Society for Testing and Materials (ASTM) and by the International Standards Organization (ISO) that guide ski retailers on generic ski-binding testing procedures.
The objective of consumer and/or retailer ski-binding release-testing is to assure that the actual ski-shop-related release-settings that are being measured are testing within the expected/published release tolerances that are supplied by each respective ski-binding company. If the actual-release is measured outside of the expected/published tolerances — service must be performed to the binding, the boot, or both, as specified by Howell SkiBindings. If after proper service is performed, and the measured-release still remains outside of the expected/published release tolerances, the binding should be returned to Howell SkiBindings company under warranty-replacement; the boot should be returned to the boot company; both should be returned to their respective origins for service or warranty replacement; or if the binding is outside of the warranty-period, the binding should be retired — not sent to a 2nd-hand event.
Manufacturer-level release-testing for tibia-friendly skiing
Above and beyond the minimum international ‘release’-standards ISO 9462 and ISO 8061 — to which standards all binding companies must comply — release should occur in a way that limits the selected peak-torsional-torque and limits the selected peak-bending-moment on the tibia — to be as nearly as constant as possible — independently of the location of where almost any injury-producing force enters the ski. This requirement is a fact of nature: a tibia cannot 'know' where a potential injury-producing force enters a ski. To quote Nobel Prize winning scientist, Francis Arnold— “Nature does not care about our calculations.”
However, in practice, it is nearly impossible to achieve a constant peak-release-load into the tibia independently of where a force enters a ski, because (a) the ski is a lever, where the applied force can become concentrated at many possible locations; and (b) the pivot-points between the ski and the boot — in both torsion and bending — are not always aligned with the weakest points of the tibia. Never-the-less, it's the belief of Howell SkiBindings that each binding manufacturer should try to seek a nearly-constant load on the tibia, at release, no matter where an applied force enters the ski. Some binding companies achieve this scenario better than others. Why? Because most binding companies comply with binding function only through Annex-A of ISO 9462 and ignore the ‘optional alternative’, Annex-B. But the key to how a binding should behave, biomechanically, is exposed in Annex-B, not in Annex-A. Annex-A is mostly about how a binding should behave at the end of the manufacturing assembly-line (which has a different significant importance). Several so-called leading binding companies do not even have the equipment to test according to Annex-B ! ( It appears that no pin-binding companies test according to ISO 9462 Annex-B: clearly, pin-binding companies have no bona fide understanding of ski-binding design/function that addresses basic human-biomechanics — but they do seem to be experts at manufacturing.)
Method to measure resultant-release consistency on the tibia
To approach the goal of achieving a constant peak torsional-release-torque and a constant peak forward-bending-release-moment on the tibia — no matter where a potential-injury-producing force enters the ski — test-forces are applied to a range of positions along the length of an unconstrained ski, while at the same time a standardized test-sole is rigidly held by a surrogate metallic foot / tibia — while measuring the resulting torsional-torque and resulting bending-moment on the surrogate metallic tibia. In essence, this is the type of testing that is defined by ISO 9462 Annex-B. Unlike the type of release-testing that is conducted by ski shops (and by TÜV) while using ISO 9462 Annex-A, the ski is not held fixed when conducting tests according to Annex-B. In Annex-B, the opposite (proximal) end of a surrogate metallic-tibia is rigidly connected to a test frame while the ski floats in unconstrained space, held only by the binding. This special type of test apparatus allows the simulation of 'rigid-body mechanics' at peak release conditions — in a way that allows the ski to 'float' as it would during actual skiing. This method allows functional decoupling of the test device from the unique kinematic function of each type of binding design. By allowing the ski to freely float during release, each binding design’s unique kinematic path of motion can uniquely control the ski’s path of motion during release. The ski’s release-path, relative to the tibia’s position, directly effects the resultant-(net)-load on the tibia at release. Unless properly engineered, the unique kinematics that are generated by each unique binding design has the possibility of varying the peak-resultant-(net)-load that flows into the tibia — at levels that far exceed any ski-shop-measured release setting. Testing ski-binding release according to ISO 9462 Annex-A does not explore ski-binding kinematic function and does not explore the full resultant-(net)-loading on the tibia during potential injury-producing force-vectors that can enter a ski in a wide-range of locations/positions.
Decoupling the test device from the kinematics of ski-binding release-function provides a clear unconstrained exploration of each binding design’s unique kinematic release-function with respect to the variation of the resultant-(net)-loads that flow into the tibia when applied-forces enter the ski in varying locations. The exploration and understanding of ski-binding kinematics — through experimental testing as provided by ISO 9462, Annex-B — is therefore, essential for the development of top performing ski-binding function. Binding companies that do not test according to ISO 9462 Annex-B are not only lazy — but in the opinion of Howell SkiBindings — they are incompetent, fraudulent, and knowingly misleading skiers and ski shops about their bindings’ less-than-stellar function ... even if they meet the minimum safety standards according to optional ISO 9462 Annex-A. Meeting minimum optional standards is ‘the floor’. Howell SkiBindings seeks to exceed ‘the ceiling’. (There is even one alpine ski-binding company that sells and ships bindings that do not meet minimum international safety standards according to ISO 9462 Annex-A or Annex-B ! )
Expressing the results of the peak resultant-load on the tibia (at release) during varying trauma-scenarios.
A graphic representation of the test-results obtained from the use of ISO 9462 Annex-B can be depicted by plotting ‘release envelopes’. ‘2D release torque envelopes’ express the peak torsional torque that is applied to the tibia as a specific point in graphic-space that is plotted laterally of the center-line of a graphic-ski — laterally of each graphic-point where a test-force is applied to a ski. Each point in graphic-space that corresponds to each point where the force is applied to the ski can then be graphically-connected to form a 2D 'release-envelope' — a composite of many related tests. The ideal shape of a 2D release-torque-envelope is a straight line that is parallel to the ski, originating 45cm forward of the projected-axis of the tibia then flowing-forward; and another line parallel to the ski that originates 45cm aft of the projected-axis of the tibia then flowing aft-ward. This ideal 2D graphic-representation would depict a binding that limits the resultant torsional torque that is applied to the tibia — to a constant torsional magnitude — no matter where the lateral test-force is applied along the length of the ski, forward of 45cm or aftward of 45cm of the projected axis of the tibia. This ideal characteristic is nearly impossible in practice — but it is important to know what the ideal goal should be. See 2D release torque envelopes, below.
(( See ‘red’-marked lines. (The ‘valgus (abduction) moment’ release envelopes (‘green’-marked) are discussed in Part-2, below. ))
Practical considerations for tibia-friendly ski-binding function
A binding must address the functional relationships between applied-force, leverage, fulcrum-positioning, torsional-torque and forward bending-moments to attempt to modulate consistent resultant-(net)-loading into the tibia during release.
Influence of fulcrums on tibia-friendly ski-binding function
As noted above, the magnitude of the resultant-(net)-loading into the tibia is caused not only by the binding’s release setting but also — importantly — by the kinematic path of the ski’s release — which kinematic path is controlled by the location of the binding’s unique torsional-pivot-points and by the binding’s unique forward-release-fulcrum-points between the boot and the ski — relative to the position of the tibia.
The leverage-effect supplied by the length of the ski boot is also important. Its effect is defined by the distance between the toe-piece of the binding and the center-of-rotation between the boot and the ski — relative also to the position of the projected-axis of the tibia — during torsional-release. In the case of forward-bending release, the leverage-effect is defined by the distance between the heel-unit and the leading edge of the anti-friction-device (AFD) that's located under (or near) the ball of the foot. The leading edge of the AFD forms the fulcrum for forward release.
In these 2 modes of release — lateral at the toe and vertical at the heel — it's important to remember the simple relationship of ‘torque = force X distance’. The equation is not, ‘torque = 2(force) X distance’ ... or ‘3(force) X distance’. Distance (leverage) has an equal effect on torque as does force. Release torque is not controlled solely by changing the force setting of the binding. The built-in design of a ski-binding's pivot-points in torsion and bending — the distance between the force-imparting mechanisms of the bindings and the pivot-points and fulcrums — has an equal effect on the resultant-(net)-load that is applied to the tibia as does the force supplied by the binding toe-piece or heel-unit [see footnote 7]. This basic physics concept is important but largely ignored by skiers and ski-shops when selecting a ski-binding design. All Howell SkiBindings deploy this functional-concept of uniquely building-in specially-positioned pivot-points and specially-positioned fulcrums to flatten the release-torque-envelope and the release-bending-moment-envelope as best as possible when applied-load-vectors enter the ski forward of 45cm or aftward of -45cm from the projected axis of the tibia — thus holding the resultant (net) peak torque and resultant (net) peak bending-moment that is resolved into the tibia as close to a constant-magnitude as possible, independently of where an injury-producing force enters the ski. This special, ‘nearly-constant’, release characteristic that is uniquely supplied by Howell SkiBindings can actually be felt by skiers during necessary release. The feeling is a ‘remarkably smooth release’.
Unique signature of each binding design on resultant-load on tibia at release.
Each unique binding-design causes unique release-function that produces a unique release-envelope — each binding design has a uniquely-shaped envelope-signature.
Please note that unlike the large amount of information about the function of a binding that is expressed in a release-envelope, a ‘release-setting’ simply moves the entire release-envelope upward or downward: different release-settings do not change the shape of a release-envelope. Different release settings do not change the unique kinematic-function of each binding design.
Combined-loading-function of ski-bindings — for tibia integrity
All structures become weaker during combined loading. During the combined loading that naturally occurs while skiing, the tibia becomes weaker, too. Graphically representing the results of ski-binding release-function during combined loading is accomplished through the use of 3D release-envelopes. A combined-load test involves the application of a preload in one direction — for example, a forward bending-moment — then, a lateral load is applied to the ski until it releases from the boot. The forward-bending preload is represented, graphically, in the 3D release-envelope, by plotting a point a certain distance above the top surface of the ski: this distance represents the magnitude of the applied forward-bending pre-load. Another point is then applied to the graphic presentation — laterally of the pre-load plot — at a distance that is proportional to the peak torsional torque that is resolved into the tibia at release. Similar plots are generated to represent the resulting combined-load on the tibia — at release — when forces are applied to varying locations along the length of the ski. Each successive test along the length of the ski can become connected in graphic-space. This approach generates a 3-dimensional release-envelope. An ideal 3D release-torque-envelope is shaped like 2 rectangular boxes — one box positioned 45cm forward of the projected-axis of the tibia, the other box positioned 45cm aft of the projected-axis of the tibia. In practice, there are distortions in 3D release-torque-envelopes, too, that are caused by the positions of the lateral-release-pivots and forward-release-fulcrums that are located between the boot and the ski, relative to the position of the tibia.
Bindings that produce small distortions in the graphic release-envelopes hold the peak resultant loading into the tibia (in both torsion and bending; and combined torsion-be fun) closer to constant compared with bindings that have larger graphic-distortions in their 2D or 3D release-envelopes.
Howell Ski Bindings have the least distorted 2D and 3D release-envelopes of any ski-binding. This outstanding function is accomplished through the use of dual-alternating — floating — pivot-points in torsion and by locating the leading edge of the AFD as far aft of the tip of the boot as possible.
(( The unique AFD-location of Howell SkiBindings provides additional benefits for edge-control, too. ))
Overall epidemiology of tibia fractures in skiing
Tibia-fractures involving adult skiers are significantly less frequent than MCL and ACL injuries. Tibia-fractures have a prevalence of ~4% of all skiing injuries and an incidence (not 'incidents') of ~4,000 mean-days-between-injuries (MDBI) today.
This data implies that adult alpine ski-bindings, release-settings, and the boot-binding interface are functioning well.
However, It is important to note that a few other bindings that supply ‘good’ release-function may not supply good retention-function. Even though other bindings are typically set to release according to ‘standard guidelines’ — they can pre-release due to poor decoupling-factors. Pre-release shifts injury-patterns to upper-body injuries such as to the head, spine, shoulder, wrist, spleen, etc. Upper body injuries can be far more severe than tibia fractures. Pre-release can be averted through robust decoupling-function, precluding the need for elevated release settings (see sub-topic — ‘Retention’).
Sub-notes regarding tibia-friendly ski-binding release-function.
1— Tibia fractures among children-skiers are on the rise ((prevalence = 5% of all children's skiing injuries; incidence = 3600 MDBI — compared with 3% and 4500 MDBI 12-years ago) higher incidence #’s are ‘better’)). Children must have low-friction interfaces between boots and bindings. Children's boots must have upper-shells that are made of materials that are semi-hard, 50 to 55 D-Shore, in order for the ski-boot-binding system to provide proper release-function and proper retention-function by decisively transferring injury-producing loads that flow between the snow and the skiers’ legs — into the bindings. Children's boots must be well fitting — not overly-large to grow into. Boots must be firmly buckled at all times while skiing. 'And children's bindings should include a low-friction AFD — such as pure-Teflon — with a well-defined leading edge (a well-defined fulcrum) that is located ~3cm aft of the tip of the boot sole.
2— Other types of previously obscure tibia-fractures are now on the rise: severe, high-energy tibia-plateau fractures, severe tibia-tuberosity fractures, and high-energy spiral-tibia-fractures are greatly on the rise. Each of these types of tibia-fractures presently comprise the fastest-growing categories of injuries in skiing — paralleling the advent of fat-skis and pin-bindings (causation is still not linked, epidemiologically — but is strongly ‘associated’, clinically and biomechanically). The high-energy nature of the new types of skiing fractures involve multiple-fragments, difficult surgical reconstruction, and 10 to 15-months of aggressive rehabilitation. Some skiers who sustain these types of severe tibia fractures never ski again. Fat skis on firm snow; and pin-bindings in any snow (except Trab TR2; Diamir Vipec; Salomon Shift and Atomic Shift — though Shift brand bindings do not mitigate ACL or MCL injury-mitigation) — are a serious problem for the sustainability of our beautiful sport. Howell SkiBindings principle, Rick Howell, has tested and generated extensive release-envelope data involving 20 brands of pin-bindings. All pin-binding release-function (except Trab TR2; Diamir Vipec; Salomon Shift and Atomic Shift) is horrendous at best — many times requiring 2 Very High Level releases in order for the ski to fully-separate from the boot ... which release-levels are well above fracture-limits at any gap-setting ... meaning that the tibia becomes fractured twice during one injury-producing event. Further, pin bindings have nearly zero lateral elasticity — thus causing 'high-energy' tibia fractures involving many bone-fragments. Fat skis are causing tibia-tuberosity fractures (and MCL and meniscus injuries) because the wide-width of fat skis — when skiing on firm snow — induces large lateral bending-moments (abduction-moments) at the top (proximal end) of the tibia. Fractures in this location often extend into the surface of tibial plateau, causing damage to the menisci that are seated on the top of the tibial plateau surface. The knowingly-negligent, overly-loose ISO standards for pin-bindings (wrongly called 'tech-bindings' — they are hardly 'tech') must be changed to reflect human-biomechanics, not just manufacturing tolerances that have little to do with basic human biomechanical requirements [see footnote 10]. Fat skis are great in powder or in loose-snow — but skiers should be advised that skiing on fat skis (wider than 87mm at the waist) on firm snow could end one's skiing career. Do not use fat skis on firm snow. Skiing with pin-bindings and fat skis on firm snow invites trouble. If you are skiing with AT pin-bindings (other than Trab TR2; Diamir Vipec; Salomon Shift or Atomic Shift) — no matter what the release settings are adjusted to — do not fall in the touring-mode.
3— Special settings for ’unique’ tibia’s. The extensive biomechanical engineering work that was performed during the late 1960's through the early 1970's by several leading researchers produced data that provides tuning of release-settings for individual physiologies. Key factors that compensate for different physiologies include — weight; height (to correct for over-weight skiers); velocity (‘skier type’); age; gender; boot sole length, and recent amounts of cumulative aggressive skiing (triggering Wolfe’s Law for increased/discretionary settings). See the beginning of this essay, above.
Longitudinal epidemiology trend, adult skiers:
Incidence, adult skiers: MCL, ACL, Tibia (bending), Tibia (torsion) trends, 1972 - 2016. Data 1972 - 2006: Johnson, Ettlinger, Shealy, Update on Injury Trends in Alpine Skiing, 2008, Journal of ASTM International, Vol. 5, No. 10; Data 1992 - 2016: Binet, Laporte, Skiing Safety Network National Results - France, Médecins de Montange, 2019, Abstract Presentation ISSS Squaw Valley, California USA. (Tibia-plateau / tibia-tuberosity fracture trends not shown here.)
A time-line on the incidence (not ‘incidents’) of MCL, ACL and tibia injuries in alpine skiing. Tibia fractures are sub-divided into ‘torsional’ and ‘bending’ fractures. Tibia-plateau and tibia-tuberosity fractures are not shown. Data is derived from 2 government funded research studies: Sugarbush (depicted as “USA”) and Médecins de Montange (depicted as “France”). Statistical significance is strong throughout all of this data — 1972 - 2016. Larger incidence-numbers are ‘better’ due to more days between injury (note inverted vertical-axis). ‘Incidence’ accounts for the ‘population at risk’ at any given time interval.
Conclusion: tibia-related release-function of alpine ski-bindings
Integrating robust, non-pre-releasing, release-function into top-of-the-line alpine ski-bindings is well within the domain of Howell SkiBindings that are designed by Rick Howell. Rick Howell's education and experience in the ski-binding category is unprecedented (see 'About Us') — Howell SkiBindings reflect this background.
Further, Howell SkiBindings provide all of the positive functions that are outlined above — with less parts than other bindings. Minimal parts often leads to durability.
The release function of a ski-binding is regulated by international ski-binding standards. All ski-bindings must be certified for their compliance with the minimum international standards — ISO 9462, 9465 and 11087 — through testing by the only independent ski-binding lab in the world — by TÜV, in Munich, Germany [footnote 9]. Even if there is no 'local rule' enforcing ski-binding certification — for example, there are no certification statutes or enforcement laws in USA or Canada — we urge you to seek only alpine ski-bindings that are independently certified by TÜV in Germany for their function according to ISO 9462, ISO 9465 and ISO 11087 — and that meet ‘standard industry practice’ for anti-pre-release and durability.
It is anticipated that Howell SkiBindings will be independently certified in Germany before being shipped into the stream of commerce.
Part 2 — ACL / MCL / meniscus friendly skiing.
The low stand-height, non-pre-releasing, ACL / MCL / meniscus friendly, pure-alpine ski-binding function that is patented into Howell SkiBindings is explained in scientific-detail in the slide-show presented by Rick Howell at the International Olympic Committee (IOC) conference — Prevention of Injury in Sports, March 17, 2017 in Monte Carlo, Monaco. The presentation — ACL Integrity Through Special Ski-Bindings — was updated and presented at the International Society for Skiing Safety (ISSS) conference in Innsbruck, Austria on April, 2017; at the International Conference on Science in Skiing (ICSS) in Voukatti, Finland in March, 2019; and at the ISSS conference in Squaw Valley, California on April, 2019.
How Howell SkiBindings uniquely provide ACL / MCL / meniscus friendly skiing:
First, the epidemiology and biomechanics of skiing-ACL and MCL injuries.
MCL and ACL injuries are, by far, the most frequent types injury in alpine skiing, today. The incidence (not incidents) of skiing MCL-injury is ~2750 mean-days-between-injury (MDBI). The incidence of ACL-injury is ~3000 MDBI. [Binet and Laporte] Higher incidence numbers are better when there are more ‘days between injuries’.
Over the past 15-years, the incidence of skiing-ACL injuries appears to have stabilized at 3000 MDBI. The incidence of MCL injuries is slowly but steadily improving during the past 24-years — but MCL injuries remain the most frequent injury in skiing. During the 2019-‘20 ski-season, approximately 30,000 skiing-ACL ruptures were estimated to have occurred, worldwide. See injury-incidence trends, below. ‘Prevalence’ is not reported here because this form of data appears to be misleading to many non-epidemiologists. Again — and it is worth repeating — MCL and ACL injuries are, by far, the most frequent injuries in alpine skiing, today. See graph.
Incidence, skiing MCL / ACL / tibia injuries, 1970 to 2016.
ACL injuries are severe: ~80% of all diagnosed skiing ACL-injuries are Grade-III — complete rupture. Approximately 40% of all skiing ACL-ruptures are repaired or replaced. ACL replacement surgery requires US$20,000 to US$50,000 for diagnosis, treatment and rehabilitation — not including the cost of lost work and an average of loss of 200 days of less-than-normal athletic-function. Even highly rehabilitated World Cup ski racers rarely return to their full athletic potential after ACL-rupture. ~50% of all skiers with Grade-III ACL-injury (complete rupture) develop Grade-3 Kelgren-Laurence or Grade-2 Tönnis classified osteoarthritis within 10-years of reconstructive surgery. This magnitude of arthritic severity can last a lifetime. ACL-rupture is severe. Skiing-ACL injuries are both frequent and severe.
MCL injuries — the most frequent type of injury in alpine skiing, today — are not as severe as ACL injury. An average of 120-days of less-than-normal athletic function is lost. This difference in severity is because the MCL is surrounded by a robust supply of oxygen-rich blood-flow to promote healing. Comparatively, the ACL is surrounded by minimal blood flow. This means treatment and rehab of MCL injury is less severe than ACL injury.
Female ACL epidemiology
Female skiers incur ~3-times the amount of ACL injuries compared with male skiers (7-times more in basketball—though different injury-mechanisms are involved in skiing and basketball). It appears to leading orthopedic researchers that the main factors associated with the gender differences in ACL injuries might be that females have: (1) greater valgus-angle (Q-angle) which pre-loads the ACL (and MCL); (2) sharper femoral-notch in which the ACL is positioned, which notch can cut the ACL; (3) a lower ratio of ACL-strength to body-weight; (4) steeper, reverse-sloping tibial-plateau, which steepness serves as an inclined-plane to elongate the ACL during large ground reacting forces; and (5) weakening of the ACL during the pre-ovulatory phase of the menstrual cycle. Evidence-based research on causation remains scientifically unclear since June, 2018 because the studies were not normalized for age. So far, current (March, 2020) research by Bruce Beynnon, PhD, appears to show that gender-differences in tibia-plateau-slope-angle produce the largest gender differences in the risk of sustaining ACL-rupture — but this finding is not skiing-specific: the primary injury-mechanism in skiing involves abduction-dominant loading (75% to 80% of all skiing ACL-injuries), not BIAD-loading that biases tibia-plateau slope-angle (~10% of all skiing ACL-injuries). ‘BIAD’ is acronym for ‘boot induced anterior drawer’. Irrespectively of defining causation, current epidemiology clearly correlates female skiers to a significantly greater risk of ACL-rupture compared with male skiers (Johnson; separately, Binet-Laporte).
Skiing ACL injury mechanisms
The most prevalent skiing-ACL injury-mechanism appears to be, ‘Slip-Catch’ (Bere; Senner) — which mechanism is similar to ‘Phantom-Foot’ (Johnson, Shealy, Ettlinger) because both mechanisms involve abduction-dominant loading. Slip-Catch is shown at the instant of ACL-rupture in this photo:
In the predominant Slip-Catch scenario, the outside ski 'slips' laterally in the snow, then the edge 'bites', laterally, during the compressive-build-up of snow under the ski — producing a large ground-reaction force. This scenario causes the lateral component (lateral and co-planar to the top and bottom surfaces of the ski) of the ground reaction force to generate an abduction-force located slightly behind the projected-axis of the tibia. When famous Burke Mountain Academy ski coach Warren Witherell visited Howell’s biomechanics lab, he coined the location of the abduction-force on the test ski — the ‘Sour Spot’. How true.
The key component of the applied-load at the Sour Spot on the ski is an abduction-force that acts over the length of the lower-leg — including the thickness of the boot-sole and the standheight of the binding — to produce a large abduction-moment through the center of the knee, generating large strain across the ACL. See drawing below.
In a ‘Slip-Catch’ scenario the ski slips while the skier's body-mass continues to load the edged-ski. The knee is forced into an exaggerated valgus-angle. This form of kinematics produces a large abduction-moment. ‘And because the Sour Spot on the ski is located slightly behind the projected-axis of the tibia, a Slip Catch episode also generates a small amount of torsional-torque about-the-long-axis-of-the-tibia. (The concept of "twisting", as a stand-alone term, is meaningless: "twisting" about what? Most of the ‘twisting’ in a Slip Catch scenario is about the femur, not the tibia.) Clearly also, the downward compressive-component of a Slip Catch event pushes the distal-end of the femur (the condyles) downward on the reverse-sloped surface of the tibial-plateau (causing anterior-drawer loading) further increasing strain across the ACL. In a Slip-Catch scenario, compression-loading combined with a large abduction-moment plus a small amount of tibia-torque — produces massive strain across the ACL, the MCL and the meniscus.
( When a backward-bending-moment that is centered at the proximal end of the tibia has greater magnitude than a lateral abduction-moment that is centered within the ACL, the injury mechanism converts from Slip Catch (or Phantom Foot) to ‘BIAD’.)
All of these forces, torques, moments, valgus-angles, and tibial-plateau slope-angles mix together to produce large strain across the ACL, the MCL and compresses the lateral side of the meniscus. Depending on the magnitude of these loads the ACL can become mildly sprained ('Grade-I'), significantly-sprained ('Grade II'), or ruptured (Grade III); the MCL can be over-strained; and the meniscus can become torn.
‘Experts’ who are also orthopedic-researchers — and some who are also PhD's in mechanical engineering — have, for 4 decades, rendered a myriad of loading-scenario opinions on these various skiing-ACL injury-mechanisms — only to be disputed by other groups of 'experts'. Here's one possible — perhaps plausible — opinion on the prevalence of the 3 main types skiing ACL-injury-mechanisms.
This opinion about the prevalence of skiing ACL-rupture mechanisms comes from Robert J. Johnson, MD, Director of Orthopedic Research at University of Vermont College of Medicine, Department of Orthopedics and Rehabilitation (speaking also on behalf of his research-colleagues, Jasper Shealy, PhD and Carl Ettlinger).
Large abduction-moments are involved in the most prevalent skiing-ACL injury mechanisms
If the mechanism-prevalence opinion by Johnson/Shealy/Ettlinger is correct, the most prevalent mechanism representing ~75%-to-80% of all skiing-ACL injuries appears to be abduction-moment dominant. In this scenario, compression-loading and tibia-torque are present, too — but tibia-torque is very low in magnitude — equivalent to lite children’s torsional release settings (1, 2, or 3 daNm). With respect to compression-loading, it is inappropriate to have release in response to large downward-compressive loads because pre-release could occur as a dangerous side-effect during many controlled skiing maneuvers. Release in response to tiny amounts of tibia-torque, would — for adults — cause the dangerous side-effect of pre-release during minor skiing-technique errors. Pre-release is unacceptable because it can cause severe head and spine injury — injuries far worse than ligament damage.
Further, release in response to BIAD-loading is possible through vertical-toe-release (Geze SE3) or with downward actuation of a special heel-pad (a variant of the Rolf Storandt patent that Professor Chris Brown is theorizing based on a good algorithm theory published by Dan Mote) — but essential skiing-control loads, such finishing a turn with rear-weighting, involve significant BIAD-loading — causing frequent pre-release for Type-3 skiers. That’s why the Lange RRS ski-boot and Geze SE3 ski-binding failed. Again, pre-release is unacceptable because the injuries sustained from pre-release can be far worse than the injuries sustained by non-release. Pre-release can cause severe head / back / mid-organ injury. Further, BIAD-related ACL-ruptures comprise only ~10% of all skiing ACL-ruptures — whereas abduction-dominant ACL-ruptures comprise ~75% to 80% of all skiing ACL-ruptures. Because of the adverse side-effects of pre-release involving bindings that address the pure-BIAD ACL-injury mechanism, intervention-focus on pure-BIAD is attenuated.
Backward-twisting induced ACL-injury can be resolved through multi-directional toe release. Backward-twisting-related ACL-ruptures comprise only ~10% of all skiing ACL-ruptures — whereas abduction-dominant ACL-ruptures comprise ~75% to 80% of all skiing ACL-ruptures. Almost all ski-binding toe-pieces already provide multi-directional release to address this 10%-prevalence episode.
To address the primary ACL-injury mechanism involving abduction-loading — special lateral-heel release must be the focus of intervention.
( It’s important to note that when large downward compressive-loads — vertical ground reaction forces — and anterior-drawer loads are present, large abduction-moments are also present. Therefore, ‘special’ lateral-heel release in response to large abduction-moments also addresses large compressive-loading and anterior-drawer-loading that can contribute toward ACL-rupture. )
Additional lateral-heel release responds directly to abduction-moments that would otherwise cause ACL-rupture and MCL-rupture — but only if (a) the magnitude of lateral-heel release is specially tuned to variation in skier-size and gender; and (b) only if pre-release is mitigated independently of the special lateral-heel release-settings.
Only Howell SkiBindings have additional lateral-heel release properly tunable for skier-size and gender — and — strongly mitigates pre-release without elevated settings.
Howell SkiBindings founder, Rick Howell, invested 47-years into the research and development of special lateral-heel release settings — that accommodate variation in skier size and gender — to mitigate ACL-rupture. The R&D behind the special lateral-heel release-settings for skier-size and gender was peer-reviewed-and-approved by the scientific committees — and presented by Rick Howell in the Spring of 2019 — at ICSS (International Conference on Science in Skiing) in Voukatti, Finland — and in the Spring of 2019 at ISSS (International Society for Skiing Safety) in Squaw Valley, California, USA.
The means-plus-function-technology that decouples lateral-heel pre-release from lateral-heel release is now ruled to be ‘prior-combined-art’, now open-art-technology, per the USPTO Patent Trial & Appeal Board Decision dated October 15, 2018, Case IRP2017-01265, involving annulled US Patent 8,955,867 B2. Case IRP2017-01265 was upheld on appeal (U.S. Patent 8,955,867 B2 was annulled) by the U.S. Court of Appeals for the Federal Circuit in 2019-1341 on December 11, 2019. It is therefore reasonable to expect that the parent-patents of the annulled-patent are also now annulled, or are imminently annullable, unless however Rick Howell controls the defense against the prospective annulment of the related parent-patents. However, irrespectively of the existing and prospective annulment-actions, U.S. Patent 9,463,370 is a separate invention from the above prior-art — and operates independently and uncontestedly of the other now-annulled patents, contractually — and is the heart of Howell SkiBindings.
Biomechanical validation of ACL-friendly function
To validate the effectiveness of specially-tuned, non-pre-releasing, lateral-heel release in response to large abduction-moments that are combined with small amounts of tibia-torque — the above-noted combined-loads that cause ACL-rupture — Howell SkiBindings rely on a proven variant of the experimental biomechanical analysis technique involving ‘release-envelopes’ first-developed by Case Western Reserve University Professor Eugene Bahniuk. See the ‘envelope’ discussions in ‘Part-1’, above.
To produce special release envelopes that reveal the ACL sour-spot and that quantify ski-binding response to the sour-spot, special test methods were developed involving metallic surrogates that model the essential anthropometrics of the lower-leg that produce ACL / MCL / meniscus injury. Four variables were measured: position of applied abduction-force; magnitude of applied abduction-force; resultant abduction-moment; and resultant tibia-torque.
The release-envelope-method converts ‘expert opinion / speculation / conjecture’ about injury-mechanisms derived from subjective visual-analysis — into deriving hard engineering data on the abduction sour-spot and ski-binding response to large loading positioned at the sour-spot. The release-envelope-method applies proven structural engineering practice to uncover the skiing-ACL problem . The Howell test-method involving a special release-envelope provides a major paradigm shift to analyze the skiing ACL injury problem.
Development of an ACL-rupture envelope.
We began by benchmarking a tibia-fracture envelope. The torsional fracture-limit of an average U.S. male’s tibia is ~11.3 daNm (~11.3 ‘DIN’) [Asang, Wittman, Hauser, 1980] no matter where an applied-abduction force enters the ski. A tibia-fracture torque-envelope produces a horizontal straight-line across the envelope to depict tibia-fracture-torque as a function of where the applied-force enters a ski. See thick horizontal black line in the torque-envelope, below, that extends from -75cm to -45cm along the section of the ski behind the projected-axis of the tibia.
Next, we sourced data on the structural threshold of an average U.S. male’s ACL when exposed to varying combinations of abduction-moments and tibia-torques [Chaudhari, Andriacchi, 2015, ‘[Abduction-Moments] Plus [Tibia-Torques] Increase ACL-Strain More Than Either Alone]’ — terms adjusted to reflect current vernacular. See curved orange envelope, below, for the extrapolated threshold of an average U.S. male’s ACL at 20% ACL-elongation.
In skiing, varying magnitudes of potential-injury-producing forces enter a ski at varying positions along its length. Due to the leverage-effect of a ski, the relative-magnitude of the resultant-tibia-torques and resultant-abduction-moments that flow into the human musculoskeletal system vary, depending on where forces enter the ski. Forces that enter the tip or tail of a ski produce a high ratio of tibia-torque to abduction-moment. Forces that enter the ski near its center produce a high ratio of abduction-moments to tibia-torques. ACL-rupture aligns with high-ratios of abduction-moments to tibia-torques. See the thick green (abduction-moment) and red (tibia-torque) envelopes, below, wherein abduction-forces are applied to various points along the length of the ski until the combined abduction-moments and tibia-torques reach the critical magnitude depicted in the orange threshold, above (the ACL-rupture threshold). These findings present a major biomechanical breakthrough:
This data — the combined resultant-abduction-moments and resultant-tibia-torques at ACL-rupture that vary, as shown, depending on the position of the applied-abduction load into the ski — is too complex for ski-bindings to address, directly.
To simplify the data for an ACL-related release-response of a ski-binding — we converted the above tibia-torque and abduction-moment data into applied-force data that’s a function of where the applied-force enters the ski. This conversion presents another major biomechanical breakthrough.
Ski-bindings — with a toe that releases laterally, mixed together with a special, non-pre-releasing, heel that additionally releases laterally — can read and react to any abduction-force that enters any point along the length of a ski when the ratio of the toe/heel settings are specially-tuned to fit within the limits of applied-force-envelope, below. The release-response must be below the tibia-fracture-threshold, below the ACL-rupture threshold and above the pre-release-threshold. This approach — and the special tuning — represents major biomechanical breakthrough:
Biomechanical thresholds of an average U.S. male’s tibia (in torsion), ACL (in combined abduction-moment and tibia-torque), and pre-release (co-planar to the top or bottom surfaces of the ski).
Testing ski-bindings in conjunction with applied-force-envelopes for ACL-integrity:
Ordinary 2-mode ski-bindings fail relative to ACL / MCL integrity.
Interposing alpine ski-bindings into this test method represents a major biomechanical breakthrough. The above force-envelopes depict the release-response of an ordinary 2-mode alpine ski-binding when set at DIN 6, 5 and 4 (actually, 6, 5 and 4 daNm of torsional-tibia-torque). See thin force-envelopes: blue/6, red/5, black/4.
Even if the ordinary 2-mode alpine binding is set at DIN-4 (thin black force-envelope) ACL-rupture (and/or MCL-rupture) can occur. DIN-4 is not skiable by an average U.S. male weighing ~170 pounds because the dangerous side-effect of pre-release occurs. Pre-release is not acceptable. No matter how low an ordinary 2-mode binding is set to release — even at levels where pre-release can easily occur — ACL-rupture and MCL-rupture is plausible. Reducing ordinary 2-mode release-settings will not reduce ACL-injury or MCL-injury. This is a major finding.
(( Notice also the large margin between all of the above ordinary 2-mode binding’s release-force-envelopes and the tibia-fracture force-threshold envelope (thick black envelope). These large (good) margins explain why skiing tibia-fractures barely exist with properly-set ordinary 2-mode ski-bindings, today. Bravo, 2-mode bindings—for providing tibia integrity. 'But these envelopes critically illuminate adverse ‘ordinary’ ski-binding function with respect to the ACL and to the MCL. This is a major finding. ))
Through the use of ‘envelope analysis’ — where ALL plausible injury-mechanisms are comprehensively tested on ordinary 2-mode bindings — the skiing-ACL and MCL problems are exposed. Shame on the other ‘ordinary binding’ companies for not addressing this engineering problem: this is why the skiing ACL-injury problem has run unabated.
New Howell SkiBindings — with additional, non-pre-releasing, specially-tuned, lateral-heel release — release below ACL-rupture, below MCL-rupture, and therefore below meniscus-rupture. See thin black release-force-envelope, below (purple is the MCL-rupture threshold):
Modes of release affect ACL-integrity & MCL-integrity
How do these two different types of bindings — 2-mode and 3-mode — produce different release-envelopes?
Howell SkiBindings uniquely produce a fundamentally different release-response to large abduction-forces that enter the back half of the ski — below theoretical ACL-rupture below theoretical MCL-rupture — through specially-tuned, non-pre-releasing, lateral-heel release.
Specification for additional lateral-heel release to mitigate ACL and MCL injury.
Recommended lateral-heel release settings — only for Howell SkiBindings — are based on the biomechanical engineering science presented by Rick Howell at ICSS-Finland and ISSS-Squaw Valley USA and based on the open-art anti-pre-release function of each mode of release within Howell SkiBindings.
For example, each time the ski flexes — even slightly — the unique open-art lateral-heel release mechanism within Howell SkiBindings powerfully forces the heel of the boot to re-center — laterally and vertically — unless the above-specified lateral-heel release settings are approached ... at which point the lateral-heel release mechanism provides elastic re-centering to dissipate innocuous loading OR the lateral-heel release mechanism provides full lateral release when a potential ACL / MCL injury-load persists for a few milliseconds toward approaching the critical elastic-limit of the ACL or MCL.
For convenience, the visual release indicator on the lateral-heel release adjustment mechanism of Howell SkiBindings has a numbering-system based on these factors:
1— Lateral-heel release-force specified by Howell SkiBindings for any given visual indicator number is not the same lateral-force supplied by the same visual indicator number in the toe. It is not the same force supplied by other bindings with lateral-heel release (e.g. - not the same lateral-heel release-force as in the ‘Marker Kingpin’ AT pin-binding).
2— Recommended lateral-heel release-settings for Howell SkiBindings include an additional correction factor for gender: females are provided with a lower lateral-heel release-setting compared with males — based, in-part, on the skiing-ACL / MCL epidemiology and skiing-ACL / MCL biomechanics outlined above.
3— For skiers who select settings above ‘8’ for lateral-toe release — the lateral-heel release-setting should remain at ‘8’. If a skier prefers to waive ACL / MCL-friendly skiing, the top of the lateral-heel release-adjustment scale — beyond ‘8’ — only provided in Howell SkiBindings — provides a fully ‘BLOCKED’ setting — as denoted on the visual indicator ( “BLOCK” ).
The derivation of Howell-recommended lateral-heel release-settings is based on 47-years of biomechanical research and development that was presented at ICSS-Finland and ISSS-Squaw Valley USA in 2019.
Additionally, the low 17mm standheight in patented Howell SkiBindings biomechanically reduces cumulative and episodal strain across the ACL, MCL and meniscus.
And, finally, lateral-heel release in Howell SkiBindings is functionally decoupled from edge-control. Intentionally putting a ski up on edge on ice — fully loaded — does not actuate the lateral-heel release-mechanism in Howell SkiBindings. You can ski flat-out in full-control without dangerous pre-release.
In these unique and patented ways, Howell SkiBindings provide an extraordinary tibia-friendly, ACL-friendly, MCL-friendly and edge-control skiing experience — importantly noting that Howell SkiBindings can significantly mitigate, but never fully-eliminate these or any other types of skiing-injuries.
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U.S. Patent 9,463,370
Footnote 1: The engineering terms, "bending-moment" or “abduction-moment” are applied to structures (such as the tibia) when forces and lever-arms cause the structure to 'bend' about its long-axis. The related term, "torque" is applied to a structure (such as the tibia) when forces and lever-arms cause the structure to twist about its long-axis. In both cases — 'moment', or 'torque' — the simple engineering equation that applies to the phenomena is, "T = f X r", where "T" can be either 'torque' or 'moment'; "f" is the applied-'force'; and "r" is the 'distance' between the applied-'force' and the point at which the 'torque' or the 'moment' is being resolved, measured or analyzed. In the case of a 'moment', one must select a singular point along the length of a column (tibia) to analyze the instant bending-'moment' at that instant-point (the resolution of a bending-moment is position-dependent — e.g., ‘where’, along the length of the column is the resultant bending-moment being analyzed ? ). Alternatively, ‘torque’ can be measured at any point along the length of a column (tibia) to analyze the magnitude of the torsional-load. When the term 'forward-release' is utilized with ski-bindings — it is intended to mean 'forward-bending-moment at release'. (The term 'forward lean release' is an incorrect misnomer: 'forward lean' is the angle of a boot's upper-shaft relative to the ski. The person who coined the term, 'forward lean release' was not much of a skier and did not really understand skiing. Besides, Spademan — when it was fully-developed just before its demise — could no-longer release in a pure-forward-shear direction, so there is no longer a need to differentiate between 'forward-lean release', ‘forward-shear release’ and just plain 'forward release', especially since ‘lean’ means boot-shaft-to-ski-angle, not mode of release.)
Footnote 2: The lay-term “load” means — 'torques', 'bending-moments', ‘abduction-moments’, ‘edging-moments’ and/or 'forces' in the above essay.
Footnote 3: Biomechanical tibia-fracture data: Skiing Safety II; Editor, Jose Figuras, MD; 1978, ISBN 0-8391-1209-2, chapters by Ernst Asang, Gerhard Wittman and Wolfhart Hauser, MD.
Footnote 4: Current anthropometric data: U.S. National Highway Traffic Safety Administration, Research & Data, 2017; and The Measure of Man and Woman: Human Factors in Design, Alvin Tilley, Henry Dreyfuss, ISBN-10: 0471099554.
Footnote 5: 'Ski Binding Settings Based on Anthropometric and Biomechanical Data'; Malcolm H. Pope, DrMedSci, PhD; Robert J. Johnson, MD; Human Factors, Vol.18, pp 27-32, 1976.
Footnote 6: 'Discretionary Settings' are allowed by specific provisions contained within international ski binding release recommendations standard DIN/ISO 8061.
Footnote 7: 'The Biomechanics of Contemporary Ski Bindings'; Journal of Safety Research, Vol. 4, pp 160-171, 1972, Eugene Bahniuk; 'Analytical Studies of the Biomechanics of Contemporary Ski Bindings', Mechanics and Sports, The American Society of Mechanical Engineers, pp 221-236, 1975, Eugene Bahniuk; 'Theoretical Estimation of Binding Release Values', Orthopaedic Clinics of North America, Vol. 7, No. 1, pp 117-126, 1976, Eugene Bahniuk; and 'A Method for the Testing and Analysis of Alpine Ski Bindings', Journal of Safety Research, Vol 12, No. 1, pp 4-12, 1980, Eugene Bahniuk et al.
Footnote 8: When release settings are changed upward or downward, the entire uniquely-shaped release-envelope of any given ski-binding design, shifts upward or downward: the shape of each unique ski-binding's release-envelope does not change. This means that a release-setting prescribes only one small aspect of the overall release function. This issue is key and important to understand and recognize in terms of critical limitations of all release-settings in all ski-bindings. Some bindings’ unique design-parameters address functional-requirements far better or far worse than others. Any binding’s release setting does not control the shape of its envelope (see complete essay, above). Release-envelopes derived by the method that is standardized according to ISO-9462 Annex-B — which standard provides a method to compare different binding function (set at the same release-levels according to ISO 9462 Annex-A) exposes large functional differences with regard to the resultant loads that flow into the tibia; and — in the Howell-modified-version of ISO 9462 Annex-B — measures additional applied-forces and additional resultant abduction-moments (as specified by Howell, see above) to expose diametric differences among ‘ordinary’ 2-mode alpine ski-bindings compared with ‘extraordinary’ 3-mode alpine ski-binding with respect to the resultant loads that flow across the ACL.
Footnote 9: Certification of compliance with ISO 9462 ('ski-binding release characteristics' and some functions pertaining to 'retention'); ISO 9465 (lateral toe retention during dynamic impact); and ISO 11087 (ski-brake function) — conducted by an independent lab — is mandatory according to statutory law in Germany, Austria, and Switzerland. In Switzerland, bindings that are not certified by the world’s only independent ski-binding testing lab in Munich, Germany that is equipped to test alpine ski-binding function according to the minimum international safety standards, ISO 9462, ISO 9465 and ISO 11087— are physically removed from retail ski shops by the Swiss-BfU (Swiss Bureau for Prevention of Injury) according to Swiss statutory law. In Vermont, USA, the judicial branch of government believes (in case law) that ‘meeting safety standards adversely affects the growth of a company’ and therefore safety standards must not apply to alpine ski-binding function. The Howell SkiBindings enterprise believes that meeting minimum international ski-binding safety standards ISO 9462, 9465 and 11087 as certified by the world’s only independent ski-binding testing lab — TÜV-Munich — must apply to all ski-bindings made, used, sold or induced to be sold anywhere, including Vermont, despite the rulings of the Vermont state judiciary.
Footnote 10: References: (1) Dominik Heim, MD; SITEMSH-Japan, 2016. (2) Zorko; Nemec; Matjacic; Olensek; Alpine Skiing Simulations Prove Ski Waist-Width Influences Knee Joint Kinematics; ISSS-Innsbruck, Austria, 2017. (3) Stenroos; Pakarinen; Jalkanen; Mälkiä; Handolin; Tibial Fractures in Alpine Skiing and Snowboarding in Finland: A Retrospective Study on Fracture Types and Injury Mechanisms in 363 patients; Scand J Surg Off Organ Finn Surg Soc Scand Surg Soc., Sept 2015, doi:10.1177/1457496915607410. (4) Improved Short Term Outcomes in Tibial Plateau Fractures of Snow Sports Injuries Treated with Immediate Open Reduction Internal Fixation; Janes, MD; Leonard, MSPH; Phillips, PA-C; Salottolo, MPH; Abbott, MD, Bar-Or, MD; ISSS-Innsbruck, Austria, 2017.
It was inevitable.