INFORMATION FOR ENGINEERS, ORTHOPEDIC SURGEONS, EPIDEMIOLOGISTS AND PHYSIOLOGISTS — ABOUT ‘RELEASE’.
The release decision of all ‘certified’ alpine ski-binding is based on the structural thresholds of the tibia — plus a margin — as indirectly prescribed by the international alpine ski-binding safety standards, DIN/ISO 9462 and ISO 8061 — as well as being based on pre-release thresholds and respective anti-pre-release (retention) margins.
Howell SkiBindings also uniquely provide ACL-friendly skiing — based on extraordinary, new, biomechanical research. See Part 2 below.
‘Measuring peak applied abduction force along a range of positions on a surrogate biomechanical skier. The resultant torsional-torque about the long-axis of the surrogate-tibia and the resultant abduction-moment in the center of the surrogate-knee 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 torsional-fulcrums and bending-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'), and (c) strain across the ACL, MCL and into the meniscus through the use of a special, open-art, additional, non-pre-releasing, lateral-heel release mechanism that functions within the heel-unit of Howell SkiBindings. Regarding (c) ‘ACL’, see Part 2 below.
( Special note — No ski-boot can release ‘laterally’ through the side-lugs of any pivot-turntable. This is why pivot-turntable bindings can cause ACL / MCL / meniscus injury. Further, bindings with ‘diagonal heel release’ cannot read or react to ACL / MCL / meniscus injury loads that typically involve the combination of a large abduction-moment PLUS downward-heel-weighting — because ‘diagonal heel release’ (formerly-offered by another binding company) responds only to abduction-loads plus upward. Abduction-loading plus upward-loading does not produce strain across the ACL / MCL / meniscus. Howell SkiBindings respond to large abduction loads that typically include downward loading. Again, see Part 2, below re ‘ACL’. )
For important information about the retention-function of ski-bindings, see the 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 (see footnote 2) that are applied to the tibia into a release-response.
When engineering a building 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 reaches its elastic limit (fractures) at ~11.3 daNm during slow-torsion and ~25 daNm during slow forward-bending. These average thresholds apply to male skiers who weigh ~170-pounds who are between 20 and 53 years-old. 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 [footnote 3]. For practical use with ski-bindings, Asang's tibia-fracture data is reorganized, biomechanically [footnote 4]. This essay discusses some of the reorganized tibia-fracture data.
Weakest sections of the tibia
On alpine skis with an ISO-standard alpine ski-boot properly (firmly) buckled …
the tibia is weakest in forward-bending at its proximal (top) end if a large-vertical-force is applied to the ski-boot-binding-human-system under-or-near a binding’s forward-release-fulcrum when the forward-release-fulcrum is located near the tip (toe) of the ski-boot (as with pin-bindings). If a binding provides a forward-release-fulcrum (e.g., the leading-edge of the Teflon-AFD) that’s located under-or-near the ball-of-foot, the resultant maximal forward-bending moment within the tibia — arising from the same large-vertical-force that’s applied near the tip (toe) of the boot — is not only significantly reduced in magnitude, it’s also re-located lower on the tibia AND is more-likely to be ‘detected’ by the ski-boot-binding-system in a way that produces a necessary forward-release. See below.
In torsion, the tibia is weakest where its cross-sectional-diameter is the smallest. This is because — unlike bending-moments that maximize at the fixed-end of a ‘member’, which fixed-end is located at the opposite-end of the point where a perpendicular-load is applied to the member — peak torsional torque is exactly the same at any point along the full-length of the same ‘member’. If, however, the cross-section of the ‘member’ varies along its length, torsional loading becomes concentrated where the cross-section is the smallest.
The differences between measuring torsion and bending are night and day. Torsion can be measured anywhere along the length of a member to gain the peak torsional-load. Bending-moment measurement is location-dependent: if one want to determine the peak lateral-bending-moment (the ‘abduction-moment’—again, see Part 2, below) within the ACL, the bending-moment-sensor must be located at the point of where the surrogate-ACL is located. If one wants to measure the peak forward-bending-moment just-below the tibial-plateau (to analyze skiing-loads that cause tibia-tuberosity fracture), the bending-moment sensor must be position at the desired-point below the tibial-plateau. When measuring the peak edge-control moment resisted by a ski-binding — the bending-moment-sensor that measures this lateral-bending-moment must be located in-line with the long-axis of the ski through the long-center-axis of the toe-and-heel of the binding. These differences between measuring torsion and bending are diametrically different — and key toward properly understanding the interaction between the human musculoskeletal system and ski-bindings.
In the presence of combined torsion/forward-bending loading on alpine skis, the tibia is weakest where the net-vector-sum of the two types of loads (torsion; and bending) is the greatest, as well as where the cross-section of the tibia along its length is smallest (all 3 factors contribute). With respect to the binding’s influence on distributing combined torsion-bending loading into the tibia — the net-vector-sum of the peak torsional and peak bending loads are adversely amplified when a given binding’s fulcrum’s are not located where the tibia is weakest: this means that blind-spots are developed between what a given type of binding reads and reacts-to compared with the net-load received and resisted by a tibia. Binding -fulcrum-location (between the boot and ski) in all 3 rotational axis is key to the flow of net-loading into the tibia.
Tibia fractures that occur inside a properly standardized alpine ski-boot occur when the boot is not properly (firmly) buckled — because the full injury-producing-load did not pass between the boot and the binding (obviously, a large portion of the load flowed directly into the tibia, never reaching the binding).
(The fibula receives injury-producing (fracture) loads that largely never flow through a binding. Fibula-fracture typically occurs when large loads are applied directly to the lateral-side of the lower leg — such as when falling to the side and then having the lateral-side of the lower-leg impact the top of a firm mogul or other solid-object. Bindings cannot release in response to loads that never flow through the binding.)
No protection of the tibia by muscle activity
Muscle activity cannot intentionally add strength to the tibia because skiing injury-loads can occur faster than 'fast-twitch' muscles can be turned-on in a direction and magnitude that could reduce an injury-producing load, but intentionally contracting a large cluster of muscles can attenuate some externally-applied loading. Inversely, there is no experimental, epidemiological or observational scientific proof that muscle activity can subtract appreciable strength from the tibia if inadvertently applied in a way that amplifies an externally applied load. The failure criteria of the tibia for use in ski-binding engineering must 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 some of the injury-producing load to not flow through the binding. Boot-fit and proper-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 leg / ski-boot / binding / ski. If a boot is buckled too loosely — an injury-producing-load cannot be fully-transferred into 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 diameter to length (also see above).
(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.)
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 correction factors based on height are found within the international safety standard for the selection of alpine ski binding release settings, ISO 8061, as well as within all of the alpine ski-binding release adjustment charts that are supplied by all of the alpine binding manufacturers.
(Note: no release setting recommendations can be effectively applied to pin-bindings because pin-binding function is inherently/fundamentally flawed.)
Corrected skier-weight is a practical predictor of tibia strength.
Further however, in orthopedic research and biomechanical engineering research, the application of x-ray-derived or MRI-derived tibia geometry — such as for learning more about factors that relate to the strength of the tibia; or learning more about tibial plateau compression-fracture characteristics to help ACL-research — is essential for the development of ACL-friendly ski-bindings and other related injury prevention interventions.
• 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 the 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, including ski-bindings, become compounded during slow-moving mechanical operations. See graph, below.
• Combined-loading into the tibia — Again (see above) bones are weaker during combined torsion-bending loading when compared with pure-torsional loading or pure-bending 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 significantly 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 is 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 added strength). Bone fractures that are not fully healed can cause the tibia to 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 medical 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 medical doctor for medical advice.
Practical reality of ski-binding release-settings on mitigating tibia fracture.
The relationship between an individual's scaled anthropometrics and bone strength is well-correlated. Ski binding release settings are 'adjustable' expressly to accommodate the prime anthropometrics 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 and 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 engineer the binding-mechanism to supply maximum retention while meeting essential release-functions. 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-based release threshold.
The French approach is to engineer the binding mechanism to supply maximum multi-directional release while meeting essential release-functions. Then, if the release-function of the binding is performing as defined throughout this essay on release — the binding's setting is adjusted to a minimum skiable retention threshold.
Howell SkiBindings company believes that a binding must 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 standards ISO 8061 and ISO 9462. The pre-setting can then be fine-tuned through the proper use of the 'Self-Release Method' (see below). With the special know-how that’s engineered into Howell SkiBindings, most skiers can leave the pre-settings — as recommended by ISO 8061 — unchanged. This unique outcome is a major advancement in alpine ski-binding function. See also the ‘Retention’ sub-section within the ‘Tech Info’ section of this website.
’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 new Howell SkiBindings. In this way, release is both (a) smooth — only when needed, biomechanically — and (b) retention / anti-pre-release is powerful — always when performing controlled skiing and even during controlled-aggressive skiing. Only Howell SkiBindings deploy fully-decoupled Axiomatic Engineering technology. Only Howell SkiBindings deliver powerful anti-pre-release / powerful retention / independently of the release-function. Howell SkiBindings are uniquely the 1st bindings that can be skied at 'DIN chart settings' (DIN/ISO 8061) without pre-release. This is a 1st — a major new advancement — 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. Properly derived “discretionary settings” are within the provisions of DIN/ISO 8061. The correct application of the Self-Release Method also helps to (a) assure the settings that are 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, Howell SkiBindings must be mounted and adjusted for proper (Howell SkiBindings specified) function by a Certified Howell SkiBinding Technician. You can become one, on-line. See Catalog section within the menu.
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 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 the possibility of falling.
- Readjust the heel setting until forward 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 ... laterally AND 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 (fast loading does not account for the effects of visco-elasticity).
- 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.
Final lateral-toe and final forward-heel settings can be different (as provided by the ‘Discretionary Settings’ exception within DIN/ISO 8961.
Lateral-Heel Self-Release Setting:
• Match the lateral-toe indicator-setting that is derived by the use of the Self-Release Method onto the lateral-heel indicator-setting of Howell SkiBindings.
ALL of the above information pertaining to the use of the Self-Release Method to derive special release settings is applicable ONLY to Howell SkiBindings.
WARNINGS ! Injury can occur during improper methods being used to apply the Self-Release Method, itself: follow the above specified processes, closely, to avoid injury. Further, during skiing, lowered settings derived by the Self-Release Method may cause inadvertent pre-release; increased settings derived by the Self-Release Method may block necessary-release. Self-Release-derived settings are critically and adversely ineffective if the binding is not supplying ‘proper function’ as defined in the Howell SkiBindings Technical Manual, which manual relies on the functional-specifications provided by ISO 9462 and ISO 9465. 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’. For example, if the binding is significantly and adversely contaminated by road-salt, the release-settings derived through the use of the Self-Release Method will most likely become too low under certain conditions that override certain types of contamination (causing DANGEROUS pre-release under certain loading conditions) and release will most likely become too high under certain other conditions that bias certain other types of contamination (causing non-release / INJURY / under certain other loading conditions). The Self-Release Method is highly useful ONLY when Howell SkBindings’ release-mechanisms and retention-mechanisms are fully-functional according to ISO 9462, ISO 9465 and ‘Standard Industry Practice’ for durability and anti-pre-release function.
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 (medial & lateral directions); forward-heel; lateral-heel (medial-direction) — as described in detail in the Howell SkiBindings Technical Manual; take appropriate corrective-service-action, if necessary; document the measurements of 3 tests in each of the 3 modes of release (18-tests); and (optionally) indelibly-record the quantitative-middle measurement of each of the 3 modes of release on the top-surface of each ski — left ski and right ski (3 values on each ski).
Howell SkiBindings must be mounted and serviced by a Howell SkiBindings Certified Technician (you can become one, on-line if you have the specified tools) — 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. See above warning in red. The corollary: high release settings together with bindings that provide poor retention-function and/or poor release-function (“release function” is meant here to be different from “release settings”) — are meaningless and dangerous ‘release’ settings. Again, the binding should provide retention-function that is decoupled from the release-function: this can only be accomplished with properly engineered 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 Howell SkiBindings Technical Manual AND in-box instructions supplied with Howell SkiBindings — for all of the service-information that provides ‘proper’ retention-function independently of the release-function and release settings.
Howell SkiBindings have been designed to release the ski from the boot laterally at the toe, in the vertical-mode at the heel, and laterally-outward at the heel — (3 modes) — as well as to retain the ski to the boot during controlled skiing maneuvers. Despite these features and functions, injury may result from simply falling down or from impact with an object: an appropriately functioning ski binding may not release under all skiing-injury-producing circumstances. Skiing, like all athletic endeavors, involves a certain degree of risk that must be recognized and accepted. Again, additional information about the care and maintenance of Howell SkiBindings can be reviewed in the Howell SkiBindings in-box instructions, the Howell Technical Manual and through the on-line Howell SkiBindings Help Center.
 The optional Self-Release Method is not a direct provision within DIN/ISO 8061 or any other National or international standard.
 The recommended settings within the Howell Release Adjustment Chart conform to ISO 8061 and conform to related provisions within ISO 9462. Boots must conform to the international alpine ski-boot standard, 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 with any ski-binding, especially with the use of short-skis.
Proper 'test measurement' (optional, though strongly suggested) of the release-settings of the complete ski-boot-binding system must involve the use of properly calibrated release measuring instruments by a Howell SkiBindings Certified Technician. Testing the complete ski-boot-binding system for basic release-setting-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 suggested information on how to properly calibrate certain ski-binding release measuring instruments: the best ski-binding release measuring instruments for ski-ships (and for skiers personal use) are ones that directly-measure torsional-torque, forward-bending-moment (and ‘abduction’ pertaining to lateral-heel release). For (optional) torsion and bending testing, we suggest the Vermont Release Calibrator by Vermont Safety Research. Howell SkiBindings is not affiliated with Vermont Safety Research. For ‘abduction’ testing, see the Howell Technical Manual. See the Catalog section of this website. ))
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., magazine ‘binding reviews’ and popular blogs contain dangerously adverse misleading misrepresentations based on zero measurements: these writings have a reasonable expectation of causing serious injury or worse to skiers).
Consumer-level ski-binding 'inspection' for tibia integrity.
Beyond the Self Release Method that helps to fine-tune release settings for special circumstances (see above) and which method also helps to identify ‘gross impediments to release’ — skiers using Howell SkiBindings should know what constitutes proper ski binding function and skiers should know their own individual release settings. Howell SkiBindings in-box instructions provide a wealth of information in this way (link non-published until 1st shipment of bindings planned for October, 2023).
(Beta) Howell SkiBindings Recommended Pre-Settings Adjustment Chart — ONLY for forthcoming Howell SkiBindings. BETA: this chart will be upgraded.
(Beta) Specifications for testing the recommended settings for lateral-heel release to mitigate (never ‘eliminate’) ACL, MCL, meniscus and tibial-plateau injury ( ‘Friendly Skiing’ ). ONLY for Howell SkiBindings. BETA. See Section-2, below for detailed info on ACL-friendly skiing with Howell SkiBindings.
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 and Indemnification programs (link is non-published until 1st shipments, October, 2023). 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 and rental operators on retailer 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 that is measured is 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 (destroyed for industrial recycling) — 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 DIN/ISO 8061 — to which standards all alpine ski-binding companies must comply as certified by an lab — release should occur in a way that limits the selected peak-torsional-torque and bending-moments on the tibia — limits these resultant loads to be as constant as possible — independently of the location of where almost any potential-injury producing force enters the ski (see above). 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; and (b) the pivot-points between the ski and the boot — in both torsion and bending — cannot be perfectly aligned in ways that mitigate a concentration of loading to the weakest points of the tibia. Never-the-less, it's the belief of the Howell SkiBindings company 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 goal 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. Annex-B tests the sensitivity of a binding’s release-function based on where the applied load enters the ski. The key to how a binding should function, biomechanically, is exposed in Annex-B, not in Annex-A. Annex-A is mostly about how a binding should function at the end of a manufacturing assembly-line (which has a different, but significant, importance). Some so-called alpine binding companies do not even have the equipment to test according to ISO 9462 Annex-B ! ( It appears that no pin-binding companies test according to ISO 9462 Annex-B because a watered-down ISO standard was promulgated by one of their own! Clearly, pin-binding companies have no bona fide understanding of ski-binding 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 a ski that is constrained only by a binding while at the same time a standardized test-sole is rigidly held by a instrumented, 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, only the opposite (proximal) end of a surrogate metallic-tibia is rigidly connected to a test frame. 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 also — importantly — allows decoupling of the test device from the unique kinematic function of each type of binding-engineering. By allowing the ski to freely float during release, only the unique engineering of each type of alpine binding controls the kinematic path of motion between the ski and the leg 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 type of alpine binding 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 — and at levels that exceed the structural integrity of the tibia. 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 kinematics of the test device from the kinematics of the ski-binding provides a clear, unconstrained, exploration of each binding’s unique release-function relative to the resultant-(net)-loads that flow into the tibia when applied-forces enter the ski in varying locations. This is important. It is dangerously ignored by some alpine binding companies — and it is ignored by all pin-binding companies that do not also make alpine bindings. The exploration and understanding of ski-binding kinematics — through experimental testing as provided by ISO 9462 Annex-B — is 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, Inc. — 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 ISO 9462 Annex-A. Meeting minimum standards is ‘the floor’. Howell SkiBindings seeks to exceed ‘the ceiling’ through the use of Annex-B — and even more so by using special improvements that stretch far beyond even Annex-B. (There is even one alpine ski-binding company that sells and ships bindings that do not meet any minimum international safety standards according to ISO 9462 Annex-A or Annex-B ! We won’t name that company — but everyone can see that it is not ‘Approved’ by TÜV according to ISO 9462, 9465 and 11087. Read the labels. )
Expressing the results of the peak resultant-load on the tibia (at release) during varying injury-producing 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 depicted by a specific point in graphic-space that is plotted laterally of the center-line of a graphically-depicted ski — laterally of each point where a test-force is applied to the graphically-depicted ski. Each point in graphic-space that corresponds to where the force is applied to the ski can then be graphically-connected to form a 2D 'release-envelope' — a composite of many individual tests that are applied along the length of the ski. The ideal shape of a 2D release-torque-envelope is a straight line parallel to the ski but off-set laterally to the ski, originating 45cm forward of the projected-axis of the tibia then continuing to flow-forward, parallel to the centerline of the ski; and another line parallel to the centerline of the ski that originates 45cm behind the projected-axis of the tibia then continues to flow toward the tail of the ski. This ideal 2D graphic-representation would depict a binding that holds the resultant torsional torque that is applied to the tibia — to a constant magnitude — no matter where the lateral test-force is applied along the length of the ski, 45cm forward and 45cm behind the projected axis of the tibia. This ideal release-characteristic is nearly impossible in practice — but it is important to know what the ideal goal should be. See thec2D 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 ski — relative to the position of the tibia.
The leverage-effect supplied by the length of the ski boot is also important. The boot sole length amplifies the locations of the binding’s fulcrums. 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 (hopefully) located under or near the ball of the foot. The leading edge of the AFD forms the forward release fulcrum.
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 / fixed engineering of a binding's pivot-point locations — in both torsion and bending — the distance between the force-imparting mechanism of the binding and the binding’s fulcrum-locations — 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 concept in physics is central to the grand-overall function a binding — but this concept is unknown by most skiers and ski-shops when selecting a specific ski-binding. A good structural engineer should be able to see this — but skiers should not have to be a structural engineer to select a binding!
All Howell SkiBindings deploy the concept of building-in specially-positioned fulcrum-points to flatten the release-torque-envelope (and the bending-moment-envelope) as best as possible when loads enter the ski 45cm forward or 45cm behind the projected axis of the tibia — to hold 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. 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’ — without pre-release.
Unique signature of each type of binding-engineering on the resultant-load on the tibia.
Each unique type of binding-engineering causes a unique release-function that produces a unique release-envelope — each type of binding has a unique 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’s type of engineering.
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 partial forward bending-moment — then, a lateral load is applied to the ski until it releases from the boot. The partial 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 graphic pre-load — at a distance that’s proportional to the peak torsional torque that is resolved into the tibia at release. Similar graphic-points are plotted to represent the resulting combined-load on the tibia — at release — when forces are applied to varying locations along the length of the ski. The results of each successive test along the length of the ski can then be connected in graphic-space. This approach generates a 3D 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 that are caused by the positions of the lateral-release-fulcrums and forward-release-fulcrums that are formed between the boot and the ski, relative to the position of the tibia — that are unique to each binding’s engineering. These factors are independent of release settings.
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-bending) 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. See above graphs. 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 behind of the tip of the boot as possible. The standardized-length of all boots’ Glide-Zones limits how far the forward-release-fulcrum can be positioned behind the tip of the boot-sole. There are other engineering-design elements that limit the position of the forward-release-fulcrum, too.
(( 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 less frequent than MCL and ACL injuries. Tibia-fractures have an incidence (not 'incidents') of ~4,000 mean-days-between-injuries (MDBI) today.
1— Tibia fractures among children-skiers are on the rise. Incidence = 3600 MDBI — compared with 4500 MDBI 12-years ago. Higher incidence #’s are comparatively ‘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 binding to provide proper release-function for children’s weaker tibia. 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 super-low-friction AFD — such as pure-Teflon — with a well-defined leading edge (a well-defined fulcrum) that is located ~3cm behind the tip of the boot sole.
2— Other types of previously obscure adult tibia-fractures are now on the rise: severe, high-energy tibia-plateau fractures, tibia-tuberosity fractures are greatly on the rise. 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 type of snow (except Trab TR2; Diamir Vipec; Salomon Shift and Atomic Shift — though Shift brand bindings do not mitigate tibia-fracture in the touring-mode and there are no ACL or MCL injury-mitigation features) — 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-bindings’ release-function (except Trab TR2; Diamir Vipec; Salomon Shift and Atomic Shift: see above) is horrendous at best — many times causing two very high magnitude releases in order for the ski to fully-separate from the boot ... which release-levels are well above the fracture-limits to which any gap-setting can be adjusted ... meaning that the tibia can become fractured twice during one injury-producing event. Further, pin-bindings have nearly zero lateral elasticity before release — 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 future-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 reflect only 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 on the combination of fat skis with pin-bindings on firm snow invites serious trouble. If you are skiing with 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, do not get partially (or fully) trapped in an avalanche: you cannot self-release out of pin-bindings once trapped in an avalanche.
3— Special settings for ’unique’ tibia’s. The extensive biomechanical engineering work that was performed during the late 1960's through early 1970's by several leading researchers produced data that provides tuning of release-settings for individual skier anthropometrics — uniquely for Howell SkiBindings. Key factors that compensate for different anthropometrics include — skier weight (best correlate to tibia strength AND to anti-pre-release); skier height (to correct for over-weight); ‘skier type’ (to tweak the margin of retention); age (to compensate for age-related bone factors); gender (to address differences in risk-taking behavior relating to anti-pre-release. See AfNOR); boot sole length (the leverage-effects noted extensively, above), and discretionary settings that compensate for cumulative-time skiing on firm-snow (triggering bone-strength increases resulting from Wolfe’s Law).
Epidemiology time-line trend, adult skiers:
Incidence, adult skiers: MCL, ACL, Tibia (bending; torsion) trends, 1972 - 2006: Johnson, Ettlinger, Shealy, Update on Injury Trends in Alpine Skiing, 2008, Journal of ASTM International, Vol. 5, No. 10.
Incidence, adult skiers: 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.)
Scroll right for full time-line on the incidence (not ‘incidents’) of adult tibia injuries in alpine skiing (two solid black lines). Tibia fractures are sub-divided into ‘torsion’ and ‘bending’. 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 (“FR”, France). Statistical significance is strong throughout all of this combined data — 1972 - 2016. Larger incidence-numbers are ‘better’ due to more days between injury (note inverted vertical-axis). The calculation of ‘incidence’ in each study accounted for each year’s variation in the ‘population at risk’ (each year’s control-group) at any given interval in time.
Conclusion: tibia-related release-function of alpine ski-bindings
Engineering robust, non-pre-releasing, release-function within top-of-the-line alpine ski-bindings is well within the domain of Howell SkiBindings that are designed by Rick Howell. Rick Howell's engineering-technician education, high-level ski racing, and top-level corporate experience in the ski-binding category is unprecedented (see 'About Us'). The biomechanical function of Howell SkiBindings reflects Rick Howell’s 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 alpine ski-bindings is regulated by international ski-binding standards. All alpine ski-bindings sold in Austria, Switzerland and Germany must be certified for their compliance with international standards ISO 9462, ISO 9465 and ISO 11087 by the only independent ski-binding testing lab in the world — TÜV, in Munich, Germany [footnote 9]. Even if there is no 'local rule' enforcing ski-binding certification — for example, there are no statutes or case laws in USA or Canada requiring certification according to the above ISO standards — we urge all skiers and ski shops to seek only alpine ski-bindings that are independently certified by TÜV — 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, as planned, October, 2023.
Part 2 — ACL / MCL / meniscus friendly skiing.
The low stand-height, non-pre-releasing, ACL / MCL / meniscus friendly, pure-alpine ski-binding function provided by Howell SkiBindings is explained in scientific-detail in the slide-show presented by Rick Howell at the 2017 International Olympic Committee (IOC) conference — Prevention of Injury in Sports — in 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, 2017; at the International Conference on Science in Skiing (ICSS) in Voukatti, Finland, 2019; at the ISSS conference in Squaw Valley, California, 2019; at the ESSKA conference, 2021 (virtual); and again recently at the IOC conference on Preventing Injury in Sport, in Monaco, November, 2021.
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 annual incidence of skiing-ACL injuries has remained nearly constant — and alarmingly high — at ~3000 MDBI. Skiing MCL injuries have mixed reporting (see year 2005 comparing USA MCL-data with “FR” (French) MCL data. It’s estimated that during the 2019-‘20 ski-season ~30,000 skiing-ACL ruptures occurred.
Incidence, skiing MCL and ACL injuries, 1970 to 2016.
ACL injuries are severe: ~80% of all 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 ACL-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.
Scroll right to see full ‘Severity’ graph.
MCL injuries — the most frequent type of injury in alpine skiing, today — are severe, but not as severe as ACL injuries. An average of 120 days of less-than-normal athletic function is incurred with MCL injury. 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 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 skiing 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 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 an acronym for ‘boot induced anterior drawer’. Irrespectively of defining causation, current epidemiology clearly correlates female skiers to a significantly greater frequency 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. The Slip-Catch ACL-injury mechanism 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 about 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 an abduction-moment centered within the ACL is greater in magnitude than a backward-bending-moment that produces anterior-drawer loading on the ACL, the injury mechanism has converted from BIAD (~10% prevalence of all skiing-ACL injuries) to Slip Catch or Phantom Foot (~75% of all skiing-ACL injuries). )
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 overly compressed and torn.
‘Experts’ who are also MD orthopedic-researchers — and some who also combine a PhD in mechanical engineering — have, for 4 decades, rendered a myriad of loading-scenario opinions based on visual observation of these various skiing-ACL injury-mechanisms — only to be disputed by other groups of visual-observation 'experts'. Here's one possible — perhaps plausible — opinion about the prevalence of the 4 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 (D) ).
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% of all skiing-ACL injuries appears to be abduction-dominant. In this scenario, vertically-compressive ground-reaction-forces are present and small amounts of torsional-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) whereas the abduction moment during skiing ACL-rupture events can become very large (as much as 30 daNm with a 50th-percentile male). With respect to large vertical ground-reaction forces / large vertical compression-loading / that can become present during ACL-injury producing events, it is inappropriate to signal the need for ski-binding release solely based on vertical-compression loading because many controlled, non-injurious skiing maneuvers produce large, vertical-compressive ground-reaction forces that do not include large, injury-producing abduction-moments, which abduction-moments are necessary to cause the dominant mechanism in skiing ACL injury. If a binding were to release mostly in response to large vertically-compressive loading, pre-release could easily occur as a dangerous side-effect during many controlled — and importantly innocuous — skiing maneuvers. However, the presence of large abduction-moments during skiing typically includes large vertically-compressive loads: therefore, the binding should respond mostly to large abduction loading, not to large vertically-compressive loading, expressly to avert dangerous pre-release. Further, release in response to the tiny amounts of torsional-tibia-torque that are present during ACL-injury could also easily cause the dangerous side-effect of pre-release during minor skiing-technique errors that induce pure torsional tibia torque at levels that are clearly innocuous in the absence of additionally large abduction moment loads. Pre-release is unacceptable because it can cause severe head and spine injury — injuries that are potentially far worse than knee ligament damage.
Further, release in response to BIAD-ACL-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 Professor Dan Mote) — but essential skiing-control loads, such finishing a turn with large rear-weighting that involves significant BIAD-loading — can easily cause frequent and severe 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 / neck / back / mid-organ injury. Further, BIAD-related ACL-ruptures comprise only ~10% of all skiing ACL-ruptures — whereas abduction-dominant ACL-ruptures comprise ~75% 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 loading is binding-model-segmented to lite but strong female skiers. See Howell Venus model in the Catalog.
Backward-twisting induced ACL-injury can be resolved through multi-directional toe release. Backward-twisting-related ACL-ruptures also comprise only ~10% of all skiing ACL-ruptures — whereas abduction-dominant ACL-ruptures comprise ~75% of all skiing ACL-ruptures. Almost all ski-binding toe-pieces already provide multi-directional release to address this 10%-prevalence ACL-injury episode. Depending on the ratio of multi-directional toe release to pure-lateral toe release — a large, strong, type-III skier should consider the rewards associated with release in response to a non-dominant ACL-injury mechanism (10% prevalence of ACL-rupture during backward-twisting scenarios) compared with the risk of possible multi-directional-toe pre-release during aggressive but innocuous controlled skiing.
To address the primary ACL-injury mechanism involving abduction-loading (approx 75% prevalence) — special lateral-heel release must be the focus of intervention. This focus also mitigates the possibility of pre-release because a special type of open-art lateral-heel release can mitigate (never eliminate) pre-release.
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 — only Howell SkiBindings 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 2019 — at ICSS (International Conference on Science in Skiing) in Voukatti, Finland, in 2019 at ISSS (International Society for Skiing Safety) in Squaw Valley, California, USA, at ESSKA-virtual 2021, and at the recent IOC conference on Prevention Injury in Sport, in Monaco, in November of 2021.
The means-plus-function-technology that decouples lateral-heel pre-release from necessary lateral-heel release is now ruled to be ‘combined prior-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. Further however, irrespectively of 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 core-technology 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 and meniscus injury. Four variables were measured: position of applied abduction-force; magnitude of applied abduction-force; resultant abduction-moment; and resultant tibia-torque.
The envelope-method over-rides ‘expert opinion / speculation / conjecture’ about injury-mechanisms derived from subjective visual-analysis — by providing practical, quantitative, abduction-dominant load-threshold data. The release-envelope-method applies proven structural engineering practice to uncover the skiing-ACL problem . The Howell abduction test-method involving the application of a special release-envelope provides a major paradigm shift to analyze the skiing ACL injury problem.
Development of an ACL-rupture envelope.
Rick Howell 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 the threshold of tibia-fracture-torque as a function of where the applied-force enters a ski. See thick horizontal black line in the tibia-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 can enter a ski at varying positions along its length. Due to the leverage-effect of a ski, the relative-magnitude (they ratio) of the resultant-tibia-torques and resultant-abduction-moments that flow into the human musculoskeletal system vary, depending on where the abduction-forces enter the ski. Abduction-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 at ACL-rupture) 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 abduction-moments and tibia-torques at ACL-rupture that vary, as shown, depending on the position of the applied-abduction force into the ski — is too complex for ski-bindings to address, directly. This depiction is incommensurable.
To simplify the data for a measurable ACL-related release-response by a ski-binding — Rick Howell converted the above combined (incommensurable) tibia-torque and abduction-moment data into applied-abduction-force data that’s a function of where the applied-abduction-force enters the ski. This conversion from incommensurable to measurable presents another major biomechanical breakthrough.
Ski-bindings — with a toe that releases laterally, mixed together with a special, non-pre-releasing, heel that can additionally release 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 the applied-force-envelope, below. The complete 2D release-response must be below the tibia-fracture-threshold, should be below the ACL-rupture threshold and must be above the pre-release-threshold. This approach — and the special lateral-heel release adjustment tuning — represents yet another major biomechanical breakthrough:
Biomechanical thresholds of an average U.S. male’s tibia (in torsion about the tibia’s long-axis), the ACL rupture threshold (during combined abduction-moments and tibia-torques); and the pre-release thresholds (laterally-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.
Testing alpine ski-bindings with this test method represents a 4th major biomechanical breakthrough. The above applied abduction-force-envelopes depict the relative 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) compared with the rupture threshold of the ACL, the torsional fracture threshold of the tibia and the lateral pre-release threshold. See thin applied abduction-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 of the dangerous side-effect of pre-release. 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 5th major finding.
(( Notice also the large margin between all of the above ordinary 2-mode bindings’ 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’ 2-mode ski-binding function with respect to the ACL and MCL. This is a 6th 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 wild and 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 Howell-posited 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 applied-abduction-forces that enter the back (medial-edge) 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.
Beta recommended lateral-heel release settings — only for Howell SkiBindings — are based on the biomechanical engineering-technology science presented by Rick Howell at ICSS-Finland, ISSS-Squaw Valley USA, ESSKA-Virtual 2021, and recently at IOC-Monaco (November, 2021) — and based on the open-art, anti-pre-release function of each mode of release within Howell SkiBindings. These settings are BETA.
For example, each time the ski flexes — even slightly — the unique open-art lateral-heel release mechanism within Howell SkiBindings powerfully causes 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 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 no higher than ‘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, ISSS-Squaw Valley USA in 2019, ESSKA-virtual 2021 and IOC-Monaco 2021.
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 powerful edge-control skiing experience — importantly noting that Howell SkiBindings can significantly mitigate, but never fully-eliminate these or any other types of skiing-injuries resulting from non-release or pre-release.
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Howell SkiBindings, Inc.
PO Box 1274 • Stowe, Vermont 05672 USA
1.802.793.4849 • email@example.com • www.howellskibindings.com
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.