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ACL and Related Knee Injuries.....Shaped Skis Vs Straight Skis - Page 7

Poll Results: Which cause more ACL and Knee related injuries Shaped Skis or Straight Skis

 
  • 50% (9)
    Shape Skis cause more.
  • 50% (9)
    Straight Skis cause more.
18 Total Votes  
post #181 of 192
Quote:
Originally Posted by beyond View Post

I knew there was a reason I usually avoided the Discussion forum, and now I remember. Hi CT.... 

 

If you think he's qualified to tell us all that the debate's over, and here is the Truth about bindings and injuries and such, happy for you. Or if you just want to defend him because I called him on something, not surprised and again happy for you. wink.gif

You again resort to trying to make something personal.  FWIW, I went back and read the guy's posts, again, figuring I'd missed all sorts of caps and stuff.  There were a few, but the main thing I was struck by was the very detailed and thoughtful replies he took the time to direct to a number of questions.  That was a very generous thing for someone with his background in the industry to do.  It doesn't make him the last word on bindings, but his background does make him someone worth listening to.   Same as when a surfboard shaper takes time to discuss shapes, the response should be to be appreciative.   I am sure this thread has been stickied by a lot of people for the rich, technical discussion, of which he was an integral part. 

post #182 of 192
Thread Starter 
Quote:
Originally Posted by beyond View Post

I knew there was a reason I usually avoided the Discussion forum, and now I remember. Hi CT. OK, here goes: 1) Never said you had to be a professional statistician to "understand" statistics, but it helps to have studied statistics formally, because many of the relevant tests, their assumptions, and their specific idiosyncracies, don't pop up in Stat 1 or a book/DVD set. Kind of like folks don't have to be a physicist to "understand" physics, in the sense of what they learned in high school or college intro classes. You get a good overall sense that way. But like the aphorism sez, a little knowledge can be a dangerous thing. I wouldn't want me (whose physics stopped with a year in college) doing anything with it that might involve other folks health. 

 

2) Wasn't attacking either engineers or their track record. We'd all be in bad shape without them. Or we are, compared to countries like China that graduate 5x as many per capita. In fact, I suggested Mr. Howell stick to that, if that's his specialization. 3) You misread my syntax. The "laymen" comment was directed at (drumroll) laymen. Eg, people with no formal training in a particular area. I did not affix this to Mr. Howell; assume he's an engineer of some sort. Industry professional. Of course he becomes a laymen if he's characterizing topics outside his background, regardless of what it is. I'm sure he's worked with statisticians. I doubt he's done much himself. Kinda like politicians explaining economics when they know two well researched staff briefing papers more than the audience.

 

4) IMO, any guy, involved in the field or not, is a problem when he begins to capitalize a lot (which is web yelling, if you recall) and fling his authority around as if he's the last word on any topic he addresses. So I'm fine with Mr. Howell going on at length - which he does, if you follow his presence here - about binding design. Or the mechanics of same - though I'm not convinced he's the only engineer who's ever worked on these issues, or the last word on same - I'm less fine when he strays over into areas that appear to outside his actual training, like epidemiology, medicine, and statistics. His language and explanation of that stuff signal his lack of expertise, actually. I'm especially not fine when he announces various studies he's culled out of the lit as "proving" stuff, or in general reveals his actual ignorance of statistical design. 

 

If you think he's qualified to tell us all that the debate's over, and here is the Truth about bindings and injuries and such, happy for you. Or if you just want to defend him because I called him on something, not surprised and again happy for you. wink.gif

Lies, Lies and damn statistics wink.gif.

 

Fair enough, I don't care what opinion is taken even if it is opposite of what the general direction is, as it is a challenge and in some cases a correct challenge to to get one thinking.  If it is backed up it leads to proper discussion and thereby greatly adding to the discussion.

 

So lets get back to the thread (more or lessrolleyes.gif) and enjoy and learn.

post #183 of 192
Quote:
Originally Posted by oldschoolskier View Post

I believe I've seen one recently some where on some post or another.  This boot may protect against some of the ACL injuries, but I don't think it will in PF.

 

The PF mechanism for ACL injury is not well described but let me try and explain it in layman's terms (as I understand it)

 

Leg bent at 90 degrees at the knee (or more).  This loads the ACL.

 

Imagine the upper leg knee joint is sort of like a "Y" with the 2 top ends of the "Y" being the bearing surface of the knee, the lower leg knee joint is a "T"  with the flat part being the bearing surface.  The ACL hold these 2 piece together and works sort of like the draw string on a Compound Bow.

 

Now with the leg bent, apply sideways pressure at the heel of the foot outwards (our hips rotate in but not out) this causes the "Y" and "T" to separate at the inside edge.  This separation applies additional load on the ACL and in some cases to the breaking point (injury).

 

This is also why there is little torque for the conventional binding designs to release  (this is what Mr. Howell is talking about).  There is little or no loading at the toe. It just feel like steady outwards pressure and knee pain to the point of failure.

 

This is PF as I understand it.

 

Once you grasp this idea the understanding and logic behind straight vs shaped (wide) skis becomes more evident as you now can see the cause, because you see the effect (mechanism).

 

Hopefully, I haven't missed anything or made it to simple.

 

Thanks,

This release cuff can help un-trap the knee in the 90 degree angle and allow for a greater angle relief to occur. Since the shaped ski is more likely to cause a twisting motion to the 90 degree (or less) bent knee more quickly, with a greater change in vector and with its more powerful carve effect vs a slide, it would seem the shaped ski is more likely to create an injury opportunity. On the other hand, the shaped skis are much shorter, and therefore less likely to trap the leg in a vulnerable position as the tail is more likely to come free. Interesting Q. 

post #184 of 192

The Lange RRS ( Rear Release System ) expressly addressed the BIAD ( Boot Induced Anterior Drawer ) injury mechanism, not the PF ( Phantom Foot ) injury mechanism.  Both the BIAD and the PF injury mechanism have been described in great detail, above, and in many other places here in Epic — and in scores of research papers published world-wide (where the term, "Slip Catch" nearly also means Phantom Foot).  The concept of the BIAD injury-mechanism was first described by Henry Crane, MD (God bless his soul — he was a Great Man) at an ASTM meeting in Boston in the mid-1970's;  then, at the next ASTM meeting in Waterville Vally, NH, Gail Gibson, DMV and I (together) introduced the notion that (based on our analysis assuming that rabbit and human musculoskeletal structure are 'very similar') a boot that unlocked it's rear-cuff might mitigate some of the strain across the ACL during BIAD loading.  Jay Pierce of Stowe, Vermont co-invented the ski boot mechanism that did this.  Jay assigned his IP to Lange.  The problem with the RRS was that it often pre-released during aggressive (but non-injury producing) skiing — causing uncontrollable skiing — which then led to the types of crashes that generate severe upper-body injuries that were far worse than an ACL injury.  Lange therefore withdrew the boot after only a few seasons on the market.  I withdrew the Geze SE3 (which addressed the same BIAD injury mechanism) for the same reason — inadvertent pre-release.  However, we know (sorry, Beyond about "knowing" this) that the BIAD injury mechanism is (biomechanically, not epidemiologically-statistically) equally likely to precipitate strain across the ACL with either shaped or straight skis.  :)  :)

 

@ Beyond:  As for my personal experience with skiing injury statistics:  I admit that I only took 2 semesters of undergraduate college statistics;  4 semesters of graduate-level statistics;  commissioned only about $800,000 worth of statistical predictive analytics when I worked in corporate and have only sat through about 15 week-long ISSS (International Society for Skiing Safety) conferences where well-over a hundred statistically-valid research papers ( as well as biomechanics-based papers ) have been presented since the time when I 1st started to attend those conferences while in college (all of which was done  after  I had already co-developed the #1-selling alpine ski binding in the world for Salomon while in high-school).  'Sorry, Beyond, but my exposure to statistics relative to the above-described experiences might cause 'some degree' of awareness about how epidemiology-statistics ( and, independently, biomechanics ) might be properly applied it toward this thread-topic on how shaped or straight skis might induce differing effects on the ACL.

 

There also seems to be some confusion about the term, "statistics" ('very interestingly — often also similarly confused by another Epic blogger who also lives in Stowe and is a stage actor .... as well as by two other Epic bloggers who have recently been warned to cease the disparaging comments that intend to discredit dignity, honor and reputation ... all 3 of whom have exactly the same grammar and the same orientation toward disparagement):  they cannot distinguish between 'physics', 'biomechanics', 'engineering' and 'epidemiology'.  Pls let me be clear:  my above analysis about the interaction between shaped and straight skis relative to strain across the ACL is based upon biomechanics.  However, when I first presented this research at an ISSS conference in Japan in 2005, not only did world-leaders in the field of knee-orthopaedic-biomechanics provide me with a standing ovation, but so also did several world-leaders in ski injury epidemiology (statistics) stand with their ovation, too.

 

But the bottom line is this:  I was 1st to invent (validated by the US Patent Office) the 1st hands-off clipless bicycle system (creating the category) — with over a million pair sold per year for the past 25 consecutive years;  the leading line of snowshoes (Tubbs) which caused the total snowshoe category to expand by 50 X while simultaneously generating a sustained 85% market share, world-wide;  and invented and co-developed several leading alpine ski bindings that have greatly reduced skiing injuries.  None of this is abstract theory or abstract discussion on blogs:  over 25 million people are utilizing products that incorporate my work as I type this post at this moment;  I'm probably the only ski binding engineer who has ever raced at the level that I've raced—with their own hand-made alpine ski bindings, which bindings after successfully completing 80 mph downhills could be 'twisted-out' at the finish line on straight skis — and lastly, I worked for the ski company who developed the 1st commercial shaped skis ... and we were exposed, real-time, during that development to the comparative-changes AND EFFECTS caused by transforming from straight to shaped skis.

 

(( Sorry that's "so long" of a post for the 3 of you with different pseudonyms — but who have exactly the same grammar and the same tone — but I intend to discuss this topic about the effects of straight or shaped skis on the ACL, in depth, freely, and irrespectively of your malicious intent. ))   :)  :)


Edited by Richard Howell - 12/22/12 at 11:12am
post #185 of 192
Thread Starter 
Quote:
Originally Posted by Downhilll View Post

This release cuff can help un-trap the knee in the 90 degree angle and allow for a greater angle relief to occur. Since the shaped ski is more likely to cause a twisting motion to the 90 degree (or less) bent knee more quickly, with a greater change in vector and with its more powerful carve effect vs a slide, it would seem the shaped ski is more likely to create an injury opportunity. On the other hand, the shaped skis are much shorter, and therefore less likely to trap the leg in a vulnerable position as the tail is more likely to come free. Interesting Q. 

Not so sure, I nearly experienced this and the boot cuff release would not have helped enough to release the ski or de-load the ACL.

 

As to the leverage, there really is none that you would normally feel when the ski is twisted about the foot were most bindings would release at the toe.  The a rotation is about the knee in-line with the upper leg and the lower leg acting as the lever arm.

 

Close to 47 years on skis (with 46 of those on straight skis) and never experienced loading (despite many stupid stunts as a youth...I'll leave it at that) like this until I got on shaped skis.  Relative easy run at higher speeds, poor lighting and got caught during a transition and compressed a little, hooked the inside rear ski just slightly, wow the loading on the knee.  I can guaranty that I've done worse things on long skis and skied (powered) out of the situations,  trying this on the the shaped skis would have torn the ACLU.

 

Like I said, before in earlier posts part of what makes the shapes ski perform like they do, also seems to lock in a caught ski shaped better frown.gif.  I agree the twist about the boot is greatly reduced (which is covered under the toe release) almost like  less concentration is required to keep the shaped skis straight smile.gif.

 

As I see it two different mechanisms and injuries.

post #186 of 192

Regarding the discussion of the KneeBinding as a means for avoiding some ACL injuries, am I right in thinking that these heel pieces release laterally or is there more to this. Please explain.  I am curious. i apologize if this has already been covered. I imagine there are a few others who haven't been able to follow this all the way through the preceding 6 pages.

 

Also, didn't Tyrolia used to have a binding whose heel piece released laterally? I don't know that mine ever released that way but I recall that when you snapped into the heel piece they were a little weird. If your heel was not centered the heel piece would move laterally or at least diagonally as you pressed it downward.  Did these not afford some ACL protection?

 

Great topic by the way.

post #187 of 192

Good morning, Oisin—   Tyrolia's Diagonal feature was 1st introduced within a line of Tyrolia bindings that contained the feature in 1969, coined 'Clix Diagonal'.  This feature was invented and developed by Tyrolia's Joseph Svoboda ( also a Very Good man ).  The Tyrolia heels that utilize the Diagonal feature allow the heel of the boot to displace (relative to the ski) laterally only after the heel unit of the binding displaces upward.  You can see how this works by observing the cam and mating cam-follower that are exposed to open view in all of the Tyrlolia (as well as Head, Fischer and Elan) bindings that contain the Diagonal feature.  Therefore, the only way that these bindings with the Diagonal feature can allow the boot's heel (relative to the ski) to displace laterally is during a forward twisting event or fall.  Phantom Foot induced ACL injuries have a large backward weighting component, not a forward-component.  Therefore, in a PF scenario, it is impossible for the Diagonal to allow any lateral displacement of the boot relative the the ski.  Shaped or straight, the Diagonal feature cannot respond to PF events.

post #188 of 192
Quote:
Originally Posted by Richard Howell View Post

Good morning, Oisin—   Tyrolia's Diagonal feature was 1st introduced within a line of Tyrolia bindings that contained the feature in 1969, coined 'Clix Diagonal'.  This feature was invented and developed by Tyrolia's Joseph Svoboda ( also a Very Good man ).  The Tyrolia heels that utilize the Diagonal feature allow the heel of the boot to displace (relative to the ski) laterally only after the heel unit of the binding displaces upward.  You can see how this works by observing the cam and mating cam-follower that are exposed to open view in all of the Tyrlolia (as well as Head, Fischer and Elan) bindings that contain the Diagonal feature.  Therefore, the only way that these bindings with the Diagonal feature can allow the boot's heel (relative to the ski) to displace laterally is during a forward twisting event or fall.  Phantom Foot induced ACL injuries have a large backward weighting component, not a forward-component.  Therefore, in a PF scenario, it is impossible for the Diagonal to allow any lateral displacement of the boot relative the the ski.  Shaped or straight, the Diagonal feature cannot respond to PF events.

Thanks Richard

I had a suspicion that the release of the heel was diagonal and not lateral but since I'm not aware of them ever having released on me, or at least not in that way, I wasn't certain.

Does it make any sense for a binding to communicate upward pressure at the toe piece to effect a lateral release of the heel then?

post #189 of 192

Excellent idea, Oisin !   However, this great idea (sincerely) has been posited and tried.  The problem is that upward force on the toe is often associated with aggressive skiing when lateral heel release is not needed (when, sometimes, there is no PF scenario) — especially with straight skis where large tail pressure is sometimes needed to finish sharp slalom turns.  Tail pressure can be applied by loading the boot, rearward — which also causes upward toe pressure.  Therefore, significant inadvertent lateral heel pre-release resulted when prototypes with this feature were tested in practice, on-snow.  Because a large 'backward bending moment' that's associated with PF scenarios can also generate a large 'normal-force' (a force that's perpendicular) to the top surface of the heel pad (as well as a large upward force on the toe) ... but minimally increase the resultant tibial-femoral torque (strain across the ACL) that's limited by a lateral heel release ONLY IF the top surface of the heel pad has a low coefficient of friction (e.g. Teflon or a mechanical heel AFD such as a Lipe Slider band) — then, lateral heel release can be 'reasonably' consistent PLUS not cause excessive pre-release.  Shaped skis require less tail pressure to finish sharp slalom turns than straight skis, so lateral heel pre-release is even less evident with heels that provide this extra mode of release in the presence of low-coefficient of friction heel pad surfaces when using shaped skis.  The downside effect of a mechanism that supplies an 'indirect assist' to another mechanism is analogous to the so-called 'friction-compensator' mechanism found under some of the toe-AFD's on previous Geze bindings such as the Geze 952 TC (invented by Geze's Ulrich Kolvatsch ... another 'good guy').  With the so-called 'friction compensator', release was outstandingly consistent during forward twisting events, but the toe's recentering force was lessened due to the way the 'friction compensator' backed-off the lateral toe release spring to 'compensate' for the increased force of friction during forward twisting events.  The full potential of mechanical recentering was reduced in order to make release consistent during this combined load, thereby causing some pre-releases.  In the same way, the prototype upward toe mechanisms that 'assisted' lateral heel release (in order to make lateral heel release consistent) 'sacrificed' powerful retention in this same way.  However, the utilization of simple Teflon or a simple and effective mechanical AFD such as a slider-band 'reasonably maintains' a consistent level of lateral heel release while also not reducing lateral heel recentering — thus maintaining powerful recentering (minimal lateral heel pre-release) even in the presence of combined loads such as the ones you note — upward at the toe.  :)   In summary, your idea would be good in terms of mitigating ACL injuries — but pre-release would be a significant issue.  Pre-release is worse than no-release because pre-release can cause severe upper-body injuries (head and spinal cord injuries), while no-release can only cause less severe leg fractures or (in the event of no lateral heel release) ACL injuries.  The patents by CFE and DD are problematic in this way.  :)   Bindings that have consistent release in the 3 modes of release discussed (lateral at the toe, forward at the heel and lateral at the heel) — with minimal pre-release in each of these 3 modes — are the key to mitigating leg fractures and ACL injuries on straight or shaped skis.   :)  :)


Edited by Richard Howell - 12/23/12 at 8:33pm
post #190 of 192

Thank you. You've given me something to digest here.

 

Quote:
Originally Posted by Richard Howell View Post

Excellent idea, Oisin !   However, this great idea (sincerely) has been posited and tried.  The problem is that upward force on the toe is often associated with aggressive skiing when lateral heel release is not needed (when, sometimes, there is no PF scenario) — especially with straight skis where large tail pressure is sometimes needed to finish sharp slalom turns.  Tail pressure can be applied by loading the boot, rearward — which also causes upward toe pressure.  Therefore, significant inadvertent lateral heel pre-release resulted when prototypes with this feature were tested in practice, on-snow.  Because a large 'backward bending moment' that's associated with PF scenarios can also generate a large 'normal-force' (a force that's perpendicular) to the top surface of the heel pad (as well as a large upward force on the toe) ... but minimally increase the resultant tibial-femoral torque (strain across the ACL) that's limited by a lateral heel release ONLY IF the top surface of the heel pad has a low coefficient of friction (e.g. Teflon or a mechanical heel AFD such as a Lipe Slider band) — then, lateral heel release can be 'reasonably' consistent PLUS not cause excessive pre-release.  Shaped skis require less tail pressure to finish sharp slalom turns than straight skis, so lateral heel pre-release is even less evident with heels that provide this extra mode of release in the presence of low-coefficient of friction heel pad surfaces when using shaped skis.  The downside effect of a mechanism that supplies an 'indirect assist' to another mechanism is analogous to the so-called 'friction-compensator' mechanism found under some of the toe-AFD's on previous Geze bindings such as the Geze 952 TC (invented by Geze's Ulrich Kolvatsch ... another 'good guy').  With the so-called 'friction compensator', release was outstandingly consistent during forward twisting events, but the toe's recentering force was lessened due to the way the 'friction compensator' backed-off the lateral toe release spring to 'compensate' for the increased force of friction during forward twisting events.  The full potential of mechanical recentering was reduced in order to make release consistent during this combined load, thereby causing some pre-releases.  In the same way, the prototype upward toe mechanisms that 'assisted' lateral heel release (in order to make lateral heel release consistent) 'sacrificed' powerful retention in this same way.  However, the utilization of simple Teflon or a simple and effective mechanical AFD such as a slider-band 'reasonably maintains' a consistent level of lateral heel release while also not reducing lateral heel recentering — thus maintaining powerful recentering (minimal lateral heel pre-release) even in the presence of combined loads such as the ones you note — upward at the toe.  :)   In summary, your idea would be good in terms of mitigating ACL injuries — but pre-release would be a significant issue.  Pre-release is worse than no-release because pre-release can cause severe upper-body injuries (head and spinal cord injuries), while no-release can only cause less severe leg fractures or (in the event of no lateral heel release) ACL injuries.  The patents by CFE and DD are problematic in this way.  :)   Bindings that have consistent release in the 3 modes of release discussed (lateral at the toe, forward at the heel and lateral at the heel) — with minimal pre-release in each of these 3 modes — are the key to mitigating leg fractures and ACL injuries on straight or shaped skis.   :)  :)

post #191 of 192
Thread Starter 

Rick,

 

The more I understand that more I begin to suspect that a lateral heel release is the only simple form of decoupling the different forces acting on the binding.   Correct me if I'm wrong here, would it be correct to assume that one setting would be effective for most (say 80-90%) skiers for lateral heel release as regardless of wt. the torque in this instance would be very similar with little variation that causes the injury.  The main variation would occur with young (teen and under as joints are not yet fully developed) or very aggressive (expert and above).  In the case of expert skiers an optional lock out may be preferred when, like you said, pre-release is bad, but then again, at that level we know the risks (hopefully).

 

G

 

BTW.   When anyone (myself included) seems to think they gotten one step ahead of you, you always manage to be at least three steps further ahead biggrin.gif.

 

Everyone, have a Merry Christmas and a New Year.

post #192 of 192

This thread continues to be extremely informative.  Thanks to all who keep making it that way!  The level of detail and thoughful discussion really is a gift itself.

 

Merry Christmas and Happy New Year.

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