Two years ago I was riding up a chair over the race team training trail as they were taking down the gates and slipping the hill.  One of the coaches was the last to come down from the top after they were pretty much done.  He was carving magnificent arcs at moderate speed and his arm suddenly shook as he had hooked his edge in transition.  He darted hard left right in to the woods and rocks, fell (intentionally) just on the edge as he slid in to the trees and a pile of rocks.  He wasn't moving or responsive when the patrol put him on the sled.  I've seen this scenario more than once in the past 5 years.  Hooked edge is a big problem with deep sidecuts if you're near the edge of the trail.  Not such a big problem with a straight ski as you tend to keep going straight instead of changing direction in a 17'-30' arc while hooked..

I've experienced that momentary helpless feeling while my edge is hooked.  It doesn't happen often, but I can guarantee it will happen to me again if I continue to ski.  It's just part of skiing, we all make small mistakes from time to time.  Consequences differ depending on what gear we are on.

Quote:

Originally Posted by Cody Feuz 

1 - When it comes to ACLs, I place the "blame" more the boot rather than the ski.  In the 60's and 70's we had far more lower leg / ankle breaks.  As boots stiffened and technology improved, it all but eliminated lower leg breaks.  Where is the next point of weakness for the stress?  The knees, therefore blown ACLs.

Generally speaking, you get boot-top fractures and ankle breaks when your ski stops suddenly with your boot still attached to it.  Or when you go hit your leg/foot into a fixed obstacle like a rock or tree.  Modern release bindings are pretty good at stopping the first cause, and hard plastic boots help with the second.

You hurt your ACL when you get significant torque/strain on your knee without the binding releasing, or it releases after your ACL has already torn.  This can happen at very low speeds, especially in backwards twisting falls.

Quote:

Originally Posted by crgildart 
Bindings and boots haven't changed nearly as much as ski design has since 1999, yet ACL injuries per skier visit has gone up dramatically.

Do you have a source for that?  (Not doubting you, just curious where that figure came from and what constitutes a 'dramatic' increase.)

Another potential factor is that the average skier age is probably significantly higher now than it was in 1999.  What with all the young whippersnappers taking up snowboarding and all.

Quote:

Originally Posted by Matthias99 

 

Do you have a source for that?  (Not doubting you, just curious where that figure came from and what constitutes a 'dramatic' increase.)

 

 

Wish I had better. but here is something..  Iriponsnow probably has something to add.

I have a hunch that the recent inflection point back trending fewer per visit may have something to do with the recent popularity of fat powder skis over racing and carving skis.  The fatties aren't as deeply cut at all. If I'm right that only adds more evidence to to the shape+ -> ACL Injuries + hypothesis.

Quote:

Originally Posted by crgildart 
I have a hunch that the recent inflection point back trending fewer per visit may have something to do with the recent popularity of fat powder skis over racing and carving skis.  The fatties aren't as deeply cut at all. If I'm right that only adds more evidence to to the shape+ -> ACL Injuries + hypothesis.

Just above that quote they also reference that "last three to five years" figure when talking about research that had been presented in 2003.  So I'm not sure if they are referring back to that (now almost 10-year-old) data, or something else.

This article seems relevant: http://www.ncbi.nlm.nih.gov/pubmed/18614888 (not available for free).  Their conclusion was that injury rates went down between 1998 and 2003, which is when 'super-sidecut' skis really took off.

Another recent one: http://www.ncbi.nlm.nih.gov/pubmed/21695668, says in the abstract that "...since the introduction of carving skis ACL injury risk seems to have decreased. No study has yet investigated the distribution of ACL injury mechanisms in male and female carving skiers. ...The forward twisting fall seems to have become the dominant ACL injury mechanism both in male and female recreational skiers since the introduction of carving skis."

This article on WC injuries (full text: http://bjsm.bmj.com/content/45/16/1294.full.pdf+html) concludes that "...factors related to skier technique, skier strategy and specific race conditions were identified as the main contributors leading to injury situations."

The short answer seems to be "it's complicated".

Typo correction to my above post re ISO ski equipment standards:  these standards provide "functional requirements", not "design requirements".

Rick Howell

Stowe, Vermont

Perhaps blending/modifying skills learned from straight skis and shaped skis. Gentle and swift.......

Rick - The dictators of FIS are making the change to longer skis/radii for world cup and pretty much all of ski racing.  What they really need is data that pertain to exact falls/cause/injuries from world cup (NorAm, Euro Cup, etc etc) trainings and races.  That data should be easy to collect.  This will be the best data that tells us if indeed changing the radius/length of skis will help or not.  FIS isn't changing my non-racing skis, so we don't really care.  The party who really cares need the data to prove.

As far as your ACL injuries directly related to short/shaped skis.  My small sample size of about 50 skiers I know.  Three of whom had ACL tears in the last 2 years.  None of them were on a groomed trail.  All of them had wider/fatter skis and were injured in powder.  All of them were not moving more than 5 MPH.  One hit a pile of heavy stuff head on.  One fell backwards on the steeps, and started to slide backwards downhill and the tail of her skis hit a heavy pile.  Albeit a small sample size, I'd venture to guess that not all increase/decrease of ACL injuries are due to shaped skis as you've pointed out in your post in ski racing magazine.  Longer skis has a longer lever arm; and therefore higher torque.  But you argue that that torque is about a diff point and location, which I won't dispute.  When looking at ACL injury data over the years, what about the fact that we have grown more obese over these years.  Obese upper bodies on seldomly exercised thighs/knees put a lot more force/torque on these ligaments.  Age is another major factor.  Menisci becomes dry and brittle.  Elasticity diminishes with tendons and ligaments.

Back to longer skis/radii.  Is allowing the longer ski to slip at the tip or tail the best solution?  When my skis slip on ice, they become immediately uncontrollable.  This will also cause a slip/fall--likely injuring the spinal/head areas (as you said MUCH more important than ligaments).  Furthermore, 30m-40m turning radius skis make straighter turns.  Straighter turns produce more speed.  Velocity is squared in the momentum equation.  Now you're going to allow the ski to slip on the ice after going even faster than before.

The best change for a FIS race course is to regulate (or better regulate) the lateral (side to side) distance between gates.  Yes, it makes the course easier, but that's better than putting racers on the same course as before but giving them lower performance equipment.  I paraphrase from the ski manufacturer's industry to FIS:  Equipment changes affect milliseconds to the run.  Course changes affect seconds to the run--orders of magnitude more.  I liken it to a zig-zag race track for my car.  Putting bald tires on my car so that I don't slip-catch-roll doesn't make sense.  Building a narrower course so that the tires won't experience as much G-forces is a better solution.  Similar to what I said above, first we need proof that my tires are INDEED causing the slip-catch-roll problem in my specific use case--car race track.  THEN we can go on and start working towards a solution.

As far as your bindings.  I am confident you have devised something that is genuinely effective.  I think maybe most folks are baffled by your technical jargon.  I have a masters degree in engineering and I've taken more math/physics than mathematicians, so I understand what you're saying.  However, I think to the lay folks, they might be thinking that you're just trying sell your new bindings.  I'm with you on trying to sell something, but perhaps paying for an 'independent' third party with the highest endorsements (like from FIS) to show that those Valgus Loads you're talking do indeed exist.  This would be paramount in making your case.  I know you're the only guy who measures this stuff, but there isn't a problem until FIS says there's a problem.  Quoting ISO specs with technical babble doesn't sell bindings.  Just my 2 cents. - Steve W from Squaw Valley

Shaped skis do cause more injuries, I just did a research paper on ACL injuries and although the argument was not shaped vs straight, a lot of the information backed the logic of shaped skis cause more injuries due to their nature to want to turn. Take for example a phantom foot mechanism, the leader in ACL injuries, that shaped ski is going to want to hook a lot more than a straight one.

After thinking this over for a couple of months I am now of a different opinion.  I now think that shaped skis, as in say 13-m side cut radius skis are more likely to cause injury to the unwary knee, or leg for that matter, in a number of circumstances.

1) Slow twisting backwards falls with the ski hooking up and taking off on a tangent.  The direction change can be bigger.

2) While we get the SL ski for SL speed carved turns, some of us can't help from not sticking to SL speeds when out on the hill.   A top end recreational racing SL ski a la WC SC, will have no problem smearing a big high speed turn while skied faster and in longer radii than tht for which it was designed; it will not vibrate off you feet like, say, a SL ski from 1985,  BUT it may, while doing so in anything but  very hard surfaces decide to hook up instead of smearing.   That's when, if you are lucky your binding is set correctly and there is nothing in your spill zone, and if you are unlucky you are looking at serious damage.

3)  Say you slide out at high speed and lift you skis off the snow while you do a little hip or back slide until you can get lined up and get the boards pointed down the hill.  with the old 65 m radius skis, it was not all that much of a miracle to put the skis back down and continue skiing.  Good luck trying that at speed with a 13 - m radius ski!

I don't think it's a direct result of shape skis but rather a side effect.
Skiers have been able to turn faster, on well groomed maintained slope all leading to a significant increase in speed. Now, if we assume that the likelihood of falling as remained the same, just the fact that skiers are falling faster will increase the chances of injury.

Are skiers really skiing faster?  The still seem to be skiing as slow as ever to me.

Faster speed through the turns, straight line hasn't changed much. 

I'm guessing you are thinking of the hooking problem? 
I agree that these skis are more grippy, but IMO that is what leads to higher speed because you can generate more Gs. Which is fine if you stay up, but when you crash that extra speed will translate in higher forces on your knees and therefore greater risk for injury. 
I did a quick search but only found an old study from the 80s-90s which showed a slight increase in injury but they were not able to pin point it to anything in particular. (study done at mammoth and another CA resort lol)

It's a good point.
 

It comes down to injuries due to blunt force (you crash ==> you break) and injuries due to MOI (bad position ==> ligament gives) for lack of a better word.

IMO most skiers will fall before getting to the situation you described (getting hurt as a result of it), but I can see the issue for an advanced/pro skier who is still "in control" and by trying to salvage the situation actually ends up hurt.
 

Honestly I wouldn't be able to say which one is more common but the study I mentioned showed that intermediate skiers had the greater amount of injuries

Quote:

Originally Posted by crgildart 

Two years ago I was riding up a chair over the race team training trail as they were taking down the gates and slipping the hill.  One of the coaches was the last to come down from the top after they were pretty much done.  He was carving magnificent arcs at moderate speed and his arm suddenly shook as he had hooked his edge in transition.  He darted hard left right in to the woods and rocks, fell (intentionally) just on the edge as he slid in to the trees and a pile of rocks.  He wasn't moving or responsive when the patrol put him on the sled.  I've seen this scenario more than once in the past 5 years.  Hooked edge is a big problem with deep sidecuts if you're near the edge of the trail.  Not such a big problem with a straight ski as you tend to keep going straight instead of changing direction in a 17'-30' arc while hooked..

 

I've experienced that momentary helpless feeling while my edge is hooked.  It doesn't happen often, but I can guarantee it will happen to me again if I continue to ski.  It's just part of skiing, we all make small mistakes from time to time.  Consequences differ depending on what gear we are on.

  Similar thing happened to me, railroading down a not so flat cattrack on my sl's, next thing I know I'm flying over the edge and looking down (while still in the air, but horozontally...) at a big log and several stumps. Somehow missed them all....It happens fast!!

'C'm on you guys, pls do your homework !   :)  :)   Pls order this paper (the abstract alone does not go into the real meat of the research:  purchase and read the whole thing) that shows definitively what's going on:  [Med Sci Sports Exerc. 2004 Jul;36(7):1218-25.

Effect of ski binding parameters on knee biomechanics: a three-dimensional computational study.

Purchase the whole paper, coupled together with my presentations and abstracts that were provided at the ISSS conferences in Japan in 2005 and Scotland in 2007 ( and further abstracts and presentations that were barred by fraudulently induced injunctive orders regarding ISSS Germany 2009 and ISSS Keystone CO, 2011 ) — then each of you will become fully briefed on this subject.

It's all there.  The leading researchers all 'go' with this work ... and it's proven by statistically-correct epidemiology to drive ALL of the plausible the biomechanical parameters.

Valgus torque is oriented 90-degrees and completely decoupled from tibial torque:  ordinary bindings read and react to ONLY tibial torque and bending moments.  Shaped skis, when loaded in a Phantom Foot (PF) scenario, simply produce two vectors — one at the tip and one at the tail (downhill ski fully on edge, skier's center of gravity 'falls' straight down between the legs / skis, knee flexion is maximal) — that a straight ski does not produce when fully loaded in the valgus direction (one end slides-out, while the other end 'bites').  Loaded in this way, the two end-point vectors of a shaped ski resolve very simply into one resultant-vector that's simply located under (or near) the tibia.  This scenario produces ZERO torque about the tibia.  The noted 'resultant vector' acts over the LENGTH OF THE TIBIA to produce Very Large valgus torque about the knee.  Valgus torque can EASILY cause strain across the ACL at a level that exceeds the elastic limit of the ACL.  Approx 75% of all skiing knee injuries occur based on that scenario.  Alternatively, when a straight ski is loaded as noted above, one end 'bites' while the other end 'slides-out' (most of the time):  this scenario produces one vector located at which ever end of the straight ski that 'bites':  this single vector acts over the LENGTH OF THE SKI (from the point at which the ski 'bites' in the snow to a point located under the tibia [sic]), causing torque about the TIBIA ( NOT the knee ) — to which torque about the tibia ALL ordinary bindings read and react by 'releasing' if the pre-selected level of torque '[with]in' all ISO-compliant alpine bindings ('ordinary' or otherwise) is less than the elastic limit of the tibia in this rotational / torsional (torque-about-the-tibia) direction.   Torque about the tibia does NOT cause strain across the ACL.  Valgus torque ( oriented 90-degrees to tibial torque ) directly-produces strain across the ACL.   Ordinary bindings do NOT read or react to valgus torque because valgus torque is oriented 90-degrees to tibial torque.  Again, PF-induced 'falls' (or events) produce the above scenarios with shaped skis — and alternatively, with straight skis.  In summary regarding PF — PF-induced loads coupled together with shaped skis produces valgus torque that directly generates strain across the ACL to which no 'ordinary' binding can read or react;  while PF-induced loads coupled together with straight skis generates torque about the tibia that causes tibia fractures (not knee injuries) unless the pre-selected binding release torque is less than the elastic limit of the tibia in torsion, in which case the binding will release at a limit that's lower than the elastic limit of the tibia.

Also, ~15% of all skiing ACL injuries occur due to the BIAD (boot induced anterior drawer) scenario (straight backward loading) causing the proximal end of the tibia to drive forward (due to the semi-rigid rear spoiler of the boot) relative to the distal end of the femur (relative to the tibia, the femur is quasi-static due to the inertia supplied by the upper leg and central mass of the skier being greater than the inertia of the tibia / lower leg) when knee flexion is greater than 80-degrees (ortho's measure the 'excluded', not 'included', angle).  Bindings with upward toe release read and react to BIAD-induced loading scenarios.  Presently, there are NO bindings on the market with pure upward toe release — due to pre-release problems with all binding designs that have attempted to provide pure upward toe release.  Tilting toe release is not pure vertical toe release.  Skis that are shaped OR straight generate BIAD loading.   In summary regarding BIAD — BIAD-induced events cause (directly) strain across the ACL.

PF (and, btw, "Slip Catch") includes a combination of valgus and BIAD.   If the BIAD component is greater than the valgus component, its BIAD.  If the valgus component is greater than the BIAD component, it's PF.   Due the Enrico Fermi's fundamental laws of entropy, BIAD will 'hunt' to PF if small amounts of valgus arise during BIAD-events thereby causing bindings with certain 'non-ordinary' modes of release to read and react (release) if the pre-selected non-ordinary release limit is less than the elastic limit of the ACL during PF loading.

PF and BIAD scenarios are completely different scenarios arising from Very Different skiing scenarios causing completely different internal-knee biomechanical effects — both of which scenarios and both of which 'effects', however, easily produce large strain across the ACL when the magnitude of these types of induced loads are large.  Shaped skis can produce PF whereas it's 'difficult' (though not impossible) for straight skis to produce PF;  while both shaped and straight skis can produce BIAD.

( 80% of all skiing injuries occur due to 'falling' — and the above scenarios describe what happens in the event of the above-described specific type of 'fall-mechanics'.  Because these types of falls and 'events' occur within a few milliseconds, even highly trained WC athletes cannot turn-on the specific fast-twitch muscles that have the possibility of averting these specific loading conditions:  that's why all 'abilities' of skiers are exposed to these kinds of loading scenarios.  However, 'skiing experience' has a directly correlated effect on averting falls.  A few, Very Rare, instances have been captureed on video with WC racers making a perfectly carved turn on radically-shaped skis where the kinematics of the induced loading environments exactly match the above-described loading-environments .... instantly causing ACL rupture — further validating the above described loading parameters.  It is hypothesized that during a PF-event in most (not all) snow conditions, the tail of a straight ski will 'slide-out' before the ACL reaches its elastic limit — or, it is believed by this blogger (and others) that during a PF-event in the presence of either a shaped OR straight ski, a binding with a certain 'non-ordinary' mode of release ( adjusted to release in this 'non-ordinary' mode of release at a certain pre-selected limit) will release before the ACL reaches its elastic limit even if the tail of a shaped or a straight ski does not 'slide-out').

In a scenario where both the tip and the tail are 'biting', large valgus loading is present;  if the tail 'slides-out', the loading instantly converts from valgus-about-the-knee to torque-about-the-tibia.

Period.  It's that simple.  We measured it.  We've recorded it.  We've driven the whole thing in the inverse, too, just like in forensic structural engineering of bridge and building collapses. 

Why are we having this 'debate' ?   Pls, kindly do your homework.   :)  :)

(( I am not "selling" those bindings":  those bindings are presently the subject of other parties, pending the outcome of 5-years of 'other activity'. ))

Respectfully  :)  :)

Seems to me that if toe pieces had an upward release it could help reducing PF injuries...

Lots of very specific physics discussion here, but I will dumb it down in a very unscientific way and just talk about my personal experience.

I suffered a severe knee injury in Summer 2001. I was building a large shed and was laying shingles, when I slipped and fell. On my way down to reach the ground, I made a real attempt to get my legs under me with a big swining motion.

The result of this is basically that I kneed a sawhorse on my way down with the combined force of the fall and me swinging my leg trying to bring my feet around. The impact was directly on the kneecap, which imparted a significant medial miniscus tear and sprained but did not tear all ligaments in the knee.

To add insult to injury, there was also a nail lying on the sawhorse. The nail punctured my kneecap, head end first.

This happened in my early 20's. before the injury, I was a young, expert skier. I skied on straight skis, at that point an aging set of 205 Salomon Equipe's from about 1993 or so.

Post-injury, the condition of the cartilage in that knee has been described by several doctors as "normal and healthy, if you were a 70 year old man). Nothing is directly wrong, but the cartilage is heavily worn everywhere from the accident (my other knee has normal cartilage).

Because of the kneecap puncture, I have severe scarring inside the knee. Even today, this leads to severe Chondromalacia, which is inflamation from the kneecap tracking badly as the joint moves.

On days where the knee is really hurtying, if I do stupid things like put weight on the knee while it is bent, I will totally dislocate my kneecap causing unbelievable pain.

Doctors are unwilling to do surgery on the knee to address this, because of concerns that they will make things worse by going in to address the scar tissue. Basically, the advice is to ski the knee until it won't work anymore, and hope knee replacement technology has advanced to the point where I will only need one in my lifetime that will still allow me to ski. 

My knee issues are different than most because my ligaments are in place.

Anyways, this is a long post to say that I could not ski if it was not for shaped skis. When I returned to the snow in the 2003-2004 season, I did so on a pair of 170 CM foam core shaped skis, the lightest I could find. The light weight and easy turn initiation put far less pressure on my knee than what a much longer shaped ski would impart.  For the first few years, I could only managed groomed runs or my knee would give out. Since then, that has gone away and I can ski the whole mountain again, but generally I will only have 1 or 2 moguel runs in my knee any given day.

I'm also a little confused, because it seems to me that a heel pivot turn, which 99% of people were doing on straight skis, imparts more knee torque than a carving turn which is made possible by the general population on shaped skis.

If we look at how skis are actually being used (most straight skis were turned with heel pivots, while many, many more people carve modern designs) I would think that shaped skis are easier on the knees. In my case, that is definitely true.

From a (simple) physics perspective, a 'purely carved' or 'arced' turn should have almost all of the turn forces aligned up through your legs, so there should be very little torque on the knee.  Certainly less than if you're stemming or sliding the skis out to start your turn.  'Arced' turns are a LOT easier to do on "shaped" skis, and can be done at far lower speeds and at smaller turn radii.

Of course, if things go wrong at high speed you can get a lot of torque in a hurry.  Because modern ski designs can be VERY stiff torsionally while keeping reasonable longitudinal flex, they can 'rail' under at even low speeds if you fall in such a way that you put pressure on them at a high edge angle.  A "straight" ski would usually break loose in such a situation.  Which is sort of what Mr. Howell seems to be saying in his last post.

Quote:

Originally Posted by jzamp 

Seems to me that if toe pieces had an upward release it could help reducing PF injuries...

They already make those!

http://vimeo.com/52802844

The problem with your question, and why I couldn't answer it, is lumping ACL with all other knee injuries. ACL appears pretty securely linked to modern short shaped skis, just like tibial fractures changed when we went to rigid high shafted boots. But I haven't seen much that addresses other sorts of injuries that involve other biomechanical models. In fact, I'd guess that the twisting sideways falls often initiated by catching or burying a tip were more prevalent on 217 cm "straight" skis. 

Now a word about manic enthusiasm. Richard H's caps notwithstanding, ACL vs. medial injuries assumptions contain patent sampling problems. The majority of medial and the rarer lateral injuries go unreported precisely because they are trivialized as "sprains." (Incidentally, there is no such animal as a sprain. A sprain is simply mild to moderate tissue shear that tends to resolve on its own. But "resolve" here means loss of swelling and discomfort, not a return to previous state.) ACL, on the other hand, tends to be immediately incapacitating. 

Many cartilage tears are not diagnosed until months or years later when the cartilage fragment(s) create loss of motion or abrupt discomfort under certain load angles. By then, it's no longer statistically associated with a "skiing injury," let alone with a specific study. However, in both cases, the scaring or partial loss of function that produces changes in mechanics will significantly increase your risk of osteoarthritis down the line. We even understand the progression from "sprain" or "tweak" to OA on a molecular level now. 

Moreover, Ettlinger et al. do not address this issue in anything I've seen from the VT study. The design, which is really about whether bindings are associated with particular injuries, rests on staff diagnosis on site; not sure what "randomized double blind" means in the context of ACL versus other injuries since it refers to information evaluators of injuries has access to, such as skis and bindings, not the types of injuries. Also, the phrase "repeatedly proven epidemiological studies" makes no sense, since epidemiological studies neither prove anything nor are they themselves "proven." They test hypotheses and may falsify them. 

A better way to say it, sans screaming caps or breathless syntax, is that the large majority of serious, immediately diagnosed knee injuries are ACL's.

For the record, incidentally, Kuhn is not much in vogue anymore except as a history piece; Holton and others disproved his central hypotheses years ago. Most significant scientific change is neither "revolutionary" nor inevitably connected with younger challenging older. We all sure do like "paradigm," though, as a buzzword for almost anything we want it to mean. Kuhn himself used it in more than a hundred ways, literally. 

Quote:

Originally Posted by east or bust 

They already make those!

 

http://vimeo.com/52802844

thanks for the link! any news on them? are they effective?

They already make what?   I've been involved in shipping hundreds of thousands of ski binding toe pieces with various forms of upward toe release — and NONE of them have any effect on PF knee injuries.