ACL Injury

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ACL Injury

Postby cheesehead » Sat Dec 10, 2016 9:46 am

One of the skiers on Facebook said, "the closer my knee gets to 90 degrees the more I am in danger of blowing out the knee."

I have a feeling that is wrong. I have a feeling that the knee is more protected the more flexed it is and that ACL injuries happen when the knee is extended, not flexed.

But, I would like to ask those of you with vastly more skiing experience, do you think that the knee is more likely to be injured when it is flexed or when it is extended?
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Re: ACL Injury

Postby h.harb » Sat Dec 10, 2016 12:40 pm

If your 90 degree bend, is putting your weight on the tail of the ski in a locked arc, you can blow out your knee big time. Usually, it's from a reengagement after a skid, or from leverage off the tail, but in this case the knees are very bent. So the statement, that a bent knee is less vulnerable to ACL injury isn't accurate.

Can you name two statements here that are inaccurate for potential knee injury from Vermont Ski Safety's list? It indicates Vermont Ski Safety doesn't understand ski technique.


Six elements define the profile:
Uphill arm back.
Skier off-balance to the rear.
Hips below the knees.
Uphill ski unweighted.
Weight on the inside edge of downhill ski tail.
Upper body generally facing downhill ski.
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Re: ACL Injury

Postby jbotti » Sat Dec 10, 2016 10:27 pm

You can see and ACL tear in action here at 1:21 into this video.

https://www.youtube.com/watch?v=G830ds3CQMI
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Re: ACL Injury

Postby NoCleverName » Sun Dec 11, 2016 5:05 am

h.harb wrote:Can you name two statements here that are inaccurate for potential knee injury from Vermont Ski Safety's list? It indicates Vermont Ski Safety doesn't understand ski technique.


Six elements define the profile:
Uphill arm back.
Skier off-balance to the rear.
Hips below the knees.
Uphill ski unweighted.
Weight on the inside edge of downhill ski tail.
Upper body generally facing downhill ski.


To be fair, they are not saying "don't do this" and your risk of knee injury goes away. No, they are saying that "all these things are generally true" when injury occurs. I take it to mean that just because you are skiing generally OK that doesn't mean the other elements can't kick in to wipe you out. And it's been a while since I checked their mitigation list but I think the actions they give to avoid injury when things start going bad are pretty much PMTS skiing technique, anyway.
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Re: ACL Injury

Postby DougD » Sun Dec 11, 2016 11:48 am

h.harb wrote:Can you name two statements here that are inaccurate for potential knee injury from Vermont Ski Safety's list? It indicates Vermont Ski Safety doesn't understand ski technique.


Six elements define the profile:
Uphill arm back.
Skier off-balance to the rear.
Hips below the knees.
Uphill ski unweighted.
Weight on the inside edge of downhill ski tail.
Upper body generally facing downhill ski.

Uphill ski unweighted
Upper body generally facing downhill ski

These are normal aspects of good ski technique, especially as taught by PMTS.

Hips below knees is also sometimes correct technique, but ONLY during transition by an expert skier (e.g. Hirscher or Shiffrin, etc.). In some high energy turns, the legs must be flexed so much to unweight the skis that the hips may briefly be below the knees. However, when this occurs there is no pressure on the skis or legs. No one ever tore their ACL during the float phase.

For most skiers, however, hips below knees occurs when they're off balance to the rear and in imminent danger of losing control. If the skis are pressured and the skier lacks flexibility or strength to pull them back beneath him/herself, a twisting motion combined with forward pressure by the boot cuff can damage the ACL, as described in the VSS article.
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Re: ACL Injury

Postby Obrules15 » Sun Dec 11, 2016 1:09 pm

h.harb wrote:Can you name two statements here that are inaccurate for potential knee injury from Vermont Ski Safety's list? It indicates Vermont Ski Safety doesn't understand ski technique.

Uphill ski unweighted.
Upper body generally facing downhill ski.



I think this is a situation where a picture is worth a thousand words. I've watched some of the video of that type of ACL injury and while the words (unweighted uphill ski & upper body facing downhill) were technically accurate, the people I saw that fit their model in no way shape or form were skiing those principles properly.

One guy was cockeyed on his downhill ski with his torso flopped over and his head below his a**, and his uphill ski seemed like a meter away with divergent tips. Not good PMTS weighting and counteracting, but his torso was facing downhill and his uphill ski flapping away. It also seems like people weren't skiing that way but were getting themselves into trouble with recovery moves.

I feel like they should have chosen better wording, maybe "inadvertent, uncontrolled, unweighted, or asymetric uphill ski" and "uncontrolled/inappropriate downhill facing torso". I don't know the best way to describe it, but I definitely think there is a difference between what they mean and good ski technique. What was it the supreme court said, "I may not be able to define it, but I know it when I see it".

Another thing, at least one brace company designs rigid braces to protect the ACL, which prevent rapid full extension because the mechanism of injury in other sports seems to involve full extension. Methinks ACL's are probably more complicated than we try to make them. I've read that 70% of ACL's are torn skiing through the mechanism VSS is trying to describe, but that means a full 30% occur in some other fashion.
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Re: ACL Injury

Postby h.harb » Sun Dec 11, 2016 3:28 pm

DougD, you are right, in fact if you put less weight on your uphill ski you have a much better sense of how you stand on your skis in balance. And about the facing downhill thing, it is only relevant at the bottom of the arc before release. Which is the right way to ski, if you turn to face your ski tips your body rotates and the back of the ski loses contact. This offers less control and releasing ability, especially in off piste it can spin you around an up-pside down.
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Re: ACL Injury

Postby rnordell » Mon Dec 12, 2016 1:14 pm

There is lots of good info about the mechanics of ACL failure and what binding manufactures have tried, some more successfully than others, to prevent injuries from happening. If you want all you ever wanted to know about binding design searching for Rick Howell of Knee Bindings a good place to start. Or try these links as a starting point.
http://www.newschoolers.com/news/read/A ... -bindings/
https://www.wildsnow.com/15123/tech-bin ... roken-leg/
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