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risk of tearing the ACL in small edge angle on icy slope.

post #1 of 22
Thread Starter 
Imaging in small edge angle carving turn on an icy slope. When the skier enters the fall line in a seriously back seated balance. The skis tail pressure gets too high and break the gripping. Because the skis tip still have gripping, the outside skis turns sharply into the turn and therefore twisting the lower leg about the knee. However if the edge angle is big enough the snow surface would keep the lower leg from rotating about the knee.

Is it reasonable to think this way?
post #2 of 22
Carver,

If the ski is gripping and turning, and the body completely stays where it is, the lower leg could severly rotate and cause knee injury. It really depends on how quickly it happens.


Here's some info taken from :
http://www.vermontskisafety.com/kneefriendly.php

quote from above:

THE PHANTOM FOOT ACL

One common ACL injury scenario has been termed the Phantom Foot because it involves the tail of the ski, a lever which points in a direction opposite that of the human foot. Phantom Foot injuries can occur when the tail of the downhill ski, in combination with the stiff back of the ski boot, acts as a lever to apply a unique combination of twisting and bending loads to the knee.

To help reduce the risk of Phantom Foot injury, skiers must first learn to recognize potentially dangerous situations while there is still time to respond.The list that follows represents a profile of the Phantom Foot ACL.

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.
Although these elements may fall into place in almost any order during a sudden loss of balance or control, the order shown here is characteristic of the chain of events which can often put the average skier at risk.


The following actions are a good example of an appropriate initial response:
  • 1.) Arms forward.
  • 2.) Feet together
  • 3.) Hands over skis.
Phantom Foot injuries occur when the tail of the downhill ski, in combination with the stiff back of the Alpine boot, apply a combination of twisting and bending loads to the knee.

The plan above was developed to:
  • Reposition the downhill thigh in line with the downhill ski in order to reduce twisting loads on the knee
  • Reposition the uphill ski so that it is available for weight transfer
  • Put the skier in a good position for either a recovery or a controlled fall (bail-out)
However, this plan is only one example of the type of response that may help reduce the risk of injury. With time you can develop your own plan and with practice your response can be quick and effective.
post #3 of 22
Tog, good response. The tail is always a more risky place to be, for this very reason. Not sure a smaller edge angle would intensify the risk. Without knowledge of any studies of that aspect of the equation, my intuition tells me it would be just the opposite, as the amount of sudden twisting while in an aft position would be even more severe when on a higher edge. Although, on a lesser edge, might ski runaway but one even further aft, thus at even higher risk?

Obviously, caution on getting in out of control aft positions is highly advised. My theory may seem a bit radical, but I actually advise learning to ski aft. Done in controlled situations, and in progressive steps, skills can be developed that allow skiers to ski aft in very stable and safe states. This can prove a valuable skill when circumstance suddenly lands a skier in an aft state. Rather than like the unskilled skier thrust into this position ill prepared to cope with it,,, the trained skiers finds themselves in a balance state they are familiar with, and can perform in. They are more able to gracefully recover back to a neutral state, where as the untrained skier is more likely to panic, flounder, end up in an even MORE out of balance and dangerous position,,, and get hurt.

Aft training also develops better fore/aft awareness, which lends to being better able to maintain safer (neutral) fore/aft states, or being able to utililize conservative/functional amounts of aft when desired.
post #4 of 22
Thread Starter 
Quote:
Originally Posted by Rick View Post
my intuition tells me it would be just the opposite, as the amount of sudden twisting while in an aft position would be even more severe when on a higher edge. Although, on a lesser edge, might ski runaway but one even further aft, thus at even higher risk?
Because tearing the ACL is very serious injury. I ll be very grateful if you can offer more detailed analysis of what happen precisely in each case ( bigger, smaller edge angle) if one does lost grip and the outside skis slip outward causing a twist.

I have some experience with this situation and therefore I post up the question. However I am not sure what is the various forces involve that lead to the results I am seeing. My current experince is that on high edge angle staying too far back only lightens the tipping pressure and causing micro steering while small edge angle gave me outside skis runaway.
post #5 of 22
carver,
I've had two acl tears and neither of them has been from being in an aft state as described above in the Phantom Foot. No relation to the "Phantom Move" by the way. While that is a common method of injury it is by no means the only one for acl tears.

My second acl tear in some ways relates to what you are talking about. I was going fast down the side of the slope in a shallow right turn, my right ski must've gone into a small hole and then been quickly turned to the inside. I was launched into the air and traveled head first down the side but I already knew that the acl was gone from that quick twist to the inside.

My lower leg might have been twisted in and pushed back from the hole but it basically happened in the blink of an eye so I don't really know. I felt it go, did not hear a "pop", and it didn't really hurt.
post #6 of 22
Thread Starter 
Quote:
Originally Posted by Tog View Post
carver,
I've had two acl tears and neither of them has been from being in an aft state as described above in the Phantom Foot. No relation to the "Phantom Move" by the way. While that is a common method of injury it is by no means the only one for acl tears.
Sorry to hear that you get hurt twice. You are very brave when you are still skiing. I think that the "Phantom Move" is more related to lost-balance type injury. What is being discussed and in your case is not lost-balance but something happen to the outside skis that make it turns into the turn sharply. I don't think there are many thing we can do to recover from this kind of situation. What I am trying to do is to find out what is knee friendly move and what is not.


Quote:
Originally Posted by Tog View Post
My second acl tear in some ways relates to what you are talking about. I was going fast down the side of the slope in a shallow right turn, my right ski must've gone into a small hole and then been quickly turned to the inside. I was launched into the air and traveled head first down the side but I already knew that the acl was gone from that quick twist to the inside.

My lower leg might have been twisted in and pushed back from the hole but it basically happened in the blink of an eye so I don't really know. I felt it go, did not hear a "pop", and it didn't really hurt.
Can you try hard to figure out the real cause? What make you think its a hole?
I would think you were launched into the air because your skis was locked into the snow but your body was not. Were you carving when you hit the 'hole'?
post #7 of 22
For what it's worth, if you are concerned about ACL injuries -- and who isn't! -- then you might want to think about skiing with knee braces. I use the RonJoy PlayMaker -- not too expensive, and works well in preventing one category of ACL injuries: over extending the knee forward (as in upward.)

As discussed, it can also be that turning, or rotation, that does damage; at least of one kind.
post #8 of 22
Quote:
Originally Posted by carver_hk View Post
I think that the "Phantom Move" ....
What I am trying to do is to find out what is knee friendly move and what is not.
Carver,

The phrase associated with ACL injuries is "Phantom Foot".

Study the Vermont Ski Safety site. If you are that interested, get the video. They recommend three easily remembered concepts that can help prevent ACL injuries: keep the hands above the hips, don't fight falls and don't try to get up from a fall while still moving. When you see some of the knee wrenching falls on video in slow motion that did not result in injury, you'll feel less worried about the situation you are asking about. Although ACL's can get injured from causes other than phantom foot, this is one cause of ski injuries that you can do something to prevent other than not participating.
post #9 of 22
Thread Starter 
timremple - I also got one. But I really doubt its effectiveness if only the lower leg is being twisted.

Quote:
Originally Posted by therusty View Post
Carver,

The phrase associated with ACL injuries is "Phantom Foot".
Thanks for the correction. Its such a terrible mistake. I have studied the web pages in Vermont Ski Safety site. I haven't got the vid though. I am not sure if they already contain the scenario I described somewhere. Maybe its already in the wet site just that I don't know where because its not easy to relate what they say with my special situation, ie icy+carving at low edge angle+back seat.
post #10 of 22
Quote:
Originally Posted by carver_hk View Post
timremple - I also got one. But I really doubt its effectiveness if only the lower leg is being twisted.

Thanks for the correction. Its such a terrible mistake. I have studied the web pages in Vermont Ski Safety site. I haven't got the vid though. I am not sure if they already contain the scenario I described somewhere. Maybe its already in the wet site just that I don't know where because its not easy to relate what they say with my special situation, ie icy+carving at low edge angle+back seat.
Why is the "small edge angle" so important in your scenario? I would think that a high edge angle would be even more dangerous.
post #11 of 22
Quote:
Can you try hard to figure out the real cause? What make you think its a hole?
I would think you were launched into the air because your skis was locked into the snow but your body was not. Were you carving when you hit the 'hole'? -carver_hk
carver, my original description was a bit off, it was a shallow right turn, but it was the outside ski, the left which twisted in. The left acl was torn in this scenario. The snow was somewhat loosely packed on top of firm.
It was not a high angle edge carve but a fast shallow low angle edge turn.

I suppose the hole was more of a dip followed by a bump. I think the outside ski twisted in at the same time as being held back as my body went over it. I was definitely launched head first down the side of the trail parallel to the trees. It happened under the lift and as I went into the woods out of sight the people on the lift I think were convinced I'd hit a tree and was dead. That's what the patroller said when he arrived anyway as he was convinced I was somehow paralyzed. When he felt the bump from the camelback I was wearing I think he briefly thought he'd found the problem!
Fortunately it was rather funny except for the knee.

What is your actual concern here?
post #12 of 22
Quote:
Originally Posted by carver_hk View Post
Maybe its already in the wet site just that I don't know where because its not easy to relate what they say with my special situation, ie icy+carving at low edge angle+back seat.
The edge angle, icy and carving factors are not directly relevant. In general, we talk about back wards twisting falls as being of higher risk of ACL injury. A higher edge angle COULD mean a higher amount of twisting in a fall, but it's not necessarily so. Icy snow could mean a higher likelihood of being in the back seat, but it's not necessarily so. Carving could mean a higher likelihood of the skis jetting forward during a backwards fall, but a skidding ski only needs a little edge grab component in order to jet forward during a backward twisting fall.

Per the web site, being in the back seat is one of the critical components. However all components need to be present in order for ACL injury to be likely. Absence of just one of the components is a critical factor for ACL injury not being likely despite the presence of other contributing factors. This is a key concept that means you don't need to worry about icy snow or soft snow, carving or skidding, high or low edge angles and so on. ACL injuries can happen under all of those conditions. The things you need to do to minimize your risk of injury are the same under all of those conditions.
post #13 of 22
Thread Starter 
Thanks all for the contributions.

therusty - I understand that following the website helps to reduce ACL risk generally. This discussion is about a special scenario that occurs to me very often. Understanding it certainly help to save my ACL. Besides I also like to learn how experts think what is going to happen between the skis and the snow when gripping is lost at the skis tail.

TDK - I ll explain my thinking below:

I'll consider two scenario, both lost grip at the tail and the skis is about to turn inward.

case a: 5 degree edge angle carving. With this low edge angle carving the lower leg is almost perpendicular to the snow surface, therefore the snow surface is not stopping the skis from rotating about the lower leg. The lower get twisted.

case b: 50 degree edge angle. with this high edge angle carving, the skis cannot rotate about the lower leg because if it does the ski tip have to stab deeply into the snow to make way for the rotation.

Tog - Thank you for taking the pain to recall how you torn your ACL. I am sure your experience helps readers to reduce the risk of tearing ACL in their skiing.

Quote:
Originally Posted by Tog View Post
I suppose the hole was more of a dip followed by a bump. I think the outside ski twisted in at the same time as being held back as my body went over it. I was definitely launched head first down the side of the trail parallel to the trees. ...
What is your actual concern here?
I'll just make a guess. Lets see if it reflect what was happen. The dip ease off your tipping pressure. All the pressure suddently went to the skis tail causing a lost grip. The tail got pushed outward and regain gripping. The new gripping now points somewhat too inward because of low edge angle and therefore blocked your way. Because you are going fast you have no time to adjust to bring your outside skis back into the proper direction. The little bump further locked your skis and therefore thrown your body out head first.
What do you think? anyone is welcome to correct me. If its really the case what could be done to avoid tearing the ACL in similar situation?
post #14 of 22
carver_hk, I still dont get it.... at 5deg edging there would not be any carving. And even if there was the turn radius would be 21m on a 12m sl ski. What exatly is the mecanism for tearing the acl? I think the risk of tearing the acl gets bigger when your speed increases. That is the biggest risk factor. Also, if you are not fit enough you easily slip into the back seat. Same applies to skill level. In other words, a skilled skier that is fit skiing fast is at less risk of tearing his acl than somebody with lesser skills and in bad physical condition. Nothing to do with edge angles.
post #15 of 22
Quote:
Originally Posted by tdk6 View Post
carver_hk, I still dont get it.... at 5deg edging there would not be any carving. And even if there was the turn radius would be 21m on a 12m sl ski. What exatly is the mecanism for tearing the acl? I think the risk of tearing the acl gets bigger when your speed increases. That is the biggest risk factor. Also, if you are not fit enough you easily slip into the back seat. Same applies to skill level. In other words, a skilled skier that is fit skiing fast is at less risk of tearing his acl than somebody with lesser skills and in bad physical condition. Nothing to do with edge angles.
First bolding: At 5 degrees, a 12M ski will carve a radius of 12 x COS(5). Which is less than 12 degrees. by definition, a 12 M ski cannot "carve" anything above 12 M.

Second bolding: It does not matter much how fast you are going -- it's a twisting thing....
post #16 of 22
Carver, your low edge angle scenario presents a danger, but I'm not sure you're fully understanding the context of that risk. At low edge angles sudden twisting of the ski caused by terrain irregularities can be more easily resisted through maintaining rotational tension in the legs. The minor edge engagement with the snow at those low edge angles is more easily overcome, and ski direction maintenance more easily achieved.

The greater risk actually comes when terrain irregularities suddenly wrench your low edge angle ski onto a higher edge angle, and your skis "hook up" and crank an abrupt direction change right or left. Because of the low edge angle you were riding, your body is too much over your skis to be able to be propelled by the skis such that it turns with them. The result: the skis and the body part ways, body pummeling over the top of the skis, much in the manner Tog did with his.

This does not describe every manner in which to do an ACL,,, but from my unscientific observations over many years on the slopes its a popular one. I remember attending a presentation way back when. The Vermont gang had just compiled their data and recommendations on ACL injury and avoidance, and it was being handed down to our ski school. I remember thinking at the time that while their work was at the time ground breaking and valuable, some of their recommendations, especially in the area of "just fall and relax" sounded a bit difficult to follow in a sport where the general objective is to constantly manage balance and recover from occasional (or for some, frequent) cases of poor management. Deciding on the fly to suddenly abandon ship, and knowing the precise instance and situation when that should be done seemed to me to be a lot to ask. To be really safe using that methodology I would think one would need to error on the side of safety, and that would have skiers flopping all over the slope.

It's a tough situation to totally avoid,,, an inherent risk in our sport. We could go back to dead straight skis and low cut leather boots, and trade knee injuries for boot top fractures, but I don't think anyone wants to do that. I guess my best advice would be to work diligently on developing your balancing and edging skills. Acquire a keen sense of where your balance point is at any and all moments. Learn how to adjust it at will, on the fly, in any manner you choose. Also, learn how to perform at a high level in those less than ideal balance states. This will go a long ways in improving your ability to avoid getting into situations that carry the highest degree of risk. Learn how to manipulate your edge angle and usage over a broad spectrum. Develop your angulation skills, and stray away from knee anglulation as a default turning means. A long and strong leg, such that hip angulation provides, is your best bet. Go for outside ski dominance, as overly weighing the more highly flexed inside leg puts you on a weaker platform, and further aft, leaving you more prone to injury. Stay aware, look ahead. Ready yourself for undulating terrain by getting in safe states of balance and structural alignment. Relax as you go over/through rough spots so that your body can absorb and adapt to sudden changes without a stiff body driving the skis into an edge lock that allows the skis to take over as leader of the band.

It's a fun sport, but it carries risks. While skill development can't totally eliminate that risk, it can go a long way in avoiding it. 46 years on skis here, and knock on wood, not a knee injury yet.
post #17 of 22
Quote:
Originally Posted by BigE View Post
First bolding: At 5 degrees, a 12M ski will carve a radius of 12 x COS(5). Which is less than 12 degrees. by definition, a 12 M ski cannot "carve" anything above 12 M.
It all depends on the skis but my point was to question the need for carving at 5deg. Do you think its possible?

Quote:
Originally Posted by BigE View Post
Second bolding: It does not matter much how fast you are going -- it's a twisting thing....
Surely faster speeds cause more accidents. If you get your ski twisted at 5mph or 50mph it makes a lot of difference.
post #18 of 22
Thread Starter 
Thanks Rick. It helps a lot to my understanding.

Quote:
Originally Posted by Rick View Post
The greater risk actually comes when terrain irregularities suddenly wrench your low edge angle ski onto a higher edge angle, and your skis "hook up" and crank an abrupt direction change right or left. Because of the low edge angle you were riding, your body is too much over your skis to be able to be propelled by the skis such that it turns with them. The result: the skis and the body part ways, body pummeling over the top of the skis, much in the manner Tog did with his.
This certainly helps to understand what happen. I would also think lost gripping at the tail due to excessive pressure will causes the outside skis push outward and regain gripping. Effectively an abrupt direction change. Followed by your logic is going to cause the same risk.

Quote:
Originally Posted by Rick View Post
..46 years on skis here, and knock on wood, not a knee injury yet.
I think this is a great achievement every skier want to achieve.

I understand one should develop the many skills as your other paragraph described. Its a long way to go afterall. For a quick fix do u think one should keep a certain edge angle so that the body is not too much over the skis?
post #19 of 22
Quote:
Originally Posted by tdk6 View Post
It all depends on the skis but my point was to question the need for carving at 5deg. Do you think its possible?
It does not depend on the ski. The nominal carved turn radius is always calculated as ski radius x Cos(edge angle). Of course it is possible. Skiing arc-to-arc demands that the ski carves at low edge angles just after edge change.

Quote:
Surely faster speeds cause more accidents. If you get your ski twisted at 5mph or 50mph it makes a lot of difference.
If you twist the knee far enough to snap the ACL, speed is irrelevant.
post #20 of 22
Quote:
Originally Posted by tdk6 View Post
Surely faster speeds cause more accidents. If you get your ski twisted at 5mph or 50mph it makes a lot of difference.
One of the most common mechanisms for tearing the ACL is sitting back while in a wedge at 2mph (or someone else catching the tail of your ski and forcing it into a wedge as you fall getting off the chairlift).
post #21 of 22
Quote:
Originally Posted by jdistefa View Post
One of the most common mechanisms for tearing the ACL is sitting back while in a wedge at 2mph (or someone else catching the tail of your ski and force it into a wedge as you fall getting off the chairlift).
:::
post #22 of 22
Agree with that one - have known one person it happened to and was on a chair when the guy next to me did it also. That guy sued the ski area and I had to make a statement about what happened. I think it was either settled out of court or thrown out because I never had to testify. He claimed the operator should've stopped the lift because there were people down in front of us.
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