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Old 03-19-2014, 09:52 AM   #1 (permalink)
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Default Amputee with Valgus Knee

I know this is an unusual question that many might not feel qualified to answer but I would appreciate any educated guesses.

I am a beginner snowboarder who inherited a 134 Burton Nugget (correct size for me) with EST Stiletto bindings. I am also a left below the knee amputee with a valgus knee. In other words, my knee on that side falls inward (knock kneed).

I am boarding with my amputated side in the back (although feel comfortable both ways). What I am struggling with are the binding angles. I have asked multiple people with adaptive programs as well as my prosthetist and get different answers. 50% say go with a forward stance and the other half say go with a duck stance.

What angles do most people with knocked knees go with? Aside angles, is there any other set up considerations specific to the valgus knee? I am not looking to become a park rider. Mostly on piste.

Best, Essie
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Old 03-19-2014, 10:12 AM   #2 (permalink)
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in snowboarding that has been called the A-frame stance since forever, it's actually a really powerful, solid position. forward angles, back foot canted forward help bring the back knee forward locked in behind the front. sounds like you are most of the way there, though i have no idea what its comfortable for you or anything about prosthetics and riding.
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Old 03-19-2014, 10:28 AM   #3 (permalink)
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find your inner Craig.


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Old 03-19-2014, 10:33 AM   #4 (permalink)
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Quote:
Originally Posted by ShredLife View Post
find your inner Craig.
Well, I have the Chemical Engineering part :P

Forward stance, aye?

Last edited by essie52; 03-19-2014 at 10:58 AM.
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Old 03-19-2014, 11:10 AM   #5 (permalink)
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I dont know much about prosthetics but the angle is determined by how joints work differently on different people. because a normal leg's ankle and knee can only rotate so little without loosing range or motion, that's why you find the best angles that work for you.
I am no doctor but from my point of view as an engineer since your knee is rotated inwards I would say a more forward stance. however it really depends on your stance and how your prosthetic is set up. the best way is to try stand on it and squat down see if you feeling any abnormal pressure or stress in the knee.
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Old 03-19-2014, 11:14 AM   #6 (permalink)
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Quote:
Originally Posted by essie52 View Post
Well, I have the Chemical Engineering part :P

Forward stance, aye?
yea, he was something like 0 or 6 degrees on that back foot i think
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Old 03-19-2014, 11:41 AM   #7 (permalink)
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Default As it turns out...

I'm a prosthetist and a snowboarder, so I should be able to answer your question. However, that's kind of a tough one to align without a visual. Intuitively I'd say:

-widen your stance to disperse force through the knees,
-use whichever stance (reg or goofy) that causes the least stress on your prosthetic side knee,
-use supportive inserts (ie Superfeet) to enhance medial support and promote varus alignment,
-Bring extra prosthetic socks so you don't go home with an angry residuall limb. Or use a thicker gel liner for more cushion when riding (if you wear one).

Ideally you would have a snowboarding prosthesis with an exaggerated inset of the foot to promote varus at your knee. But insurance rarely covers this sort of thing. Maybe next time you get a new prosthesis have your prosthetist turn your old one into a snowboard leg. Additionally you might be able to customize the cant on the footbed of your prosthetic side binding so that you have an angle that's high to the medial side to control some of that valgus.

It will be a give and take experiment. The body will only allow so much postural deviation off of how it has wound up to this point. Good luck and have fun.
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Old 03-19-2014, 04:05 PM   #8 (permalink)
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Thank you for all your responses.

Fergatron2000: please humor me just a bit more.... I went for a lesson at a fairly well established adaptive program and their strong recommendation was for the amputated leg to be in the back (this is their recommendation for all of their lower limb amputees) making me a goofy rider.

Why is this? I know I should have asked but I was more excited to get on the snow than worry about reasoning. I think if my leg was not amputated I would naturally be goofy however, when a position myself with my amputated leg (left) in the front (+28,+9) I feel the most solid and can lean on the front leg with much more force.

When I put my amp in the back in a duck stance (+15, -15) my knee doesn't fall inward as much but I do not feel as though I can apply as much force through the board on either foot.

With both feet forward riding goofy (+21, +9) I am comfortable but my amp knee falls forward (maybe this is a good thing????) and I cannot apply much force through the amp leg.

What is the downfall to having my amp in the front? Will I loose control? Do I need to be able to apply force through the back leg? Will riding goofy in a duck stance but additional pressure and force on that knee?

I have a ski specific leg with a rampro foot but it does not translate well. My prosthetist is great but not a snowboarder or skier.

Thank you!
E
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Old 03-19-2014, 04:34 PM   #9 (permalink)
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My guess is they want you to put your sound side fwd to absorb impacts and protect your prosthetic side. Makes a lot of sense, especially if you plan on progressing into more advanced riding/terrain.

Some experts here could probably answer your questions better than I, but in general you should have even weight distribution through both legs. Turnin is not done by one leg or the other but by weight shifting with coordinated upper body movement as you transition from edge to edge. So yes, not so much appying firce through both legs, but letting your weight fall evenly through both. And keep your knees flexed.

Stance is a preference/comfort issue. What works for one rider will be totally opposite for another. One thing to keep in mind is that your foot (if it's this one: Rampro - Activankle) has an ankle that articulates in one plane vs. the triplanar motion of a normal ankle. So if you're stance is aligned with your prosthetic side at a enough +/- angulation it may want to pull your knee with it. This could result in pain and/or excess socket pressure. I'd be tempted to start you with a flat back prosthetic foot (i.e. zero angle) or maybe -5deg of duck. Too much either way I would think you risk injuring your knee ligaments which sucks.

Do they have a prosthetist that can adjust your stance on the hill while at your lesson? That would be ideal. Even simple things like toe out/in could make a huge difference.

If your snowboarding prosthesis is endoskeletal (has a pylon showing) I'd be tempted to add a rotation unit to reduce some torque on your limb. Rad to hear you like your prosthetist. Some good ones and bad ones out there.
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Old 03-19-2014, 04:43 PM   #10 (permalink)
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if you go with a forward stance (+/+) it's 60/40 weight on the front foot, more if you are carving hard. less so if it's pow. in my mind, if i lost a leg i would def be wanting it to be my back one...
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