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Boot knee alignment

post #1 of 9
Thread Starter 

How do you test knee alignment?

I've been to many bootfitters before that don't bother, they look at your knees and say the alignment's "pretty good" and then say, ski on them and if you feel like you're edging too much on one side or the ski wants to pull this way, then come back and we'll do alignment.

post #2 of 9

Go get a plumb bob from a hardware store. Attach a string. Put string at middle of patella (kneecap). See where the point of the bob is on your buckled boot when you're in skiing stance. Bingo. 

post #3 of 9

 

Quote:
Originally Posted by beyond View Post

 

Go get a plumb bob from a hardware store. Attach a string. Put string at middle of patella (kneecap). See where the point of the bob is on your buckled boot when you're in skiing stance. Bingo. 

 

You left out some key details...

 

What should the point of the plumb bob align with on your boot when you're in the stance?

 

If it's off then what adjustment should be made?

post #4 of 9

 

Quote:
Originally Posted by Magnus_CA View Post

 

 

 

You left out some key details...

 

What should the point of the plumb bob align with on your boot when you're in the stance?

 

If it's off then what adjustment should be made?

Sorry. As I do it, and I may be hilariously off on all this, these assumption: 1) In a skiing stance with the proper sole insert/orthotic, your foot is neutral (neither pronated nor supinated), 2) In this stance, since your CM is forward of your normal standing CM, it is distributed more toward the base of the first metatarsal/BOF, and 3) the midpoint of your patella should be at your BOF. Therefore, the tip of the bob should bisect the BOF line. Put in a less technical way, when you load your leg, your kneecap should always be over the middle of your foot just behind your toes. Works for all sports I know of. 

 

That takes care of the longitudinal axis. If the bob tip is medially or laterally off from the bisect point, you have two options. The best is to get thee to a bootfitter and get a different insert, since odds are yours is still off. The quick and dirty solution is to adjust the cant of the boot with the handy allen wrench. But of course it's not a real sole cant but just an adjustment of the barrel of the boot as it sits on the body. This will help align your leg and patella relative to the boot body, but won't do much to help the distribution of force as you flex, since the tibia will still be misaligned relative to the foot, and it will tend to create interesting new pressures/hot spots on the ankle as the barrel takes some of the force each flex cycle. 

 

Now if you have messed up knees that actually don't align with the tibia, or if you've got curved tibia, you're pretty much screwed in terms of simple solutions. Maybe a real medical knee brace, or a good fitter can do more nuanced stuff using an orthotic, or actually plane down the boot sole (which is what racers do). Do not try any of this this at home. 

 

So that's my longwinded version. See, "bingo" was actually better.  

post #5 of 9
Thread Starter 

 

Quote:
Originally Posted by beyond View Post

 

 

Sorry. As I do it, and I may be hilariously off on all this, these assumption: 1) In a skiing stance with the proper sole insert/orthotic, your foot is neutral (neither pronated nor supinated), 2) In this stance, since your CM is forward of your normal standing CM, it is distributed more toward the base of the first metatarsal/BOF, and 3) the midpoint of your patella should be at your BOF. Therefore, the tip of the bob should bisect the BOF line. Put in a less technical way, when you load your leg, your kneecap should always be over the middle of your foot just behind your toes. Works for all sports I know of. 

 

That takes care of the longitudinal axis. If the bob tip is medially or laterally off from the bisect point, you have two options. The best is to get thee to a bootfitter and get a different insert, since odds are yours is still off. The quick and dirty solution is to adjust the cant of the boot with the handy allen wrench. But of course it's not a real sole cant but just an adjustment of the barrel of the boot as it sits on the body. This will help align your leg and patella relative to the boot body, but won't do much to help the distribution of force as you flex, since the tibia will still be misaligned relative to the foot, and it will tend to create interesting new pressures/hot spots on the ankle as the barrel takes some of the force each flex cycle. 

 

Now if you have messed up knees that actually don't align with the tibia, or if you've got curved tibia, you're pretty much screwed in terms of simple solutions. Maybe a real medical knee brace, or a good fitter can do more nuanced stuff using an orthotic, or actually plane down the boot sole (which is what racers do). Do not try any of this this at home. 

 

So that's my longwinded version. See, "bingo" was actually better.  

 

When you hold the string in the middle of your knee cap, where should the bob be on the boot. Middle of tip of boot or just on inside of that?

post #6 of 9

 

Quote:
Originally Posted by GordonFreeman View Post

When you hold the string in the middle of your knee cap, where should the bob be on the boot. Middle of tip of boot or just on inside of that?

Nowhere near tip of boot, so unclear how you got there; if "inside" means medial (toward inside of leg), well that's complicated. The CM does not move in a straight line forward and aft, since as our weight shifts forward we go from mild supination to mild pronation, from lateral to medial. So technically the further forward you are, the more the bob tip should be slightly medial to the midline of the foot. But a simple bisection of the foot is probably fine. For one thing, the foot doesn't sit perfectly inside the boot, so you can get crazy trying to get more exact than the situation allows. Hell, even the knee and ankle joints are designed to slide around a bit. 

post #7 of 9


 

Quote:
Originally Posted by beyond View Post

 

 

Nowhere near tip of boot, so unclear how you got there; if "inside" means medial (toward inside of leg), well that's complicated. The CM does not move in a straight line forward and aft, since as our weight shifts forward we go from mild supination to mild pronation, from lateral to medial. So technically the further forward you are, the more the bob tip should be slightly medial to the midline of the foot. But a simple bisection of the foot is probably fine. For one thing, the foot doesn't sit perfectly inside the boot, so you can get crazy trying to get more exact than the situation allows. Hell, even the knee and ankle joints are designed to slide around a bit. 

or over the second toe
 

post #8 of 9

 

Quote:
Originally Posted by 2-turn View Post

 

or over the second toe
 

Yeah, if you're a forward pressure kinda skier, that works too. Assuming you can figure out when it is directly below the bob on the boot surface. Personally I sometimes have trouble finding inside stuff from the outside. Guess if you have a transparent shell you could take out the liner, mark it, all that. Or do the tap method we use for BOF. YMMV.

post #9 of 9

firstly i like to deal with centre of knee mass not centre of patella as the two are not the same, as a starting point i want to see the centre of knee mass liner up with or be up to 1 degree inside of centre of the boot...in days gone by [straight skis] then 1-2 degrees inside of centre was one theory of where things should be, with modern skis that is too much

 

how you get to that point depends on the body and the boot, i like to check using 2 or 3 methods...firstly either a plumb bob or a framing square and secondly using a set of cant co. rockers, i use these to see what the leg is doing and to assess any rotational or twisting forces.... depending on the results of the assessment depends on what the remedy is...... do you shim the binding, plane the boot sole, cant the boot or fill the gaps   all these things depend on the available range of motion in the knee and hip joint, if there is simply not the available joint ROM to make a correction then it is better to fill the gap to allow the skier to stand on a flat ski rather then cant them to try and get perfect alignment

 

normally i would carry out an assessment then suggest the skier try a temporary experimental cant to assess how things feel when actually skiing, especially if it is a large change.  there is no subsitute for on hill testing for things like this.

 

another thing to consider is fore / aft alignment is often a bigger cause of problems then lateral alignment.

 

 

 

 

of course you could have asked this when you were in the other day.... i hate trying to put it into written words

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