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Deviation of STJ axis etc..

Discussion in 'Biomechanics, Sports and Foot orthoses' started by JM82, Dec 13, 2011.

  1. JM82

    JM82 Welcome New Poster


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    Hello, As a student just getting to grips with the biomechanics side of the job I would just like to clarify if I have an understanding of how a medially/lateraly deviated STJ axis affects the muscles that control the moments about the axis. We haven't been taught a great deal about this in uni, I was actually shown on a placement how to plot the axis by putting the foot in neutral and trying to eliminate any frontal plane motion when pressing on the heel.....Anyway the pod i was with said (although not definitively) that the muscles inserting around the axis would change functionally if the axis was medially or laterally deviated due to longer/shorter moment arms created by the deviation. For example if the axis was medially deviated then the peroneous brevis muscle would gain a greater mechanical advantage and pronate the foot further....That bit seems clear, but the functioning of tibialis posterior not acting to invert the foot?? Or contributing to the pronation moment about the axis?? It was explained to me that if the axis crossed the insertion of the tibpost then its function would change.

    What Dr's Kirby, Spooner and others are writing on this site seems to make more sense than the Root theory that we are being taught. I appreciate that looking at biomechanics from a historical perspective in terms of Root/Hicks and how ground breaking their work is needs to be a part of our course, but things do seem to have advanced to new paradigms such as 'tissue stress' and pointed in the direction of Benno Niggs work. We have touched on tissue stress in my final year and the biomechanics sessions do appear to be focusing on presenting pathology and how to best alleviate the patient of any pain they are experiencing instead of trying to realign or correct their foot function to a theoretically norm.

    I'm having Dr Kirby's 3 books for xmas so hopefully that will help greatly with my studies of this fascinating subject.

    Would be great if someone could help me with clarification of the above...

    Cheers

    Mike..
     
  2. Mike

    Have you had a look through these threads market . STJ axis Threads

    Especially this thread - Thought Experiment #3: Effect of STJ Axis Location on PT Muscle Tension

    Good luck and :welcome:
    Seems the Pod you went to was a good one.
     
  3. JM82

    JM82 Welcome New Poster

    Mike

    Thank you for the link and the welcome....One has a lot of reading to do it appears. Yes he was a good pod who gave up his time for us poor confused students...not sure if i'm allowed to name names and all...

    The problem I see with being a student from a biomechanical perspective is that we don't see enough feet. Doing one 3 hour session every 3 weeks and only seeing two or three patients - not enough! I would like to persue a career in this area of podiatry upon qualification, but i've been told that it would be 2 years or more before I could specialise in this. I have no aversion to doin general, after all you gotta love the old dears and their bunions. Clinic wouldn't be the same without them....

    Cheers
    Mike
     
  4. Mike , look for the biomechanics learning opportunities in all of your patients , not just the ones in the so called "biomechanics" clinic. Robs biomechanics corner in this months shamopody now touches on this.



     
  5. efuller

    efuller MVP

    I think that plotting the axis is one of the most basic and important things to understand as a student. When you push on one side of the axis the foot pronates and when you push one the other side of the axis the foot supinates. Using your finger to push on the foot is the same as the center of pressure of ground reaction force pushing on the foot. (The center of pressure is essentially the average point of force.) That said, I would put the foot in the position that it is in when in stance as opposed to neutral position. (If you've read Kevin's paper on palpation of the axis (hint), he describes plantar parallel position that tries to recreate the stance position) The reason for this is that the foot moves around the projection of the axis as the STJ pronates or supinates.) To figure out the moment from ground reaction force you need to know the position of the axis when ground reaction force is applied. A foot that rests in neutral position is very very rare.


    You may be confusing Anterior tibial and posterior tibial muscles. The position of the STJ axis will pretty much be a line between the posterior lateral heel and the talar head. It will be nearly impossible to get the posterior tibial insertion on the lateral side of that axis. The anterior tibial muscle can shift to the other side of that axis when the forefoot is abducted on the rearfoot.

    There is some good stuff in Root. For example the concept of a partially compensated rearfoot/forefoot varus is important. However the distinction between rearfoot varus and forefoot varus doesn't make any sense. The STJ knows it's maximally pronated in both cases.

    Kevin's JAPMA articles are also good. It would be good to read rotational equilibrium at the same time you read Hicks the function of the muscles.

    Anybody who is good at biomechanics has to have sat and thought about how the foot works. Keep thinking.

    Eric
     
  6. There is, there really is. But it has to be proper root, not the watered down, weak ass straw man which people have tried to make it. If you have a library, get the book out and read it.

    But your understanding seems to be on the money Mike. Well done for stepping through the looking glass. And well done to the pod who explained it to you. Adhere yourself to him as a leech and suck as much knowledge from him as you can before he approaches you with a lit cigar to burn you off.

    Nice to see an undergrad with the enthusiasm to look deeper, and the gumption to ask about it here. You should go far.
     
  7. Or, her.
     
  8. We need more Female biomechanists. It seems to attract males for some reason.
     
  9. K, I'll give you that one... but we shall meet again... I'll get me coat- it was you wasn't it? :drinks;) How much did you pay JM82 to write this Robeer?
     
  10. Actually, I think not! I've done a few in Scotland, plenty in England and one in Northern Ireland, but never lectured in Welsh Walesland. The mysterious Welsh Guru will remain a mystery. I can't take credit for this one.
     
  11. Maybe they crossed the border to hear you Rob? I would, but then I'm close to the land of the pointy heads with the chewing-gum feet.
     
  12. JM82

    JM82 Welcome New Poster

    A big thanks for all the encouragement help and advice fellas...I would have said thanks earlier, but the little on e has been a bit ill unfortunately. There are some instances when I need to be elsewhere and not on podiatry arena..lol.

    Simon....I do try to look for the biomechanical reasons in most patients I see..One of the most common questions I get asked after 'How can you touch feet?' and 'Why did you go into this profession' is 'Why have I got that corn or hard skin there? I try my best to offer an explanation....Using mechanical therapies such as SCF padding etc seems to be met with a blank expression by tutors...???

    Eric...Yes I think I was getting confused with tibposterior and tibanterior muscle. I dug out the rough diagram he drew and I can see what you mean now that it couldn't be tibpost. I read Kevin's paper yesterday on locating the STJ axis and this makes things clearer regarding what position you put the foot in. I'm also reading your paper on the Hicks windlass mechanism - force couples confused me slightly at first, but I think I'm getting there.

    The 'Guru' as you call him was a pod from Swansea NHS and I only spent an afternoon with him, but a lot of light bulbs went on in that short time. I say we're not taught much about STJ axis theory, but we are encouraged to read around what we are taught and to explore other paradigms. The concept of independent learning isn't lost on me as I prefer not to be spoonfed as a lot of students do...After all being a student is a full-time occupation as far as i'm concerned. Maybe its my age..lol..

    Thanks again for your wise words and nice to know I'm not too far off the mark

    Cheers

    Mike...
     
  13. David Smith

    David Smith Well-Known Member

    Why? Discuss - Perhaps that could be a new thread

    Dave
     
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