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Polio (R leg), inverted foot, why?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by markjohconley, Aug 23, 2011.

  1. markjohconley

    markjohconley Well-Known Member

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    No Tib.Ant.mm. innervation (polio), very strong gastrocnemius mm, peronei seems to be weakened or overused, why a inverted foot? Is it from proximal, laterally rotated hip? Thanks
  2. RobinP

    RobinP Well-Known Member

    What is mm please?
  3. Page23

    Page23 Active Member

    I'm assuming mm means muscle mass?

    The foot is inverting due to the (relatively) strong calf. This muscle often casues a degree of inversion (with the obvious plantarflexion). Tib post may also be (relatively) strong adding to the postural position you have observed. In fact, it's likely to be more of a supinated position you are seeing. Clearly there is gross muscular imbalance due to weak/inactive tib ant and peroneals.
  4. efuller

    efuller MVP

    I don't quite understand "weakened or overused." If they are weak and have little passive tension, normal tension in the posterior tibial muscle will supinate the STJ. Also the gastroc can be a strong supinator as its insertion is usually medial to the STJ axis. If there is a laterally deviated STJ axis, the gastroc will create an ankle plantar flexion moment and a STJ supination moment, and the ground may create a small pronation moment with the anterior shift in the center of pressure. So, the net effect with the lateral axis is that you get a supination moment from the gastroc.

    It's very difficult to get a non muscle created moment from proximal that would supinate a weight bearing STJ. In Root, et al, 's books there was a demonstration in which if you twisted the pelvis in the transverse plane you would supinate one STJ and pronate the other. However, if watch carefully, you can see individuals performing this task use their peroneal and posterior tibial muscles to twist the hip. That is why I think the supinated foot you see in your patient, is not caused by proximal non muscle moments.

  5. markjohconley

    markjohconley Well-Known Member

    Thanks all.
    Not sure where I picked up mm. for muscle, apologies.
    The distal attachment of the gastrocnemius muscle is medial to the STJ axis so applies an internal supinatory moment on the STJ. The shortened (tight) muscle, from the ankle dorsi-plantar flexion imbalance, therefore causes a greater supinatory moment than for a 'normal' length muscle.
    The peronei have been stressed by 'attempting to balance' this. Is there a 'Peronei Tendon Dysfunction'?.

    What has always confused me is in a pes planus the gasctrocnemius muscle is also 'tight', this is due to the plantarflexed rearfoot?
    So a tight gastrocnemius muscle can be in both pes planus (as a result) and in pes cavus (as a cause)? Is this right????? Thanks, fighting dementia, Mark
  6. Mark:

    A tight gastrocnemius-soleus complex (GSC) will cause an increase in subtalar joint (STJ) pronation moment in a foot with a medially deviated STJ axis and a tight GSC will cause an increase in STJ supination moment in a foot with a laterally deviated STJ axis. Need to write a paper on this subject one of these days.:cool:
  7. markjohconley

    markjohconley Well-Known Member

    Thanks Prof. Kirby, am I the only one having trouble with this???
    Looking forward to that paper!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  8. efuller

    efuller MVP

    I did write a paper on this
    Fuller, Eric The Equinus Paradox Podiatric Biomechanics Group Focus Issue 5 April 1998 p.17-19
  9. Would love a copy, Eric.:drinks
  10. markjohconley

    markjohconley Well-Known Member

    Thanks Dr Fuller
    It wouldn't let me access, naturally, Mark
  11. markjohconley

    markjohconley Well-Known Member

    Anyone educate me on this. To the unknowing, like myself, it appears, since the distal attachment of the gastrocnemius muscle would be medial
    to the STJ TP axis, that the vector would cause a supinatory STJ moment? I thought that only the Tibialis Anterior muscle's STJ moments would depend upon TP orientation of the STJ TP axis??

    In feet with laterally deviated STJ TP axis wouldn't this occur? Known by another name?

    Thanks, it's alright if it's too frustrating to reply as I am retiring tomorrow after winning a big lottery prize tonight YES!
  12. Mark maybe this thread helps - Gastrocnemius: supinator or pronator?

    ps if it is lots I too would like to retire :drinks
  13. markjohconley

    markjohconley Well-Known Member

    Thanks Mike, will read now.
    Sorry Mike that last line is illegible, check your end!
  14. shereenix

    shereenix Welcome New Poster

    Just thought I would add another perspective:
    If there is significant tib ant weakness, then perhaps peroneus longus (although weak itself) is gaining a mechanical advantage in its ability to plantarflex the first ray, leading to an inverted rearfoot?
    Food for thought ...
  15. Page23

    Page23 Active Member

    Although peroneus longus causes plantarflexion of the 1st ray and contributes towards a degree of plantarflexion of the foot, it does not cause inversion of the hindfoot. It causes eversion here.
  16. Orthican

    Orthican Active Member

    I'm going to say right now that I love reading this forum. The information you have all compiled here is without doubt second to none. I appreciate the effort many of you take with the information sharing and that you get right to the point.

    This thread peaked my interest as well as I have several patients with polio.
    To the point.
    When looking at the patient with polio also consider that the amount of recruitment of each individual muscle has been altered due to the original viral attack and but also there will be later in life a loss of individual neurons as well as a result of attrition. So the amount of saltitory action leading to an action potential in each muscle will be a crap shoot. Not all of the fibres of that gastroc will be firing. Sometimes it can be mixed and present as generalized weakness and sometimes it will test as weakness but with assymmetry from lateral to medial head. (this is more seen when watching contractions as opposed to a feel thing) Also, when testing individual groups for strength test again at follow up but at a different time of the day as well. You will note a difference. Obviously mornings for most will be best but afternoons not good due to exhaustion. These are small points I know, but thought it might be worth noting.
  17. admin

    admin Administrator Staff Member

    ...funny you should say that. I just came across a post on another forum that quipped that there is never anything useful on Podiatry Arena .... don't figure!

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