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Function of Flexor Hallucis Longus

Discussion in 'Biomechanics, Sports and Foot orthoses' started by angermayer, Apr 15, 2013.

  1. angermayer

    angermayer Member

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    Hi, I am new here (and new to podiatry) and perhaps lacking the skill to browse the forum, for what I am looking for... Therefore, I thought I will raise my questions.

    I have recently been intrigued by one of my biomech tutors on the function of Flexor Hallucis Longus... Why is such a huge structure so poorly described in literature? What are its functions and is there any evidence on its isometric action during gait?

    I would really appreciate, if someone could recommend any reading for me - latest articles, etc.

    PS. I have similar interest in Peroneus Longus but thought I'd focus on one at the time..

    Thank you!
  2. Rob Kidd

    Rob Kidd Well-Known Member

    Well lets take one at a time. The following comments are far from gospel, but me thinking aloud. You say "such a huge structure"........... Is it? I have seen far bigger structures I think that the likely story lies in the changing role of the foot from being a unit of fine tactile manipulation, as in the hand, to being the foot of the striding biped that we are today. A part of that process was one of a reduction in digital size, and a huge increase in the overall proportion taken up by the tarsus - very nearly 50%, compared to about 10-15% in a gibbon. I would suggest that the long flexors and extensors are now little to do with their original function, and are now synergists of either ankle joing flexion or extension.

    However, we should not foget the enlarged sesamoids, and how, being in the heads of FHB, a channel is formed for the long flexor tendon to travel through. Anecdotally, in a N=2 sample, those people I know that have had traumatic removal of most (but not all) their hallux, once the trama had settles, they showed no loss of function. In both cases FHL was not deliberately reattached, though might have done itself.

    As for Fibularis longus (I have eventually capitulated and changed names), note how it, along with a few others, has an insertion that spands a joint, thus renering it much less mobile. Note how it forms a sling around the apex of the arch with TA - wich also spans the same joint. I would suggest that this is much a part of its modern function, but do not knock comments like "stabilizes the first ray during stance.

    Hope that has helped.
  3. efuller

    efuller MVP

    One of the best things I've ever read on the function of the foot muscles is one of the oldest. J.H. Hicks IV. written in th 1950's. Hicks mounted cadaver feet on a platform and attached weights to tendons and looked to see what happened and recorded it. At one point we had links here on the arena to that paper.

    To assess the function of any muscle you have to look at the line of action of the muscle as it crosses a joint. FHL crosses many joints. At the ankle it runs much further posterior to the ankle joint than post tib or FDL and thus has a longer lever arm than those muscles to plantar flex the ankle joint.

    At the STJ, the STJ axis pretty much splits the talus and the FHL tendon runs through the notch at the posterior of the talus so the lever arm here is small. So, there is little direct effect from EHL on the STJ. (muscles may have an indirect effect that is more important than their direct effect. For example, the Achilles tendon has a relatively small lever arm relative to the STJ, but the ankle joint plantar flexion effect will shift the location of the center of pressure anteriorly and in most feet that will increase the pronation moment from the ground.)

    The EHL tendon runs plantar to the MTJ, navicular cunieform, met cuniform, and MPJ, so it will create a plantar flexion moment on each of those joints in proportion to the distance of the line of action of the force from each of those joints.

    Whether or not a joint will move is dependent on the net moment at that joint. Just because a tendon has a plantar flexion lever arm, does not mean that it will always plantar flex a joint. There may be forces from some other source that overpower the muscle.

  4. HansMassage

    HansMassage Active Member

    Do your own study. With a subject having good reflexes have the head turned and extended over one foot. Does the hallucis planter flex? Is the reflex the same on the other side. Extend the arm over the foot; is the reflex the same or greater? Is the reflex changed by external rotation?
    Being familiar with the motion palpation in normal foot will help you understand problematic motion or lack of motion in foot problems.
    Hans Albert Quistorff, LMP
    Antalgic Posture Pain Specialist

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