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Is the persistent 'foot guard tendon reflex' the cause of functional hallux limtus?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, Feb 4, 2017.

  1. Craig Payne

    Craig Payne Moderator

    Articles:
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    I first came across this in a blog post proposed by the physical therapist, Sean Gibbons (which does not explain it very well).

    The foot guard tendon reflex:
    This is a normal reflex (opposite to Babinski): when there is a stimulus from stroking from the plantar first metatarsal head posteriorly along the medial arch towards the heel --> the medial column of the foot dorsiflexes when this reflex is normal. The reflex is generally active from birth until around 2 years of age.
    Stimulation of this reflex when learning to walk would tend to offload the medial column of the foot and load the lateral column, assisting with postural stability. Sometimes the primitive reflexes persist to become what is known as unintegrated reflexes.
    HOWEVER: the whole 'retention of primitive reflexes'/'unintegrated reflexes' is a bit of an alternative popular fad with limited evidence supporting it, so any link to functional hallux limitus will have to be on that shaky ground

    Relationship to FnHL:
    If the foot guard tendon reflex does not integrate and continues to exist, then there is assumed to be a tendency for the load to be more on the lateral the lateral column of the foot more as stimulation of the medial column from the ground initiates the reflex. This also tends to be the weight-bearing pattern seen in functional hallux limitus.
    The 'reflex' initiated dorsiflexion (or inhibition of plantarflexion) of the first ray (medial column) would limit first metatarsophalangeal joint dorsiflexion, theoretically producing a functional hallux limitus.

    What say you?
    • there is no evidence to support this (mainly as no one has done any research on it!)
    • it is possibly a plausible alternative explanation for the phenomenon of functional hallux limitus
    • when you look at the exercises advocated for the integration of this reflex, they are not too dissimilar to the manipulation that is advocated by some for functional hallux limitus.
    • does the manipulation work because it integrates the foot tendon guard reflex?
    • does the above hypothesis work because the exercises to integrate the reflex are really a 'manipulation' for FnHL?
    Always willing to learn...not totally convinced; willing to keep an open mind
     
    Last edited by a moderator: Feb 5, 2017
  2. Admin2

    Admin2 Administrator Staff Member

  3. efuller

    efuller MVP

    The non weight bearing "foot guard)" reflex is mediated by contraction of the anterior tibial muscle. The direct attachment of the anterior tibial muscle dorsiflexes the first ray (flattening the arch) which increases the distance from the first met head to insertion of the plantar fascia on the heel. That increased distance will cause the windlass mechanism to work in reverse and plantar flex the first toe. Tension in the plantar fascia is causing plantar flexion of the toe. You have to look at the forces involved to understand what is going on. It's not just a "reflex". It is a reflex that causes muscle contraction.

    So, if this reflex were working in gait we should consistently see contraction of the anterior tibial muscle in the presence of functional hallux limitus. There are some people who do contract their anterior tibial muscle in gait (extensor substitution), but they are a small portion of the people you see with functional hallux limitus. The lateral weight bearing in functional hallux limitus, in my opinion, is a pain avoidance response where there is increased activity of the posterior tibial muscle causes supination to shif the load to the lateral forefoot. I think both the anterior tibial (extensor substition) and posterior tibial contractions are CNS learned response to avoid pain.

    I still like the explanation of the forces in the windlass mechanism as a better explanation of functional hallux limitus.

    Eric
     
  4. DaVinci

    DaVinci Well-Known Member

    The last I heard was that this retention of reflexes was bogus
     
  5. mazzopod

    mazzopod Member

    What about hyperactivity of the flexor hallucis longus in trying to stabilize the medial column of the foot in the negative windlass compensation ?
     
  6. efuller

    efuller MVP

    What is a negative windlass compensation?
     
  7. mazzopod

    mazzopod Member

    What I mean is: as seen in FHL the hallux plantarflexes and the 1st ray dorsiflexes. Could this be due to a compensatory mechanism of the flexor hallucis longus in attempting to stabilize the medial column creating a supinatory moment to improve the rigid lever effect in toe-off.
     
  8. efuller

    efuller MVP

    Functional Hallux Limitus (FnHL) and Flexor Hallucis Longus (FHL) have the same initials. It can get confusing if we use abbreviations and talk about them in the same sentence. From context, it appears you are saying that FHL is functional Hallux limitus. To to get the hallux to plantar flex you need a plantar flexion moment. A distal to proximal force acting on the base of the proximal phalanxs and a proximal to distal force acting on the base of the proximal phalanx will create a plantar flexion moment acting on the proximal phalanx. The FHL tendon attaches to the distal phalanx. The FHL tendon could create a plantar flexion moment on the proximal phalanx if the interphalangeal joint was held rigid. That would not happen non weight bearing. Weight bearing, ground reaction force will tend to dorsiflex the interphalangeal joint and it is conceivable that the IPJ could be held rigid. Or, tension in the FHL tendon could case plantar flexion of the IPJ which would cause dorsiflexion of the MPJ as seen in a hallux hammertoe.

    So to figure out why the hallux plantar flexes when the first met dorsiflexes we should look at the base of the proximal phalanx. The distal attachments of flexor brevis and the plantar fascia are into base of the proximal phalanx. The windlass working in reverse will cause the hallux to plantar flex.

    There are much better muscles than FHL to "stabilize" the first ray. There are also much better muscles than the FHL to supinate the STJ. The peroneus longus muscles inserts into the plantar base of the first ray and can easily create a plantar flexion moment acting on the first metatarsal. FHL tension could plantar flex the first ray, but it would also tend to cause a hallux hammertoe. Hicks showed that FDL (flexor digitorum longus) and posterior tibial (PT) tendons have a much better lever arm to supinate the STJ than FHL does. It is unlikely that the CNS would recruit the FHL over the PT and FDL to supinate the STJ.

    Passive tension in the platnar fascia will make the foot a rigid lever. Pronation of the STJ and dorsiflexion of the first ray will increase tension in the plantar fascia thus making the foot more rigid. There was an old and discredited idea that pronation of the STJ made the foot a mobile adapter and supination of the STJ made the foot a rigid lever. The reasoning behind that was flawed.

    Eric
     
  9. mazzopod

    mazzopod Member

    Am I wrong in saying that in FnHL most people present with excessive STJ pronation causing the foot to abduct and therefore reducing the plantarflexion sagittal plane force of the Peroneus longus muscle and increasing the transverse plane force. Is the lever arm effect of the PT and FDL not reduced in these cases causing a decreased inversion moment ?
     
  10. efuller

    efuller MVP

    Yes, that theory on peroneus longus is out there. I presented a lecture on why I thought that was wrong at a PFOLA meeting maybe 10 years ago. I need to get around to writing that paper. Basically, the analysis that you are familiar with is wrong because it is not the frontal plane direction of pull of the peroneus longus muscle that determines the leverage the muscle has to plantar flex the first ray. The correct way to analyze it is to look in the sagittal plane. The proximal pull of the tendon at the plantar base of the metatarsal creates a reactive force from the cuneiform on the base of the metatarsal. When you combine those two forces you get the force couple that creates the plantar flexion moment on the first metatarsal.

    The peroneus longus muscle does create a pronation moment at the STJ. When there is STJ eversion there is a tendency for an increase in ground reaction force under the first met head. This creates an interesting situation where one effect of the muscle is to plantar flex the first ray and another effect of the muscle is to dorsiflex the first ray. I created a mechanical model that showed that position of the STJ axis was important for figuring out which effect creates the greater moment. When the STJ axis is more medial the tendon has a greater lever arm to pronate the STJ and can even lead to a net dorsiflexion moment on the first ray. When the axis more lateral, the increased ground reaction force under the first met head actually increases the supination moment from the ground to the point that you can get a net STJ supination moment.

    Your second question about the lever arm of the PT, FDL and FHL tendons: Yes, as the talus adducts there will be a tendency for the STJ axis to be more medial and a tendency for all of those tendons to have a reduced lever arm. The anatomical arrangement of the tendons determines the lever arm of the tendon. The FHL tendon is always the most lateral tendon as it progresses from the notch at the back of the talus down under the sustentaculum tali. Whereas the other two tendons are farther medial as they come around the medial maleolus and have their proximal pull directed more medially. The old Hicks paper provides evidence for the relative ability of these muscles to create supination moment.

    Eric
     
  11. mazzopod

    mazzopod Member

    Eric thank you for your time and explanation. It's always a pleasure reading what the experts have to say.
    Maurizio
     
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