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Plantar pressure distribution, windlass and FnHL

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Petcu Daniel, Oct 14, 2018.

  1. Petcu Daniel

    Petcu Daniel Active Member

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    I'm interested to understand the link between barefoot plantar pressure distribution in walking and windlass mechanism or functional hallux limitus. I've read articles which is studying the link between force (but in a static trial) or hallux dosiflexion angle and windlass but not between pressure and windlass. Something about plantar pressure and FnHL was in a narrative description in PodChatLive [ ] but I would like to see some pressure graphs/values!
    Any reference provided will be appreciated! Thanks in advance!
  2. Petcu Daniel

    Petcu Daniel Active Member

    “Pressure and Force Distribution Characteristics under the Normal Foot during the Push-off Phase in Gait - ScienceDirect.” Accessed October 15, 2018. https://www.sciencedirect.com/science/article/pii/S0958259299905187.

    Forty-two persons (19 males, 23 females) with asymptomatic feet.
    Force distribution (%BW): MTH1=29.1; MTH2=28.3; Big toe=23.8
    Peak pressure distribution (kPa): MTH1=372.8 ( = 80% from Big toe); MTH2=435.2 (=94% from Big toe); Big toe=462.4 (=100%)

    Mechanical model of the windlass mechanism of the foot (https://www.ncbi.nlm.nih.gov/pubmed/10659531 ) predict that high first metatarsal and hallux forces will lead to some patologies. First paper shows almost equal forces between MTH1 and MTH2 in a normal population. It is right to assume that a MTH1 force significant greater that MTH2 (or a pressure under MTH1 approximately equal with that under MTH2) is associated with a dysfunction of the windlass?
  3. efuller

    efuller MVP

    It's not just the metatarsal head forces. The windlass tends to cause supination of the STJ. So if there is high pronation moment, from muscle or ground reactive force, there will be more resistance to the windlass causing supination. Another thing that I've been meaning to look at is how much first ray plantar flexion with non weightbearing dorsiflexion of the hallux. The amount of ray motion varies across people. My sense is that those with more first metatarsal plantar flexion dorsiflexion range of motion will have more resistance to the windlass.

    An interesting question is what is meant by dysfunction of the windlass. The windlass, when operating normally, will tend to create a plantar flexion moment at the MPJ. So a "normally" functioning windlass could be creating functional hallux limitus where one would see very high pressures on the first toe and very little pressure on the first met head. (this would occur after heel off). I think we should focus not on "dysfunction" but on pathology caused by high load in the anatomical structures of the windlass. The attachment of the fascia at the calcaneus, the articular cartilage of the MPJ, the hallux interphalangeal joint, etc.

    In treating the windlass, we do want to lower loads on the windlass. If the MPJ is held rigid by the windlass, when the heel lifts, there may be low loads on the first met head and very high loads on the hallux. If the internal loads on the windlass are reduced, the hallux may be allowed to dorsiflex after heel lift. If that happens, one might see an increase in force on the first metatarsal head. My point is that we need to be looking at the internal loads of the windlass when treating the windlass. I do believe that treatments designed to decrease loads on the first met head will tend to reduce internal forces of the windlass, but we might not see a decrease in load on the windlass. I remember Howard Dannanberg mentioning with successful treatment of functional hallux limitus he did see increase in pressure under the first met head. The timing of the force on the met head and the internal forces of the windlass are important to note.

  4. Petcu Daniel

    Petcu Daniel Active Member

    Can we speculate that the 'very little pressure on the first met head' is in fact very little pressure between the plantar fascia and supporting surface in the area of the first met head and high pressure between plantar fascia and first met head (which could mean that the plantar fascia is rising the first met head)?
  5. efuller

    efuller MVP

    What I am speculating is that pressure sensing mat will show low loads on the first met head. The distal attachment of the plantar fascia is the sesamoids. So if you include the definition of the sesamoids, then there is decreased upward force from the ground on the fascia.

    In terms of force from the fascia on the first met head. The tension in the fascia will pull the proximal phalanx into the first met head. The force from "fascia" (actually proximal phalanx) on the first metatarsal head is distal to proximal, at the distal aspect of the metatarsal head, and not on the plantar aspect of the metatarsal head. The plantar flexion moment (from pull from fascia and push from metatasral head) acting on the proximal phalanx is keeping the mpj rigid as the whole foot rotates relative to the floor with plantar flexion of the ankle. Daniel, this is just a little bit different from what you said. You said the plantar fascia is lifting the metatarsal head off of the floor. I don't think that the fascia is creating a plantar to dorsal force on the bottom of the first metatarsal to lift it off of the ground.

  6. Petcu Daniel

    Petcu Daniel Active Member

    Yes, this is what I'm saying! Why this system can't be viewed as a second class lever?

    Source of the image: http://www.oocities.org/rjwarren_stm/College_Physics/Mechanical_Systems.html
  7. Petcu Daniel

    Petcu Daniel Active Member

    Using free body diagrams, Wyss and all [ https://www.ncbi.nlm.nih.gov/pubmed/2229095 ] are estimating in the case of 10 subjects a mean of 1.3 N/Kg for the force between sesamoidis and metatarsal head while for the force between the metatarsal head and the proximal phalanx a mean of 2.89 N/Kg. This means that first one is around 45% from the second.

    Attached Files:

  8. efuller

    efuller MVP

    Their diagram makes sense. I was wrong to say there is no force from the sesamoids on the metatarsal head.
  9. Petcu Daniel

    Petcu Daniel Active Member

    Yes, I know that image. In my understanding of that image, which is somehow similar with that of the second class lever, the fulcrum is the proximal phalanx of the hallux while the first metatarsal head is the load.
  10. efuller

    efuller MVP

    I don't really like classifying levers. It gets confusing when you identify only one force as the "load". The force on the fulcrum is a load too. You should draw a free body diagram to identify all of the forces (loads). I showed how important that is in this thread when I opined without drawing, and came up with a bad conclusion.

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