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Effects of a calcaneal dorsiflexion moment

Discussion in 'Biomechanics, Sports and Foot orthoses' started by daisyboi, Mar 18, 2015.

  1. daisyboi

    daisyboi Active Member


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    Just wondering if anyone can enlighten me. Thinking through sagittal plane theory, I understand that one goal of intervention is to increase the plantarflexion of the 1st ray. I was wondering whether designing an orthosis to increase the dorsiflexion moment of the calcaneum would have this effect. Also, would it have any negative effects, in terms of impeding progression etc. I'm thinking about something which would be an inclination from zero at the proximal aspect of the plantar surface of the calc to a few degrees as the post progresses to the distal aspect. What are the pitfalls in such an approach?

    Regards

    Dave
     
  2. efuller

    efuller MVP


    To get the rearfoot to dorsi flex you have to get the forefoot to plantar flex on the rearfoot. The problem here is that the orthotic pushes upward on the bottom of the calcaneus. Where the forefoot goes is dependent on many other things. Just because you dorsiflex the calcaneus does not mean that the forefoot will plantar flex. What's pulling the forefoot down versus what's pushing the forefoot up? You are only looking at half of the foot.

    Eric
     
  3. Phil Wells

    Phil Wells Active Member

    Dave

    Just to look at things from a different angle, have you thought about trying to reduce calcaneal plantarflexion moments at initial contact e.g. the SACH modification done to AFO's and shoes?
    The problem with trying to increases dorsiflexion moments is that you could affect CoP progression and create unwanted issues.

    Phil
     
  4. efuller

    efuller MVP

    A SACH heel decreases plantar flexion moments, on the entire foot, at the ankle joint by altering center of pressure. In a normal shoe, at heel contact, the center of pressure is posterior to the ankle joint. Upward force posterior to the ankle joint will cause an ankle plantar flexion moment. (This moment is usually opposed by a dorsiflexion moment from the anterior tibial muscle, that allows a slow platnar flexion.) In a SACH heel the heel of the shoe deforms effectively moving the center of pressure anteriorly and this will tend to slow ankle plantar flexion. (The actual speed of plantar flexion will depend on how much change there is in muscle activity.) So a SACH heel does affect CoP progression.

    Eric
     
  5. daisyboi

    daisyboi Active Member

    Thanks for the replies guys. Eric, do I understand you correctly? an increase in dorsiflexion moments of the calcaneum may result in a decrease in the plantarflexion moment of the forefoot (maybe it's dependant on that ellusive phenomena midtarsal stiffness. I heard about that at university but never understood what it actually is meant to be). Decreasing the plantarflexion moment of heel strike as suggested by Phil does not have the same effect as increasing the dorsiflexion moments during propulsion. How then do we assess the correct rearfoot position in an orthosis? If the rearfoot plantarflexion moments are too great then presumably this means that the dorsiflexion moments of the forefoot will increase, resulting in a loss of the windlass and a failure of the 1st ray's plantarflexion mechanisms. Conversely however, if the dorsiflexion moments of the rearfoot are increased excessively, the ability of the forefoot to contact the ground is compromised.
     
  6. efuller

    efuller MVP

    Daisy, or is it boi,
    I'm having a little trouble following what you are saying. When you describe a moment you need say what is applying the moment and what the moment is applied to. For example, Ground reaction force, at heel contact will apply a plantar flexion moment to the foot about the ankle joint axis. You can go a little deeper and identify individual forces that create a force couple. For example, body weight applied to the top of the talus, by the tibia and ground reaction force will create a force couple that will plantar flex the rearfoot unit of the talus and calcaneus. You might be able to answer your own question if you were to better describe the moments and the time during gait which they are applied.

    Eric
     
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