Apart from its indication in orthoses to be used in a wound clinic for decreasing plantar metatarsal head ORF, why does it have to be included?
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In 'medially deviated STJ' patients the arch would either be increasing STJ pronatory moments, be 'beneath' the axis or providing such a short lever arm to be insignificant?
Obviously not wanted in a 'laterally deviated STJ' patient's orthoses.
To increase rearfoot dorsiflexion moments / increase forefoot plantarflexion moments, if contains a 1st ray cutout, fair enough, any other indications?
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Midfoot position, ROM and stiffness
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Mechanical factors contributing to foot eversion moment during running
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You also need to consider if you add a Medial skive the STJ axis position will be more deviated laterally and of course the STJ axial position is always moving and then there is the timing of ORF to consider in relation to the STJ axis
You also need to consider the MTJ or Talo-Navicular Calcaneo-cuboid joints and how the medial arch will affect those joints ( as Simon Said)
Plus there is Plantar tension ie Plantar ligaments, fascia Muscle to consider -
Thanks Mike for replying
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There are numerous functions of the medial longitudinal arch (MLA) of a foot orthosis:
1. Increases the ground reaction force (GRF) in the MLA of the foot.
2. Increases the external subtalar joint (STJ) supination moment acting on the foot versus no MLA in orthosis.
3. Increases the external rearfoot dorsiflexion moment and decreases the external forefoot plantarflexion moment (i.e. decreases the flattening moment on the MLA of the foot).
4. Will decrease tension load on plantar tension-load bearing elements of the MLA of the foot (i.e.plantar ligaments of MLA, plantar fascia, medial plantar intrinsic muscles, posterior tibial muscle, etc).
5. May function to decrease GRF on lateral column of foot by shifting more GRF to medial plantar midfoot.
6. Will promote more normal 1st ray-1st metatarsophalangeal biomechanics during gait in foot with functional hallux limitus by reducing tension in medial slips of central component of plantar aponeurosis.
7. Works along with medial heel skive modification to increase external STJ supination moment and increase comfort and "anti-pronation-controlling" ability of foot orthosis in patients suffering from pathologies due to excessive external STJ pronation moments.
8. Reduces dorsal interosseous compression forces in medial midtarsal and midfoot joints.
Hope this helps.:drinks -
The paper is on my other laptop right now so I stand to be corrected but is it reasonable to assume a more convex MLA will may increase tension in the medial fascia, where a concave arch profile may not? -
Any paper studying plantar fascial dynamics without loading the Achilles tendon, which has been shown to have a direct action on plantar fascial tension, will not answer the questions we need to have answered.
That being said, I am certain in some instances, a foot orthosis with an exceptional high, stiff MLA could increase the plantar fascial tension. In patients where I want to specifically decrease the tension within the medial band of the plantar fascia, I put a plantar fascial accommodation into the MLA of the orthosis to "stress-shield" the plantar fascia. Clinically , this seems to work very well. However, until dynamic studies are done in live subjects, we simply don't have adequate data to either support or refute these hypotheses. -
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I thought that the ORF from an 'angled' region of the orthosis, say the medial arch area, was indeed 'angled' having a vertical and a horizontal component, thus wouldn't it be applying a STJ pronation moment for the most part as the STJ axis passes superiorly to the midfoot. This is where the transverse plane STJ axis has its shortfall as a predictor of STJ moments surely, mark
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... fully realising the horizontal component would have both a medial-lateral and a, depending on which part of the orthosis arch, distal-proximal or proximal-distal; and that the ORF's would be subject, activity, surface (as in stiffness and slope) specific; and most importantly, i suppose, the part of stance phase the foot is at.
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In the case of an "arch support" an interesting article (also from PA) is: EFFECTS OF FOOT ARCH IMPEDANCE ON NAVICULAR DROP AND CALCANEAL EVERSION DURING WALKING: http://www.asbweb.org/conferences/2004/pdf/277.pdf
"SUMMARY
These preliminary findings suggested a greater calcaneal eversion might occur when the foot arch is impeded during the midstance of walking. As orthoses are often prescribed to correct excessive rearfoot motion, constraint on midfoot navicular drop
needs to be considered."
Daniel -
And even this will not answer to "why is medial arch needed...?" at least will try to answer to the question "how the arch height is determined ?" in the case of Blake Inverted Orthotics
http://www.drblakeshealingsole.com/2010/09/inverted-orthotic-technique-determining.html
Daniel -
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Daniel -
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Eric -
For those following: tan α =μ
where:α = Angle of friction; μ = Coefficient of friction
Out of interest here is a slide from one of my lectures where I measured a couple of angles from the superior surface of an orthosis shell, as you will see, we got angles here exceeding the angle of friction for certain top-cover to hosiery interactions.Attached Files:
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The horizontal forces must cancel when there is no acceleration of the foot relative to the orthotic. Now, there might be some configuration where the lateral heel cup or lateral flange forces could create some net moment at the STJ. But the fact that there is not net lateral to medial forces makes me thing we can get away with just looking at center of pressure and transverse plane projection of the axis.
Eric -
Daniel -
I find that some people like extra pressure in the arch and others can't wear the device that has too high of an arch. Since I've been doing standing medial arch height measurment, I haven't been pushing the limits, nor have I been experimenting with very high arch heights. I would bet that those that can't tolerate high arches are those that have high supination resistance and medially deviated STJ axes. High arches would push up on the foot in a location where there is little leverage to cause supination.
Eric
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Midfoot position, ROM and stiffness
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Mechanical factors contributing to foot eversion moment during running
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