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One of the effects of the windlass mechanism is to supinate the rearfoot. If its already supinated (ie rearfoot inverted), then the windlass does not have to work so hard to achieve this.
Also, invert the rearfoot also plantarflexes the first ray - this also will help facilitate the windlass.
Can someone please further explain how inverting the rearfoot will lower the force used to establish windlass mechanism
I am slightly confused
Dear Slightly confused pod t.
Maybe some other things to consider on top of Craigs. When you invert the rearfoot the Centre of Pressure( COP) will be more lateral, therefore less resistance to the supination effect that you describe.
Also the STJ axis will deviate more laterally which may mean that more of the plantar fascia is medial to the axis, which will have a stronger supination effect. If that makes you scratch your head alittle see the below thread, that Simon Spooner started and follow the posts as he walks me through how the position of the subtalar joint axis will effect what moment ( pronation, none or supination) occurs at the subtalar joint axis from a windlass effect.
Can someone please further explain how inverting the rearfoot will lower the force used to establish windlass mechanism
I am slightly confused
Confused PodT:
This is a fairly easy one.
During relaxed bipedal stance, there will be ground reaction force (GRF) plantar to the first metatarsal head which will, in turn, cause a first ray dorsiflexion moment. The greater the GRF plantar to the first metatarsal head then the greater the first ray dorsiflexion moment. As GRF increases plantar to the first metatarsal head then so does dorsiflexion of the first ray also increase which will cause an increase in stretching of, and an in increase in tensile force within the medial band of the plantar fascia (MBPF) which attaches to the sesamoids. The sesamoids are attached to base of the proximal phalanx of the hallux by short ligaments so that when the MBPF has increased tensile force within it, there will be an increase in hallux plantarflexion moment. Therefore, any increase in tensile force within the MBPF, which will be caused by any increase in GRF under the first metatarsal head will, in turn, cause a hallux plantarflexion moment, which will increase the GRF plantar to the hallux.
The greater the magnitude of tensile force within the MBPF, then the greater will be the force required to dorsiflex the hallux to "establish the windlass mechanism" or, in other words, to cause first ray plantarflexion, to cause subtalar joint supination and to cause external rotation of the tibia. Inverting the rearfoot during relaxed bipedal stance will simply reduce the GRF plantar to the first metatarsal head and increase the GRF on the more lateral metatarsal heads. The decrease in GRF plantar to the first metatarsal head will, in turn, decrease the tensile force in the MBPF, decrease the hallux plantarflexion moment and decrease the manual force required to dorsiflex the hallux to "establish the windlass mechanisim" by the examiner.
Hope this helps.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Can someone please further explain how inverting the rearfoot will lower the force used to establish windlass mechanism
I am slightly confused
First you have to define what you mean by inverting the rearfoot.
To some it would mean to take standing foot and grab it and invert it. That will decrease the force on the first metatarsal head. When the hallux is dorsiflexed the first ray will tend to plantar flex. When the foot is held in an inverted position there will be less force on the first met head and there will be less resistance to metatarsal plantar flexion.
Another meaning of invert the rearfoot is to apply a supination moment by shifting the center of pressure under the foot more medially with a varus wedge (medial heel skive or inverted type of orthotic.) In most feet the windlass causes supination of the STJ at the same time it plantar flexes the metatarsal. So, you have to examine the moments that resist "activation of the windlass" (my definition for this discussion: arch raising in response to dorsiflexion of the hallux in a standing foot. There are other definitions out there, but that is what Hicks described in his papers.)
So a pronation moment from the ground and a dorsiflexion moment on the first ray from the ground will resist activation of the windlass as Kevin described in his post where he discussed tension in the plantar fascia. If you decrease pronation moemnt from the ground, you will decrease the resistance to activation of the windlass. (Decrease pronation moment = increase supination moment.)
There's a lot more in my paper that Ian posted.
Regards,
Eric
The Following User Says Thank You to efuller For This Useful Post:
Maybe some other things to consider on top of Craigs. When you invert the rearfoot the Centre of Pressure( COP) will be more lateral, therefore less resistance to the supination effect that you describe.
Although the windlass is easier and the center of pressure is more lateral with the foot in a supinated position they are not cause and effect. To invert the STJ you have to apply a supination moment (from some source). The foot will supinate until something stops it. As it inverts the CoP will move laterally which increases the pronation moment from ground reaction force. Eventually the STJ will reach equilibrium and stop moving. Now if the source of supination moment e.g. tension in the posterior tibial tendon is reduced, the lateral CoP will create a net pronation moment and the foot will pronate until a new equilibrium position is reached. So, the windlass is not easier because the COP is more lateral. See other posts for that explanation.
Although the windlass is easier and the center of pressure is more lateral with the foot in a supinated position they are not cause and effect. To invert the STJ you have to apply a supination moment (from some source). The foot will supinate until something stops it. As it inverts the CoP will move laterally which increases the pronation moment from ground reaction force. Eventually the STJ will reach equilibrium and stop moving. Now if the source of supination moment e.g. tension in the posterior tibial tendon is reduced, the lateral CoP will create a net pronation moment and the foot will pronate until a new equilibrium position is reached. So, the windlass is not easier because the COP is more lateral. See other posts for that explanation.
Regards,
Eric
I see what your saying here, Which means I was correct in some Questions that Kevin asked me on another thread, but if you assume that the inverted heel come from a wedge then will not the COP be lateral as the supination moment provided by the wedge will be greater that the Pronation moment from GRF ?
I see what your saying here, Which means I was correct in some Questions that Kevin asked me on another thread, but if you assume that the inverted heel come from a wedge then will not the COP be lateral as the supination moment provided by the wedge will be greater that the Pronation moment from GRF ?
There is a net moment from ground reaction force and that is from the position of the CoP relative to the STJ axis. The wedge is part of ground reaction force. The wedge will shift the CoP and the STJ may or may not supinate in response to the wedge. (It will supinate when there is a net supination moment from the ground and then achieve a new equilibrium position. The wedge may not even change the position of the STJ when there is still a net pronation moment from the ground.
The article that really helped me understand the Windlass as a student was Eric's which I have attached. Well worth a read.
Ian
Colleagues:
Like Ian said, everyone should take the time to sit down and read Eric Fuller's article here at least once, but, better twice, since the physics/engineering principles that Eric discusses here can be applied to nearly any mechanical analysis of the foot and lower extremity. I just found out that the chapter that Eric and I wrote together on Tissue Stress Theory, where wediscuss similar concepts, should be published within the next six months. I'll believe it when I see it.
Nice to read this article again after all these years, Eric!
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Windlass Mechanism
Linear Mode
