11 Apr The windlass mechanism of the foot; What is it and why is it important?
What are we talking about when we are discussing the windlass mechanism with regards to the foot? The windlass mechanism is an integral part of normal foot mechanics and gets the name from the similarity to that of the windlass in sailing where it describes the pulley system used to raise and lower sails. In the foot the action is created by the plantar fascia, the band of strong, thick connective tissue that spans the base of the foot from the calcaneus to the toes, as it stretches around the metatarsal heads when the foot comes into dorsi flexion during the propulsive phase of the gait cycle.
The plantar fascia ties the bones together preventing the arches of the foot from collapsing under our own weight. During the gait cycle the windlass effect creates even more tension in the plantar fascia as it is wound around the metatarsal heads. This increase in tension actually increases the tensile strength of the fascia and aids in stiffening the foot during the late stance phase of the gait cycle by creating a dynamic but stable arch. As a result of this we get a more rigid and level foot for push off, when we need it, which is more suited to transferring the power generated into forward movement but allows the foot to remain mobile enough to move through the actions required of it during the rest of the gait cycle. If the mechanism doesn’t occur or is in some way functioning poorly then the medial arch of the foot would collapse resulting in poorer force transmission.
The mechanism, through tensioning the plantar fascia, brings an end to pronation in the foot and re-supinates it. On the Research Junkie Craig Payne lists Kevin Kirby, of California School of Podiatric Medicine at Samuel Merritt College, suggested fuctions of the plantar fascia and the windlass mechanism as;
1. Serves to support the medial and lateral longitudinal arch in a higher arched position (i.e. increases the dorsiflexion stiffness of the medial and lateral forefoot)
2. Assists in resupination of subtalar joint (STJ) during propulsive phase of walking
3. Assists the deep posterior compartment muscles by limiting STJ pronation
4. Assists the plantar intrinsic muscles in preventing longitudinal arch flattening
5. Reduces tensile forces in plantar ligaments
6. Prevents excessive interosseous compression forces on dorsal aspects of midfoot joints
7. Prevents excessive dorsiflexion bending moments on metatarsals
8. Passively maintains digital purchase and stabilizes proximal phalanx of digits within sagittal plane
9. Reduces ground reaction force on metatarsal heads during late midstance and propulsion
10. Helps to absorb and release elastic strain energy during running and jumping activities
If we look at the proposed functions of the windlass mechanism we can see how important it is to good mechanics in the foot. From assisting the muscles of the lower leg to absorbing/releasing energy during running and jumping if the mechanism isn’t working well then the slack needs to be taken up else where. This might mean an increased load on the lower leg musculature as it is required to do more work whilst running and jumping or a greater load on the intrinsic muscles of the plantar foot to maintain the longitudinal arch. The lack of force to resupinate the foot may lead to increased rotational stress on the tibia as the body looks to adjust and balance the movements involved in gait possibly leading to knee and hip issues if not addressed. We would also see a poorer transfer of power into forward movement as the foot would be significantly less stiff. The overall effect of a dysfunctional windlass mechanism is to, unscientifically, mess up your gait.
When it comes to correcting the any faults in the windlass mechanism it is really beyond the scope of this very short piece. The process starts with making sure that the musculature of the hip, thigh and lower leg /foot are working well to allow good movement through the gait cycle. Once this has been achieved a clearer picture of what is happening can be seen.