In this second installment of the Foot Anatomy 101 series I’d like to discuss what’s known as the windlass mechanism. As discussed in the previous post, the foot arches are the centerpiece of foot function, and the medial longitudinal arch in particular is central to windlass mechanics.
The ‘truss’ of the medial longitudinal arch is formed by the calcaneous (heel bone), the midtarsal joint and the head of the first metatarsal. The plantar aponeurosis forms the ‘tie-rod’ that spans from heel to toes. The attachment of this aponeurosis to the toes beyond the metatarsophalageal (MTP) joints forms the basis of the windlass mechanism.
A windlass is a mechanical device for lifing heavy weights. It usually consists of a spool around which a rope is cranked, the weight being lifted by the rope. A common example is the crank, rope and bucket used to raise water from a well.
In the foot, a windlass is created by the plantar aponeurosis passing beneath the MTP joints, in particular the first MTP joint. When the big toe is dorsiflexed during walking, the aponeurosis winds around the first MTP joint and pulls the heel and toes slightly closer together, raising the medial longitudinal arch and also locking the bones of the foot. It’s an ingenious way of stiffening the foot and converting the supple ‘landing’ foot into a rigid ‘propulsion’ foot.
Unfortunately for shoe-wearing people, none of the above windlass foot mechanics happens in shoes, and this is one reason why shoes are so damaging to feet. Whether you’re wearing a wedge or a sneaker, the foot is immobilized inside the shoe. The toes are kept in a dorsiflexed position by the toe spring (or by virtue of the heel height in a wedge or pumps); the MTP joint does not move at all and windlass mechanics is eliminated. In addition, the constant strain on the plantar aponeurosis likely causes it to weaken (along with associated foot muscles) and this may be a leading cause of shoe-induced flat foot and fallen arches, which is epidemic in shoe-wearing societies.
For proper foot biomechanics… walk barefoot!