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Engineering of the foot: The windlass mechanism

Leonardo da Vinci famously said ‘The foot is a masterpiece of engineering and a work of art’. This article investigates a specific mechanism in the foot called ‘The Windlass mechanism’, one of the most important foot functions for efficient walking and running.

What is a ‘Windlass’?

A windlass is the tightening of a rope or cable around a pivot point. It is typically used to haul or lift something. In the foot, the plantar fascia acts as the cable and the metatarsal heads are the pivot point.

Why do we need a windlass mechanism?

The windlass mechanism is important during our gait cycle, when we need the foot to be in a strong, stable position to absorb shock on heel strike, and to become a lever to propel us forward when we walk.

How does it work?

The plantar fascia is a tight band of connective tissue that attaches to the heel bone (calcaneus) at one end and the base of the toes (metatarsal heads) at the other.

With an effective windlass mechanism, the plantar fascia tightens when the toes extend towards the shin (dorsiflex) due to the fascia band wrapping around the metatarsal joints. This pulls the toes and heel closer together and raises the arch of the foot, compacting the small bones in the foot together to form a strong rigid lever.

We call this raising of the arch a ‘supinated’ foot position. When the windlass relaxes and the toes plantarflex back down, the arch flattens into a ‘pronated’ foot position which is more mobile. During a walking or running stride, the foot utilises both properties at different times.

During a gait cycle, the foot moves from a supinated position on heel strike, to a pronated position as the foot contacts the ground (1st rocker).

As the foot accepts bodyweight, it becomes more mobile, adapting to terrain. Pronation stretches the plantar fascia, storing energy whilst the ankle rocks the tibia forward (2nd rocker).

When bodyweight is over the centre of the foot in mid to late stance, the heel starts to lift and the toe joints dorsiflex, activating the windlass to re-supinate the foot (3rd rocker). The supinated foot forms a rigid lever for push off. Stored energy in the fascia is released and the elastic properties in the foot’s arch helps to spring us forward.

Windlass dysfunctions

1. No windlass

Two things can prevent the windlass from working. The 1st is when there is lack of movement in the big toe joint or the big toe is rigid. If the big toe is not able to dorsiflex, the windlass mechanism can’t work.

The 2nd is if the plantar fascia is ruptured. No plantar fascia means no windlass mechanism.

If there is no functioning windlass mechanism, the foot is unsupported during the propulsive phase of the gait cycle when loads on the foot are high.

2. High forces to get the windlass established

One of the tests we do to check the windlass mechanism is called the ‘Jack’s test’. This is when we try to lift the big toe up when someone is standing, to see the arch lift. The amount of force needed to establish the windlass varies widely between individuals. In some people it is easy to lift the big toe and raise the arch. In others you can hardly lift it at all.

If it takes a lot of force to establish the windlass, loads may be greater through the plantar fascia and if the big toe joint is hard to move, it will be hard to lift the heel when walking. This increases loads in tissues and alters gait patterns to compensate.

3. Delayed onset

It is assumed that as soon as the heel lifts and load is applied during propulsion, the windlass should start straight away. Therefore, if the windlass is delayed, it could reduce the foot’s ability to resist the loads that are starting to be applied.

When we perform the jack’s test on a group of individuals, some people have up to 15 degrees of dorsiflexion before the arch starts to raise. The heel would therefore need to come off the ground to the same degree before the foot becomes stable due to the windlass mechanism.

Conditions related to a dysfunctional windlass

Plantar fasciitis: Prolonged foot pronation and delayed supination is thought to be a contributing factor in some cases of plantar fasciitis (heel pain).

Hallux limitus/rigidus (big toe pain): A type of arthritis that reduces mobility of the big toe joint and therefore prevents the windlass functioning efficiently.

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