I know I love the foot, but I’ve resisted writing about it for a while and the urge to write about it again has now overcome me!! I thought I’d write about the windlass mechanism, as to date I don’t believe I’ve really talked about it? I’ve talked about how the mid tarsal joint locks and unlocks, however I didn’t really talk about this. Please excuse the child like drawings I did on my iPad…the quality of art is poor, but they are easy to understand…and that’s the main thing!!
The Theory of the Windlass Mechanism
The theory behind the Windlass Mechanism has been around for about 50-60 years and is a very mechanical thought process. It’s pretty cool and fits into my thought process of the foot loading and exploding really well. In almost everything I do and write about I think of the loading and exploding of gait. The foot will try and complete many tasks during gait, but there are two key ingredients to successful foot function. Firstly, the foot needs to be relatively flexible during the loading phase, in order to effectively absorb the landing forces and adapt to the surface. And secondly, become relatively rigid during the propulsive, exploding phase of gait. This is in order that there is effective transfer of force into the desired direction of travel and that the forces involved are transferred through the appropriate tissues/structures to protect the more sensitive ones.
This mechanism allows for both of these to be achieved and uses a lever (the big toe), a pivot (first metatarsal head) and a tensile structure (the plantar fascia) to allow for the flexible loading and the rigid exploding. The foot can be described in terms of it’s arches (I think there are 3?), with the windlass mechanism taking advantage of the medial longitudinal arch.
While the foot is loading and adapting to the ground surface the big toe is in a relatively neutral position, leaving less tension in the plantar tissues and allowing them to load. The joints of the foot go through pronation, the soft tissues load and are now ready to go through supination.
On the right hear you can see a simplified version of the mechanism and on the left you can see the mechanism in the foot itself. Obviously, in function it is the foot going over the toe rather than the toe extending over the foot that creates the mechanism, this can be seen in the picture below. Here you can see the foot coming over the toes, tensioning the plantar fascia and drawing the calcaneus towards the metatarsal heads.
There are many mechanisms that contribute to the supination of the foot. however, the windlass mechanism plays a key role. You can see in the picture how the extension of the big toe tensions the plantar fascia and draws the calcaneus towards the metatarsal head, raising the arch and assisting in re-supinating the foot. This supination decreases/locks the motion in the mid tarsal joint stabilising the foot for the explode. If this does not occur it is possible that the patient is more vulnerable to injury, for example, Plantar Fasciitis.
Assessing the Windlass Mechanism
I personally only know one way of assessing the windlass mechanism. It’s pretty simple. You ask the patient to stand in front of you and relax. You manually extend their big toe and observe the medial arch of the foot to see if the arch raises with the big toe extension. If it does then I am satisfied it can work (at least statically) and if it doesn’t I may need to investigate further. For example, you may try to position their foot (in sub talar neutral for example) and re-test to see if it capable of working. If it is capable of working you may try treating to to achieve the appropriate foot position in function so it can work. Or if that is not possible, you may try an orthotic to help position the foot for better function.
So it is a fairly simple mechanism, but vitally important to function. Even this simple assessment can give you a massive amount of information and lead you down a very effective treatment pathway. The other advantage is that it takes 2 seconds to assess and gives you some great info…so you can check loads of patients to get a feel for it while you gain experience and not waste any treatment time….well that’s how I did it!!
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