This is an expanded explanation of how I am coming to view possible mechanical causes of plantar fasciitis.
Obviously any mechanical problem will be exacerbated by overweight, poor footwear, and heavy load bearing exercise on hard surfaces – particularly if a person is not accustomed to it.
The simplest ‘explanation’ for the cause of plantar fasciitis is over pronation – but why does the foot overpronate? Though the reasons are not limited to the foot, this post covers foot problems that can cause overpronation and stress the plantar fascia.
The midtarsal joint is meant to lock and stiffen the foot when rolling over onto the ball of the foot during the gait cycle. If it doesn’t, the foot ‘flattens’ and twists and causes a lot of strain on the plantar fascia insertion into the calcaneus. Passive and active examination of the midtarsal joint is important – if it doesn’t lock up passively or actively, a structural problem in the midfoot could be to blame and an orthotic may be required. If it locks up passively but not actively, a more movement based problem may be contributing to failure of the joint to lock when it needs to.
Why might it not lock?
Foot Based Reasons
A very mobile subtalar joint could prevent the midtarsal joint from locking because the foot would be everting through a greater part of the gait cycle. So the foot would evert and rotate outward, causing ground reaction forces to be placed through the foot a bit more medially. As the foot everts and avoids the protective and supportive and propulsive effects of appropriate midtarsal joint locking, the plantar fascia has to take up the strain.
Lack of talocrural dorsiflexion could also cause excess eversion during gait, as the foot has to ‘get out of the way’ of the floor and roll early through the ball of the foot in order to create a propulsive force
A rigid great toe can also be problematic. If the foot cannot ‘toe off’ and leave the floor in time because the great toe cannot extend, the subtalar joint will evert in order to allow the foot to clear the floor.
Non Foot Based Reasons
It may well be that the hips could be the source of a midtarsal locking mechanism problem. Lack of hip extension or internal rotation could contribute to movement based foot problems. If the left foot plantar fascia strain is a problem, it could be that the left hip doesn’t want to extend and/or internally rotate. Loss of extension would mimic a lack of dorsiflexion in the foot and the foot would have to evert in order to clear in time. Loss of internal rotation (or walking with relative external rotation when the foot is weight bearing) would cause increased subtalar eversion. All of these things could alter the force distribution through the foot.
Even thoracic spine and upper girdle pain could cause excessive pronation in gait. Normal walking gait ideally requires the thoracic spine to rotate and for the arms to swing from the shoulders. If you don’t rotate (for whatever reason) to the right, you won’t get complete internal rotation in the left hip. Try it and see what your left foot does!