If you are a runner or stand up for many hours a day, you might have had plantar fasciitis and you would like to know what this injury is about. Well, the first question you should ask yourself is “What is the plantar fascia?” Remember, first things first, know your body and then try to understand what’s wrong with it.
And here is the answer to the question:
The plantar fascia is a thick and broad triangular connective tissue ( biological tissue that supports, connects, or separates different tissues and organs of your body) situated beneath the skin on the sole of the foot. It runs from the medial calcaneal tubercle (heel bone), blending with fibres of the Achilles tendon, towards the front of the foot, at the mid-metatarsal level (midfoot). It divides into five sections, each extending into a toe inserting into its metatarsophalangeal joint (MTPJ) , connecting to the sesamoids (two small bones under the MTPJ) and bases of proximal phalanges of all digits ( see picture below to understand this more clearly).
It consists of three sections: the medial, the central and the lateral section. The central section is the most important structurally and functionally. The medial section overlies the muscles to the big toe and the lateral section overlies muscles to the little toe.
An interesting fact is that it is thought in youngsters the plantar fascia is intimately related to the Achilles tendon, with a fascial connection between the two. Nevertheless, the continuity of this connection decreases when you age to the extent that in the elderly there are few connecting fibres.
What is its function?
The plantar fascia has multiple functions that are important in allowing normal biomechanics of the foot and lower extremity. The primary function of the plantar fascia is to support the arch of the foot and facilitate the foot’s movement.
It is seen as part of a truss which is a triangular structure (the most stable structure in geometry). When standing your body weight acts on the truss by pressing downwards. This causes a ground reaction force. The bones in the foot are compressed by these two forces: body weight and ground reaction force, and the plantar fascia acts as a tight-rope between the forefoot and the calcaneus (heel bone) preventing the arch from collapsing. In brief, the plantar fascia helps to support your weight, and it is thought that it carries as much as 14% of the total load of the foot. In other words, the plantar fascia provides shock absorption when the foot hits the ground.
During gait, the plantar fascia becomes part of the foot’s windlass mechanism. Windlass is an apparatus for moving heavy objects that consists of a horizontal axle around which a rope is wound. An example is the mechanism used in wells to raise and lower the bucket. In the foot the rope is the plantar fascia, the handle the big toe and the axle the metatarsal heads. When the toes are dorsiflexed ( bent upwards) in the propulsive phase of gait (when your foot propels you forwards) , the plantar fascia is pulled tight, resulting in elevation of the longitudinal arch and shortening of the foot. All this will help to stabilise the foot. Also, this mechanism assists the gastroc-soleus (calf) in producing subtalar joint supination (sole turns inwards) during propulsion and decelerating subtalar joint pronation (sole turns outwards) in early stance phase (when your foot hits the ground). See this video to understand what supination and pronation are.
You might find this blog post a bit hard to understand. I would be happy if you are clear that the plantar fascia functions both to absorb and release elastic strain energy during running and jumping activities.
The most common injuries related to the plantar fascia are plantar fasciitis and calcaneal spur.
Remember that I am happy to help you if you have any questions. Contact me on The Physical Therapy, Physiotherapy Clinic based in Southampton.