The Structure and Function of the Plantar Fascia
The plantar fascia is a tight band of connective tissue, and is the largest ligament of the foot, covering the majority of the bottom of the foot. It starts at the heel bone (calcaneus) at the medial calcaneal tubercle. And the main central band extends all the way to the toes, inserting into the base of the proximal phalanges.
Also known as the plantar aponeurosis, on average, the plantar fascia is:
12cm long
2cm wide at the heel and 6cm wide at the toes
4mm thick
The Plantar Fascia is Rather Unique in it's Structure and Function
The plantar fascia is highly innervated and these nerves help it provide stability and control of foot movements. Structurally:
It’s a bit like ligament, but it stretches and recoils more than a ligament.
It’s a bit like a tendon, but it doesn’t connect muscle to bone.
It’s often referred to as an aponeurosis, but its fibres are aligned in different directions.
And yet it is referred to as fascia.
Health professionals think of the plantar fascia as being most like a tendon in terms of its cellular make up. This is particularly helpful when it comes to treating a common problem known as “plantar fasciitis”, as it often responds to similar types of therapeutic movements to increase load tolerance and overcome pain.
Function of the Plantar Fascia
The plantar fascia is in contact with the first layer of small foot muscles and they actually have direct attachments to the plantarfascia. The most well-known function of the plantar fascia is to help hold up the arch of the foot (the medial longitudinal arch). In reality, it contributes to overall foot stability and function in many ways, along with nearby muscles and ligaments. Its functions include:
Resisting longitudinal arch flattening
Preventing bony compression at the instep (top of the foot)
Helping the foot become a rigid lever for effective propulsion (push off)
Helping to keep the toes straight
Helping absorb and release elastic strain energy during walking and running
“The longitudinal arch of the human foot is a complex mechanical structure that must be compliant on uneven surfaces and also have sufficient stiffness to allow the foot to be an efficient propulsive organ during walking and running gait.” Dr Kevin Kirby
The Windlass Mechanism of the Plantar Fascia
When the toes bend up, like during propulsion, tension increases in the plantarfascia. This effective raises the arch of the foot, converting the foot into a rigid structure for effective push-off. This raising of the arch as the toes bend up is called the windlass mechanism.
The windlass mechanism: As the toes bend up, it increases tension in the plantarfascia, helping to raise the arch.
It’s important to remember that tension in plantar fascia is normal and it happens with every step we take. The plantar fascia is designed to handle a lot of it to allow us to walk and run for prolonged periods.
The Plantar Fascia and the Achilles Tendon
The Achilles tendon is the tendon of the calf muscles at the back of your leg. The Achilles inserts into the back of the heel bone (calcaneus). However, we know that in some people, fibres of the Achilles tendon sheath (paratenon) continue right under the heel and help form the plantar fascia. Regardless of the presence of a physical connection between the two, the Achilles tendon and plantar fascia function very closely together and tight calf muscles/Achilles are often associated with plantar fascia pain due to the way force is transferred to the plantar fascia. Indeed, research shows that thickening in one is very often seen in the other.
Some fibres from the Achilles tendon travel right around to the bottom of the heel to help form the plantar fascia.
This symbiotic relationship between the Achilles and the plantar fascia is an important consideration for your podiatrist in choosing the best treatment for your heel or arch pain. But it’s not the only consideration for someone presenting with heel or arch pain. Anatomically, the following also requires consideration:
intrinsic foot muscles
leg muscles (whose tendons insert into the foot)
integrity of the heel fat pad
nerves, both nearby and in your lower back
And then there’s other factors to consider, like your activity, footwear, the surfaces you’re standing on, your injury history, recent health, general health, medications and many other factors.
Rebecca Understands the Structure and Function of the Plantar Fascia
Rebecca has a thorough understanding of the anatomy around the heel and function of the plantarfascia. Importantly, she is well-versed in all of the many differential diagnoses of heel pain, including but not limited to plantar fasciitis.
If you’re experiencing heel or arch pain, please feel free to make an appointment to see Rebecca. Be sure to bring in the shoes you wear most often - no matter what condition they’re in (Rebecca won’t mind of they’re old, worn or stinky!).
What’s next?
In the next article, we’re going to look closer at how things can go wrong with the plantar fascia.