Causes of Plantar Fasciitis

The Gait Cycle and Plantar Fascia

Understanding the mechanics of the foot can help explain the development of plantar fasciitis.  Connecting the hind foot and the fore foot, the plantar fascia undergoes tension during gait (walking). The action of the plantar fascia during weight bearing is compared to a windlass or a rubber band. When there is no weight on the foot and plantar fascia, the elastic band is relaxed.  As weight is put on the foot and the plantar fascia, the elastic band stretches out.  A band that is too short results in a high arch, whereas a band that is too long results in a low arch, which is commonly termed as flatfeet.

The gait cycle refers to the continuous repetitive pattern of walking. One complete gait cycle consists of 2 main phases: the stance and the swing. The stance phase is the part of the cycle where the foot is in contact with the ground. The swing phase is the period when the foot is off the ground. The stance phase is further discussed, as it has a more significant effect on a plantar fascia injury.

The stance phase has 3 sub-phases:

Contact phase – The phase is initiated when the heel strikes the ground and ends when the entire foot comes in contact with the ground. The foot has to be flexible and mobile during this phase to adapt to any uneven terrain.

Mid-stance – In this phase, the weight is shifted from the back of the foot to the fore foot. The stance phase is the period when the stance limb bears the body’s entire weight; therefore, it is during this period when the foot is most susceptible to injuries. The arch of the foot flattens to absorb the stress of ground contact and the plantar fascia is stretched.

Propulsion – This phase begins as soon the heel is lifted. The toes are pushed off to propel the body forwards. It is during this phase that the windlass effect occurs. The plantar fascia is tightened over the plantar surface at the base of the toes, raising the arch. This allows the stance foot to become an efficient lever. Exaggerated or prolonged propulsion phase can increase the risk for plantar fascia injury.

What Causes Plantar Fasciitis?

The cause of plantar fasciitis may be for many reasons. The term fasciitis is believed to be inaccurate because the damage incurred by the plantar fascia is mainly brought about by degenerative changes owing to overuse or reinjury, which may occur with our without inflammation. Microtrauma and degeneration are commonly caused by prolonged or repeated overstretching of plantar fascia due to walking, jumping, landing and running.  Weakened foot and lower leg muscles, a tightened Achilles tendon or any activity in which the weight is taken on the ball of the foot can put a lot pressure on the fascia, resulting in plantar fasciitis. Like tendons, the planter fascia is poorly supplied with blood; therefore, once it is damaged, the healing process may be markedly slow.

Decreased healing response, in addition to decreased elasticity that comes with aging and repetitive tearing, puts the middle-aged population especially at risk of plantar fasciitis.  As you get older, the plantar fascia usually loses its ability to stretch. The fat pad on the heel also thins and weakens, decreasing its capability to absorb the shock or pressure of walking. Excessive pressure applied on the heel damages the plantar fascia, making it vulnerable to swelling, tearing and bruising.

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Rick Kaselj, MS