The plantar fascia is a band of tissue, similar to a tendon, which runs from the front of the heel bone (calcaneus) to the ball of the foot. This dense strip of tissue helps to support the arch of the foot.
When the foot is on the ground the full weight of the body is concentrated on the plantar fascia. This force stretches the tissue as the arch of the foot tries to flatten from the weight of the body. This leads to stress on the plantar fascia where it attaches to the heel bone. Small tears of the fascia can happen. However, the body normally repairs these tears.
As this process of injury and repair repeats itself over and over again, a bone spur (a pointed outgrowth of the bone) sometimes forms as the body’s response to try to firmly attach the fascia to the heel bone.