A strong ligament called the plantar fascia runs along the sole between the heel and the bone of the foot. This ligament works like a bow string, flexibly stretching under pressure, thus reducing and supporting the body weight. The plantar fascia forms an articulated structure together with the Achilles tendon, pivoting on the heel bone. For this reason, the stretching of both the plantar fascia and the Achilles tendon has an effect on the heel bone.
With flat feet, the constant pulling of the plantar fascia affects the heel bone from the direction of the sole. This results in periostitis (inflammation of the membrane lining the surface of the bone) where the ligament joins the bone, which gradually induces a protrusion on the heel bone called a heel spur to form. The stretching of the ligament on the sole and its painful inflammation is called plantar fasciitis. It is important to understand that the heel spur is a secondary effect caused by the overstretching.
For heel spurs orthotic insoles with a hole which relieve the area of the periosteum under pressure are prescribed. If periostitis is present, a compress, rest and medication to reduce inflammation are suggested. Surgery is only rarely used.