Plantar fasciitis is the most common cause of heel pain. It is commonly referred to as a heel spur, although a heel spur, or bony growth on the heel bone, develops as a result of plantar fasciitis. The condition occurs when the long, flat ligament on the bottom of the foot (plantar fascia) stretches irregularly and develops small tears that cause the ligament to become inflamed. This inflammation is most often caused by walking with an abnormal inward twisting of the foot, called pronation. Over time, this slightly abnormal step may increase tension on the plantar fascia and cause it to become inflamed.