Calcaneal spur: A bony spur, also known as a heel spur, that projects from the back or underside of the heel bone (the calcaneus) and that may make walking painful. Calcaneal spurs are associated with inflammation of the Achilles tendon (Achilles tendinitis), and cause tenderness and pain at the back of the heel, which is made worse by pushing off the ball of the foot. Spurs under the sole (the plantar area) are associated with inflammation of the plantar fascia, which is the bowstring-like tissue that stretches from the heel underneath the sole. These spurs can cause localized tenderness and pain that is made worse by stepping down on the heel. Calcaneal spurs and plantar fasciitis can occur alone, or they can be related to underlying diseases that cause arthritis, such as reactive arthritis and ankylosing spondylitis. Treatment is designed to decrease the inflammation and avoid reinjury. Heel lifts reduce stress on the Achilles tendon and relieve painful spurs at the back of the heel. Donut-shaped shoe inserts take pressure off plantar spurs. Infrequently, surgery is done on chronically inflamed spurs.