A calcaneal spur is a bony outgrowth from the calcaneal tuberosity (heel bone). Calcaneal spurs are typically detected by x-ray examination. It is a form of exostosis. When a foot is exposed to constant stress, calcium deposits build up on the bottom of the heel bone. Generally, this has no effect on a person's daily life. However, repeated damage can cause these deposits to pile up on each other, causing a spur-shaped deformity, called a calcaneal (or heel) spur.
An inferior calcaneal spur is located on the inferior aspect of the calcaneus and is typically a response to plantar fasciitis over a period, but may also be associated with ankylosing spondylitis (typically in children). A posterior calcaneal spur develops on the back of the heel at the insertion of the Achilles tendon.
An inferior calcaneal spur consists of a calcification of the calcaneus, which lies superior to the plantar fascia at the insertion of the plantar fascia. A posterior calcaneal spur is often large and palpable through the skin and may need to be removed as part of the treatment of insertional Achilles tendonitis.