A calcaneal spur is a bony outgrowth of the calcaneal tuberosity (heel bone).  Calcaneal spurs are usually detected by X-ray examination.  It is a form of exostosis. When a foot is exposed to constant pressure, calcium deposits build up in the heel bone. In general, this has no effect on a person's daily life. However, repeated damage can lead to accumulation of these deposits on top of each other, causing a spur-like deformation, called heel spur.  A lower heel spur is located on the underside of the calcaneus and is usually a response to plantar fasciitis over a period of time, but may also be associated with ankylosing spondylitis (usually in children). Achilles tendon is inserted when the heel behind the posterior calcaneal spur develops.  A lower calcaneal spur of the calcaneus, which is superior to the plantar fascia when inserted. A posterior heel spur is often large and palpable through the skin and may be removed as part of the treatment for insertional Achilles tendinitis