A calcaneal spur (or heel spur) is a bony outgrowth from the calcaneal tuberosity (heel bone). Calcaneal spurs are typically detected by a radiographic examination (commonly referred to as an "x-ray"). 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.