Heel spurs, also referred to as calcaneal spurs, are bony protrusions that grow on the bottom of the heel. Heel spurs develop as a bone’s response to stress from straining foot muscles and ligaments, over-stretching the plantar fascia, or repeated tearing of the thin lining of the heel bone. People who have these spurs are sometimes diagnosed with heel spur syndrome. The vast majority of heel spurs do not cause pain.