Plantar fasciitis: Inflammation of the plantar fascia, the bowstring-like tissue that stretches from the heel bone to the base of the toes. Plantar fasciitis can be due to calcaneal spurs, which typically cause localized tenderness and pain that is made worse by stepping down on the heel. Plantar fasciitis may be related to physical activity overload, abnormal foot mechanics, or may be due to underlying diseases that cause arthritis, such as Reiter disease, ankylosing spondylitis, and diffuse idiopathic skeletal hyperostosis. Treatment is designed to decrease inflammation and avoid reinjury. Icing reduces pain and inflammation. Anti-inflammatory agents, such as ibuprofen and injections of cortisone, can help. Infrequently, surgery is done on chronically inflamed spurs. A donut-shaped shoe insert can take pressure off a calcaneal spur and lessen plantar fasciitis.