Calcaneal spur and foot pain. Illustration showing causes of pain in the foot. At top left are the calf muscles which attach to the calcaneus (heel- bone) via the Achilles tendon (white). Where this tendon attaches to the calcaneus, the bone has become inflamed (red). This may be caused by faulty running technique or incorrect footwear. At the base of the heel-bone is a bony projection, a calcaneal spur, which may develop as a result of chronic inflammation. The blue areas are bursas, fluid-filled pads which cushion pressure points, for example, where a tendon crosses a bone. Pressure, friction or injury may cause bursitis, pain and swelling in and around a bursa.