Ankylosing spondylitis. Coloured X-ray (side view) of the lumbar (lower) spine of a sixty-two year old man with ankylosing spondylitis. Extra bone (bright white mass, lower left) has been laid down between the vertebrae (horizontal bands on right). This disease is a form of inflammatory arthritis that mainly affects the spine and is most common in men. The joints between the vertebrae become inflamed and then during the healing process extra bone forms between the vertebrae, eventually fusing them. This causes chronic back pain and immobility. Treatment is with anti-inflammatory drugs, physical therapy, and in extreme cases, surgery.