Ankylosing spondylitis. Coloured X-ray of the spine of a patient with ankylosing spondylitis, a form of arthritis. This is the lumbar region in the lower back. The condition, which causes inflammation of the joints, has led to severe deformity of the spine; the patient has a fixed kyphosis, an outward curvature of the spine. Ankylosing spondylitis commonly affects the joints between the spinal bones (vertebrae, mainly brown) and the sacroiliac joints (not seen), which link the spine to the pelvis. The joints become painful and stiff. In severe cases, the vertebrae may fuse together completely. The condition is treated with painkillers and regular exercise.