Ankylosing spondylitis is primarily a primary, chronic, vascular cataract destructive inflammatory disease with ossification of the ligaments. It extends up the spine from the sacroiliac joint, affecting the synovial membrane and joint capsule of the small intervertebral joints, and in advanced stages the entire spine is calcified and ossified by soft tissues such as the peripheral ligaments. The disease occurs in men aged 16 to 30 years and develops intermittently. The disease begins with sacroiliac joint pain and lower back pain, radiating to the buttocks and thighs. The pain increases with activity and is relieved with rest. The spine is stiff in the morning. HLA-B27 is mostly positive. Radiographic manifestations: initial pseudo-widening of the sacroiliac joint space, with jagged joint edges and sclerotic dense changes. In the late stage, the gap becomes narrower and the joint is bony fused. There are bridge-like bones at the edge of the intervertebral space, and the ligaments around the intervertebral joints are ossified, resulting in a bamboo-like spine. Treatment principle: to relieve pain, prevent deformity and improve function. Lumbar osteotomy may be considered for severe hunchback. Total hip replacement can be performed for hip ankylosis and persistent pain.