Hip lesions are often insidious, with atypical early symptoms, which can be unilateral or bilateral hip intermittent pain and do not attract attention, but tendonitis and synovitis are constantly developing. When there is significant hip pain or even limited movement, the hip cartilage has been destroyed and the joint space has been narrowed. The pathological changes in ankylosing spondylitis include tendonitis (tendonitis) and synovitis. In the medial joints of ankylosing spondylitis, the pathologic changes that lead to joint damage and ankylosis are primarily tendonitis. Although ankylosing spondylitis also often involves peripheral synovial joints (e.g., knees, ankles, etc.), rheumatoid arthritis-like bone erosion is rarely seen, a phenomenon for which there is no definitive scientific explanation. It is believed that osteoclasts play an important role in the pathological changes of rheumatoid arthritis, as osteolysis is greater than osteogenesis, so there is significant bone resorption; in ankylosing spondylitis, osteogenesis is greater than osteolysis, so it is more likely to form bone fragments. Hip lesions are not yet identical to true peripheral joints. Some scholars believe that the hip joint is neither a medial joint nor a peripheral joint, but is referred to as a root joint. Root joints also include the sternoclavicular joint, shoulder lock, and shoulder. In fact, the hip joint is both a synovial joint and has tendon bone attachment points (garden ligament, etc.). Therefore, hip joint damage in ankylosing spondylitis may contain 2 types of pathological changes, namely synovitis and tendonitis.