Ankylosing crepitus (AS) is a common rheumatic disease whose cause is not well understood, with genetic and environmental factors playing an important role in the pathogenesis of the disease. The development of AS has been shown to be closely related to HLA-B27, with a significant tendency for family aggregation. The prevalence is between 10 and 40 years old, with a mean age of onset of 25 years. It is more common in males than females, with a male to female incidence ratio of (2-3):1. The incidence is higher in those with a positive family history of AS. AS mainly affects the sacroiliac joints, crest, paracristal soft tissues and peripheral joints, and may be accompanied by extra-articular lesions. The disease starts insidiously, and patients gradually develop hip and hip or low back pain and/or stiffness, especially when lying down (at night) or sitting for a long time, with difficulty in turning over, and stiffness in the low back in the morning or when rising from a sedentary position, but decreases after activity. Some patients feel severe pain in the hip and hip area, which occasionally radiates to the periphery. In the early stage of the disease, the pain is mostly intermittent on one side, and after a few months, the pain is mostly persistent bilaterally. As the disease progresses from the sacroiliac joint to the lumbar spine, thoracic and cervical spine, pain and limited movement will occur in the corresponding areas, and in severe cases, crestal deformity and joint ankylosis may occur. Some patients start with peripheral arthritis. In a few severe cases, there is fever, fatigue, wasting, anemia or other organ involvement. Plantar fasciitis, Achilles tendinitis, and other sites of tendon terminal disease are common in this disease. Uveitis occurs in approximately 25% of patients during the course of the disease, alternating unilaterally or bilaterally, and usually resolves spontaneously; recurrent episodes may result in visual impairment. Very few patients develop fibrosis of the upper lobe of the lung. It is sometimes accompanied by cavity formation and is considered tuberculosis, and can also be exacerbated by concurrent mycobacterial infections. Inadequate aortic valve closure and conduction disturbances due to focal mesangial necrosis of the aortic root that can cause annular dilatation of the aorta and shortening and thickening of the aortic valve cusps are seen in 3.5% to 10% of patients. Ankylosing crepitus can also be complicated by IgA nephropathy and amyloidosis. Early diagnosis is the key to treating AS. Routine ancillary tests include: 1. Blood tests: elevated platelets, anemia, increased sedimentation and elevated C-reactive protein are often seen during the active phase of AS; rheumatoid factor is generally negative, and immunoglobulins may be mildly elevated; about 90% of AS patients are positive for HLA-B27, and about 10% of AS patients are negative for HLA-B27. However, a small percentage of the normal population is also positive for HLA-B27 (6%-8%), and about 80% of these HLA-B27-positive patients do not develop AS. 2. X-ray: subchondral bone margins of the sacroiliac joints are blurred, the joint space is blurred, and there is increased bone density and joint fusion. Usually, the degree of lesion of sacroiliac arthritis on X-ray is divided into 5 grades: grade 0 is normal; grade I is suspicious; grade II has mild sacroiliac arthritis; grade III has moderate sacroiliac arthritis; grade IV has joint fusion ankylosis. Radiographic manifestations of the crest include vertebral osteophytes and square changes, small vertebral joints that are modulated, calcification of the paravertebral ligaments, and bone bridge formation. Late extensive and severe ossification of the bone bridge performance is called “bamboo-like” changes. 3.Sacroiliac joint CT: increased density of sacroiliac joint, blurred joint space, obvious destruction and joint fusion. 4.Sacroiliac joint MRI: subchondral fat accumulation; bone marrow edema; cartilage irregular thickening and distortion, cartilage surface irregularity and fragmentation; bone erosion.