The difference between sacroiliac arthritis and ankylosing spondylitis is mainly manifested in the etiology, clinical manifestations, laboratory tests, X-ray manifestations and so on. For example, ankylosing spondylitis can be manifested as spinal stiffness, while sacroiliac arthritis is often not. 1. Etiology: sacroiliac arthritis is mainly caused by long-term chronic strain, local ischemia and other factors; ankylosing spondylitis is related to genetic factors. 2. Clinical manifestations: sacroiliac arthritis occurs in adult women, which can be manifested as limited activity of sacroiliac joints, pain and numbness of waist and legs when resting; ankylosing spondylitis occurs in young and middle-aged men, in addition to the above manifestations, it can also have other parts of the symptom such as spinal rigidity, knee osteoarthritis, ankle osteoarthritis, and neck and thoracic pain. 3. Laboratory examination: sacroiliitis usually has no obvious abnormality, while ankylosing spondylitis may have abnormal test results such as increased blood sedimentation, elevated C-reactive protein, anemia, and HLA-B27 positivity. 4. X-ray manifestations: sacroiliac arthritis can be manifested as osteoporosis of sacroiliac joints, narrowing of joint cavities, worm-eaten changes of articular surfaces, joint ankylosis, etc. Ankylosing spondylitis, in addition to the above mentioned manifestations, can also appear as a “bamboo-like spine”. There are many other differences between sacroiliitis and ankylosing spondylitis. If any of the above abnormalities occur, it is recommended to go to the hospital in time for consultation, to clarify the cause of the disease with the help of doctors, and to carry out regular treatment as soon as possible.