Ankylosing spondylitis is characterized by pain in the sacroiliac joint that cannot be relieved by rest and can only be relieved by activity, which is a point of difference from lumbar disc herniation, lumbar spinal stenosis, and lumbar trauma. In mild cases of ankylosing spondylitis, only the sacroiliac joint is stiff and the muscles are sore. The cause is inflammation of the tendons, ligaments and bone attachment points of the sacroiliac joint, i.e. tendon terminalitis. It is easily misdiagnosed as lumbar disc herniation and rheumatism. Pain in the posterior aspect of the hip and thigh is easily misdiagnosed as sciatica, but pain in the lower extremities due to ankylosing spondylitis rarely radiates below the knee. Ankylosing spondylitis alternating right and left sacroiliac joint area pain is the most characteristic symptom of ankylosing spondylitis in the middle and early stages. It is a deep and gradual pain in the fixed part of the sacroiliac joint, first significant on one side, then developing into alternating left and right pain, and in severe cases the pain is at one point in the sacroiliac joint. The sacroiliac joint pain can move up to the lumbar spine and down to the sciatic pain or iliac pain in the thigh, and the pain is aggravated by coughing, sneezing or other tugging movements. The pain may begin unilaterally and intermittently and progress to bilateral, persistent pain with low back stiffness over several months. All ankylosing spondylitis invades the sacroiliac joint and moves up to the lumbar spine painfully, so ankylosing spondylitis sacroiliac joint pain is often accompanied by low back pain and lumbosacral pain with morning stiffness. First, it is recurrent, intermittent or alternating soreness on both sides, with the development of the disease, or persistent deep hidden gradual dull pain or stabbing pain, accompanied by lumbar soreness and general fatigue and weakness, which is characterized by aggravation after rest, cloudy days or exertion, and pain relief after activity and heat.