The sacroiliac joint is a component of the pelvic ring, with a normal joint capsule and strong ligaments to increase its stability, and under normal circumstances the joint has very little mobility, mainly to support weight and cushion the vibration brought about by the activity, the joint has normal synovium and cartilage, many clinical diseases can be involved in this joint, or even the first to start here, and has certain characteristics, such as ankylosing spondylitis, psoriatic The most common clinical condition is lower back pain. Lower back pain is one of the most common clinical symptoms, which is due to the connection of the active lumbar spine and the relatively fixed pelvis, making this part of the stress more concentrated and prone to lumbar muscle strain, lumbar disc herniation, lumbar dorsal myofasciitis, small joint disorder syndrome, etc. However, there are times when this pain also responds to some other less common diseases, therefore, in daily life, if there is persistent lower back pain, also Today, the more common ankylosing spondylitis and sacroiliac joint dense osteoarthritis are briefly introduced to facilitate the distinction: ankylosing spondylitis is a multifactorial autoimmune disease, starting with morning stiffness and low back pain, often concentrated in the lumbosacral region, insidious onset, slow progression, generally in adolescent males, and the disease is characterized by aggravation after rest, after appropriate activity X-rays often show blurring of the sacroiliac joint space, destruction of the joint surface, insect-like, no clear boundaries around the lesion, infiltrative changes, and local sclerotic bone can also be seen, in addition to the fusion of small joints of the lumbar spine, and bamboo-like changes of the spine. In addition, fusion of the small joints of the lumbar spine and bamboo-like changes in the spine can be seen. In AS, early combination of medications is emphasized to control the disease and to pay attention to functional training of the spinal joints to prevent serious dysfunction. Dense osteitis is a benign lesion, mostly seen in women of childbearing age 20-35 years old, mostly in the postpartum period, mainly as a non-specific inflammation of the sacroiliac joint, mainly manifested as aggravation after walking and standing and weight-bearing exertion, which can be relieved after rest, generally pain does not radiate to the lower limbs, X-rays can often be seen as a local increase in density of the sacroiliac joint surface, sclerosis is obvious, can be unilateral, the joint surface is generally not involved, around the lesion can be seen Clear triangular borders are seen around the lesion. For dense osteoarthritis, since the disease is self-limiting, the clinical symptoms will gradually improve or even completely resolve after a period of time, and the treatment is mainly symptomatic and physical therapy.