Synovitis is a non-specific synovitis that occurs in children between the ages of 3 and 10, and in adults as well, more often in men than in women. The hip joint is more affected, while the knee, shoulder, and elbow joints are in decreasing order of incidence. The cause of the disease is unknown, but some scholars believe that it is related to viral infection, bacterial infection, trauma and allergic reaction. The pathological changes are characterized by synovial congestion, edema, exudation, synovial hyperplasia, and joint effusion. Synovitis may be preceded by upper respiratory tract infection, enteritis, pharyngitis, measles, rhinitis, pneumonia, and tonsillitis. The onset of synovitis is characterized by mild pain in the knee joint and anterior medial thigh, with pain shifting to the hip joint after 24 hours or more, and limping and limited joint movement. The hip joint showed pain and limited movement, and the patient was afraid to move the hip and knee joints. Passive activity causes crying and restlessness, refusal to examine the affected limb of the hip, and obvious claudication. The affected limb shows hip inversion, internal rotation and flexion, but hip external rotation, abduction and flexion are more common, and a few patients have fever. There is deep pressure pain in the front of the hip, and the pain is positive for internal and external rotation of the hip by passive activity, but most of them are mild, and some children do not complain of pain, but only show limp. X-ray examination showed swelling of the hip capsule and widening of the hip joint space. Ultrasonography showed that the synovial membrane in the hip joint was mainly distributed around the joint and the synovial membrane was thickened. In laboratory examination, blood leukocytes were normal or mildly increased, lymphocytes were slightly high, and blood sedimentation was increased (20-40mm/h). The hip joint fluid was mostly clear and transparent, but it was also mildly turbid or blood-colored. C-reactive protein was high or normal. The synovial membrane of the hip joint produces an inflammatory response when stimulated by various etiologies (such as osteophytes, arthritis, joint tuberculosis, rheumatism, etc. and traumatic trauma, bone injury, intra-articular injury, peripheral soft tissue injury, surgery, etc.) or directly stimulated by synovial injury, and the synovial membrane responds to the stimulation of inflammation by secreting synovial fluid and producing pain. Strictly speaking, as long as there is exudate accumulation in the joint, it proves the existence of synovial inflammation, whose main manifestations are joint congestion and swelling, pain, increased exudate, joint effusion, difficulty in moving and squatting, and functional limitation. Synovitis is a sterile inflammation caused by poor microcirculation, and the main symptom is the production of fluid. The production and absorption of joint fluid is a “dynamic balance”. When the reabsorption of joint fluid is impaired, the dynamic balance between the production and absorption of joint fluid is broken, and the production of joint fluid is greater than the reabsorption, then “joint effusion” will occur. The main treatment for synovitis is to regulate the microcirculatory system, as long as the microcirculation is smooth, the fluid will disappear, and the inflammation will also be lifted, try not to strain during the period of fluid accumulation, and reduce the frequency of pumping injections, too much pumping injections will stimulate the subsynovial connective tissue group fiber proliferation, as well as synovial tissue aging, so that the regeneration and repair ability of synovial tissue is significantly reduced, and then the treatment will be more troublesome. Patients suspected of having hip synovitis should be differentiated from the following diseases: tuberculous synovitis of the hip, septic arthritis, rheumatoid arthritis, epiphyseal chondromalacia of the femoral head, hemophilic arthritis, etc. After the appearance of symptoms, we must carefully examine and exclude the above diseases to make a clear diagnosis. Early after the diagnosis is clear, bed rest should be given, primary diseases should be actively treated, the causes should be eliminated, water-electrolyte balance should be maintained, and bacterial and viral expansion should be controlled. Application of non-steroidal drugs and local physiotherapy will help the synovitis to subside and reduce swelling and pain. Skin traction is used on the affected limb, which should be placed in abduction and braked at 15° of knee flexion. After 1-2 weeks, the systemic symptoms subside, but the hip condition, which has to be treated continuously. The prognosis of hip synovitis is good, usually no recurrence and no sequelae, but there are a few cases of ischemic necrosis of the femoral head due to persistent increase in intra-articular pressure, which affects the blood supply to the femoral head and causes ischemic necrosis of the femoral head, so a review is required 2 and 6 months after the onset.