Hip synovitis is a non-specific synovitis that occurs in children between the ages of 3 and 10 years, and in adults as well, with more men than 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 metabolic reactions. The pathological changes include synovial congestion, edema, exudation, synovial hyperplasia, and joint effusion. Synovitis of the hip joint may be preceded by upper respiratory tract infection, dysentery, pharyngitis, measles, rhinitis, pneumonia, boils, tonsillitis, etc. The onset of the disease is mild pain in the knee joint and anterior medial thigh, and after 24 hours or more the pain is transferred to the hip joint with limp and limited joint movement. The hip joint is painful, swollen, and limited in movement, and the patient is afraid to move the hip and knee joints. Passive activity causes crying and restlessness, refusal to examine the affected hip and limb, and obvious limping. The affected limb shows hip inversion, internal rotation and flexion, but external rotation, abduction and flexion of the hip are more common. A few patients have fever, with body temperature at 37.3-39.7℃. There is deep pressure pain in the front of the hip, positive pain in internal and external rotation of the hip by passive activity, hip pain caused by tapping on the heel of the lower limb in extension, and hip pain caused by tapping on the knee in flexion position, but most of them are mild. X-ray examination shows swelling of the hip capsule and widening of the hip joint space. Ultrasound, CT or MRI examination shows that there is synovial accumulation in the hip joint mainly distributed around the joint. Laboratory examination showed normal or mildly increased blood leukocytes, slightly high lymphocytes, and increased blood sedimentation (20-40mm/h). The hip joint fluid was mostly clear and transparent, but it was also mildly turbid or blood-colored. However, there was no bacterial growth in culture. Complement binding test is negative, Ig, AggG, IgM are slightly high or roughly in the normal range. c-reactive protein is 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.