Acute septic arthritis is most often seen in the knee, hip, shoulder, and elbow joints. In infants and young children, it is often closely related to osteomyelitis of the epiphysis. However, there are also many cases in which the synovial membrane is invaded through the bloodstream, and eventually the epiphysis is destroyed and osteomyelitis ensues. The disease is often complicated by bacteraemia or sepsis of Staphylococcus aureus. The common pathogenic bacteria are Staphylococcus aureus and occasionally Streptococcus, Escherichia coli, S. pneumoniae, or S. meningitidis can be found. Special care should be taken when performing femoral venipuncture in children with sepsis to avoid accidental entry into the hip joint. Bacterial invasion of the joint can occur through 1) hematogenous invasion from infected foci far from the affected joint such as boils, abrasion infections, upper respiratory tract infections or otitis media, where the bacteria invade the bloodstream and remain at the synovial membrane causing disease. 2) direct invasion from nearby foci such as osteomyelitis spreading to adjacent joints. There are usually manifestations of sepsis or history of trauma, such as fever, rapid pulse rate, and increased white blood cells. X-rays show swelling of the joint capsule and swelling of the surrounding soft tissues. If the treatment is not timely, destruction and degeneration of the cartilage surface of the glass-like joint will occur quickly, and the joint will be filled with pus, and pathological dislocation may occur due to muscle spasm, which may cause deformity and limitation of movement. Most cases have a history of trauma or infection, such as otitis media or skin infection. The onset is acute, and the prominent complaint is localized pain in the joint. If the joints of the lower extremities are involved, there is a limp. The child is soon unable to walk due to increased pain from weight bearing. In addition, there is irritability, loss of appetite, fever, and temperature up to 40°C. Signs include increased local temperature of the inflamed joint, swelling, and joint effusion. The joints are semi-flexed due to protective muscle spasm. On palpation there is widespread pressure pain along the joint line. Automatic or passive movement of the joints is painful, due to which pseudo-paralysis occurs. In neonates and small infants, the systemic response is mild or absent, and the only signs are joint swelling and flexion contractures. Symptoms: 1. Arthrocentesis may yield cloudy fluid or viscous pus with a cell count of more than 4×109/L (4000/mm3), with predominantly neutrophilic multinucleated granulocytes. Fibrin is increased in the joint fluid and coagulates quickly after extraction. The sugar content was lower than in the blood. Smear gram stain can be seen with pathogenic bacteria.2. X-ray, ultrasound, MRI examination early manifestation of joint capsule fluid expansion, if it is hip joint, there will be femoral head outward displacement or even prolapse. If the infection persists, bone decalcification and narrowing of the joint space can be seen. Early treatment with arthrocentesis for bacterial culture and smear for bacteria is necessary. If pus is obtained by joint puncture, early surgical treatment is indicated. At the same time, high-dose antibiotics should be administered intravenously immediately. The principles and methods of antibiotic selection are similar to those for acute osteomyelitis. Give the necessary systemic supportive therapy such as antipyretic, sedation, nutrition and blood transfusion. Skin traction is used on the affected limb to reduce pain and prevent pathological dislocation. Arthrocentesis should be performed every 1 to 2 days to drain the fluid and inject low concentration antibiotics into the joint cavity. If the fluid is pus and the amount is large, an arthrocentesis should be made early to drain the joint, and the joint capsule can be sutured after cleaning the joint cavity, or two silicone tubes can be left in place for irrigation. Septic arthritis should be treated as an emergency due to the severity of the disease. The aim of treatment is to control the joint infection, remove the fibrin produced by the infection and prevent deformity; restore the normal anatomical relationship of the joint and thus preserve the function.