Hemophilia is an inherited clotting factor deficiency disease. It is inherited from women who carry the hemophilia gene and affects up to half of their boys. Intra-articular hemorrhage is the most common form of hemophilia and is most common in the knee joint, accounting for about 2/3 of all cases. repeated intra-articular bleeding leads to degenerative joint degeneration called hemophilic arthritis. 1. Etiological typing According to the different deficient factors, there are type A (factor VIII deficiency), type B (factor IX deficiency) and type C (factor XI deficiency). Types A and B are X-chromosome recessive, with only males and females as carriers, and have a pronounced tendency to bone and joint hemorrhage. Type C is autosomal dominant and can occur in both sexes. This type is rare, with mild bleeding and rare bone and joint involvement. 2, pathology Hemophilic arthritis early only intra-articular bleeding, rest after slow absorption, repeated bleeding again, due to the gradual deposition of iron-containing heme, synovial membrane stained brown or red-brown, followed by villi proliferation, cartilage surface loss of glossiness. Finally, it leads to degenerative changes of articular cartilage and fibrous thickening of synovial membrane. 3.Clinical manifestations According to the amount of coagulation factor deficiency, clinical manifestations are divided into severe, moderate and mild cases. Those with coagulation factor less than 1% of the normal value are considered severe, and intra-articular bleeding can occur about one year after birth, and abnormal bleeding occurs in about 90% of cases before school age; those with coagulation factor less than 5% are considered moderate, sometimes bleeding, but less frequently than the former; those with coagulation factor 5-25% are considered mild, and spontaneous bleeding is hardly seen, and abnormal bleeding only occurs during trauma or tooth extraction. Thus, no bleeding factor is noticed in infancy, and only about half of them have a history of unstoppable bleeding until school age. A coagulation factor of 70-100% is considered normal. Hemophilic arthritis is mainly characterized by recurrent intra-articular bleeding throughout childhood, and in severe cases, intra-articular bleeding is seen at the onset of walking, mainly in the knee, followed by the ankle, elbow, shoulder and hip. The disease is divided into three phases: the first phase is the hemorrhagic phase, with sudden acute intra-articular hemorrhage accompanied by severe pain, significant swelling of the joint, increased local skin temperature, significant pressure pain, limited movement, and protective stiffness of the joint. Sometimes the body temperature rises and the leukocytes increase, so it is easy to misdiagnose as septic arthritis, or even to perform puncture or incision by mistake, which may cause fatal danger. The hematoma is slowly absorbed, taking about 3-6 weeks. The second phase is the inflammatory phase, which is characterized by recurrent intra-articular bleeding, thickening of the joint capsule and synovial membrane, secondary joint swelling and restricted motion with friction sounds. The third stage is the degenerative stage, in which the joint movement is severely restricted and the muscles atrophy, often with flexion contracture deformity and even severe disability. 4. Diagnosis (1) Family history (2) Previous history of bleeding (3) Clinical manifestations (4) Prolonged clotting time and other laboratory findings (5) It should be noted that biopsy should be avoided because it is easy to cause rebleeding. 5.Prevention and treatment The child should not participate in strenuous sports and should prevent trauma. Active measures should be taken for acute joint hematoma in order to prevent future complications. (1) Rest in bed and elevate the affected limb. (2) Apply ice and splinting. (3) Transfusion of fresh blood or component blood to improve anticoagulant substances. For patients with B and C types, transfuse stored whole blood or plasma for two weeks. (4) Infusion of adrenocorticotropic hormone can reduce the inflammatory response. (5) Intra-articular injection of hyaluronidase helps in the absorption of hematoma. For advanced contracture deformity of the joint, continuous skin traction can be mildly performed. If orthopedic surgery is necessary, coagulation factors should be supplemented preoperatively, intraoperatively, and postoperatively.