Three types of hemophilia are known to exist in humans: ① Classical hemophilia, or hemophilia A, which lacks factor 8, or anti-hemophilic globulin (AHG). It is an inherited disease, all occurring in males and passed from female to female; that is, the diseased father passes the disease gene to his healthy daughter, who in turn passes it to the boy she gives birth to. ②Christmas disease, or hemophilia B, is deficient in factor 9, the plasma thromboplastin (PTC). It is also a genetic disorder and can be acquired by women. Hemophilia C, which lacks factor 11, plasma thromboplastin (PTA), is also a hereditary disease. The main pathological changes: Repeated bleeding and blood accumulation in the joints, stimulation of synovial thickening, erosion of iron-containing heme, causing destruction of articular cartilage, followed by invasion of subchondral bone, especially around the articular cruciate ligament bleeding, due to pressure, erosion of iron-containing heme, resulting in the widening and deepening of the intercondylar concavity of the femur, recurrent lesions, severe cases cause joint dislocation and joint fibrous ankylosis (common) or bony ankylosis, with secondary effects such as reactive osteosclerosis. In severe cases, the lesions may cause joint dislocation, fibrous ankylosis (common) or bony ankylosis, with secondary osteoarthrosis such as reactive osteosclerosis. Long bone epiphysis and intraosseous hemorrhage can lead to long-term compression and necrosis of bone trabeculae, and resorption of bone trabeculae to form cystic cavities. Subperiosteal hemorrhage stimulates the periosteum causing a periosteal reaction. Soft tissue hemorrhage leads to increased density of soft tissue. Clinical manifestations]: The main clinical manifestations of hemophilic arthritis are caused by bleeding in the joint cavity. According to the degree of coagulation factor deficiency in the plasma of patients can be divided into: ①, light The concentration of coagulation factors in the plasma is 20-60% of normal, and these people will bleed heavily only during surgery. ②, medium The concentration of coagulation factors in plasma is 5-20% of normal, and there will be hemorrhage after surgery or trauma. ③.Severe cases The plasma level is only 1-5% of normal. ④.Extremely severe cases Plasma level is less than 1% of normal. Anyone with a plasma concentration of clotting factors less than 5% can bleed profusely after minor trauma without attention, and can even bleed “spontaneously”. About half of all hemophiliacs have the severe form. Intra-articular bleeding in hemophiliacs usually begins around the age of 8 to 9 years, with varying degrees of bleeding during adolescence and significant joint destruction by the time the patient reaches his or her twenties; it is rare for intra-articular bleeding to first occur after the age of 30. Hemophilic arthritis can be divided into three main types: acute, subacute and chronic. Acute: Intra-articular hemorrhage The most common sites are the knee, elbow, ankle, hip and shoulder. A history of injury is often not asked. Boys are active and are likely to go unnoticed for minor trauma. The hemorrhagic joint is swollen, hard, hot, and painful to pressure, with bright red skin on the surface. The joint remains in a flexed position and movement is limited. The pain disappears rapidly with supplementation of clotting factors. If treated promptly and no further bleeding occurs, there can be no sequelae. ②Subacute: intra-articular hemorrhage There are no clear rules for subacute intra-articular hemorrhage, and generally more than 2 acute intra-articular hemorrhages can be classified as subacute type. Pain is less pronounced, synovial thickening is significant, and joint movement is moderately limited. ③ Chronic: intra-articular hemorrhage Sub-acute intra-articular hemorrhage lasts for more than 6 months. There is progressive destruction of the joint until it is completely destroyed, with arthrofibrosis, contracture and subluxation, but rarely with bony ankylosis. The radiographic presentation can be divided into 5 stages: Stage 1: No skeletal changes on the radiograph, only soft tissue swelling shadows due to hemorrhage and increased density of the suprapatellar bursa due to blood accumulation. Stage 2: The epiphyseal area is osteoporotic due to disuse and congestion, and the epiphysis grows rapidly. The joint space is not narrowed and there is no subchondral cyst formation. Stage III: Subchondral cysts of varying sizes are formed, occasionally communicating with the joint cavity. The joint space is not narrowed. There is a decrease in translucency due to iron-containing haematoxylin deposition on the synovial membrane. This stage is characterized by the articular cartilage surface remaining normal and is the final reversible stage of hemophilic arthritis. Stage 4: The cartilage is destroyed and the joint space becomes narrow. In the knee, this is characterized by a widening and irregularity of the intercondylar notch and a squaring of the inferior pole of the patella. The patellar changes are somewhat similar to ischemic necrosis of the femoral head. Stage 5: The final stage of changes, there is no joint space, the joint structure is extremely disturbed, there is flexion contracture or subluxation, and osteoarthritic changes are very obvious. In addition to intra-articular bleeding, patients with hemophilia may also have the following musculoskeletal system changes. (a) Hemophilic cysts and pseudosarcomas The following three manifestations are possible: 1. Simple cysts Substantially, they are intramuscular hematomas confined to the muscles, wrapped by the muscle membrane and do not affect the bones. 2. Intramuscular cyst adjacent to bone with thinning of the bone cortex by compression. 3. subperiosteal and intraosseous hemorrhage causing pseudosarcoma changes. x-ray shows osteolytic changes, cortical defects, indistinct margins, shadowing of soft tissue masses, and in case of subperiosteal hemorrhage there may be periosteal reaction and new bone formation, much like osteosarcoma. (B) Intramuscular hemorrhage Intramuscular hemorrhage in the iliopsoas muscle is the most common, and the bleeding is often spontaneous and may be due to sprain during sleep. Intramuscular injections in the gluteal region may also cause deep hematomas. (iii) Peripheral nerve damage The most common sites are femoral nerve, common peroneal nerve, sciatic nerve, median and ulnar nerves. It often occurs in conjunction with intramuscular hemorrhage and manifests as nerve palsy, suggesting that the hematoma is due to compression or pulling on the nerve.