Fibrous dysplasia (fibrous dysplasia) is a developmental malformation that occurs in the formation of mesenchymal bone, in which bone development stops at the immature woven bone stage and normal bone trabeculae cannot be formed. Presentation:Most lesions are of growing bones. The age at presentation varies widely, and the multiple bone lesions are in younger patients. The main symptoms are mild pain, swelling, and localized tenderness, and repeated pathological fractures leading to limb deformity are common. In the femur, the hip may be inwardly turned or angulated, with short limb deformity, and in severe cases, shepherd’s crook deformity, resulting in claudication. Those occurring in the skull may have a peculiar facial appearance with protruding eyes and forehead. Occasionally, it can occur in the spine, mostly in the lumbar spine, and more rarely in the cervicothoracic spine, which can produce retroflexion and scoliosis deformity. On radiographs, the solitary type mainly shows a thinning of the bone cortex to form a defect, which in tubular bones mostly occurs in the diaphysis or epiphysis and develops in the long axis direction, showing a blurred intra-medullary radiolucent area, described as frosted glass-like. Multiple lesions often involve several bones and may invade adjacent bones. Long bone lesions of the extremities often involve all of the bone, with uneven width of the medullary cavity and thinning and expansion of the bone cortex where it widens. In a few cases, malignant changes are seen, and radiographs show signs of malignancy such as osteolytic destruction, cortical breakthrough, Codman’s triangle, and soft tissue masses. Treatment:There is no specific treatment for this disease, and most of the monogenic types only need to be observed. Surgical treatment is mostly used to prevent pathological fractures and correct deformities. Surgery is mostly taken to scrape the bone graft for internal fixation. It is mainly indicated for adults with limited and symptomatic fibrous heteroplasia. Because of the tendency to recur, children are best treated with limited osteotomy and internal fixation of the deformity. Surgery is generally not indicated for multiple lesions, but it may be indicated for severe deformities that affect limb function.