Bone fibrodysplasia is a lesion characterized by fibrous degeneration of bone, also known as osteochondral dysplasia, of unknown etiology. It can be clinically classified into monogenic, polygenic and Albright syndrome. Clinical characteristics 1. Age: The first symptoms of this disease are mostly seen in adolescents, and the age of onset is mostly between 5 and 20 years old. 2. Gender: More females than males, with a male to female ratio of 1:(2-3). 3, site: the disease can occur in any bone of the body. The monogenic lesions are mostly located in the femur, ribs and maxillofacial bones, while the polygenic lesions attack multiple bones, often on one side of the limb, with the femur, tibia, humerus, radius and ilium being the main ones, followed by the palm and metatarsal bones. 4, symptoms and signs: fibrous structure of bone malformation according to the occurrence of different sites and various deformities. When the long tubular bones of the limbs are involved, deformities such as hip inversion, knee inversion and knee valgus often appear due to the expansion and bending of the backbone, and the affected limbs are shortened due to the bending of the bones and the early closure of the epiphysis. When the metacarpal and metatarsal bones are involved, localized bulging of the extremities may occur. Patients with multiple forms often have short stature. Rib and spine involvement may result in asymmetry of the thorax, local bulge, scoliosis, and occasionally spinal cord compression. In the case of maxillofacial involvement, facial asymmetry, localized bulging or protruding eyes, nasal obstruction and other signs of compression may occur. Pathological fractures can occur in 2/3 of cases, and some cases have this as the first symptom. They are often characterized by pain, swelling, and impaired movement at the fracture site after minor trauma, but they rarely displace and heal with external scabs after fixation, and rarely fail to heal. In addition, mild pain, claudication, and gait abnormalities due to pain or deformity may occur in osteochondral dysplasia. Multiple forms of osteochondral dysplasia combined with endocrine disorders are called Albright syndrome. The majority of these patients are females, and the majority of them are born with patchy yellowish-brown skin pigmentation, not raised, scattered in the waist, buttocks, thighs, etc. Vaginal bleeding can occur at 3-4 months of age, and secondary sexual characteristics can appear early in childhood, occasionally with mental retardation and other endocrine abnormalities. Imaging features 1, X-ray features: poor bone fiber structure mostly involving the long bone epiphysis or bone stem, the lesion bone expansion thickened, with bending deformity. The bone cortex is thin, the medullary cavity is enlarged, and there are frosted glass-like changes, which may be accompanied by cystic shadow and patchy osteosclerosis shadow, without periosteal reaction. 2. MRI features: the lesion has a clear border, a uniform slightly low signal in the T1-weighted phase, and a high signal or mixed signal in the T2-weighted phase. Pathological changes 1. Gross: The lesion is located in the medullary cavity, with grayish white tough and brittle tissue, rubber-like hardness, and gritty feeling on the cut surface. Sometimes jelly-like mucous changes or cystic changes can be seen. Microscopically: normal bone structure disappears, replaced by proliferating fibroblasts and woven bone trabeculae, the arrangement of bone trabeculae is disorganized and varies, the ratio of bone to fibrous component can be 1:1 in many cases, but only 1:50 in few cases. Differential diagnosis 1. Isolated bone cyst: most of them are located in the proximal end of humerus and femur, patients have no obvious pain and swelling, and are prone to pathological fracture. X-ray lesions show central osteolytic destruction with reactive sclerotic bands at the edges, and yellow serous fluid in the capsule at the time of puncture. 2. Endogenous chondrosarcoma: It occurs in short tubular bones of hands and feet. The cystic destruction of endogenous chondrosarcoma is located in the medullary cavity, and gravel-like calcification can be seen in the low-density area within the destruction zone. 3. Hyperparathyroid brown tumor: Due to excessive secretion of parathyroid hormone (PHT), osteoclasts are actively proliferating and absorbing large amount of bone, resulting in generalized osteoporosis and reactive fibrous connective tissue hyperplasia, often forming masses in local bones with cystic changes, which are often accompanied by bleeding and rich in iron-containing hemoglobin, and are brownish red in color, so they are called brown tumors. The X-ray shows systemic diffuse osteoporosis, while brown tumor shows limited cystic bone destruction, thin shell-like bone cortex, increased blood calcium, decreased blood phosphorus, increased alkaline phosphatase, and increased calcium and phosphorus in urine. Treatment and prognosis Surgical treatment is the main treatment. In the case of solitary type, bone grafting with scraping of the lesion is feasible, and in the case of extensive tumor segment excision and functional reconstruction is feasible. If pathological fracture occurs, plaster, splint or traction can be used to fix the fracture, and then bone grafting can be performed after the fracture is healed, and sometimes scraping and bone grafting and internal fixation are also used. If the deformity is serious, osteotomy orthopedic surgery is feasible, during which the lesion is scraped and bone is implanted. Radiation therapy is not suitable because it can cause malignant changes. Multiple lesions are treated by surgery only on symptomatic areas, mainly to treat deformities and fractures. There is no specific treatment for skin pigmentation and precocious puberty.