Osteoid osteoma is a benign osteoblastic tumor of osteoblast origin, which was first named after osteoid osteoma in 1935. Osteoid osteoma is characterized by a core of vascularized bone-like tissue in the center of the lesion surrounded by a sclerotic zone. Osteoblastoma is usually smaller than 1.5 cm, but if it is larger than 1.5 cm, it is considered an osteoblastoma. Age of onset: Osteoid osteoma can occur at any age, but most often occurs between the ages of 4 and 25. It is more common in males than females, with a ratio of 3:1. Site: Osteoid osteoma can occur in any part of the body, but it is common in long tubular bones, most commonly in the femur and tibia, especially the proximal femur. The site analysis of a group of 661 cases of osteoid osteoma abroad showed that 71% of the total number of tumors occurred in the long tubular bone, 20% in the hands and feet, and 9% in the spine. The most common site of development in the long tuberosity was the femur, followed by the tibia, which accounted for approximately 57% of the total number of cases. In the hand, osteoid osteoma is commonly found in the proximal phalanges and metacarpals; in the carpal bones, it is more common in the navicular bones; and in the foot, it is more common in the heel and talus bones. In the spine, osteoid osteoma is most commonly seen in the posterior structures of the spine, such as the base of the transverse process, the vertebral plates and the pedicle, with the vertebral body rarely involved. Clinical manifestations: The most distinctive clinical feature of osteoid osteoma is pain, which is often localized, persistent and dull at night, and is not relieved by rest. The pain caused by osteoid osteoma is quickly relieved by taking aspirin or non-steroidal anti-inflammatory and analgesic drugs. Soft tissue swelling and pressure pain may be present at the lesion site. Muscle atrophy and skeletal deformities may occur in immature skeletal development. Osteoid osteoma of the spine may lead to oblique neck and scoliosis. Radiographs: A typical radiograph shows a circular or oval translucent area less than 1 cm in diameter in the center of the lesion, called the nest of the tumor, which may have calcified spots surrounded by sclerotic reactive bone. The radiographic appearance of osteoid osteoma varies depending on the site of origin. The thickness of the surrounding sclerotic bone is related to the site and the duration of the disease, and some tumors have small nests that are not clearly visible on X-ray. Osteoma of the femoral neck is usually located on the medial aspect of the femoral neck, and the nest is located under the periosteum or in the bone cortex. Osteoma of the wrist and tarsal bones, which occur in cancellous bones, appear on X-ray as a partially or completely calcified round lesion with no surrounding reactive sclerotic bone, which is completely different from that of the backbone and is more difficult to diagnose. Most patients have scoliosis due to pain, and the lesion is often located at the apex of the concave side of the scoliosis, and sclerotic bone can be seen in the arch, vertebral plate, and articular processes. 2.CT examination: Most osteoid osteoma can be clearly diagnosed with typical clinical manifestations and typical X-ray films. For a few osteoid osteoma, the x-ray performance is atypical, and sometimes the nest is so small that the x-ray does not show well, especially in the spine, pelvis and femoral neck, etc. CT examination is needed to make a clear diagnosis, which can show the location of the lesion and the size of the nest, which is important for the doctor to determine the surgical approach. 3.Bone scan: Bone scan of osteoid osteoma shows a double density sign at the lesion site, i.e. radionuclide concentration at the nest site and little radionuclide concentration in the surrounding sclerotic area. 4.Differential diagnosis: osteoid osteoma should be differentiated from the following diseases or tumors: bone abscess, stress fracture, eosinophilic granuloma, intracortical hemangioma, bone island, intracortical osteosarcoma and Ewing’s sarcoma, etc. 5. Pathological examination: Microscopically, osteoid osteoma consists of immature bone and osteoid tissue with different proportions of osteoid tissue and new bone trabeculae, with more cells and abundant blood vessels. Treatment: Osteoid osteoma has a tendency to heal on its own. For those with relatively mild symptoms or those who can tolerate pain, observation is feasible, and self-healing may take several years. For those with severe symptoms, or those with less severe symptoms, but the patient and family are unwilling to tolerate the wait, surgical treatment is feasible. The key to surgical treatment is the complete removal of the nest, and the recurrence rate of scraping out is about 5%-30%; another method is the use of CT-guided percutaneous percutaneous nest radiofrequency ablation technique, which has been adopted abroad in recent years, with an efficiency of 90%. No malignant transformation of osteoid osteoma has been reported so far.