Osteoid osteoma is the third most common benign primary bone tumor, accounting for about 10-12% of benign bone tumors. The most common sites of osteoid osteoma are the proximal femur and the tibia and fibula. The clinical symptoms are often severe pain, which increases at night and is relieved by the administration of NSAIDs. However, due to the reactive osteosclerotic hyperplasia caused by osteoid osteoma, it is difficult to determine the location of the nest intraoperatively, and extensive osteotomy often results in the inability of the affected limb to bear weight or even combined with fracture and affects bone development, etc. The surgical treatment is limited due to more postoperative complications and longer hospital stay, which affects patients’ studies. In recent years, image-guided minimally invasive interventional therapy has been more and more widely used in the treatment of osteoid osteoma due to its advantages of small trauma, high safety and short hospitalization time. Currently, radiofrequency ablation is mostly used in clinical practice, but the treatment is limited by the fact that radiofrequency treatment cannot show the treatment range under CT or MRI surveillance and the high temperature generated during the treatment process causes distance pain. We are the first to adopt CT/MRI-guided cryoablation for osteoid osteoma at home and abroad to obtain high efficacy. Basic methods: 1. Preoperative preparation: Check blood routine, coagulation function, blood biochemistry and serum four (hepatitis B, hepatitis C, AIDS, syphilis), establish intravenous access. Prepare electrocardiography, heart rate and oxygen saturation monitoring equipment. intravenous anesthesia is given to patients under 16 years old who cannot cooperate with the treatment. 2. Intraoperative: guide the device using a precise scan of the lesion using large-aperture multilevel spiral CT or MRI guidance (layer thickness 2 mm), determine the needle route (avoiding important nerves and blood vessels), disinfect the skin on the surface, lay sterile sheets, and inject local anesthesia with 2% lidocaine. The 8-G (4.2 mm OD) bone puncture needle was used to puncture to the center of the lesion margin, the core was withdrawn, the 17G cryoprobe was inserted through the jacket needle, and the jacket needle was backed up to the lesion margin so that the tip of the cryoprobe was positioned through the puncture needle to insert the biopsy needle into the tumor nest. A small amount of filtered sterile air was injected subcutaneously at the puncture site to form an air cushion to prevent skin frostbite. A 17G cryoprobe was used with 2 cycles of freeze-retemperature mode (8 minutes of freezing and 5 minutes of retemperature). During freezing, the tip temperature can reach as low as -175°C. CT scanning allows real-time monitoring of ice ball formation and surrounding soft tissue. The shape of the formed ice ball depends on the diameter of the cryo-needle, the length of the exposed needle tip and the length of the freezing time. During the freezing process, a sterile hot water bag is applied to the skin on the surface of the puncture site and a warm blanket is placed under the patient’s body to maintain the patient’s body temperature. At the end of two cycles, the needle was removed. Postoperative CT scan (layer thickness 2 mm) was performed to assess whether the tumor nest was completely ablated and to predict possible complications. 3. Postoperative care: After needle removal, the puncture site is pressed for 5-15 minutes to prevent bleeding, observed for 30 minutes, and returned to the ward if there is no discomfort. Cardiac monitoring is performed within 6 hours, oral antibiotics are given for 3 days (500 mg twice a day), and intravenous drip of lithotripsy, alkalinization of urine and diuretics are given for 2-3 days. Cryoablation has unique advantages over other methods: 1. During the ablation process, CT/MRI scan can clearly show the boundary of the ice ball, determine whether the tumor is completely ablated and protect the surrounding important tissues (nerves, blood vessels, etc.) to the maximum extent, while RF ablation cannot show the ablation range on CT images. 2.For larger lesions, cryoablation can be combined with multiple needles. According to the size and shape of the lesion, multiple cryo-needles can be selected and reasonably distributed to freeze the tumor to achieve better ablation effect. 3.Cryoablation can treat bone tumor more efficiently than RF ablation. 4. Compared with other treatments, cryoablation is less painful and more tolerable to patients. All patients above 16 years old are under local anesthesia, and the operation is performed under consciousness, and the pain of patients does not increase significantly during the operation. In contrast, patients often suffer from severe pain during radiofrequency ablation, and therefore need to implement epidural anesthesia or general anesthesia. Therefore, cryoablation is more suitable for the treatment of osteoid osteoma in children. Notes for case selection: Clinical symptoms are consistent with the diagnosis of osteoid osteomaC onset of at least 3 months, severe pain at the site of onset, aggravated at night, pain relief after oral NSAIDs, ineffective with other drugs or other treatments.2. Imaging performance is consistent with the diagnosis of osteoid osteoma: sclerosis of bone around the lesion, cortical thickening, translucent nests.3. For atypical cases or cases with doubts CT-guided puncture biopsy.