I. Cryotherapy The purpose of cryotherapy is to kill tumor tissue by inducing tissue necrosis through low-temperature frostbite. The use of cryotherapy for the treatment of diseases can be traced back to ancient Egypt, using the method of cold application to treat inflammatory diseases and complex cranial injuries. With the invention of the mercury thermometer in 1714, people could accurately measure and record temperatures, making it possible to communicate and record cryotherapy. Cryotherapy of tumors was first reported in 1850 when Arnott used ice salt complexes for the treatment of breast and gynecological tumors and observed significant anesthetic effects, hemostatic effects, and retardation of tumor growth. Subsequently, cryotherapy, including dry ice, cold gas injection and liquid nitrogen freezing, was gradually introduced in neurosurgery, gynecology and urology. In 1964, Marcove first applied cryotherapy to a lesion of bone. The patient was a 48-year-old patient with metastatic lung cancer in the proximal humerus. After 4000 rads of radiotherapy the patient had no significant reduction in pain, and then the patient underwent liquid nitrogen cryotherapy with scraping of the lesion, after which the patient’s pain symptoms were significantly reduced. Subsequently, Marcove et al. conducted an extensive and in-depth study using cryotherapy on metastatic cancer, benign invasive bone tumors, and low-grade malignant bone tumors, and initially established the specific operation of liquid nitrogen cryotherapy. The results of early surgical treatment alone for giant cell tumor of bone were not satisfactory, and studies reported a 40-55% tumor recurrence rate after surgery. 1973 Marcove reported the results of a study of cryotherapy after scraping the lesions of giant cell tumor of bone, based on the treatment of other tumors. In 1978, Marcove et al. treated 52 cases of giant cell tumor of bone with a large incision, adequate windowing, thorough scraping of the lesion, and repeated freezing to below -20°. In 1999, Malawer MM treated 102 patients with complete scraping of the lesion, high-speed grinding and polishing of the residual cavity, liquid nitrogen freezing, and reconstruction with autologous or allogeneic bone and bone cement filling after inactivation of the tumor cavity, with a recurrence rate of 6.9%. In 2009, Abdelrahman reported 28 patients with periarticular osteoblastoma of the knee treated with tumor scraping, high-speed abrasive drilling of the residual cavity, cryotherapy, and compression bone grafting combined with bone cement filling, with a recurrence rate of 4% (1/ 28). According to the description of cryotherapy by Marcove in 1978, the following steps should be followed for cryotherapy of giant cell tumor of bone: (1) Adequate visualization of the tumor cavity. (2) Thoroughly and adequately scrape the tumor and repeatedly polish the residual cavity. ③Draw away and protect the surrounding soft tissues. ④ Liquid nitrogen freezing treatment of the tumor cavity. ⑤Postoperative tumor cavity filling and internal fixation. ⑥After cryotherapy, the bones should be protected to avoid fracture. The tumor of the limb should preferably be operated under a tourniquet to reduce bleeding and blood circulation leading to a decrease in the effect of freezing. With the development of cryotherapy, the principles and basic research on cryotherapy have been gradually developed. Studies have shown that rapid freezing and slow rewarming can lead to tissue destruction and kill tumor cells. The use of liquid nitrogen for rapid freezing and slow rewarming can lead to the formation of intracellular ice crystals, resulting in cell membrane rupture causing cell death. The principle of cryotherapy can be summarized as the following 5 parts: 1) temperature shock; 2) electrolyte alteration; 3) intracellular ice crystal formation and cell membrane rupture; 4) denaturation of cellular proteins; 5) microcirculatory alteration (. Studies have shown that repeated rapid freezing and slow rewarming after 3 cycles can increase the surgical border by up to 2 cm, and the therapeutic effect is equivalent to marginal resection. After cryotherapy, the induced necrotic bone tissue can slowly heal and new bone formation can occur, finally completing the shaping process. Care should be taken to protect the surrounding tissue during cryotherapy. When pouring liquid nitrogen directly into the tumor cavity, it is important to avoid damage to the surrounding soft tissues due to spillage of liquid nitrogen. Postoperative complications of cryotherapy with liquid nitrogen have been reported to range from 12% to 50%, including postoperative fractures, skin necrosis, transient nerve palsy, and infection. The incidence of fracture can be reduced by using bone cement filling or internal and external fixation after cryotherapy, and the high rate of fracture complications after cryotherapy reported earlier was mainly due to the absence of bone cement filling or internal fixation. In 1977, Bangfu Kao introduced cryotherapy to treat giant cell tumor of bone in China. The large number of cases reported in China using cryotherapy was reported by Liuyin et al. in 2007, who reported 116 patients with giant cell tumor of the limb treated with lesion scraping, of which 71 patients were treated with liquid nitrogen freezing combined with internal fixation of bone graft, and the other 46 lesions were scraped and then inactivated by electrocautery phenol and cement filling. The postoperative follow-up was 72.5 and 62.8 months, respectively, with recurrence rates of 5.6% and 4.4% in both groups. The study showed that both cryotherapy and phenol inactivation are effective methods for inactivation of giant cell tumors of bone. Guo Shifang et al. 1999 reported the treatment of 48 patients with giant cell tumor of the limb by cryotherapy, and the local recurrence rate was 12.5% after a mean follow-up of 54 months.