Current Situation and Prospects of Radiofrequency Ablation in Bone Tumor Treatment Radiofrequency Ablation (RFA) is a rapidly developing non-vascular interventional technique in recent years, especially in the minimally invasive treatment of tumors. It is widely used in solid tumors, such as liver tumors, to kill tumor cells by coagulation and necrosis of tumor tissues in a certain area around the electrode due to thermal damage caused by the ionic oscillation of the electrode (350 -500 kHz). The complexity of spinal anatomy makes the surgical treatment of spinal tumors difficult. In recent years, some scholars have explored the application of image-guided radiofrequency technology to the treatment of some spinal tumors with good results, which provides a new way for the minimally invasive treatment of spinal tumors. This article summarizes the progress of radiofrequency ablation technology in the treatment of spinal tumors in recent years and discusses the application of radiofrequency ablation technology in the treatment of osteoid osteoma of the spine, palliative treatment of osteolytic metastatic carcinoma of the spine, treatment of multiple recurrent refractory primary spinal tumors and intraoperative adjuvant treatment of spinal tumors. 1.Radiofrequency ablation technology applied to spinal osteoid osteoma The main clinical manifestation of spinal osteoid osteoma is pain and limitation of daily activities, and the tumor is composed of nucleus and peripheral reactive bone. The main goal of treatment is to relieve clinical symptoms and prevent recurrence. Surgical scraping or en bloc resection is the main treatment method for this tumor [2]. In recent years, radiofrequency ablation technique has been applied to osteoid osteoma of the spine, and its characteristics such as less trauma, rapid pain relief and similar recurrence rate as surgical treatment have led to its wide application. Osti et al [3] first applied RFA technique to treat a case of osteoid osteoma of the spine, the tumor was located in the L4 adnexa, and the Radionics RFG-6 system was used with a set temperature of 85°C and an ablation time of 4 minutes, and the patient had significant pain relief and no recurrence on imaging for 16 months of follow-up.Dupuy et al [4] applied the Radionics RF system to treat a case of T11 arch osteoid osteoma In one case of osteoma, the setting temperature was 90°C, the ablation time was 6 minutes, the pain was completely relieved after the procedure, and the CT examination showed that the tumor had healed at 8 months of follow-up. The authors concluded that the reactive bone and intact cortical bone around the tumor nucleus can effectively block the heat transfer into the spinal canal, while the intravenous plexus and cerebrospinal fluid circulation in the spinal canal can take away part of the heat and prevent thermal damage to the spinal cord. At the same time, it is proposed that the nucleus of osteoid osteoma is generally less than 12 mm, and the tumor can be ablated well by using ordinary monopolar radiofrequency electrodes. cove et al [5] reported in 2000 that the Radionics radiofrequency system was applied to treat 2 patients with L3 vertebral plate and transverse process osteoid osteoma with a setting temperature of 90℃ and ablation time of 4 minutes, with no operational complications and no recurrence of pain relief for 2 years of follow-up. Hadjipavlou et al [6] reported in 2003 two patients with osteoid osteoma of the spine treated with RFA, one at the superior L4 synovial process and one at the T9 pedicle, using the Radionics system with a set temperature of 90°C and an ablation time of 4 minutes, with no significant complications and no recurrence of pain disappearance at 2.5 to 3 years of follow-up. Samaha et al [7] reported in 2005 that RFA treated three cases of osteoid osteoma of the spine adjacent to nerve roots and spinal cord structures in three cases, one case located at the posterior edge of the T8 vertebral body separated from the spinal canal only by a thin layer of bone, one case located at the superior C6 articular eminence, immediately adjacent to the C7 nerve root, and one case located at the superior L5 articular eminence, immediately adjacent to the L4 nerve root. The radiofrequency temperature was set at 90°C and the ablation time was 4 minutes, and there was no obvious neurological impairment. The average follow-up of the 24 patients was 72 months. 16 patients had tumors close to the spinal nerve structures (less than 1 cm from the spinal nerve roots) and were treated with a 5-mm radiofrequency electrode, with a set radiofrequency temperature of 90 degrees and a radiofrequency time of 4 minutes. 79% of the first radiofrequency treatments were successful, and 96% of the total radiofrequency treatments were performed again for recurrence or poor outcomes after radiofrequency ablation. In addition, except for one patient who developed radicular symptoms after recurrence and underwent surgery, the results of the remaining patients were satisfactory and there were no operation-related complications. The authors concluded that RFA is safe and reliable for osteoid osteoma of the spine, and that re-ablation can still achieve satisfactory results in recurrent cases, but surgery is still recommended for those who show neurospinal compression or whose tumor margins are within 2 mm of the spinal nerve roots. Most authors agree that radiofrequency ablation can achieve the same results as surgery for osteoid osteoma. Rosenthal [9] et al. reported a controlled study of 68 cases of osteoid osteoma of the extremities treated with open surgery and 33 patients treated with radiofrequency ablation, and the average follow-up for the radiofrequency ablation group was 3.4 years, with a recurrence rate of about 12%, which was comparable to that of open surgery. This author reported in 2003 that 271 patients with osteoid osteoma treated with radiofrequency ablation 126 patients who received more than 2 years of follow-up had 89% symptom remission rate and 91% symptom remission rate in primary patients, and only 2 cases of operation-related complications occurred, 1 case of cellulitis and 1 case of sympathetic dystrophy. Radiofrequency treatment of osteoid osteoma is considered to be a safe and efficient minimally invasive method suitable for the treatment of most osteoid osteomas [10]. However, osteoid osteoma accumulated in the spine is relatively rare, accounting for only about 10% of cases, the literature reports fewer cases, the lack of randomized controlled studies with surgical treatment, and because of the proximity of the spinal nerve, there is a possibility of thermal damage to nerve tissue, in recent years some scholars have done a lot of useful exploration on the prevention of thermal damage to the spinal nerve during radiofrequency, Vanderschueren [8] summarized 24 cases of spinal osteoid osteoma radiofrequency Vanderschueren [8] summarized the experience of 24 cases of spinal osteoid osteoma with radiofrequency radius of 5 mm that the non-circulating water-cooled radiofrequency electrode could better control the ablation range, reduce the unnecessary ablation area, and prevent the possibility of thermal injury to the nerve spinal cord by excessive ablation range. Klass [11] reported that in seven patients with spinal osteoid osteoma treated with radiofrequency, the ablation process was performed by continuous warm saline perfusion to the paramedian nerve root and epidural to prevent spinal nerve thermal injury. At the outlet, 10 ml of normal temperature saline was injected through the 26G cannula before the start of RF to distribute it around the nerve root and the adjacent epidural space to start ablation, and the injection was repeated every 30 seconds to prevent neurospinal thermal injury. After the operation, 1-3 ml of 0.5% bupivacaine was injected through a 26G cannula with a view to relieving neurogenic symptoms. And 7 patients were treated with this method without complications of neurothermal injury. Compared with traditional surgical resection, radiofrequency ablation has the advantages of safety, high efficiency and few complications in the treatment of osteoid osteoma [8, 10], but the long-term efficacy needs to be further verified [8]. 2, RF ablation technology applied to the palliative treatment of osteolytic spinal metastases Bone metastases in the spine are the most common spinal tumors, and pain is the most common first symptom, accounting for about 90-95% of patients. Pain caused by metastases is often severe and unbearable seriously affecting the quality of patients’ daily life, so relieving pain and improving long-term survival are equally important goals [12]. Some patients are not sensitive to conventional radiotherapy for pain relief, and such patients are often unable to increase the dose of radiotherapy. The side effects of high-dose opioid analgesics often greatly affect the quality of patient survival. In recent years, some scholars have applied radiofrequency ablation to the palliative analgesic treatment of spinal metastases, and some authors have combined radiofrequency ablation and vertebroplasty (PVP) for the treatment of advanced spinal metastases to relieve patients’ pain and improve their survival quality. Dupuy [4] et al. first reported the application of radiofrequency ablation technique in 2000 for the treatment of a patient with malignant hemangiopericytoma L2 vertebral metastasis, in which the patient had intact bone cortex at the posterior edge of the vertebral body, and the radiofrequency ablation time was set at 12 minutes under local anesthesia combined with basic anesthesia using Radionics 3cm Cool-Tip radiofrequency electrode, and no operation-related complications occurred, and the patient was followed up for 13 months with symptoms There was no recurrence, but new sacral metastases appeared. The authors pointed out that the intact bone cortex and cancellous bone between the tumor and the spinal cord can effectively prevent the heat transfer during the RF process, and RF treatment is relatively safe for those with intact bone cortex at the posterior edge of the vertebral body.Gronemeyer et al [13] reported 10 cases of spinal metastases treated with CT-guided RF ablation, operated under simple local anesthesia, applying the temperature control mode of RITA multipolar RF electrode, setting the temperature The mean follow-up was 5.8 months, and the pain relief was assessed by VAS score. 90% of the patients showed significant pain relief, with a mean pain reduction rate of 74.4%, and the Frankel score remained the same in 9 cases and improved in 1 case compared with the preoperative period. No tumor regrowth was seen in the ablated area. The authors concluded that radiofrequency ablation is a safe and effective minimally invasive treatment for unresectable spinal tumors that are not sensitive to radiotherapy, and suggested for the first time that radiofrequency ablation combined with vertebroplasty could have a synergistic effect on pain relief. 2003 Schaefer et al [20] first reported a case of L3 vertebral metastasis from renal cell carcinoma treated with RF3000 radiofrequency ablation system from RadioTherapeutics, using impedance control mode under general anesthesia, with energy rising gradually from 40w to 10w every 3 minutes until the impedance rose to 45 ohms and the current could not flow further through the tissue. The patient was discharged after 24 h with no restriction in daily activities and no signs of nerve damage. The authors concluded that radiofrequency destroyed the blood vessels of the tumor and increased tissue homogeneity in the radiofrequency area, which facilitated the distribution of the bone cement and prevented it from leaking or entering the drainage vein. Nakatasuk et al [14] reported 17 patients with 23 malignant bone tumor lesions treated by radiofrequency ablation combined with vertebroplasty, 17 of which involved spinal lesions, 2 of which invaded the posterior wall of the vertebral body and 13 invaded the pedicle. The patient complained of radiological pain, and the operation was stopped immediately to prevent nerve injury. The success rate of postoperative technique was 96% (22/23), one osteogenic lesion failed to place radiofrequency electrodes, and the VAS score of 13 patients complaining of pain decreased from an average of 8.4 preoperatively to 1.1 one week postoperatively. MRI showed that the postoperative tumor necrosis rate ranged from 14% to 100% (71% ± 24%), and there was a significant difference in the necrosis rate between tumors smaller or larger than 5 cm (78% ± 23%: 59% ± 22%). Five patients had recurrence of pain, two had in situ tumor growth, three had new metastases, and six died during follow-up within one year. four patients had nerve damage during radiofrequency treatment (three had cortical destruction at the posterior margin of the vertebral body and one had invasion of the pedicle), three patients improved after treatment, and one had persistent symptoms. The authors concluded that the release of heat during cement sclerosis had a synergistic effect on radiofrequency thermal ablation, and that the recurrence of pain due to in situ tumor regrowth in two patients, both with tumor diameters greater than 5 cm, suggested that radiofrequency treatment of large tumors (diameter greater than 5 cm) was inadequate and that radiofrequency ablation was not indicated for the treatment of osseous bone tumors. For cases with vertebral cortical damage or tumors near spinal nerve root structures, the risk of neurothermal injury due to radiofrequency ablation is great. The initial power was 50W, rising by 10W per minute until the current could not flow further. The pain relief rate was 100% with no significant complications. This author suggested that radiofrequency for patients with incomplete posterior wall of vertebral body should avoid radiofrequency of tumor tissues in the posterior wall region of vertebral body to prevent the occurrence of neurospinal thermal injury, and also believed that the tumor tissues of patients with high-dose chemotherapy have higher impedance, which makes it difficult to reach the expected temperature of radiofrequency, and the ablation effect is poor. The authors also believed that the combination of vertebroplasty cement sclerosis and heat generation had a synergistic effect on radiofrequency thermal ablation, while the cement strengthened the stability of the spine to prevent pathological fractures and improved the quality of life of patients. der Linden et al [16] reported 12 cases of spinal tumors with vertebral body posterior wall rupture treated with radiofrequency combined with vertebroplasty. The authors selected 12 patients with osteolytic bone destruction in the cervicothoracic and lumbar spine who were older than 18 years old, with two lesions or less, and whose previous treatment was ineffective, and performed radiofrequency ablation under basic anesthesia and local anesthesia for pain associated with vertebral posterior wall destruction or pathological fracture. The RITA multi-polar radiofrequency electrode and Radionics cool-tip radiofrequency electrode were used. The output power of RITA system was set at 150W, the temperature was set at 100℃, the ablation time was 10 minutes, and if the patient complained of pain, the ablation time was extended by 10℃, and if the temperature of the electrode was lower than 60℃ after the ablation, the ablation time was extended by 5 minutes. If the temperature of the radiofrequency head is lower than 60 ℃, the ablation is extended for 5 minutes, and then the other side of the arch is ablated by the same procedure. The pain relief rate was 92% at one week after the procedure. only 6 patients were followed up after 3 months, the other 6 died of primary disease in 4 cases and 2 cases were lost to follow-up. No significant complications occurred. The authors concluded that none of the 12 patients with posterior wall injury had significant neuromuscular injury for the following reasons: 1, the rate of spinal canal encroachment in the enrolled patients was controlled to less than one-third, and only 3 of the 12 patients had intradural encroachment; 2, technical reasons, awake anesthesia can obtain direct feedback from patients, and patients with pain sensation are prevented from nerve injury by reducing radiofrequency temperature and energy; 3, avoiding the use of RF near the spinal cord and nerve root region.Nakatsuka et al [17] reported 10 cases of radiofrequency treatment for painful spinal tumors under real-time temperature-controlled monitoring in the spinal canal. For 10 patients with spinal tumors within 1 cm of the spinal cord for which radiotherapy and chemotherapy surgical methods were ineffective, radiofrequency ablation was used, using basic anesthesia with local anesthesia and Cool-Tip radiofrequency electrodes, while another thermometric electrocouple with a temperature probe was placed into the epidural space between the tumor and the dura through a 21G puncture needle to monitor the temperature change of the epidural space in real time, and the temperature exceeding 45°C was The ablation will be stopped immediately if the temperature exceeds 45℃. In 9 patients, the monitored temperature did not exceed 45℃, and in 1 patient, RF treatment was stopped immediately after reaching 45℃, but the intradural temperature eventually reached 48℃ and showed transient spinal cord damage, which was relieved after 2 days of conservative treatment. The VAS score decreased from 7.5 ± 2.7 to 2.7 ± 2 at 1 week after surgery, and all patients died after 4.5 ± 1.3 months of follow-up. 1 patient had a recurrence of pain and 2 patients had new lesions causing pain. 6 of 10 patients had the temperature-controlled probe mistakenly inserted into the subarachnoid space, suggesting that the placement of the temperature-controlled probe in the epidural space is meaningful to prevent thermal injury to the spinal cord during ablation, but it is difficult to operate. It is now generally believed that the pain relief principles of radiofrequency ablation for painful bone metastases are as follows: 1) destruction of tumor margins and subperiosteal nerve endings; 2) ablation of tumor to reduce tumor secreted cytokines; 3) stabilization of spinal structure to reduce the chance of pathological fracture and destruction of intraosseous microstructure [1]. For unresectable osteolytic bone metastases that cause significant pain, radiofrequency ablation therapy can rapidly relieve patients’ pain and improve their quality of life [1, 5, 13-17]. However, although radiofrequency ablation has a significant effect on local tumor control, it has little significance in improving long-term survival of patients [16, 17]. And some scholars [18, 19] believe that the extent of tumor ablation is not necessarily related to pain relief. Radiofrequency treatment of tumors with posterior wall breach and arch root invasion has the risk of damaging the spinal cord and nerve roots, which is considered by some scholars as a contraindication [1], and some scholars believe that maximum tumor ablation can be achieved under intracanal temperature monitoring [17]. The application of radiofrequency ablation alone for the treatment of osteolytic metastases of the spine in combination with vertebroplasty lacks randomized controlled studies. The complexity of spinal anatomy and the proximity of important structures such as spinal nerve roots often result in incomplete surgical resection, and some junctional or low-grade malignant primary spinal tumors are less sensitive to radiotherapy and have a higher rate of local tumor recurrence, making reoperation difficult or difficult for patients to tolerate reoperation. Some scholars have explored the use of radiofrequency ablation to treat some of the multiple recurrent refractory primary spinal tumors with good results. Chordoma is the most common primary spinal malignancy, and surgical resection combined with radiotherapy or proton radiotherapy is commonly used, but the extremely high local recurrence rate and the difficulty of reoperation after multiple surgeries make the treatment of this disease very difficult. The tumor recurred and increased progressively after postoperative radiotherapy, and was ablated with Cool-Tip radiofrequency electrodes under basic anesthesia combined with local anesthesia. The authors suggested that radiofrequency ablation is a minimally invasive treatment option in addition to conventional surgery and radiotherapy for chordoma that causes significant pain and rapid growth.Anis et al [21] reported two cases of recurrent sacral chordoma treated with radiofrequency ablation. One patient was unable to relieve the pain with 120 mg/d of oral morphine, so radiofrequency ablation under general anesthesia was used and the patient left the hospital after 48 hours of observation. The patient’s MRI follow-up revealed no regrowth of the tumor in the RF region, but the tumor in the non-RF region was still growing rapidly. Radiofrequency ablation is a safe and efficient minimally invasive treatment option for recurrent spinal primary tumors that are difficult to resect and insensitive to radiotherapy [20, 21]. 4, adjuvant application of radiofrequency ablation technology in spinal tumor surgery Li Haomiao and Gasbarrini [24] reported 11 cases of spinal metastases treated with radiofrequency ablation followed by tumor curettage. The single ablation time was set at 12 minutes, power 150w, and upper temperature limit 100℃. The dural sac and nerve roots were fully exposed in the posterior approach first, and the radiofrequency electrode was placed to the lesion via the arch under X-ray guidance, and the radiofrequency ablation was performed under a large amount of saline flushing of the dura and nerve roots. The authors believe that tumor tissue consolidation and vascular occlusion after radiofrequency ablation can reduce bleeding during the scraping process and improve the completeness and safety of tumor removal. The risk of neurospinal cord thermal injury during radiofrequency ablation of spinal tumors The application of radiofrequency ablation technology to spinal tumors is significantly later than that to the long bones of the extremities, and the concern for neurospinal cord thermal injury is the main reason. Dupuy et al. [3] confirmed that the temperature transfer in the vertebral body during radiofrequency ablation was much lower than that in the paravertebral muscles. Much lower than the transfer in the paravertebral muscle, the same RF temperature and time in the vertebral body and paravertebral muscle 5 mm, 10 mm and 15 mm away from the RF electrode were detected as 48°C, 41°C and 39°C, 84°C, 62°C and 58°C, respectively (p<0.01). It is believed that cancellous bone can effectively reduce the heat transfer in RF, and the intact bone cortex is a good isolator of heat. It is also believed that the abundant epidural venous plexus and unobstructed cerebrospinal fluid circulation can take away some of the heat, further reducing the temperature of the epidural space. Radiofrequency treatment that ensures the intact cancellous bone and bone cortical structures between the tumor tissue and the spinal canal will be safe. According to some scholars, radiofrequency ablation will be safe and reliable to ensure that the tumor edge is more than a certain distance from the neurospinal cord tissue and the bone cortex is intact. Goetz et al [1] believed that radiofrequency ablation can be performed only when the tumor edge is more than 1 cm away from the spinal cord according to 43 cases of radiofrequency ablation of painful bone metastases, but in clinical practice, most spinal metastases are accompanied by intradural invasion of the posterior wall of the vertebral body or the spinal canal. For example, short-acting intravenous anesthesia midazolam and fentanyl are used in combination with local infiltration anesthesia to ensure that the patient is awake and receives good analgesia during the operation, and if the patient complains of radiating pain and numbness and other signs of neurothermal injury during the radiofrequency process, the ablation process is stopped immediately or the ablation energy is reduced to avoid ablating the tumor adjacent to the spinal nerve tissue. As mentioned above, some scholars have used temperature monitoring electrodes around the RF area [17] or interventional perfusion methods to reduce the temperature of the neurospinal structures around the RF target tissues [11], which has achieved good results. Although there is a potential risk of spinal cord thermal injury, it is believed that with the advancement of technology and equipment, radiofrequency ablation will have a greater application in the comprehensive treatment of spinal tumors. It is believed that with the advancement of technology and equipment, radiofrequency ablation will have a greater prospect of application in the field of comprehensive spinal tumor treatment.