Spinal metastases are the most common bone metastases, and about 40% of cancer patients die with spinal metastases, most often in the thoracic spine (70%), followed by the lumbar spine (20%), and again in the cervical spine (10%). Due to the rich blood supply of cancellous bone in the vertebral body, spinal metastasis is slow to occur. Because of the slow blood flow, 85% of spinal metastases are located in the vertebral body and occur first in the posterior half of the vertebral body (1), therefore, spinal metastases often cause vertebral fractures, spinal instability, spinal cord and nerve root compression and other comorbidities. In patients with spinal metastases, the tumor destroys the vertebral body, decreases spinal stability, impairs robustness, causes microfractures, and leads to traumatic inflammation. At the same time, tumor infiltration and distending growth stimulate peripheral nerve endings, often accompanied by severe pain, which is difficult to be relieved by the application of analgesics. (2). Many of the patients have experienced surgical treatment, radiotherapy, chemotherapy and other treatments for the primary foci, and their general condition is relatively poor, so it is difficult to bear the surgical blows such as vertebral body resection, bone grafting and internal fixation, which will lead to the prolongation of the postoperative recovery period and make the complications significantly higher, further leading to a significantly higher mortality rate; conservative treatment is not effective, and long-term bed rest due to pain may produce pulmonary atelectasis and pneumonia and deep vein thrombosis, etc. Complications. The advent of percutaneous vertebroplasty has provided a new approach to the treatment of spinal metastases. Percutaneous vertebroplasty (PVP) is now an effective treatment for benign and malignant vertebral tumors and osteoporotic vertebral compression fractures, and the use of its counterpart, percutaneous kyphoplasty (PKP), which can be performed under local anesthesia, is rapidly increasing. Both can be performed under local anesthesia by injecting bone cement into the vertebral body to increase the strength of the vertebral body, restore part of the vertebral body height, relieve pain, and prevent vertebral fractures and resulting complications; they can also be used in conjunction with posterior spinal internal fixation surgery and radiotherapy, the most important purpose of which is rapid pain relief and symptom relief, and are essentially minimally invasive palliative procedures. Indications and contraindications: Indications for surgery include: (1) osteolytic lesions; (2) complete posterior margin of the vertebral body; (3) causing severe pain; (4) no clear spinal cord compression and nerve root compression; (5) prophylactic PVP. Contraindications include: incomplete posterior wall; with spinal cord and nerve root compression; complete collapse of the vertebral body; uncontrolled local or systemic infection; those with significant coagulation abnormalities; those with allergy to bone allergy to cement or contrast components. The choice of treatment for spinal metastases depends on the histological type of the primary tumor, the neurological status prior to treatment, the number of involved vertebrae, the level of the vertebral body, the location of the lesion within the vertebral body, and the patient’s general condition and severity of pain (3). However, there have long been many controversies regarding the surgical treatment of spinal metastases, and there are two commonly used scoring systems to make an assessment of the prognosis of patients with spinal metastases and to decide on the surgical approach. In a retrospective study of 67 patients with spinal metastases, Tomita et al. The risk ratios for each of the three important prognostic factors of primary tumor site, visceral metastasis and bone metastasis were calculated and used as the risk ratio score. The risk ratios were used as scoring scores to make the scoring system more statistically based. According to the different scores and the life expectancy of patients, the corresponding treatment goals and treatment strategies were formulated: (1) Those with Tomita scores of 2 to 3. Life expectancy is long. Surgical treatment is aimed at long-term local control of spinal metastases, with extensive or marginal tumor resection of the tumor vertebral body; (2) those with a Tomita score of 4 to 5. For medium-term local control of the tumor, marginal or intracapsular tumor resection is feasible; (3) for those with scores of 6 to 7, short-term palliation is the goal, and palliative decompression and stabilization surgery is feasible; (4) for those with scores of 8 to 10, hospice supportive care is the main treatment and surgery is not appropriate (4). Tokuhashi et al. mentioned a comprehensive score based on six items, including general condition, number of extra-spinal metastases, number of involved vertebrae, visceral metastases, primary tumor site and neurological function in patients with spinal metastases, with O to 2 points each and a total score of 12. The higher the score, the better the prognosis. If the Tokuhashi score is greater than or equal to 9, surgery is recommended; if the score is less than 5, surgery is not recommended, and palliative treatment such as radiotherapy, pain relief and symptomatic support can be considered. Several years later, on the basis of the original scoring system. The scoring of primary tumor site was more refined and increased from 2 to 5 points, while the other 5 scoring methods remained unchanged and the total score was increased from l2 to l5 points. In the Tokuhashi modified scoring system. Total scores of 0-8, 9-l1, and l2-l5 predicted a patient’s life expectancy of less than 6 months, 6-12 months, and more than 12 months, respectively. Later Tokuhashi et al. conducted a prospective study of 118 patients with spinal metastases using a modified scoring system, and their life expectancy was in accordance with the actual survival time of 86.4% (5). Although the Tokuhashi score provides a relatively objective and quantitative description of the prognostic assessment and surgical indications for spinal metastases. However, the choice of specific surgical modality has not been studied in depth. Therefore, in those with a Tomita score of 6-7 or a low Tokuhashi score, enhancing the stability of the diseased spine and relieving pain are the primary goals in the treatment of osteolytic metastases in the spine. Percutaneous translaminar vertebroplasty, a minimally invasive procedure, is an excellent choice for this purpose. Vertebroplasty can also be used for vertebral metastases, but the pressure of the balloon must be controlled to be significantly less than the pressure used to treat vertebral compression fractures due to osteoporosis. Because excessive pressure can squeeze the tumor tissue and accelerate the tumor spread. Xu Yuegan et al. applied a pressure of 100 PSI (1PSI=6, 8948KPa) (6). Choice of puncture approach and position Cervical spine: C1 and 2 vertebrae through the posterior wall of the oropharynx; the anterolateral approach was chosen for the median and inferior cervical spine (7). For the thoracic spine, the puncture approach is via the head of the rib – intervertebral arch or arch root, etc. The lumbar spine is accessed via the pedicle or paravertebral arch. The lateral position under fluoroscopy is ideal for reaching the anterior 3/4 of the vertebral body or the center of the lesion with the puncture needle. Bilateral or unilateral arch puncture may be used. Some scholars believe that unilateral arch root puncture restores the same strength, height, and stiffness of the vertebral body as bilateral puncture, and that unilateral puncture is less risky, shorter in operative time, shorter in radiation exposure time, and less expensive (8). Position: supine for the cervical spine and prone for the thoracolumbar spine. Filling material The ideal filling material for vertebroplasty should have the following characteristics (9): (1) good visualization ability; (2) easy modulation and easy injection; (3) suitable polymerization temperature; (4) operation time of 6-10 min and solidification time of about 15 min; (5) good biomechanical properties; (6) non-toxic; (7) excellent osteoconductivity and osteoinductivity; (8 ) suitable resorption rate; (9) good biocompatibility and bioactivity; (10) reasonable price; in addition, the filling material should be suitable as a carrier for some drugs and bioactive materials with slow release. However, for vertebral metastases, polymethylmethacrylate (PMMA) bone cement is currently used as the representative, which has many advantages, including easy modulation, low price, and good biomechanical properties. Although it is not biodegradable in vivo, has no potential for integration into surrounding bone, and has no direct bone attachment, this property is not necessary for vertebral metastases, and its high polymerization temperature and potential monomeric toxic effects may be beneficial for vertebral metastases. In the treatment of metastases, the literature has shown good analgesic results with PMMA (10)(11). The mechanism of pain relief after PMMA application remains unclear; the pain relief mechanism of PMMA may be (1) strengthening and stiffening of the vertebral body; (2) polymerization heat generated by PMMA and its own chemical toxicity may reach tumor necrosis and destroy the sensory nerve endings of the vertebral body; (3) bone cement isolates the tumor tissue from the feeding vessels, causing ischemic necrosis, (12);. The osteothermal necrotic effect of PMMA is still a hypothesis, and so far, there is no obvious evidence to support this (13)(14). San et al. (15) found a 3-11 mm wide necrotic area of tumor cells in and around the PMMA-filled area in an autopsy study of a patient with vertebral metastases, suggesting that PMMA does have an inactivating effect on tumor cells. In a study of vertebroplasty in baboons, some necrotic bone fragments were noted in the injected vertebrae, but it was not clear whether this necrosis was due to PMMA (13). PVP is usually performed under imaging surveillance, so the filler material must be radiopaque so that traces of the filler material can be tracked, detecting and avoiding neurological or other tissue damage caused by leakage of the filler material. Due to the poor development of PMMA itself, barium sulfate is often added as a co-developer. The bone cement used for standard joint reconstruction (which contains 10% barium sulfate by mass) is not sufficient for vertebroplasty, so more barium sulfate is added to the bone cement, and as the percentage of barium sulfate in the powder increases, the x-ray visualization ability of the bone cement is significantly improved, but the mechanical properties of the bone cement are reduced. Chen Long et al. confirmed that the bone cement with 20% barium sulfate could provide satisfactory visualization ability, and at the same time, it could effectively strengthen the diseased vertebrae and relieve the patient’s symptoms. (16) Injection volume Sun K et al. (17) studied the biomechanical mechanism of vertebral body strengthening by vertebroplasty and found that bone cement injection volume up to 20% of the intracortical space volume of the vertebral body could effectively prevent compression fractures with high risk factors, and the ability to prevent fractures was evident when the bone cement injection volume reached 5%-15%. thoracolumbar segment and each vertebra of the thoracic spine required at least 4, 4 ml, 3, 1 ml and 2, 5 ml of bone cement to restore the strength of the vertebral body. For pain caused by metastatic tumors Afshin Gangi (19) concluded that 1.5 ml of bone cement injection was sufficient to achieve satisfactory pain relief. This indicates that the degree of pain relief is not positively correlated with the amount of bone cement used. Akio Hiwafashi et al. (20) studied the correlation between vertebral body height restoration and pain relief and found that there was no necessary correlation between the degree of vertebral body height restoration and clinical pain relief. Molloy, S et al. injected 2-8 ml of bone cement into 120 vertebral bodies (T6-L5) and found that the volume injected was only weakly correlated with the recovery of vertebral compressive strength and stiffness (r2 0,121 and 0,127, respectively), and that the recovery of compressive strength and stiffness required an average of 16,2% and 29,8% of the volume injected into the vertebral body (21). However, Liebschner et al. (22) reported that the restoration of vertebral stiffness after vertebroplasty was related to the amount of cement injected, with 14% of the volume of cement injected meeting the requirements for stiffness restoration, and 30% of the volume of cement injected resulting in a significant increase in stiffness and an increased risk of fracture in the adjacent vertebral body. Cotton et al. concluded that the average volume of bone cement injection is 2-15 ml, with an average of 2.5 ml for the cervical spine, 5.5 ml for the thoracic spine, and 7.0 ml for the lumbar spine (23). The experience of Zheng Zhaomin et al. (24) is that the injection of bone cement in the thoracic spine within 3 ml and in the lumbar spine within 5 ml can achieve satisfactory results, and the leakage rate is extremely low, which is safe and effective in clinical practice. Efficacy PMMA injected into the vertebral body can significantly strengthen the vertebral body, reconstruct and stabilize the spine, relieve the compression on the spinal cord and nerve roots, and prevent the deterioration of neurological function. Moreover, its local heat production and possible monomer production have anti-tumor effects, which reduce the local tumor load and thus mitigate the destruction of bone by the tumor and prevent the further expansion of metastases. Domestic and international studies have shown that the pain relief rate of PVP applied to spinal malignancies is 88.7%-98.5% in a short period of time (25) (26) (27); Wang et al. followed up 17 patients with bone metastases for 3-17 months, and the stable non-progression rate of lesions reached 82.4% (29). Complications 1. Leakage of bone cement: relatively common, reported as 20%-67%, positively correlated with the amount of injected bone cement; due to the destruction of vertebral bone in tumor patients, the proportion of bone cement leakage is higher during PVP, mainly to the paravertebral soft tissue, intervertebral space, epidural, intervertebral foramen and vertebral vein, but most of them have no clinical symptoms, and 4% may show symptoms of neurogenic lesions, and not all bone cement leakage will cause serious consequences (28). Not all cement leaks cause serious consequences (28), only 0.15% of patients have cement leakage into the epidural space or intervertebral foramen, compressing the nerve roots or spinal cord, resulting in neurological dysfunction and requiring surgical decompression. 2, nerve root or surrounding tissue thermal injury, resulting in a transient increase in pain, can be relieved by symptomatic treatment of drugs. 3.Pulmonary embolism: rare, mainly seen in lesions with rich blood supply and rapid drainage, premature injection of bone cement or puncture needle located in the vertebral vein, mostly without clinical symptoms. 4, infection: rare. In summary, vertebroplasty can rapidly and effectively relieve the pain of patients with vertebral metastases, reconstruct and stabilize the vertebral body, better strengthen the vertebral body, and delay the development of bone metastases, with simple operation, short operation time, little trauma, relatively few complications, and can be used in combination with posterior spinal surgery and radiotherapy and chemotherapy, which can significantly improve the survival quality of patients and has been affirmed by clinical evidence-based medicine. Due to the good clinical results of bone cement, cementoplasty has now been developed to extend it to metastases in the pelvis, sacrococcygeal region and extremities. With the advancement of imaging-assisted technology, improvement of surgical instruments, and the development and application of new bone cements, this technique will be further improved and developed.