The incidence of spinal metastases is 30-40% in patients with malignant tumors, and more than half in patients with prostate cancer and breast cancer. Spinal metastases can affect the strength of the spine and cause spinal instability, which can lead to nerve root or spinal cord compression as the disease progresses. Spinal metastases that cause epidural spinal cord compression (ESCC) occur in 40% of all patients with malignancies. The goal of treatment for spinal metastases is to relieve pain, improve neurological symptoms, maintain spinal stability, and improve the patient’s quality of life. With effective treatment, patients with metastatic spinal cancer are able to maintain ambulatory function for a limited survival period, which is the goal of treatment for metastatic spinal cancer that relies on local control of the spinal metastases. Conventional treatment modalities are limited to surgery or/and radiotherapy, lacking assessment of the patient’s primary tumor and systemic condition. Currently, integrated multidisciplinary treatment is the main treatment modality for metastatic spine cancer, which includes disease assessment systems, surgical treatment, radiotherapy and drug-targeted therapy. In recent years, with the advancement of radiotherapy, segregation surgery [4-7] has been proposed in the treatment of metastatic spine cancer, which is a new concept in the surgical treatment of metastatic spine cancer. The choice of treatment options for metastatic spine cancer depends on the effectiveness of various treatment methods. In the 1970s, surgery had no significant advantage over radiotherapy in improving spinal stability due to the limited availability of internal spinal fixation materials, and postoperative follow-up revealed that the therapeutic effect of surgery was similar to that of conventional radiotherapy. However, with the development of internal spinal fixation devices and the gradual maturation of spinal surgery technology, the effect of surgical intervention has significantly improved, so surgery is playing an increasingly important role in the treatment of metastatic spinal cancer. [7] Surgical procedures can improve spinal stability, relieve nerve compression, and relieve neurological symptoms, while radiotherapy provides local control of the tumor. In the era of conventional radiotherapy, the decision-making process of spinal metastatic cancer treatment protocols classified tumors according to their sensitivity to radiotherapy. For radiotherapy-sensitive tumors, radiotherapy can achieve satisfactory local tumor control, which includes myeloma, lymphoma, small cell malignancies, lung cancer, and breast cancer, for which the 2-year local control rate of radiotherapy can reach 80-98%. However, for tumors that are not sensitive to radiotherapy, such as kidney cancer, thyroid cancer, liver cancer, colorectal cancer, non-small cell lung cancer, etc., conventional radiotherapy can only achieve 30% local control of the tumor. Therefore, surgical resection still has an active role for spinal metastases that are not sensitive to radiotherapy. In the comprehensive treatment of spinal metastatic cancer, the systematic assessment of the disease and the strategy of treatment plan selection have a very important role. The early Tomita score and Tokuhashi score are very important for assessing the degree of tumor progression, surgical modality and predicting the outcome of surgical treatment. However, these scores were developed under traditional radiotherapy techniques. With the development of radiotherapy techniques, stereotactic radiosurgery (SRS) has emerged, and tumors that were originally insensitive to radiotherapy can still be well controlled locally with SRS. This revolutionary technology has led to a fundamental change in the evaluation and treatment decision system for metastatic spine cancer. The concept of “radiation insensitive tumor” refers to the insensitivity of tumor tissues to conventional radiotherapy treatment, but image-guided high fractionated dose radiotherapy (a type of SRS) breaks through the traditional concept that radiation insensitive tumors cannot receive radiation therapy. SRS can form a steep dose reduction zone between the target area and the normal tissue, thus achieving the maximum dose to the target area and the minimum dose to the normal tissue. This is the biggest technical difference between SRS and conventional radiotherapy. This feature is of great importance for the treatment of metastatic spinal cancer, because it allows for the maximization of vertebral tumor irradiation at a safe dose to the spinal cord, which is capped at 14 Gy. Gerszten et al [10] performed SRS on 500 cases of metastatic spinal cancer, and the tumor local control rate was 90% for patients who received SRS for the first time. In a prospective study by Ryu et al. who performed SRS in ESCC spinal metastatic cancer cases due to radiotherapy-insensitive tumors, they observed an average 65% reduction in epidural tumor volume and 81% improvement in neurological function at 2 months after radiotherapy. A 1-year local control rate of 80% was achieved with SRS in cases that had failed previous conventional radiotherapy. Due to the availability of SRS, satisfactory local control of tumors can be achieved with conventional radiotherapy for radiotherapy-sensitive tumors and with SRS for radiotherapy-insensitive tumors. SRS requires a few millimeters of distance between the tumor tissue and the dura, thus allowing radical radiotherapy to be administered to the tumor tissue without affecting the spinal cord tissue. For these reasons, with the introduction of SRS into the treatment of metastatic spinal cancer, the goal of surgery has shifted from maximizing the resection of the tumor involved vertebral body to separating the dura from the diseased vertebral body so that SRS can be safely performed. The NOMS assessment system was proposed by Bilsky and colleagues at Memorial-Sloan Kettering Cancer Center [13], which includes four aspects: neurologic, oncologic, stability, and mechanical instability. Mechanical instability) and systemic metastasis (Systemic disease), and the acronym of the four aspects is the name of the system. The purpose of the system is to guide the choice of treatment plan by evaluating a specific case. The evaluation system integrates the latest radiotherapy and surgical techniques to provide a reference for the patient to develop a reasonable treatment plan. The ESCC score is used to describe in detail the degree of dural or spinal cord compression. Grade 0 means that the lesion is confined to the bone without intraspinal involvement; grade 1 means that the dura is compressed and the spinal cord is not compressed; grade 2 means that the spinal cord is compressed but the cerebrospinal fluid signal is still visible (MRI axial T2-weighted image); grade 3 means that the spinal cord is compressed and the cerebrospinal fluid signal is interrupted. Oncologic features mainly refer to the sensitivity of radiotherapy, and tumors are classified into radiotherapy-sensitive and radiotherapy-insensitive categories according to their response to conventional radiotherapy techniques. The current consensus is that radiotherapy-sensitive tumors are lymphoma, myeloma, and seminomatous cell tumors, which can be treated with conventional radiotherapy with or without ESCC. Radiation therapy-insensitive tumors include kidney cancer, thyroid cancer, liver cancer, colon cancer, non-small cell lung cancer, sarcoma, and melanoma. [13] SRS treatment for radiotherapy-insensitive tumors results in more reliable local control of the tumor. Spinal instability is an independent indication for surgical intervention and is defined by the Spine Tumor Study Group as involvement of spinal integrity due to a tumor with pain with activity under physiological load, symptomatic or progressively worsening deformity or/and neurological involvement. The assessment of spinal stability can be judged by the tumor-based spinal instability scoring system [14], and surgical fixation should be considered for cases with a score of 13-18. The degree of metastasis will mainly assess the patient’s condition as whether the surgery can be tolerated or not. The flow chart shows that currently, in cases where radiotherapy techniques can achieve SRS, surgical intervention is limited to the improvement of vertebral stability, and this for severe compression of the spinal cord caused by radiotherapy-insensitive tumors, the dura and lesion are first separated through separation surgery in order to implement subsequent SRS. it is easy to see that the significance of surgical procedures for resection of the diseased vertebral body is very limited in the current treatment strategy. Separation surgery is similar to the posterior posterolateral approach to the spine via the pedicle and involves epidural decompression and posterior fixation but does not involve resection of the tumor in whole or in parts. Typically, laminectomy is performed at the compressed segment, decompression of the spinal canal, and posterior fixation with lateral block or pedicle nailing at least 2 adjacent upper and lower segments. It is recommended that the bony structures be removed with a 3mm high-speed grinding drill. Ligamentous resection is usually performed in the non-tumor segment to better expose and separate the dura, and after complete posterior decompression, the synovial joint is removed through a lateral or bilateral transpedicular approach, and the anterior dura is exposed. If tumor resection is performed, the intercostal nerves below T1 can be ligated bilaterally. Partial resection of the vertebral body can be performed through the pedicle in order to achieve more adequate decompression, but total resection of the vertebral body is not recommended, and reconstruction of the anterior spinal column is generally not required, but if the vertebral body is resected by more than 50%, reconstruction by methods such as bone cement + Staple or titanium mesh is required. [ 4, stereotactic radiosurgery (SRS) A CT scan of the vertebral canal is routinely required after separation surgery to determine the dural boundaries, because MRI examinations in the presence of internal fixation may not determine the precise location and boundaries of the dura due to artifacts. a single high dose (24 Gy) or high fractionated dose (18-36 Gy/3-6 times) radiotherapy regimen is generally used for SRS. The specific dose of radiation therapy is generally based on factors such as prior radiation therapy, tumor sensitivity to radiation therapy, ESCC classification, paravertebral invasion and number of involved segments. Generally, high fractionated doses are used for cases with large tumors (involving more than 2 segments), ESCC of Ib or higher, and previous radiation therapy. Other cases are treated with a single high-dose radiotherapy, such as cases with one or two segments involved, ESCC of Ia, and no paravertebral masses can be treated with a single 24Gy radiotherapy. In addition, the radiotherapy dose will be adjusted according to the intraoperative radiotherapy use. The upper limit of single high-dose radiotherapy is limited by the maximum radiation dose that the surrounding normal structures can withstand, with the maximum safe dose for spinal cord being 14Gy, for esophagus 14.5Gy, and for cauda equina 16Gy. The general radiotherapy design target area is the extent of tumor invasion suggested by preoperative MRI and determined by postoperative vertebrogram CT scan results The dural boundary, the general target area design is 2-3mm outside the tumor involvement range, so as to compensate for the small radiotherapy error. SRS is usually performed 10-20 days postoperatively. 5 , Results of detached surgery combined with postoperative SRS Bilsky et al [6] reported in 2010 21 cases of metastatic spinal cancer receiving posterior decompression combined with single high-dose SRS with a radiotherapy dose of 18-24 Gy and 81% local control of the tumor. At that time, the concept of detachment surgery was not clearly proposed. Then Bilsky et al [4] introduced the concept of segmentectomy and published the article on segmentectomy combined with SRS for spinal metastatic cancer in 2013. The article reviewed a total of 186 patients from 2002 to 2011, all of whom underwent decompressive subtraction surgery combined with postoperative high-fraction dose radiotherapy or a single high-dose radiotherapy. All 136 patients had severe spinal cord compression (ESCC class II or III), and the decompression segments ranged from 1 to 8 segments (mean 2 segments). Postoperatively, 58.6% of the patients received low fractionated dose radiotherapy (18-36 Gy/5-6 sessions), 19.9% received high fractionated dose radiotherapy (24-30 Gy/3 sessions), and the remaining 21.5% received a single high dose radiotherapy (24 Gy). Radiotherapy treatment was completed at an average of 1.6 months after surgery. Postoperative application of SRS resulted in relatively durable local tumor control regardless of tumor type. Local tumor progression was 18.3% in the study, with a median time to progression of 4.8 months. 55.6% of patients did not experience tumor progression before death, with a median survival time of 5.6 months for this group of patients, and the remaining 26.3% of patients survived without tumor progression (median time of 7.1 months), with a 1-year local tumor progression of 16.4% in all cases. Univariate analysis found that the dose of radiotherapy affected local tumor progression, with single high-dose and high-fractionated dose radiotherapy better than low-fractionated dose radiotherapy, and additional factor analysis found that local tumor progression was independent of prior radiotherapy and tumor type. The data further confirm that satisfactory local tumor control can be achieved with single high-dose SRS or high-fractionated SRS, regardless of tumor type. The incidence of complications of segmentectomy combined with SRS was low, radiotherapy did not cause neurological impairment, and four patients underwent revision surgery due to internal fixation failure, one of which was a case of local tumor progression.Amankulor [17] found a revision rate of 2.8% due to metal endosseous failure by following up 318 cases of spinal metastatic cancer that underwent segmentectomy combined with high-dose SRS. Although most spinal metastases can be controlled by conventional radiotherapy, in cases of severe ESCC caused by radiotherapy-insensitive tumors, detachment surgery should be performed first, followed by SRS after release of dural compression, to achieve stable local tumor control. With the introduction of SRS into the field of spinal metastatic cancer treatment, the need for surgical resection of the diseased vertebral body was greatly diminished. Separation surgery essentially restores the cerebrospinal fluid gap around the spinal cord, relieves dural compression, and allows for safe postoperative implementation of SRS, thereby achieving effective local control of vertebral metastases and avoiding tumor progression. Separation surgery in the current comprehensive treatment of spinal metastatic cancer actually achieves effective treatment of spinal metastases by surgically releasing ESCC in cases where SRS cannot be performed in severe ESCC, thus enabling SRS to be performed.