Advances in Metastatic Disease Spinal Oncology: Novel Technology Without Forgetting the Fundamentals of Surgical Treatment
Article information
Abstract
Metastatic spine disease represents a growing therapeutic challenge that demands a balance between incorporating emerging technologies while respecting the fundamental principles during clinical decision-making. Advances in adjuvant therapies, including stereotactic body radiotherapy (SBRT) and chemotherapy, have significantly improved long-term patient survival. Surgical decision-making should be guided by well-established frameworks such as the NOMS (neurologic, oncologic, mechanical, systemic) criteria, the ESCC (epidural spinal cord compression) scale, and the SINS (spinal instability neoplastic score), ensuring a structured and evidence-based approach to treatment. The integration of minimally invasive techniques, including percutaneous instrumentation, ablation techniques, and biportal endoscopic approaches, has reduced surgical morbidity and facilitated faster recovery. Additionally, carbon fiber implants are revolutionizing spinal stabilization by allowing better postoperative visualization of any local recurrence and easier radiation planning. SBRT has emerged as a critical modality, offering precise, high-dose radiation with minimal toxicity to the spinal cord, improving local tumor control and patient outcomes. A multidisciplinary approach remains paramount, requiring collaboration between spine surgeons, radiation oncologists, and medical oncologists. In this narrative review, we aim to provide a comprehensive overview of the current state of metastatic spine tumor management, focusing on: (1) fundamentals of metastatic spine care, (2) minimally invasive surgical techniques, (3) the use of carbon fiber screws, (4) SBRT, and (5) ways to maximize patient safety.
INTRODUCTION
Spinal metastases constitute approximately 90% of spinal tumors, most commonly presenting with pain and/or neurologic compromise [1]. Metastases to the spine occur in up to 70% of cancer patients, with 10% ultimately presenting with spinal cord compression [2-5]. Advances in adjuvant chemotherapy and radiation have prolonged the survival of cancer patients, which has led to an increase in the population with spinal involvement [6].
Management of metastatic spine disease has been driven by advancements in diagnostic imaging, surgical technique, and adjunct therapy, including chemotherapy, radiotherapy, and tumor embolization [7,8]. Surgical decision-making has been facilitated via the establishment of well-recognized frameworks, including the epidural spinal cord compression (ESCC) scale [9], neurologic, oncologic, mechanical, systematic (NOMS) framework [10], and spinal instability neoplastic score (SINS) [11]. Furthermore, the surgical technique has been streamlined with the advent of separation surgery followed by high-dose stereotactic radiation therapy (SBRT), which has allowed for effective tumor control, limiting neurological compromise and decreasing the surgical footprint [12]. Concomitantly, technological advancements have become major parts of metastatic spine disease management and include navigation techniques, robotics, and augmented reality (AR) [13-15].
Despite these advances, treatment of metastatic spine disease remains a challenge with a rapidly increasing incidence. Metastatic spine care is evolving, with surgical and radiation therapies advancing with new technologies and techniques. Navigating this literature can be a daunting task, and one of the primary purposes of the following review is to provide a concise yet informative review. Most, if not all, spine surgeons will encounter spinal metastasis patients. In this narrative review, we aim to provide a comprehensive overview of the current state of metastatic spine tumor management, focusing on: (1) fundamentals of metastatic spine care, (2) minimally invasive surgical techniques, (3) the use of carbon fiber screws, (4) stereotactic body radiotherapy (SBRT), and (5) patient safety.
FUNDAMENTALS OF METASTATIC SPINAL ONCOLOGY MANAGEMENT
While recent advances in spinal oncology are revolutionizing treatment protocols, the fundamental principles must be recognized and adhered to during clinical decision-making. Wellrecognized grading systems, oncologic frameworks, and surgical strategies are the cornerstones of the effective management of metastatic spine tumors. While new technology is attractive and has potential to make surgery easier, we must not forget the fundamentals of good decision-making, technically excellent surgery, and thorough patient care.
1. NOMS Framework
The NOMS framework [10] provides a systematic and structured approach to the management of metastatic spinal disease. NOMS integrates key decision points like functional status (radiculopathy, myelopathy) and the extent of spinal cord compression, tumor type (radiosensitivity), biomechanical stability of the spine, and systemic comorbidities (ability to tolerate surgery and expected survival). Additionally, it incorporates modern techniques like SBRT and minimally invasive surgery along with conventional external beam radiotherapy (EBRT) and open surgery [10]. The evidence-based framework has influenced treatment algorithms and continues to evolve with emerging treatment modalities. The value in this framework is to stay disciplined in our evaluation of metastatic spine patients and to remember the importance of spinal cord compression extent and histology in determining the selection of surgery and/or radiotherapy.
2. ESCC Scale
The ESCC grading, described by Bilsky et al. [9] quantifies the degree of spinal cord compression due to metastatic disease using T2-weighted axial magnetic resonance images (MRIs) using the 6-point scale. It categorizes the disease from bone-only involvement without epidural extension (grade-0) to severe spinal cord compression with obliteration of the cerebrospinal fluid (CSF) space (grade-3). The intervening grades define epidural impingement (1a-no deformation of thecal sac, 1b-deformation of the thecal sac and 1c-deformation of the thecal sac with cord abutment) and spinal cord compression with CSF seen (grade-2). The ESCC is an important risk stratification tool, and high-grade scores (2 and 3), indicating spinal cord compression, should be monitored carefully as these patients are at risk for neurologic compromise.
Clinical decision-making is multifactorial, and while the ESCC is a key component, relying on any single tool in isolation is insufficient. Furthermore, patients can clinically present in a heterogeneous fashion despite having similar Bilsky scores. Uei et. al. [16] evaluated the relationship between the ESCC scale and the severity of paralysis induced by the tumor and found that the overall paralysis severity did not correlate with the ESCC grade. Conversely, Bendfeldt et al. [17] conducted a retrospective cohort study in 343 patients with extradural spinal metastasis and found that Bilsky 2–3 lesions were associated with longer length of stay, decreased survival at 1 year, and worse postoperative Karnofsky Performance Status score. Therefore, the clinical decision-making must be based on a combination of the patient history, neurological examination, and MRI findings to aid in prioritizing patients for surgical decompression. Patients with high-grade ESCC but preserved neurologic function may still be at risk for neurologic deterioration due to the severity of compression and may benefit from early surgical intervention to prevent irreversible deficits. Conversely, patients with low-grade ESCC who present with significant neurologic impairment may warrant expedited evaluation for alternative causes of dysfunction (e.g., vascular compromise, tumor infiltration) or may still require surgical decompression despite imaging suggesting lesser degrees of compression [10,11,18]. Any discrepancy in the radiological and clinical examination underscores the importance of incorporating both ESCC grade and neurologic status in clinical decision-making.
To address the broad categorization of grades 2 and 3 and enhance clinical relevance, Cao et al. [19] proposed a 12-point ESCC grading system incorporating factors like epidural invasion by the tumor, compression direction, spinal cord deformity, and swelling. While this modified scale showed improved correlation with American Spinal Injury Association grades, its external validation was limited [19]. Future studies should further investigate the clinical correlation of the original 6-point scale and validate the proposed 12-point system in larger, independent cohorts.
3. Spinal Instability Neoplastic Score
SINS remains the primary system of evaluating the mechanical stability of the spine in metastatic disease [11]. Using 6 individual components, the tumor-related instability is scored between 0 and 18: spine location (0–3), pain (0–3), lesion bone quality (0–2), radiographic alignment (0–4), vertebral body collapse (0–3), and posterolateral involvement of the spinal elements (0–3). A low score (0–6) suggests spinal stability, while a high score (13–18) indicates instability. A score between 7–12 is considered indeterminate and includes possible impending instability and frank instability. All patients with a score greater than 7 are recommended surgical consultation. Importantly, SINS was created and is perhaps most useful for non-surgeons to know when lesions are unstable; however, calculating SINS is still a mainstay of evaluation for spine surgeons.
4. Molecular Prognostication of Tumors
Molecular prognostication has become increasingly critical in the management of metastatic spine disease, as tumor biology plays a central role in guiding treatment strategies and estimating survival [20]. With the improved understanding of molecular biology and tumor markers, genetic mutations like epidermal growth factor receptor and anaplastic lymphoma kinase in non-small cell lung cancer, HER2 overexpression in breast cancer, and BRAF V600E mutations in melanoma have emerged as important prognostic markers in cancer [20,21]. Targeted therapies for these mutations have been shown to significantly improve systemic disease, spinal stability, and longevity [20]. Modern-day clinical decisions should be guided by molecular analysis along with traditional clinical and radiological markers. For patients with favorable molecular profiles and expected longer survival, more durable spinal stabilization procedures may be appropriate; however, those with poor prognostic indicators may benefit more from limited, palliative approaches. While a detailed knowledge of molecular characteristics is beyond the scope of what a spine surgeon should know, the spine surgeon must be aware of the importance of molecular testing and to discuss this preoperatively and postoperatively with the oncology team.
5. Radiation Sensitivity and Treatment Strategies
Knowledge about tumor histology and its radiosensitivity is a key component of the treatment decision-making process. The oncologic evaluation in the NOMS framework [10], emphasizes the importance of tumor histology and radio-responsiveness before any intervention. Certain cancers including myeloma, lymphoma, small cell lung cancer, and seminoma are highly sensitive to radiotherapy while some solid tumors like breast and prostate can also be considered fairly radiosensitive as long as they haven’t been previously treated with radiotherapy [22]. The advent of SBRT has allowed controlled and targeted radiotherapy to tumors, minimizing the toxicity to neighboring tissues while still providing durable tumor control [23]. It is particularly beneficial in radioresistant tumors, oligometastatic disease or cases requiring reirradiation [23]. EBRT remains a viable option for diffuse metastatic disease, radiosensitive tumors and for short-term palliation [24]. These advances in radiotherapy reinforce the importance of understanding tumor histology and radiosensitivity to avoid surgical intervention wherever possible. We present the case of a young male with acute cauda equina syndrome due to Burkitt Lymphoma who was treated with urgent radiation alone and made a complete neurologic recovery (Fig. 1A–H).
An 18-year-old male with newly diagnosed Burkitt Lymphoma presented with progressive bilateral lower extremity numbness, weakness, urinary retention, and inability to ambulate. (A) Magnetic resonance imaging (MRI) revealed epidural masses at T5–7 causing spinal cord compression and L5–S1 causing severe cauda equina compression. Preradiation sagittal MRI of the thoracic spine showed a large epidural mass at T5 to T7. (B) Sagittal MRI of the lumbosacral spine showed an epidural mass at L5–S1. (C) Axial MRI at the level of T6 showed moderate to severe thecal sac compression with complete effacement of the cerebrospinal fluid and indentation of the cord. (D) Axial MRI at the level of L5 showed an epidural mass and thecal sac compression. The radiosensitivity of Burkitt Lymphoma prompted emergent radiation therapy (800 cGy) within 14 hours of presentation. On postradiation day 1, left foot strength improved, and by day 3, full neurological function, including bladder control, was restored. Postradiation sagittal MRI of the thoracic spine (E), sagittal MRI of the lumbar spine (F), axial MRI at the level of T6 (G), and axial MRI at the level of L5 (H) showed resolution of the intraspinal epidural soft tissue lesion and thecal sac compression in both the thoracic and lumbar regions. The patient was discharged neurologically intact, requiring no surgical intervention, and continued chemotherapy as planned.
6. Surgical Considerations
A major advancement in metastatic spine tumor management has been the integration of surgical and radiation treatment. Separation surgery allows adequate separation between the spinal cord and the tumor, minimizing radiation damage to the spinal cord [18,25]. Unlike conventional decompression and excision surgery, it focuses on restoring the epidural space without compromising the structural integrity for the subsequent radiation-based tumor resection. In other words, separation surgery reconstitutes the thecal space around the spinal cord. In creating room for SBRT to be delivered, the spinal cord is decompressed. Occasionally, a decompression only without 360° separation may be indicated in the case of radiosensitive pathology with neurological decline. Breast and prostate are taken on a caseby-case basis, and surgery is often indicated for patients with recurrent tumors or ones with severe/symptomatic spinal cord compression, while EBRT can provide fairly durable local control for previously untreated breast and prostate metastases.
When performing separation surgery, it is paramount not to leave the operating room until the surgeon is confident that full 360° separation has been achieved. The ultrasound is a very useful tool for confirming this. Two cases with intraoperative use of ultrasound are demonstrated in Figs. 2A–I and 3A–J. Operative pearls for ensuring adequate separation is extensive use of the bipolar electrocautery to coagulate tumor prior to tumor removal. Moreover, cutting the posterior longitudinal ligament sharply with a knife can be helpful. Tools that can be helpful to ensure adequate ventral separation is a Woodson, but a Woodson is often not long enough to get contralateral. A pedicle sub-traction osteotomy curette is often longer and can reach all the way to the contralateral side (Fig. 4A–C).
A 62-year-old male presenting with back pain and a renal mass. T2-weighted sagittal magnetic resonance imaging (MRI) demonstrated a high-grade lesion Bilsky 3 lesion at T10 (A, C) with a lytic component on computed tomography (CT) (B). Intraoperative ultrasound demonstrated a compressive lesion (D) and after separation surgery 360º of decompression was achieved (E). Complete circumferential decompression was confirmed on postoperative CT-simulation (F) and T2-weighted MRI (G). The patient underwent a posterior spinal fusion with a structural allograft. Postoperative anteroposterior (H) and lateral (I) x-ray with T8-T12 fusion with structural allograft held in place with domino connectors are seen.
A 57-year-old female with breast cancer presenting with mechanical back pain found to have a high-grade Bilsky 3 lesion on T2 weighted magnetic resonance imaging (A, B) and a lytic component through the vertebral body (C). White arrows indicate the tumor (A) and the lytic vertebral body lesion (C). Intraoperative ultrasound demonstrated a compressive lesion (D) and after separation surgery 360º of decompression was achieved (E). (F) A structural allograft was placed for fusion purposes across the laminectomies. The patient underwent a T3–9 posterior spinal fusion with T6 vertebral column resection. Preoperative (G and I) and postoperative (H and J) standing x-rays were obtained.
(A) Woodsen curette. (B) Pedicle subtraction osteotomy (PSO) curettes. (C) Close up view of PSO curette.
7. Remembering the Fusion
With the increased life expectancy in patients with metastatic spine disease, achieving a fusion is becoming increasingly important to avoid pseudarthrosis and/or implant failure. A study by Rothrock et al. [26].0 evaluated the survival trends for metastatic spinal tumors over 20 years and found a significant improvement in survival, particularly in patients with breast, lung, kidney, and colon metastatic cancers to the spine. Advances in radiotherapy, chemotherapy, and targeted therapies for metastatic spine disease have led to improved quality of life and prolonged survival [27]. Decades ago, we wouldn’t have to worry about a fusion, and most implant failures wouldn’t happen during the patients’ short life expectancy [28]. However, patients are living long lives, and an effort to achieve fusion should be considered. A structural allograft can be a powerful yet simple tool to increase the surface area of fusion (Fig. 5A and B).
(A and B) Two illustrative cases showing the placement of a structural allograft across the laminectomy defect secured to the surrounding rods with the use of FiberWire.
While the life expectancy for patients with metastatic disease has increased in recent years, there still exists a subset of patients who undergo metastatic spine surgery with limited life expectancy, where the purpose of surgery is to minimize pain the remaining months of life. In patients with aggressive tumor pathologies, widespread systemic disease, the surgical morbidity associated with extensive reconstruction may not be justified, especially when the goal is short-term palliation and symptom control rather than long-term spinal stability. Prognostic tools like the Skeletal Oncology Research Group nomogram [29], as well as well-established scoring systems, Tomita and Tokuhashi scores [30,31], can help in estimating survival and tailor the surgical approach accordingly. Incorporating these tools into preoperative planning can help identify patients who may benefit from limited decompression alone rather than formal fusion. In a similar vein, patients with leptomeningeal disease and a limited life expectancy may be candidates for treatment via decompression alone, palliative steroids, locoregional radiotherapy, or chemotherapy [32]. However, multicenter studies have shown that patients who survived less than 3 months after surgery reported similar quality of life and satisfaction at 6 weeks postoperatively compared to those who lived longer, indicating that even patients with short life expectancy can benefit from surgery [33].
8. Sticking to Fundamentals Amidst the Sea of Enabling Technologies
While emerging technologies, including intraoperative navigation, AR, and robotic-assisted surgery, have enhanced surgical precision in spinal oncology [34,35], their adoption must align with fundamental oncologic principles. Intraoperative navigation improves the accuracy of spinal instrumentation [34], AR provides real-time 3-dimensional (3D) visualization of structures for more controlled procedures [36], and robotic-assisted surgeries are often associated with shorter hospital stays and faster recoveries [35]. Advanced tools should complement—not replace—sound clinical judgment, evidence-based grading systems, and multidisciplinary collaboration in spinal oncology decision-making [9-11]. Understanding the anatomy of the spine, the 3D spatial relationships, and ensuring adequate separation to achieve long-term, durable tumor control area paramount and in many ways agnostic to any new technology.
MINIMALLY INVASIVE SPINE SURGERY
Minimally invasive spine surgery (MISS) in metastatic spinal disease reduces morbidity, accelerating recovery and improving the quality of life of cancer patients with reduced life expectancy [37]. While open surgery provides adequate tumor control, it is associated with large intraoperative blood loss, long hospital stays, and prolonged recovery periods [38]. MISS allows for effective tumor control with decompression, stabilization, or separation for radiotherapy with minimum tissue disruption, allowing for a relatively less morbid procedure with a faster recovery [37,39,40].
1. Technique for Minimally Invasive Separation Surgery
Separation surgery is currently the treatment of choice with adjuvant radiotherapy, preferably SBRT. Though separation surgery is often done open, the theory behind it is in-fact minimally invasive given the focus on circumferential decompression rather than tumor cytoreduction. MISS approach to separation surgery leads to minimal tissue disruption while achieving tumor separation from the spinal cord [41]. The surgery is usually performed through a posterolateral approach, allowing for spinal stabilization and circumferential decompression of the cord, creating a 2- to 3-mm gap between the spinal cord and the tumor for safe SBRT delivery, postoperatively [25,42]. When done through a percutaneous fashion, navigation or a C-arm is used to identify the affected vertebral level, the position of the pedicles of the 2 vertebrae above and below the affected levels and mark the incision site based on that. Pedicle screws are implanted through a 1- to 2-cm incision via the Wiltse paravertebral muscle space approached under direct vision. Then, circumferential decompression, through a 5- to 6-cm midline skin incision is performed bilaterally. Traditionally, pedicle screws are placed at least 2 levels above and below the decompression level, however short constructs with screws placed one level above and below the tumor can also be used in patients with good bone and/or when screw cement augmentation is used. A mini-open approach can also be taken, where the fascia is intact over the screws but opened over the decompression. For osteolytic and mixed lesions, polymethylmethacrylate can be applied through fenestrated pedicle screws. After decompression is completed, tumor samples are collected for histopathological analysis. A drain may be placed at the end of the procedure. Intraoperative monitoring is used for all cases placing instrumentation, regardless of cord or cauda equina territory [41]. As stated above, the ultrasound is a very useful tool to confirm full 360° separation. Following surgery, high-dose SBRT is started in 2–3 weeks postoperatively.
2. Percutaneous Pedicle Screw Fixation
MISS techniques for spinal metastases encompass various approaches and the surgical decision is based on the patient’s neurological status, pain severity, radiological findings, oncological treatment plan, and life expectancy [43,44]. Percutaneous pedicle screw fixation is a viable option in patients with spinal instability with radiosensitive tumors or none/low-grade ESCC. Low-grade ESCC can cause extensive destruction of the cortical bone and fractures up to the posterior elements, leading to mechanical instability [44,45]. In such cases, percutaneous instrumented fixation can provide long-term stability without the need for open surgical intervention. Intraoperatively, navigation or fluoroscopy can be used to localize the disease and place the screws. Short-segment constructs, typically spanning one level above and below the affected vertebra, can be enhanced with fenestrated screws and cement [45]. Balloon kyphoplasty can serve as an adjunct to percutaneous fixation in patients with unstable pathological fractures without significant cord impingement [44,46].
3. Vertebroplasty and Kyphoplasty
Spinal metastasis commonly presents as pathological vertebral fractures, where vertebroplasty and kyphoplasty can be suitable treatment strategies. Vertebroplasty involves injection of bone cement into the vertebral body, which if supplemented by an inflated balloon, is termed as kyphoplasty [47]. These procedures are usually used to treat painful compression vertebral fractures, together with SBRT, without an interruption in the chemotherapeutic regimen [48]. Vertebroplasty or kyphoplasty for painful fractures without significant collapse or retropulsion and has been shown to be superior to medical management [49]. Kyphoplasty is also indicated in case of radioresistant tumors without cord compression. It can be performed in conjunction with percutaneous fixation if posterior elements are involved, or isolated, if posterior elements are not involved [44]. As stated above, fenestrated screws can be an efficient way to place cementaugmented screws [50,51].
4. Ablation
Image-guided ablation therapies offer a minimally invasive treatment alternative for patients with spinal metastasis who are not good surgical candidates [52]. For ablation therapies, the probe is inserted directly into the target tissue before delivering the appropriate therapy, without causing significant damage to the surrounding normal tissues. Performed under imaging guidance from computed tomography (CT) or x-ray fluoroscopy, based on the mechanism of tissue destruction, it is divided into the following subtypes: radiofrequency ablation (radiofrequency waves heats tissues to cause cell death), cryoablation (extreme cold to freeze and kill cells), and microwave ablation (microwaves are used to heat tissue and cause cell death). Newer modalities like laser interstitial thermal therapy (LITT) and focused ultrasound utilize MRI and are preferred for extravertebral disease, being quite powerful to treat mild cases of epidural disease [52]. These can be performed in conjunction with vertebroplasty for pain relief [53]. Radiofrequency and cryoablation have been shown to potentially cause thermal spinal cord and nerve injuries and are therefore reserved for intravertebral lesions [54].
5. Biportal Endoscopy Technique for Separation Surgery
Endoscopic spine surgery offers a minimal access solution for cancer patients with spinal metastases who are often frail and require prompt chemoradiation treatment after surgery for disease control. The benefit of this approach is that it is perhaps the most minimally invasive treatment within all of spine surgery. The power of endoscopic spine surgery is being realized throughout the field of spine surgery, perhaps most with the treatment of thoracic disc herniations. The biportal endoscopy technique allows for better visualization of the surgical field and easier access to the lesions with 2 access points [55], despite these advantages, several limitations and risks remain. A key limitation of the technique is the presence of blind spots outside the endoscopic field of view, making complete tumor resection challenging [56,57]. Furthermore, inadequate visualization around key neurovascular structures increases the risk of inadvertent injury. Hypervascular metastatic spine tumors can cause significant bleeding, and the limited vantage points of endoscopy makes it difficult to achieve adequate hemostasis [56,57]. Additionally, the potential for tumor cell seeding along the endoscopic tract remains a theoretical but serious concern, particularly when violating tumor margins during decompression [54]. Overall, these limitations warrant advanced training with a steep learning curve before the technique can be adopted in regular clinical practice.
The biportal endoscopic surgical technique for separation surgery has been described by Ghenbot et al. [58] After positioning the patient prone on a Jackson table, the O-arm is used to place all the percutaneous screws under navigation guidance, using navigated drill guide and k-wire. The endoscopic access is then centered using navigation, at the site of the lesion. The camera is inserted to visualize the lesion, and the anatomical landmarks are identified. After soft tissue dissection, an osteotome is used to remove the bone surrounding the lesion, which facilitates facetectomy. A 6-flute barrel burr with a 5.5-mm drill bit is used to drill off most of the facet joint, as well as the base of the lamina. The thecal sac is then visualized. A Woodsen is the used to dissect the yellow ligament off the neural elements, before drilling the pedicles medially, to allow more space. Navigation can be used at this time to confirm the location, as the tumor can distort the normal anatomy. Biportal technique allows the use of tools similar to the open technique and decompression is carried out using reverse angle curettes. Further tumor debulking can be performed using pituitaries. Thorough irrigation with water aids with hemostasis and washing out the tumor cells. A drain may be placed to remove any anticipated postoperative fluid collection. The rods are then placed percutaneously using set screws, adjusting the curvature based on the position of the lesion and ensure normal alignment [58].
6. MISS Versus Open Surgery for Spinal Metastasis
MISS has emerged as a promising alternative to open surgery for spinal metastases, offering several advantages in diverse patient populations [37]. MISS is often reserved for patients with a tumor in the lower thoracic or lumbar spine with a single-segment primary lesion, due to the space and visualization constraints [59]. MISS offers similar efficacy of tumor resection or separation with reduced operative time (~35 minutes), intraoperative blood loss (~560 mL), and blood transfusion requirement (odds ratio [OR], 0.26) [37]. Postoperatively, MISS patients have a faster recovery with decreased need for bed rest, reduced length of hospital stay (≈3 days), and a lower risk of complications (OR, 0.60). Patients with cancer are usually frail and vulnerable; in such patients, MISS offers a surgical option with reduced physiological stress and a faster recovery [60,61]. Additionally, during tumor resection, seeding of the cancer cells is always a risk, while no evidence exists comparing the risk between MISS and open surgery, some studies concluded similar long-term survival between the groups, indicating absence of difference in the risk of seeding and cancer spread; however, future studies should aim to directly compare the incidence of tumor seeding with the 2 approaches. Cost-analysis has shown that MISS leads to overall cost-savings as compared to open surgery; however, the literature is not uniform and demands further research, especially in spinal metastasis where the costs of necessary care are high outside of surgery as well [62]. It is important to note that though MISS offers a safe surgical option with less morbidity, it has a steep learning curve, high setup costs and high intraoperative radiation exposure for the patient and the operating team when intraoperative fluoroscopy is used [63]. The indications, advantages and limitations of MISS have been summarized in Table 1.
Indications, advantages, and limitations for open surgery, minimally invasive spine surgery (MISS) technique, and endoscopic technique for spinal metastasis
CARBON FIBER
Titanium-based instrumentation is the workhorse of spinal instrumentation and fusion; however, despite the ease of availability, use of titanium in oncologic cases can lead to profound artifact production on CT and MRIs [64,65]. Carbon fiber instrumentation minimizes artifact and particle scatter, leading to more robust radiotherapy dosing [66] and better detection of local recurrence [67]. Examples of separation surgery with carbon fiber screws are shown here (Fig. 6A and B).
A 49-year-old male with non-small cell lung cancer presenting with mechanical back pain. The patient underwent a T6–L3 posterior spinal fusion with a combination of both titanium and carbon fiber screws as seen intraoperatively (A) and on postoperative x-rays (B).
As with any new technology it is important to stratify the safety and efficacy of the product. Lindtner et al. [68] determined the ability of carbon fiber pedicle screws to resist load cycles until loosening and whether cement augmentation altered the biomechanical properties of carbon fiber implants. In this cadaveric study, carbon fiber, titanium, and cement-augmented carbon fiber screws were implanted and tested using stepwise compressive loads until loosening or a maximum of 10,000 cycles [68]. Carbon fiber pedicle screws proved to resist loosening with at least the same efficacy as titanium screws (3,701±1,228 vs. 3,751±614 load cycles, p=0.89) with cement augmentation significant increasing the number of load cycles until screw loosening by 1.63-fold (5,100±1,933 in augmented vs. 3,130± 2,132 in nonaugmented carbon fiber-reinforced polyetheretherketone screws, p=0.015) [68]. Additionally, carbon fiber implants have demonstrated superior osseointegration in rodent models compared to titanium. As demonstrated by Petersen [69] carbon fiber increases percent bone area to a greater extent in comparison to titanium for similarly sized rods in rodent models.
Beyond cadaveric studies, carbon fiber implants have proven to be safe in humans. One of the largest single-center experiences, by Joerger et al. [70] included 321 patients receiving carbon fiber posterior instrumentation for metastatic and primary tumors. Overall, implant-related complications were low with screw breakage reported in 3.5% and screw loosening in 2.2% patients [70]. One instance of rod breakage was reported which was titanium and not carbon fiber [70]. Cofano et al. [71] performed a retrospective study to compare the effectiveness of carbon fiber implants to titanium and found no difference in terms of implant-related complication rate. Thus, carbon fiber implants have may be a safe alternative to titanium implants and should be evaluated further.
Despite this theorized advantage of decreased artifact compared to titanium, few studies have proven this objectively. Ringel et al. [72] demonstrates the superiority of carbon fiber over titanium in radiation planning in a cohort of 35 patients. In this retrospective review, deviation of more than 100 Hounsfield units from original tissue samples was used to approximate artifact [72]. Most notably, the amount of metal volume potentially absorbing radiation was higher in titanium as compared to carbon fiber (830±130 mm3 vs. 362±49 mm3, p<0.0001) [72]. Second, Müller et al. [73] evaluated the impact of carbon fiber implants on radiotherapy treatment by generating both a volumetric arc photon therapy (VMAT) plan and intensity modulated proton (IMPT) plan. While there was no difference between carbon fiber and titanium for VMAT dose distributions, IMPT plans had more heterogeneous coverage when using titanium implants by measuring the standard deviation inside the target (7.6%±2.3% vs. 3.4%±1.2%) [73].
The overarching goal of optimizing radiation and early detection of recurrence is for improved survival and oncologic benefit. Ward et al. [74] performed a case-matched series using carbon fiber versus titanium instrumentation in 263 patients and found that local recurrence was detected 2 times earlier in patients with carbon fiber (94 days vs. 189 days, p=0.013). However, there was no difference in overall progression-free survival (143 days vs. 214 days, p=0.41) [74]. Despite the theorized advantages of carbon fiber implants, few studies outside of Ward et al. [74] have demonstrated an objective advantage over titanium implants [67].
The current literature on carbon fiber implants is predominantly composed of retrospective studies, which limits the strength and generalizability of the findings. Future prospective studies should aim at objectively demonstrating lower rates of local recurrence and a survival advantage. The widespread use of carbon fiber implants has been limited by several practical as well as economic barriers. The primary reason for the constrained use is the significantly higher costs associated with carbon fiber implants compared to the conventional titanium implants. The limited literature on a cost-benefit analysis raises concerns about cost-effectiveness, particularly in resource-limited settings [66]. Further, there are currently no carbon fiber posterior cervical or occipital fixation systems, restricting its use to certain anatomical regions. The inability to contour carbon fiber rods intraoperatively also poses a technical challenge as alignment goals are necessary for long-term patient sucess [66]. Given this emerging technology, it is important to conduct long-term studies to assess not only oncologic and biomechanical outcomes but also implant longevity, complication rates, and patient-reported outcomes over time.
STEREOTACTIC BODY RADIOTHERAPY
SBRT allows for precise and conformal delivery of ablative high-dose radiation per fraction over a small number of fractions while minimizing toxicity to the neighboring tissue [75].
1. SBRT Planning and Technique of Delivery
While SBRT has improved treatment precision, there lies a challenge in dose distributions while protecting the adjacent normal structures [76]. For SBRT planning, patients undergo a treatment planning CT scan after being immobilized in a near-rigid body frame, which improves positional reproducibility during treatment delivery [77]. Then, a thin-slice axial T1 and T2 MRI including the target segment±1 is acquired and fused with the CT for target volume delineation per International Spine Radiosurgery Consortium guidelines [78]. A CT myelogram may be used if the spinal cord is obscured on the MRI due to prior fusion hardware. The CT is used to define the tumor, whereas the MRI aids in visualizing and delineating the neighboring structures at risk for toxicity [76].
The visible tumor is contoured as the gross tumor volume (GTV) and the clinical target volume (CTV) provides an expansion around the GTV and includes adjacent marrow spaces to account for the microscopic disease. If any vertebral body region is involved, the entire vertebra is treated. Pedicles, transverse processes, lamina, or spinous processes are included if affected. All of the epidural disease must be included in the treatment volume, since this is the highest risk region, and careful attention must be paid to minimizing the dose administered to the spinal cord and other organs at risk. In postoperative cases, target volume planning must consider both preoperative and postoperative disease locations [79]. Horseshoe-type CTVs, sparing the epidural space, are suitable for anterior epidural disease, whereas circumferential donut-shaped coverage may be necessary in other cases.
The optimal fractionation for SBRT doses to the spine remains uncertain. Single-fraction radiotherapy doses range from 18 to 24 Gy, and common hypofractionated regimens include 24 Gy across 2 or 3 fractions, 27 over 3 fractions and 30 Gy over 5 fractions [76]. Higher dose per fractions of SBRT (>8 Gy) may trigger alternate tumor cell death pathways, other than mitotic catastrophe and apoptosis, including immune activation and vascular injury [76,80,81].
2. Clinical Outcomes: Local Recurrence and Overall Survival
SBRT has shown promising results for spine metastasis control as a primary form of treatment without surgery. It has reported a 1-year local control rate between 80%–96% and also results in significant pain relief [76]. Compared to EBRT, which has a local control rate between 61%–86%, SBRT is more effective, especially for traditionally radioresistant tumors [82-84].
The role of EBRT in the reirradiation of spinal metastasis is well studied [83]; however, conventional treatment is limited by dose constraints respecting the dose to the spinal cord [76]. SBRT offers a solution by allowing dose escalation to the tumor while sparing the spinal cord. Reported 1-year local control rates for reirradiation SBRT range from 66% to 92% [76], comparable to de novo cases.
Reported overall survival following spine SBRT varies widely depending on factors such as tumor histology, disease burden, and patient selection. The 1-year survival rates range from 23%– 100%, while 2-year rates fall between 23%–90%. Median survival times span from 4–76 months, reflecting the heterogeneity of patient populations and prognostic factors [85].
3. SBRT: Safety and Toxicity
Acute toxicity of SBRT is mild and relatively uncommon, with severe adverse events reported in less than 5% of cases [76,86,87]. While there have been concerns about hardware failure being associated with SBRT, the limited existing literature reports a failure rate of approximately 2% [76], further some studies suggest reduced risk of failure and a trend toward higher fusion rates with SBRT compared to EBRT [88].
The most notable acute side effect of SBRT is a transient ‘pain flare’ occurring in 23%–68% patients; however, this pain is often well-controlled with dexamethasone. Among the late complications, vertebral compression fracture is the most common, reported in 14% of patients in a large multi-institutional study but 11%–39% in single-institution studies [89-91]. High radiation doses, particularly ≥20 Gy per fraction substantially increases the risk, with single-fraction 24-Gy treatments linked to nearly a 40% incidence, although most fractures are asymptomatic and don’t require treatment. One study identified 3 key risk factors for vertebral compression fractures: preoperative compression fracture, lytic tumor lesions, and spinal deformity. Additionally, patients with a high SINS (7–12) are at an increased risk of compression fractures; however, half of them remain asymptomatic and can be managed effectively using cement augmentation alone [92].
Radiation-induced myelopathy is one of the most concerning long-term complications of spinal SBRT, which can lead to serious and disabling outcomes. However, its incidence is extremely low. In a study by Sahgal et al. [93] the maximum tolerable dose to small volumes of thecal sac were evaluated, based on which, the current guidelines regarding radiation tolerance to spinal cord are established. They concluded that for a single fractions SBRT, 10 Gy is the maximum safe dose. When given in fractions a dose of 30–35 Gy in 2/2 to the thecal sac carries a low risk of myelopathy. During reirradiation, at least 5 months after the conventional radiotherapy, 20–25 Gy dose in 2/2 to the thecal sac is safe, as long as the total dose does not exceed 70 Gy in 2/2, and the SBRT dose does not constitute more than 50% of the total dose [93,94].
4. Importance of Multidisciplinary Approach
Spinal metastasis is a complex disease that requires a collaborative, multidisciplinary effort from the radiation oncology, spine surgery and medical oncology teams for effective manage-ment. Treatment is patient-specific, guided by thorough clinical and radiological assessment. Clinically, the patient’s baseline neurological function, pain severity, age, comorbidities, functional status, life expectancy, and individual care preferences should be evaluated and considered. Tumor histology, a key disease component, should drive the primary treatment choice, along with other oncologic factors, including disease spread, and available systemic therapies. Additionally, radiological assessment of the tumor location, presence of cord compression, and ESCC grade can aid in deciding between surgical intervention and radiotherapy. Prior surgeries and radiation therapies should also be noted to plan appropriate radiotherapy, if needed, while minimizing damage to the cord. Ultimately, an individualized, patient-centered strategy, where spine surgeons and radiation oncologists discuss each case prior to surgery, we believe provides the highest level of patient care. We have utilized the current pathway to ensure good communication and planning between both the spine surgery and radiation oncology team (Fig. 7).
Pathway for spinal oncologic patients for both the preoperative (A) and postoperative (B) phases. MRI, magnetic resonance imaging; CT, computed tomography; RT, radiotherapy; f/u, follow-up.
SAFETY IN METASTATIC SPINE SURGERY
Metastatic spine surgery is a high-risk endeavor, and prioritizing safety is paramount. Given its high level of complexity, the Metastatic Spine Disease Multidisciplinary Working Group has published an algorithm to ensure proper referrals for patient care and optimize decision-making and patient safety [95].
1. Preoperative Patient Optimization
Patient optimization is key in successful metastatic spine surgery, with malnutrition affecting a significant portion of cancer patients. Surgery, chemotherapy, and radiation are poorly tolerated without optimized nutrition [96]. Preoperative nutrition consults can decrease 30-day morbidity and be a powerful tool in preoperative patient optimization [97]. While albumin is a common malnutrition marker [98], recent studies have indicated no association between albumin and survival, given that the concentration of the protein is affected by age, inflammation, and other variables [99]. Body weight and body mass index (BMI) are also commonly used to assess nutritional status. However, a comprehensive review of the literature by De la Garza Ramos et al. [100] demonstrated that commonly used markers such as albumin, body weight, and BMI found no impact on patient outcomes [100]. This highlights that there is currently a clear lack of consistency in determining the overall nutritional status of a spinal oncology patient [100].
2. Preoperative Embolization, Deep Vein Thrombosis Assessment, Use of Tranexamic Acid
Preoperative embolization should be considered in the appropriate patient, specifically, those with a known histology of renal cell cancer, thyroid carcinoma, solitary fibrous tumor, leiomyosarcoma, and other vascular lesions [8]. Preoperative embolization can reduce intraoperative blood loss and improve tumor visualization. A systematic review of 1,134 patients undergoing spinal oncologic surgery with adjunctive embolization demonstrated a mean decrease in blood loss by 284.4 mL [101]. Both polyvinyl alcohol and Onyx had similar complete embolization rates. Overall complication rate from preoperative embolization remains low at roughly 3.1% [102]. Furthermore, embolization does not impact neurologic recovery, operative time, or overall complication rate [103]. Importantly, patients with spinal cord artery feeding vessel arising from the tumor should not undergo embolization [103]. Additionally, relative complications such as difficult vascular access, allergies to iodinated contrast, or when risks of radiation exceed benefits should always be considered [104]. Future studies on the efficacy of embolization as a treatment modality and the optimal timing of surgery are warranted.
Patients should be screened carefully for the presence of a preoperative deep vein thrombosis. In a retrospective review conducted by Zacharia et al. [105] in a series of 314 patients, deep vein thrombosis was found in a total of 9.5% of the cohort. Patients who are non-ambulatory or have a history of a prior deep vein thrombosis should be stratified carefully. Intraoperatively, the benefits of antifibrinolytics such as tranexamic acid should be discussed with the multidisciplinary team. A systematic review of 408 patients undergoing oncologic spine surgery conducted by Avila et al. [106] demonstrated that tranexamic acid can safely diminish blood loss and reduce the need for blood transfusion.
3. Postoperative Care
Postoperatively, early mobilization and active/passive limb movement helps reducing opioid consumption, improves functional outcomes and shortens hospitalization [107]. As demonstrated by Chanbour et al. [108] in a retrospective cohort study of 76 patients undergoing separation surgery, early radiation is associated with improved one-year survival. While some surgeons hesitate due to wound compromise, Ahluwalia et al. [109] found SBRT timing has minimal impact on wound complications, supporting early radiation for tumor control; however, EBRT is usually avoided until at least 2 weeks after surgery. Despite these benefits, the real-world implementation can be met with obstacles. As shown by Dugan et al [110]. up to 47% of patients did not receive postoperative radiation with 80% of those patients being candidates. Inpatient and clinic nursing teams should be involved to help ensure postoperative radiation is implemented and the patient does not “fall through the cracks.”
CONCLUSIONS
Metastatic spine disease presents a growing clinical challenge that requires the appropriate adoption of modern technologies while respecting fundamental principles. Advances in intraoperative imaging, minimally invasive techniques, and SBRT have significantly improved patient outcomes and quality of life, with the increased life expectancy of this population. A multidisciplinary team integrating evidence-based frameworks is vital to optimize treatment based on patient-specific conditions.
Notes
Conflict of Interest
Dr Laufer reports being a consultant for Icotec and receives royalties from Globus. Dr. Zuckerman reports being an unaffiliated neurotrauma consultant for the National Football League and a consultant for Medtronic. The other authors have nothing to disclose.
Funding/Support
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Author Contribution
Writing – original draft: HJ, RA, SLZ; Writing – review & editing: IL, SLZ.