|SYMPOSIUM - METASTATIC SPINAL TUMORS
|Year : 2022 | Volume
| Issue : 2 | Page : 168-175
Minimally invasive surgery for spinal metastases: Principles, techniques, and outcomes
Naresh Kumar1, Andrew Cherian Thomas1, Sean Junn Kit Lee1, Keith Gerard Lopez1, Sarah Shuyun Tang1, James Thomas Patrick Decourcy Hallinan2
1 Department of Orthopaedic Surgery, National University Health System, Level 11 Tower Block, 1E, Lower Kent Ridge Road 119228, Singapore
2 Department of Diagnostic Imaging, National University Hospital, Level 3 National University Hospital Main Building, 5 Lower Kent Ridge Rd 119074, Singapore
|Date of Submission||31-Jul-2021|
|Date of Decision||03-Jan-2022|
|Date of Acceptance||08-Feb-2022|
|Date of Web Publication||08-Jun-2022|
Department of Orthopaedic Surgery, National University Health System, Level 11, Tower Block,1E, Lower Kent Ridge Rd
Source of Support: None, Conflict of Interest: None
The incidence of metastatic spine disease (MSD) is on the rise and is currently present in 70% of patients presenting with systemic cancer. The majority of patients with MSD present with clinical symptoms such as neurological deficit, pathological fracture causing pain and spinal instability. Management of MSD is a multidisciplinary endeavor that involves surgery, radiotherapy (RT), and chemotherapy. The conventional open spine surgery approach has evolved into a less invasive surgery model categorized as minimally invasive spine surgery (MISS) or minimal access spine surgery. This evolution was brought about to address the complications associated with open surgery such as longer hospital stays and wound-related problems. MISS has been now widely explored in MSD due to lower wound-related complications, decreasing operative time, less neurological complications, and shorter hospital stays. Decompression and stabilization still remain the core concepts in MISS. Kyphoplasty/vertebroplasty, percutaneous pedicle screw fixation, separation surgery, and radiofrequency ablation are some of the minimally invasive techniques and procedures for surgical management of MSD. MISS is used in conjunction with other modern techniques like intraoperative neuromonitoring to help identify any adverse neurological events. MIS techniques will evolve with time, extending their application for the management of hypervascular tumors with significant anterior cord compression and recurrent tumors in which the open surgery currently remains the choice of approach.
Keywords: Minimally invasive spine surgery, minimally invasive surgery, neoplasm metastasis, open surgery, pedicle screw fixation, spine
|How to cite this article:|
Kumar N, Thomas AC, Lee SJ, Lopez KG, Tang SS, Hallinan JT. Minimally invasive surgery for spinal metastases: Principles, techniques, and outcomes. Indian Spine J 2022;5:168-75
|How to cite this URL:|
Kumar N, Thomas AC, Lee SJ, Lopez KG, Tang SS, Hallinan JT. Minimally invasive surgery for spinal metastases: Principles, techniques, and outcomes. Indian Spine J [serial online] 2022 [cited 2022 Jul 1];5:168-75. Available from: https://www.isjonline.com/text.asp?2022/5/2/168/346974
| Introduction|| |
Metastatic spine disease (MSD) is a burgeoning clinical condition that adversely affects quality of life. Approximately 70% of systemic cancer patients experience secondary involvement of the spinal column.,,, Neural compression leading to pain with or without neurological deficits, pathological fracture leading to spinal instability, intractable pain, or a combination of the above, is usually the presenting symptom and can be severely debilitating.,, Conventionally, MSD was successfully managed with radiotherapy (RT), especially in radiosensitive cancers such as myelomas, lymphomas, and neuroblastomas. However, a combination of surgery with RT has shown improved functional outcomes, survival outcomes, and patient satisfaction scores, in the majority of metastatic cancers.,,
The evolution of spinal surgery has leaped forwards significantly over the last 50 years. Proliferation of advanced minimally invasive techniques, utilization of technology combined with the use of novel spinal implants had led to a significant reduction of morbidity and mortality. The fundamental core principles of minimally invasive surgery (MIS) approaches are to (1) minimize collateral damage, (2) preserve the natural anatomy, and (3) reduce the overall stress to the patient while keeping to the same goals as open surgery.,
The current gold standard in the surgical management of MSD is surgical decompression and stabilization via an open approach., However, such approaches are associated with poorer outcomes when compared to minimally invasive techniques. It has been widely established that open spine surgery carries a higher risk of greater blood loss, increased operative time, and intensive care unit (ICU) and hospital stay compared to minimally invasive spine surgery (MISS).,
| Common Procedures and Techniques|| |
Kyphoplasty and vertebroplasty [[Figure 1]]
Vertebroplasty is the introduction of cement in the vertebral body through delivery needles inserted preferably through a transpedicular approach where the height of the vertebral body remains the same as the preoperative presentation or it may increase slightly due to intraoperative prone-positioning. Kyphoplasty follows the same principle of cement injection of vertebra. However, the vertebral body height restoration relies on both prone-positioning and procedural balloon inflation. Vertebroplasty was originally described in 1987, for the treatment of hemangiomas via a minimally invasive approach. Since then, vertebroplasty has been adapted for the treatment of intractable, focal, intense pain localized to a vertebral fracture. Vertebroplasty has now become a well-established treatment for intractable spinal pain secondary to pathological compression fractures in multiple myeloma. In 1998, kyphoplasty was introduced to restore vertebral body height and realign the spinal column., Both vertebroplasty and kyphoplasty opened the window for the use of MIS in spine. However, these procedures have limited benefit in the setting of tumor debulking or separation surgery.
|Figure 1: Illustration of (A) vertebroplasty and (B) kyphoplasty procedure|
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The main aim of vertebroplasty/kyphoplasty would be for pain relief and improvement in quality of life. Indications and contraindications for vertebroplasty/kyphoplasty are highlighted in [Table 1].
|Table 1: Indications and contraindications for kyphoplasty/vertebroplasty|
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The complications in relation to both procedures include cement leakage which could be local or systemic, hematoma formation, development of new or worsening radicular pain and pulmonary embolism due to cement migration and lodgment in the pulmonary vasculature. Should the index of suspicious be high for complications, a CT thorax scan can be performed for further evaluation.
The outcomes of these procedures are favorable as these interventions can be carried out on patients with limited functional reserve which is commonly seen in patients with MSD. Fourney et al. directly compared vertebroplasty and kyphoplasty in patients with cancer; in 56 patients (21 with myeloma, 25 with metastatic spinal lesions) for which they have reported equivalent results in relieving pain., A systematic review and meta-analyses by Gu et al. concluded that both interventions report similar outcomes; where no significant difference was found between vertebroplasty and kyphoplasty in short and long-term pain and disability outcomes.
Kyphoplasty and vertebroplasty techniques [[Figure 1]]
Vertebroplasty/kyphoplasty is initiated through the placement of a Jamshidi needle in the vertebral body via the transpedicular route. The landmarks for pedicle recognition and Jamshidi needle insertion are described in the following section, percutaneous pedicle screw fixation (PPSF). Once successful placement of the Jamshidi needle is achieved, with the exchange of the guidewire by a working channel through which the balloon could be inserted for kyphoplasty, cement is inserted using an appropriate cement pusher.,,,
Preoperatively, a computed tomography (CT) is required to ensure no posterior wall destruction has occurred from tumor involvement, which can predispose to leakage of cement and extravasation during the procedure. Despite adequate imaging – there is still a possibility of subtle, radiologically occult wall destruction, predisposing to cement extravasation. This can be partially mitigated by using systems with controlled cement delivery and intraoperative fluoroscopy.
Percutaneous pedicle screw fixation [[Figure 2]]
PPSF has now become a common MISS modality for spinal stabilization in MSD, associated with lower blood loss, good pain relief, faster initiation time to radiation therapy, and reduced complication rates. Its main advantage is the ability to stabilize the spine without excessive dissection of the posterior skeletal musculature.
|Figure 2: Systematic workflow approach to minimally invasive spinal surgery depicting the trend that as the complexity of intervention increases, overall morbidity increases [Image reproduced with permission from Springer Nature. License no: 5081241025067]|
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Percutaneous pedicle screw fixation technique
The percutaneous pedicle screw construct is designed such that there are two or more vertebrae acting as anchors on either side of the construct (comprising of four screws on each side), with intervening segments anchored by one or two percutaneous pedicular screws per level depending on the rigidity required for the construct.
In the upper- and mid-thoracic regions, the entry point to the pedicle is at the superolateral aspect of the pedicle and base of the transverse process, using a trochar directed medially and inferiorly to lie in the center of the pedicle. Once the tip of the trochar reaches the root of the pedicle, it is then directed medially to gain purchase in the medial portion of the vertebral body.
In the lumbar vertebra, a transpedicular approach is used to insert the percutaneous screws in the vertebra. Here, the Jamshidi needle is placed at the outer aspect of the pedicle at its equator (the intersection of the lines—one bisecting the transverse process and the other along the outer aspect of the superior facet). The Jamshidi needle is then gently advanced towards the midline to ensure the screws are in the middle of the pedicle until its root and the rest of the screws are anchored in the medial vertebral body.
This is usually followed on by planned decompression, which may comprise laminectomy and/or pediculectomy with partial corpectomy. After achieving the surgical decompressive goal, the percutaneous pedicle screws are connected using a rod system which is also passed percutaneously in nearly all the current available systems [Figure 3] and [Figure 4].
|Figure 3: Illustrations of (A) preoperative sagittal MRI and (B) anteroposterior and lateral radiograph of a posterior MIS instrumentation T3 to L1 (skip instrumentation); posterior decompression T10–T11; partial corpectomy T10; Viper 2 JandJ. Underlying malignancy––Breast Ca|
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|Figure 4: Illustrations of (A) preoperative sagittal and axial MRI, and (B) anteroposterior and lateral radiographs of a spinal decompression by L2 and L3 laminectomy: Instrumentation T12 to L5 skip; Alphatec Ileco. “Haloes” around the screw indicate radiologic evidence for screw loosening (red arrows) and early screw loosening (yellow arrow)|
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In patients with extensive MSD, finding anchor points may not be as easy as multiple contiguous vertebrae may be involved. In addition, magnetic resonance imaging (MRI) tends to overestimate the tumor involvement, especially on T1-weighted images. In such cases, preoperative CT evaluation may be necessary to identify vertebra which show no pedicle involvement and help identify sclerotic secondaries which are strong enough to anchor the screws. If one cannot find such a vertebra in the segment undergoing decompression, an alternative would be to use a fenestrated screw with cement augmentation to increase screw purchase.
In the case of multiple metastatic vertebral deposits, we feel the priority of metastatic spine tumor surgery (MSTS) is to address the symptomatic levels first, even in the presence of radiologically compelling but asymptomatic vertebrae. This avoids the unnecessary burden of a lengthy surgery and its associated complications.
Systematic adjuvant therapy is still the mainstay of treatment for MSD which should address both the operated and nonoperated levels. Should the asymptomatic vertebral lesion become symptomatic in the future requiring surgery, the option of rod connectors is available for extension of instrumentation without disturbing the primary construct.
The new concept of separation surgery has changed the surgical paradigms for the treatment of metastatic epidural spinal cord compression (MESCC), shifting from aggressive cytoreductive surgery toward a less invasive surgery with the aim to achieve circumferential separation of the spinal cord. This will also allow for a safe target for high-dose stereotactic body radiation therapy (SBRT). Separation surgery is used as an adjunct to PPSF. In patients undergoing minimal access spine surgery (MASS), screw insertions are made through stab incisions dictated by standard MIS techniques. The lamina of the involved vertebra is approached by a muscle-splitting technique by joining the two stab incisions adjacent to the pathological vertebra. This minimal access approach allows enough visualization to perform an adequate laminectomy, over-the-top decompression, pediculectomy, and partial corpectomy to achieve a circumferential decompression and separation of the neural elements from the residual tumor. The side of approach is decided by the clinical and radiological assessment of neural element compression.
Barzilai et al. in a prospective study of 111 patients, reported results about QoL after “hybrid MESCC therapy.” Spine pain severity at 3 months was significantly reduced and general activity was also improved (P = 0.001); local recurrence rate resulted to be 2.1% and 4.3% at 6 months and 12 months, respectively., A similar cohort of 200 patients operated between 2005 and 2017 in our institution who underwent PPSF or separation surgery with PPSF, retrospectively studied, showed decreased blood loss, shorter length of stay, and reduced complication.
If separation surgery is the surgical aim, we recommend preoperative embolization. This is because secondaries thought to be normovascular, that is, breast, lung, prostate could still be highly vascular. This may be evident by evaluating the preoperative MRI short tau inversion recovery (STIR) sequences.
While addressing T2 to L1 secondaries, using separation surgery techniques, sacrificing of the appropriate thoracic nerve roots can be made because they carry no motor fibers of significance. We advise to tie off the nerve root with a silk stay suture, so that it can be used to evert the dura creating a surgical plane between the anterior dura and the posterior surface of the tumor. This plane is relatively avascular and easy to operate on, with the aim of creating a 3–5 mm separation.
Radiofrequency ablation (RFA) systems entail the utilization of a high-frequency alternating current passing from an electrode needle to the underlying tissues, resulting in friction heating leading to tissue necrosis. RFA arrests damage to bone and inhibits pain-inducing activities of osteoclasts, in addition to promoting the release of different cytokines and factors. Overall, it has been shown to reduce the mass effect of the tumor on adjacent organs as well as to decrease tumor burden. Dupuy et al. first reported that RFA provided pain relief in two patients––one with metastatic hemangiopericytoma and the other with an osteoid osteoma. Furthermore, although they showed that temperature levels in the spinal canal did not reach cytotoxic levels, the use of RFA is traditionally limited in posterior vertebral body lesions due to the close proximity to spinal cord and nerve roots.
The standard treatment approach utilizes two electrodes, with tips spaced at least 8–10 mm apart. The ablation zones resulting from both electrodes coalesce into a larger, singular ablation area. Based on the extent of metastases (size and location) and the expected goal of the procedure on a per-tumor basis, the operator then selects the number of electrodes, mono or bipedicular electrode tips, the length, optimal temperature, and number of ablation cycles to achieve the best result. In addition, the operator decides if any ancillary protective measures are necessary to prevent injury to the spinal cord and their respective nerve roots. The most frequently encountered minor complications are puncture site hematomas, transient hyperthermia and transient pain exacerbation. However, major complications include skin burns, which range from mild erythema to third-degree burns, and neurovascular injury which may encompass foot drop, transient bowel and bladder incontinence, and neuropathic pain.
Several factors underlying the pathophysiology and therapeutic effect of tumor RFA have been proposed:,,,
- Reduction of transmission of pain signals to the periosteum mediated by heat destruction of pain-sensitive fibers in the immediate to early-phase post-RFA
- Mechanical stabilization from the destruction of a bulging lesion
- The destruction of tumor cells that produce cytokines including tumour necrosis factor alpha, substance-P, and interleukins responsible for stimulation of sensitive nerve fibers
- Destruction of osteoclasts
A prospective, single-arm, multicenter study supported by the American College of Radiology Imaging Network found that RFA significantly reduces pain intensity and severity in patients with unremitting pain from bone metastasis. Grönemeyer et al. described 10 patients with unresectable metastatic spinal lesions treated with RFA—90% reported reduced pain across a follow-up period from 3 to 11 months, with an average reduction of 74% in pain intensity. RFA for spinal metastases is usually well tolerated and the observed toxicity rate is often low. Previous case series report low rates of major complications in RFA, ranging between 5.4% and 6.5% in two large series.,
If posterior wall destruction has occurred from tumor involvement, it would be safer to elect for RFA over Kyphoplasty and Vertebroplasty. It can be performed under conscious sedation with local anesthesia in patients who are otherwise poor surgical candidates
| Recent Advancements in Minimally Invasive Surgery for Spinal Metastases|| |
Since the 1990s, medical-grade titanium alloy has been extensively used in spine surgery owing to its good biocompatibility, mechanical strength and corrosion resistance; and remains gold standard for implants used in MSTS. However, in its application in MSTS, titanium still cannot be classed as the ideal implant material. Titanium can cause stress shielding at the implant-bone interface due to its higher Young’s modulus of elasticity compared to cortical bone (110-118GPa vs 17-21GPa, respectively). This causes bone remodeling with reduced density, weakening of the surrounding bone, and increasing the risk of implant failure. Furthermore, titanium generates artifacts on common imaging modalities, that is, MRI and CT. This hinders RT planning and detection of tumor recurrence.
Owing to these factors, other materials have been explored. Non-metallic, polymer-based implant materials such as polyether ether ketone (PEEK) have been largely researched for use in MSTS. Such materials have a lower Young’s modulus of elasticity (PEEK ~3.6 GPa), closer to that of cortical bone, resulting in less stress shielding and reduced risk of implant failure. In addition, such materials tend to be radiolucent with reduced artifacts, increasing their compatibility with MRI and CT and allowing for more accurate RT planning and detection of tumor recurrence. Examples of such implant materials include pure PEEK, carbon fiber reinforced PEEK, and PEEK composite materials such as titanium-PEEK composites.
Intraoperative neurophysiological monitoring
A recent publication from our institute showcased that strong baseline signals obtained with multimodal intraoperative neurophysiological monitoring (IONM) could be used to effectively monitor the spinal cord function of patients during MSTS. However, it was concluded that IONM is not cost-effective in MSTS patients with preoperative American Spinal Injury Association (ASIA) grades A to C. Therefore, it could be avoided in such cases without compromising on patient management. However, for preoperative ASIA grades D or E, who require instrumentation and decompression, IONM has high sensitivity and specificity in detecting significant intraoperative neurological events. This aids in preventing postoperative neurological deficits and can help identify reversible causes that may have triggered the IONM alert, although may not necessarily change the course of the surgical intervention in MSTS.
Image guidance and advanced robotics systems are becoming more widespread in their utilization and can be an invaluable intraoperative tool during MSTS. Robotic systems provide a unique theoretical advantage over freehand techniques for placing instrumentation within the spine. Although recent publications on robotic systems show a decrease in the overall incidence of malpositioned screws, their impact on clinical outcomes in this group of patients is still limited. Their overall value in improving surgical accuracy must be weighed against concerns of additional cost to the patient.
| Current Ground-breaking Research Concepts|| |
The recently introduced novel concept of “readmission-free survival”, is fast becoming a key quality metric for assessing the success of outcomes after MSTS. Readmission-free survival (ReAFS) is the time duration between hospital discharge after index operation and the first unplanned hospital readmission (UHR) or death. An ideal ReAFS should be equal to the remaining life expectancy of the patient after MSTS, which would mean an absence of UHR until their demise.
ReAFS is an integrated assessment tool dependent on patient’s general condition, appropriateness of interventional procedures, and underlying disease burden. Factors that have now been proven to associate with a decreased ReAFS are pre-op Hb <12g/dL, ECOG >2, primary lung cancer, comorbidities ≥4, preoperative administration of RT, and increased postoperative length of stay. This information allows oncologists and surgeons to identify patients who may benefit from increased surveillance post-discharge to increase the ReAFS. Furthermore, ReAFS will enhance preoperative patient counseling.
Role of endoscopic surgery
Endoscopic techniques have been utilized for management of MSD since the 1990s. Endoscopy allows for fluoroscopy guided real time visualization of the surgical site through smaller incisions. Similar to other MIS approaches, endoscopic procedures result in reduced surgical morbidity, lesser blood loss, shorter hospital stays, and quicker recovery period., Percutaneous transforaminal, posterolateral and transpedicular approaches assisted with endoscopy are the standard routes to decompress, resect or remove the offending metastatic tumor disease.
In a clinical study by Rosenthal et al., 28 patients were treated with microsurgical endoscopy for different pathologies involving the thoracic segments. Of 28 patients operated, 4 patients presented with MSD in thoracic segments and were treated with vertebrectomy and stabilization using endoscopic technique. All the four patients reported resolution of pain and were ambulant post-surgery and at follow-up at ~11 months. Similarly, in a single surgeon retrospective clinical series by Telfeian et al., 325 patients were treated with transforaminal endoscopic approach between 2014 and 2018. Of 325 patients, 4 patients were identified with neurological symptoms secondary to MSD. These patients underwent endoscopic approach for tumor biopsy and tumor debulking to decompress the nerve roots. All the patients reported resolution of pain and required shorter recovery periods.
Despite the above-mentioned advantages, potential complications associated with these procedures are as follows: intraoperative bleeding, dural tears, injury to vessel/nerve, and infection. Watanabe et al. reported extensive bleeding (~2500ml), respiratory complications, and transient neurological dysfunction in the patients who were treated with anterior endoscopic surgery for different spinal pathologies between 1996 and 2003. They reported an overall complication rate of 42.3% (20/52). In a more recent prospective study by Cofano et al., nine patients with MSD underwent separation surgery with 3D endoscope-assisted thoracic corpectomy between January 2019 and April 2019. The mean blood loss was 580ml and the mean operative time was 260 minutes. The study presented the feasibility of the technique and was reported to be safe for use in separation surgery for thoracic metastases. The learning curve for utilization of endoscopic approaches is steep owing to the technical challenges such as longer training period and competency in handling the equipment. In addition, endoscopic techniques pose a certain level of clinical concern due to higher doses of radiation exposure (1.3 to 3.1 millisievert [mSv]) for both the patients and surgeons. As endoscopic techniques continue to evolve, the complications associated with endoscopic techniques will reduce and are likely to be better managed.
| Conclusion|| |
Minimally invasive techniques are being increasingly used in MSTS owing to their better clinical outcomes compared to the open approach. MIS techniques may evolve with time, extending their application for the management of hypervascular tumors with significant anterior cord compression and recurrent tumors in which open surgery currently remains the choice of approach.
We would like to thank Dr. Balamurugan A. Vellayappan, Sridharan Alathur Ramakrishnan, and Laranya Kumar for their help in editing the manuscript.
Ethical policy and institutional review board statement
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]