|
 
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| SYMPOSIUM - METASTATIC SPINAL TUMORS |
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| Year : 2022 | Volume
: 5
| Issue : 2 | Page : 158-167 |
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Concepts, rationale, and techniques of the open approach in the surgical management of metastatic spine disease
Naresh Kumar1, Sean Junn Kit Lee1, Sridharan Alathur Ramakrishnan1, Andrew Cherian Thomas1, Sarah Shuyun Tang1, Balamurugan A Vellayappan2
1 Department of Orthopaedic Surgery, National University Health System, Singapore, Singapore
2 Department of Radiation Oncology, National University Health System, Singapore, Singapore
| Date of Submission | 31-Jul-2021 |
| Date of Decision | 28-Sep-2021 |
| Date of Acceptance | 24-Jan-2022 |
| Date of Web Publication | 08-Jun-2022 |
Correspondence Address:
Naresh Kumar
Department of Orthopaedic Surgery, National University Health System, Level 11, Tower Block, 1E, Lower Kent Ridge Rd
Singapore
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/isj.isj_73_21
Advancements in medical therapy have led to the increased incidence of metastatic spine tumor surgery (MSTS) owing to the increased survivability of cancer patients. Over the years, surgical techniques have evolved from simple laminectomy to advanced radical surgery with reconstruction. Surgery with radiotherapy (RT) and chemotherapy have been established as key paradigms for the management of metastatic spine disease (MSD). In general, surgical treatment is split into two categories, open and minimally invasive. Decompression and stabilization form the basis of the common surgical techniques for managing MSD. Pedicle screw-rod instrumentation forms the basis of fixation, whereas decompression can be achieved through techniques such as laminectomy, separation surgery, partial corpectomy, near piecemeal corpectomy, or en bloc corpectomy. However, complications such as infection, wound dehiscence, and instrument failure remain the challenges of MSTS. This gives the need for auxiliary techniques and advancements to improve the efficacy of MSTS and reduce complications. Recent advancements such as intraoperative cell salvage in MSTS have reduced the need for allogenic blood transfusion, thus reducing the risk of infection and other complications. Additionally, implant materials such as carbon-fiber-reinforced polyether–ether-ketone (PEEK) and titanium-coated PEEK with better biocompatibility, imaging, and RT compatibility have been explored for use in MSTS. Current trends in MSTS are shifting toward minimally invasive surgery (MIS); however, open surgery remains the “gold standard.” Open surgery is preferred in cases with compromised visibility, i.e., hypervascular tumor secondaries and in regions of spinal column with limited access where the MIS approach is likely to be dangerous. We recommend that all spine surgeons be familiar with the concepts and techniques of open surgery for MSD. Keywords: Corpectomy, minimally invasive surgery, neoplasm metastasis, open surgery, pedicle screw fixation, radiotherapy, spine, surgical techniques
How to cite this article:
Kumar N, Lee SJ, Alathur Ramakrishnan S, Thomas AC, Tang SS, Vellayappan BA. Concepts, rationale, and techniques of the open approach in the surgical management of metastatic spine disease. Indian Spine J 2022;5:158-67 |
How to cite this URL:
Kumar N, Lee SJ, Alathur Ramakrishnan S, Thomas AC, Tang SS, Vellayappan BA. Concepts, rationale, and techniques of the open approach in the surgical management of metastatic spine disease. Indian Spine J [serial online] 2022 [cited 2023 Apr 1];5:158-67. Available from: https://www.isjonline.com/text.asp?2022/5/2/158/346975 |
| Introduction | |  |
The number of patients with metastatic spine disease (MSD) have increased owing to advancements in medical therapy, improving survivability.[1] The vertebral column is the commonest site of bony metastasis and its proximity to the spinal cord makes conventional surgical techniques for cancers challenging.[2] Spine surgical techniques have evolved from simple laminectomy to major radical surgery with reconstruction. Posterior laminectomy has a defined place in cases where a tumor only involves the posterior elements, causing symptoms. However, in most cases, where spinal cord compression is secondary to anterior column involvement, posterior decompressive laminectomy was found to confer no additional benefit compared to conventional radiotherapy (RT) alone.[3] Direct decompressive surgery with adjunct RT is superior to RT alone for patients with MSD.[2] Superior outcomes including regaining and retaining ambulatory status, and reduced opioid analgesic requirements were shown in patients who underwent decompressive surgery with or without stabilization in conjunction with RT, therefore becoming the standard treatment.[4]
| Clinical Presentation and Disease and Survival Prognostication | | |
MSD patients commonly present with pain (95%), which results from a combination of periosteal stretching, spinal instability, and tumor or vertebral body collapse. Additionally, MSD patients may also present with neurological deficits (75–80%) including sensory, motor, and/or sphincter dysfunction.[1] Spinal instability occurs secondary to MSD, frequently presenting as pain on movement. As the term “spinal instability” suggests, pain is maximal during twisting, flexion, and extension of the spine and relieved when the spine is supported, i.e., the supine position.[1] Pain from the MSD can cause significant functional loss in the absence of neurological deficit and contributes significantly to morbidity. Mechanical instability, pathological fractures, and symptomatic cord compression—symptoms including acute and severe motor and sphincter dysfunction—often require surgical intervention.[1]
Patient selection for spinal surgery remains a difficult, ongoing topic of discussion. The surgical intent in these patients is improving pain control and preserving or restoring neurological function through decompressive surgery, achieving spinal stability through instrumentation and local tumor control.[5] Surgery remains the mainstay of treatment despite their relatively short life expectancy as it improves their quality of life (QoL) and decreases burden of care.[6]
Survival prognostication is an important component for treatment planning in MSD patients. Common survival prognostication scores include the revised Tokuhashi score, Tomita score, Oswestry Spinal Risk Index, and Eastern Cooperative Oncology Group Performance Status. These scoring systems commonly take into consideration preoperative functional status, type of primary tumor, and metastatic tumor load at the time of patient presentation. Spinal instability, another important factor in patient selection, is categorized according to the Spinal Instability Neoplastic Score. Although there are no single all-encompassing selection criteria, the decision to operate is often guided by a combination of the aforementioned scores.
| Preoperative Embolization | | |
Transarterial embolization (TAE) provides an important contribution to reducing surgery morbidity through reducing risk of intraoperative bleeding, offering a better visualization of the operating field and possibly increasing tumor susceptibility to chemotherapy and/or RT.[7] However, preoperative spinal tumor embolization should not be restricted to TAE through the dominant feeders from the primary segmental artery. Neighboring arteries that could supply the tumor should also be thoroughly interrogated and embolized if required.[8] Nonetheless, it plays an important part in pain palliation, with the unquestionable advantage of being easily repeatable in case of necessity. Its curative role as a standalone therapy is still a subject of debate, and at the present time, satisfactory results have been recorded only in the treatment of aneurysmal bone cysts.[7]
Clinical pearls
Hypervascularity of tumor indicated in magnetic resonance imaging (MRI) correlates poorly with the standard angiographic hypervascularity. This is especially true in moderately vascularized metastases.[8] MRI hypervascularity is a better predictor of estimated blood loss. As such, the operative planning should be based on MRI hypervascularity instead of standard angiographic hypervascularity.[8] In tumors with MRI hypervascularity without angiographic hypervascularity or with difficulty in achieving comprehensive devascularization, there may be a need to explore alternative embolization techniques (e.g., direct percutaneous injection) beyond the conventional transarterial ones.[8]
| Surgical Treatment | | |
Surgical indications for MSD include rapidly progressive or severe neurological deficits, spinal instability, pathological fracture or cord compression secondary to retropulsion of bone, radioresistant tumors, solitary metastases with pain, and/or a combination of the above.[9] Surgery aims to achieve mechanical stabilization, pain control, and improvement/maintenance of neurological status.[10] Choice of surgical technique, levels instrumented/decompressed, and surgical approach influence the morbidity of surgery, affecting surgical outcomes such as blood loss, operative time, and duration of hospital stay [Figure 1].[2] | Figure 1: Modalities of posterior percutaneous spinal fixation used for the management of MSD
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Surgery can be split into two broad categories: (i) open and (ii) minimally invasive surgery (MIS).
MIS results in reduced blood loss, hospital stay, and postoperative morbidity;[11] however its main limitations are namely (i) visibility—in the event of excessive intraoperative bleeding, (ii) anatomical location—limited in regions such as high cervical tumors, and (iii) surgical expertise—involves a steep learning curve resulting in longer operative times.[1] While operating with the above limitations, open surgery remains the gold standard.[1] Specific examples where open conventional surgery is indicated will be hypervascular metastases (renal, thyroid, hepatocellular, among others) with a significant anterior cord compression requiring anterior decompression, in recurrent tumors, or patients with significant comorbidities requiring shorter operative times in surgical teams who are more conversant with open techniques.[11] The open approach may be more ideal in long constructs requiring a significant extent of contouring of the fixation rod.[11] Conversion from MIS to open surgery is also indicated in significant intraoperative bleeding.[11]
| Decompression Surgery | | |
Decompression surgery is the standard technique for MSD.[2] Early strategies for decompression in the first half of the twentieth century involved posterior decompressive laminectomy alone.[1] However, this resulted in limited access to the anterior tumor and incomplete tumor debulking, and introduced iatrogenic instability, thus leading to failure.[1] Advances in the surgical technique involved introduction of stabilization techniques, which allowed for a more complete decompression while preserving spinal stability.[1] Approaches can be anterior and/or posterior depending on the site of compression, reconstruction goals, tumor type, and surgeon-specific (e.g., surgical expertise) and patient-specific factors (comorbidities and body habitus). Currently, laminectomy, transpedicular decompression, and less commonly, corpectomy (piecemeal or en bloc) are some such techniques [Figure 2].[12] | Figure 2: A—Vertebra with tumor involvement (brown color), B—laminectomy decompression, C—anterior partial corpectomy, and D—posterior near-total piecemeal corpectomy
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| Stabilization Techniques | | |
Instability can occur due to pathological fracture or iatrogenic instability from surgical decompression. Stabilization techniques include spinal instrumentation and vertebral column reconstruction.[13] Spinal instrumentation primarily consists of posterior rod and screw constructs. Vertebral column reconstruction is performed following vertebral column tumor resection, which can include a range of options, namely, mesh or expandable cages, vertebroplasty, and kyphoplasty.[13] Furthermore, expandable cages can incorporate bone autograft and/or allograft for possible osseous integration.[13]
| Surgical Options with Open Pedicle Screw Fixation | | |
Open surgical techniques include (i) open pedicle screw fixation (OPSF), (ii) OPSF with posterior decompression, (iii) partial corpectomy with OPSF, (iv) near-total piecemeal corpectomy with reconstruction and OPSF, and (v) en bloc corpectomy with OPSF. En bloc corpectomy may be performed for a small subset of patients who present with single-site metastatic disease. However, the extent of resection is dependent on tumor position, size, and other factors such as RT planning. Additionally, surgical decision-making dictates the surgical technique to be used.
| Open Pedicle Screw Fixation | | |
Posterior rod and screw constructs require a minimum of two vertebrae as anchors on either side of the construct, comprising four screws on each side. Paravertebral muscles are dissected and retracted to expose entry points on pedicles. Pedicle screws are then inserted by the free-hand technique two to three levels above and below the regions of decompression and checked using fluoroscopic guidance.[2],[14] Skip instrumentation can be performed should the levels be deemed unsatisfactory for the insertion of pedicle screws (e.g., poor bone quality from tumor infiltration and/or osteoporosis). Surgeons may elect to do instrumentation alone without decompression in the event of spinal instability with no neurological deficits [Figure 3]. | Figure 3: Treatment algorithm for management of MSD [Image reproduced with permission from Springer Nature. License no: 5081231333817]
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| Separation Surgery | | |
The emergence of high-dose ablative RT (e.g., stereotactic body radiotherapy [SBRT]) has allowed for less extensive tumor resection.[1] Separation surgery involves creating a physical space between the tumor and spinal cord to provide a safety margin for effective and precise delivery of high-dose SBRT.[1] Operative duration and bleeding rates are reduced, therefore reducing overall morbidity.[13] Separation surgery is indicated in patients with neurological deficits, spinal instability, and radioresistant tumors (i.e., renal cell carcinoma), which are now effectively treated by SBRT.[13] For centers with limited access to SBRT, a more radical surgical excision may be required.
| Corpectomy | | |
When the diseased and adjacent vertebra have been adequately exposed and appropriate OPSF done, decompression of the tumor can be started by removing an adequate number and amount of laminae. To proceed with the corpectomy, it is essential to locate the lateral border of dura and nerve roots. Generous debulking of the vertebral body can be confidently carried out having located the lateral border of the dura below the pedicle and then delivering remaining vertebra into the vertebral body resection cavity.[15]
| Partial Corpectomy | | |
When the tumor is only on the unilateral aspect of the vertebral body, a partial corpectomy can be done, usually by the posterior approach. The ipsilateral pedicle and transverse process on the side of the tumor are resected for access to the posterior part of the vertebral body [Figure 2C]]. The dura is appropriately protected; for the levels from T2 to L1, the ipsilateral nerve root can be sacrificed to expose the posterior part of the vertebral body adequately and safely.[15] A partial vertebral body piecemeal resection can be performed as necessary of up to 30% of the vertebral body [[Figure 2C]].[15] Partial corpectomy is an alternative for separation surgery where the surgical team is more inclined to consider open surgery over MIS approaches and definitive amount of tumor material is planned to be resected so as to debulk the tumor material adequately before considering RT or chemotherapy.
| Near-total Piecemeal Corpectomy | | |
A near-total piecemeal corpectomy is indicated in tumors involving most of the vertebral body and/or lamina. Both posterior and anterior approaches can be used depending on the tumor location. In the posterior approach, the lamina can be easily removed; both pedicles are resected for access to the vertebral body, and piecemeal resection of ≤90% of the vertebral body can be done [Figure 4]A.[15] If the anterior approach is chosen, then segmental vessels would be ligated at the level of the diseased vertebra and one level above and below [Figure 4]A. Major vessels anterior to the vertebral bodies can be retracted away. Adjacent discs are identified and removed by separating them from the adjacent vertebral endplates, with transection of the anterior longitudinal ligament (ALL), following which, the diseased vertebra is resected piecemeal of up to ≥90%.[15] The gap created by the tumor resection can be filled by an appropriately sized cage or allograft. Metallic cages are preferred over allografts as spinal fusion still does not remain a prime objective in tumor surgery. This particular surgical approach is preferred for tumors that are still considered as radioresistant; hence, near-total resection will provide a more effective local tumor clearance. In patients in whom chemotherapy and RT cannot be started early, generous tumor clearance may be required to achieve earlier tumor control until RT and/or chemotherapy can be started. | Figure 4: A—near-total piecemeal intralesional corpectomy, B—en bloc intralesional corpectomy, and C—en bloc wide resection of the vertebra
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| En Bloc Corpectomy | | |
The indications of en bloc corpectomy involve tumors limited to the vertebral body, and/or unilateral pedicle and transverse process. This method involves posterior ± anterior approach in a stepwise manner [Figure 4]B and C.[15]
If the procedure was only carried out via a posterior approach, adequate exposure is achieved to conduct a wide or partial laminectomy of the diseased vertebra as indicated by the Weinstein–Boriani–Biagini (WBB) classification [Figure 5]. Before the laminectomy, pedicle screws are inserted two levels above and below the diseased vertebrae, which is planned for removal.[15] The exposed dura is then retracted side to side to allow for coagulation of epidural vessels and mobilized to enable identification of adjacent disc spaces. Roots are controlled on both sides to avoid possible injury. Lateral dissection is carried out on both sides of the vertebral body to separate the segmental vessels and the major vessels away from the vertebral body. A complete posterior discectomy with cutting of posterior longitudinal ligament is carried out. A “T-Saw” is ideally passed in the space created by the finger dissection between the major vessels and vertebral body [Figure 6]. This instrument is key to cut the ALL and remainder of the annulus at the adjacent discs to free the vertebral body. This vertebral body is rotated on the convenient side without injuring the dura and neural elements. Appropriately sized cage or allograft is inserted in the space created by the corpectomy. Posterior fixation with rod and screw constructs is completed and the wound is closed in layers.[15]  | Figure 6: The application of T-saw for en-bloc corpectomy. A—diseased vertebrae, B—malleable flat vascular retractor, C—T-saw, D—pedicle screw, and E—rod
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Occasionally, en bloc corpectomy surgery may require a two-stage operation with both a posterior and an anterior approach, especially if sufficient anterior clearance is needed. The first stage involves a posterior approach with standard exposure described earlier, and the amount of lamina and pedicle to be removed will be dictated by the WBB classification. The extradural and disc work is the same as described previously. However, if the corpectomy was carried out by the anterior approach, the site opposite of the anterior approach would be thoroughly released through the posterior approach. The posterior fixation is similarly carried out along with wound closure before the second stage.[15]
The second stage can be done in the same sitting or on a different day and is usually an anterior approach from the left or right as decided. This approach includes dissection of psoas muscle off the vertebral body. After complete soft tissue elevation and vascular control, adjacent discectomy or osteotomy is completed. The vertebral body can be removed “en bloc” away from the spinal canal [Figure 4c]. The vertebral body can be reconstructed via a massive bank bone graft or an expandable cage with bone auto/allograft. Some may elect to perform anterior plate instrumentation.[15]
En bloc corpectomy is reserved for isolated metastases from renal, thyroid, or breast carcinomas. A demanding procedure like this if done successfully is likely to provide total local tumor clearance leading to least chance of recurrence and even improved overall survival in these patients.
| Intraoperative Precautions | | |
Intraoperative neurophysiological monitoring (IONM) is an effective adjunct to metastatic spine tumor surgery (MSTS) for detecting significant intraoperative neurological events.[16] In cases of instrumentation and decompression (i.e., American Spinal Injury Association [ASIA] grades D to E), IONM’s high sensitivity and specificity facilitate the identification of reversible surgically induced neurological events.[16] Although this may not necessarily change the course of the surgical intervention in MSTS, but it may help prevent postoperative neurological deficits. However, in cases where the neurological deficits documented to be ASIA grades A to C, IONM may not be cost-effective and could be avoided without compromising patient management.[16]
| Treatment Algorithm | | |
Decision-making for treatment modality is based on clinical pathways from the following algorithm [Figure 3].[1] Patients can be categorized into two groups—one with neurological deficit and one without. They are further subdivided according to the presence or absence of radiological features displaying cord compression. Patients with neurological deficit would be prioritized for early surgery, whereas patients with no neurological deficit would be considered for surgery in the event of instability or intractable pain.
Clinical pearls
Surgeons should aim to strike a balance between the patient’s comorbidities and overall health and the least invasive option for MSTS [Figure 1]. With no neurological deficits, the surgical aim would be for stabilization with instrumentation. In the event of neurological deficits with a larger scale of tumor involvement, one may consider more invasive decompression/tumor debulking surgery, i.e., corpectomy. The extent of tumor resection and surgical choice will be based on both anatomical and patient factors. The WBB staging system [Figure 5] stages the extent of tumor involvement based on anatomy and is thus used to guide adequate tumor resection.
Patient factors to consider will include patient prognosis, perioperative risk to the patient, and general fitness for surgery.[1] Bleeding risk in MSTS remains extremely high despite availability of preoperative embolization and can potentially lead to shock, multiorgan failure, and possible mortality.[17] Should patient’s health status be prohibitive for aggressive surgery, then instrumentation ± minimal decompression would be the preferred choice. For patients who have a better prognosis and can tolerate more aggressive tumor excision, surgeons can consider maximum possible resection as dictated by the WBB staging system [Figure 1] and [Figure 5].
| Surgical Complications in General | | |
It has been established that MSTS with adjuvant RT and/or chemotherapy is the paradigm for the successful management of MSD. However, surgery includes risks such as infection, wound dehiscence, and other comorbidities that can affect the surgical outcomes and QoL. Bleeding risk remains high in MSTS, and the average estimated blood loss was found to be 824.5 ± 685.4 ml.[18],[19] The overall surgical complication rate is 29%[20] but can range between 10% and 66.7%.[21] These conditions might imply requirement for revision surgery.[22]
Generally, MSD patients have comorbidities with an average American Society of Anesthesiologists (ASA) grade of 3[23] and thus increased risk of systemic, life-threatening complications such as cardiorespiratory collapse and stroke. Longer constructs or more levels instrumented or decompressed increase complexity and result in higher morbidity [Figure 1].
Novel scoring systems such as “Spinal Metastasis Invasiveness Index” can be used to predict complications such as intraoperative blood loss and surgical duration, and indirectly predict risk of urinary tract infections, pneumonia, or thromboembolic events.[18]
| Wound Complications in General | | |
Quraishi et al.[24] reported a surgical site infection (SSI) rate of 9.1% (29/318) in patients who underwent MSTS between October 2005 and October 2012. Furthermore, the authors reported that among 29 patients with SSI, 20 required the debridement procedure. Similarly, in a retrospective study by Zaw et al.,[25] the SSI rate of 6.1% (15/247) was reported in the patients who underwent MSTS between 2005 and 2014. Furthermore, the authors reported other postoperative infections such as systemic sepsis (1.6%), chest infection (4.8%), urinary tract infection (11.3%), and multiple site infection (3.2%).[25]
| Other Complications | | |
Complications like metal work failure after MSTS have also been reported.[26] Kumar et al.[27] in their clinical study reported an implant failure rate of 5.7% (14/246) and a revision rate of 4.1% (10/246) in patients who underwent MSTS. Tumor progression affects bone quality and disrupts bone formation. Furthermore, bone quality is hampered by adjuvant RT and chemotherapy, resulting in implant/construct failure at the bone–implant interface.[26] Similarly, postoperative complications in MSTS were found to be influenced by perioperative blood transfusion. Zaw et al.[25] reported an overall postoperative complication rate of 36% (48/133) in patients who received allogeneic blood transfusion. The authors reported postoperative infections such as SSI (7.5%), systemic sepsis (2.3%), chest infection (7.5%), urinary tract infection (14.3%), and multiple site infection (4.5%) in patients who received allogeneic blood transfusion (133/247).[25]
| Procedure-related Complications | | |
Open pedicle screw fixation
Main complications in OPSF are implant/construct failure and pedicle breach.[26] Implant/construct failure may result from screw ploughing, loosening, pullout, cutout, and breakage; cage subsidence, displacement, breakage; angular deformity; peri-construct failure; and rod breakage [Figure 7].[26] Pedicle breach can be iatrogenic due to an overestimation of pedicle screw diameter with respect to patient’s pedicle width or incorrect insertion angle. Alternatively, pedicle breach could be a result of screw cutout. Prolonged RT may decrease bone mineral density, possibly resulting in peri-construct failure.[28],[29] | Figure 7: Mechanisms of metal work failure [Image reproduced with permission from Springer Nature Licaense no. 5081241315016]
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Separation surgery
Complications of separation surgery are comparatively minimal.[30] However, there remains a risk of residual tumor growth. Laufer et al.[31] reported local tumor progression rate of 18.3% (34/186). Amankulor et al.[32] reported hardware failure in 2.8% (9/318) patients, which was attributed to inadequate anterior column reconstruction in separation surgery.[32],[33] Nonetheless, osteopenic side effects of SBRT (compared to conventional RT) on adjacent healthy vertebrae were reduced and led to reduced implant failure rates.[34],[35] General postsurgical complications of SSI and poor wound healing may be exacerbated by SBRT.[33] Amankulor et al.[32] reported a case of wound dehiscence resulting from both implant prominence and the use of RT.
General complications in corpectomy
In a multinational prospective study involving 223 MSTS patients, Ibrahim et al.[36] reported overall complication rate of 21%, whereas perioperative mortality rate was 5.8%.[36] Of these, 28% (63/223) patients underwent en bloc corpectomy, 46% (102/223) underwent near-total corpectomy, and 26% (58/223) underwent partial corpectomy.[36] Pneumonia, urinary tract infections, and venous thromboembolism occurred in 7.6% patients, whereas surgical complications including dural injury and damage to surrounding neurovascular structures occurred in 7.2% patients.[36] Complication rates were the highest in en bloc corpectomy (25%), followed by partial corpectomy (22%) and finally near-total corpectomy (16%). Median survival was 18.8 months for en bloc corpectomy patients, 13.4 months for near-total piecemeal corpectomy patients, and 3.7 months for partial corpectomy patients.[36] Although it appeared that patients undergoing en bloc or near-total piecemeal corpectomy survived longer (P = 0.036), this could be attributed to them having better ASA physical status than those who underwent less invasive surgery.[36]
Specific complications in en bloc corpectomy
Despite advances in surgery, this technically demanding procedure can carry a high morbidity–mortality and complication rate. Araujo et al.[37] reported an overall complication rate of 76.5% (13/17), including SSI risk of 29% (5/17) and pseudarthrosis risk of 6% (1/17), and one case of immediate postoperative mortality following hemorrhagic shock.[37] The risk is increased in anterior–posterior combined approaches versus the posterior approach,[38],[39] possibly attributed to complex anatomy and potential injury to key structures (pleura, vena cava, and aorta) in the anterior approach.[37],[40]
| Other Advancements in Metastatic Spine Tumor Surgery | | |
Intraoperative cell salvage
Intraoperative cell salvage (IOCS) can reduce allogenic blood transfusion requirements of MSTS. Despite IOCS being utilized across many oncological surgical specialties such as lung, urology, and hepatobiliary, it has, up till recently, been contraindicated in MSTS due to fear of tumor reinfusion. Kumar et al.[41] simulated the IOCS process with blood collected from 13 MSTS patients using a cell saver machine with a leukocyte-depletion filter (LDF). Although the salvaged blood may contain some tumor cells in the absence of LDF, it was reported that these tumor cells were nonviable due to damage by the IOCS process, preventing tumor cell replication and disease progression,[42] and thus, removing the danger of tumor reinfusion and dissemination. These results support the use of IOCS in MSTS, reducing the burden on blood banks for allogenic blood transfusion.
Implant materials in metastatic spine tumor surgery
Since the 1990s, titanium has been extensively used in spine surgery owing to its biocompatibility, mechanical strength, and corrosion resistance.[43] Presently, titanium is the gold standard implant material for MSTS. However, it still cannot be classed as the ideal implant material. Titanium causes stress shielding at the implant–bone interface due to its high Young’s modulus of elasticity compared to cortical bone (110–118 GPa vs 17–21 GPa).[43] This causes the bone to remodel and become less dense, weakening surrounding bone and increasing chances of implant failure. Further, titanium implants generate artifacts on common imaging modalities, i.e., MRI/computed tomography (CT). This hinders the detection of early tumor recurrence and in RT planning, resulting in dose perturbation.[43]
Owing to these factors, other materials have been explored. Nonmetallic/polymer-based implant material such as polyether–ether–ketone (PEEK) has been largely researched for use in spine surgery. Such materials have a lower Young’s modulus of elasticity (PEEK ~3.6 GPa), resulting in less stress shielding and in turn reduced chances of implant failure.[43] Further, polymer-based materials tend to be radiolucent and generate minimal artifacts on MRI/CT, allowing for better RT planning and detection of tumor recurrence.[43] Currently, PEEK and PEEK-based implants such as carbon fiber-reinforced–PEEK and titanium–PEEK composites are used in MSTS.[43]
| Conclusion | | |
Current trends in MSD are shifting toward MIS; however, open surgery remains the gold standard. Open surgery is preferred in cases with compromised visibility, i.e., hypervascular tumor secondaries and in regions of spinal column with limited access where the MIS approach is likely to be dangerous. We recommend that all spine surgeons be familiar with the concepts and techniques of open surgery for MSD.
Acknowledgements
We would like to thank Dr. James Hallinan, Keith Gerard Lopez, and Laranya Kumar for their help in editing the manuscript.
Ethical policy and institutional review board statement
Not applicable.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | | |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
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