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Year : 2020  |  Volume : 3  |  Issue : 1  |  Page : 11-25

Expanding the horizons of minimally invasive spine surgery

Department of Orthopaedics, Mumbai Spine Scoliosis and Disc Replacement Centre, Bombay Hospital and Medical Research Centre, Mumbai, Maharashtra, India

Date of Submission25-Mar-2019
Date of Decision24-Apr-2019
Date of Acceptance06-Jan-2020
Date of Web Publication05-Feb-2020

Correspondence Address:
Dr. Arvind G Kulkarni
Dr. Arvind Gopalrao Kulkarni, Mumbai Spine Scoliosis and Disc Replacement Centre, Bombay Hospital and Medical Research Centre, Marine Lines, Mumbai 400020, Maharashtra.
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/isj.isj_19_19

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The trend of using smaller operative corridors is observed in various surgical specialties. The development of smart technologies with the overall aim of reducing surgical trauma has resulted in the concept of minimally invasive surgical techniques. Enhancements in microsurgery, tubes, endoscopy, and various percutaneous techniques, as well as improvement of implant materials, have proven to be milestones. The ease of performing surgery through tubes has recently evolved into percutaneous placement of spinal instrumentation, including intervertebral spacers, rods, and pedicle screws. The advancement of training of spine surgeons and the integration of image guidance with precise intraoperative imaging, computer-, and navigation-assisted treatment modalities constitute the era of reducing treatment morbidity in spinal surgery. This progress has led to the present era of preserving spinal function. In this report, we present a chronological perspective of the use of tubular retractors, the learning curve of tubular retractor in dealing complex cases and its wide applications, and expanding the horizon using tubular retractors.

Keywords: Spine Surgery, Tubular retractors, Discectomy, Minimally invasive spine surgery, Spinal navigation, endoscopic spine surgery Key message: Tubular retractors can be used in wide range of situations. Its ability to navigate through narrow corridors taking directly to the foci of lesion with minimum morbidity and successful clinical and functional outcomes makes it a worthy surgical tool.

How to cite this article:
Kulkarni AG, Kunder TS, Das S, Tapashetti S. Expanding the horizons of minimally invasive spine surgery. Indian Spine J 2020;3:11-25

How to cite this URL:
Kulkarni AG, Kunder TS, Das S, Tapashetti S. Expanding the horizons of minimally invasive spine surgery. Indian Spine J [serial online] 2020 [cited 2021 Jan 23];3:11-25. Available from: https://www.isjonline.com/text.asp?2020/3/1/11/277799

  Introduction Top

Surgeons and patients alike share a predilection toward less invasive surgical procedures. This has compelled the development of approaches through small corridors to surgically treat a myriad of pathologic processes across a wide range of specialities. In spinal surgery, the exposure of a spotless and bloodless chalky-white bone is a matter of pride for a senior spine surgeon and a matter of delightful pursuit for a budding spinal fellow. A well-functioning Bovie, Cobb’s elevators, and self-retaining retractors have been the foundation for a gratifying exposure since the inception of spine surgery. Advancing technology and tireless enthusiasm of the spine surgeons have replaced this armamentarium of spine surgery with new less invasive and highly sophisticated tubular retractors. Since its introduction by Foley and Smith[1] in 1997, the tubular retractor has revolutionized and changed the perspective of spine surgery. It allows the surgeon to treat focal compressive and unstable lesions without disturbing the normal osteo-ligamentous structures or the surrounding muscles. Although the initial development of tubular surgery and its most common indication revolved around lumbar disc herniations, the versatility of the technique has now been widely realized.[2] This article attempts in summarizing the plethora of spinal conditions where microtubular surgery has proved its worth.

  Lumbar Disc Herniations Top

The journey of tubular retractors from a budding option in lumbar disc herniation to becoming the gold standard treatment as described by the authors has been swift.[3] Serial paraspinal muscle dilation, docking of the tube over the inferior lamina of the superior vertebra, laminotomy, and then discectomy have aided in least disturbance to the natural anatomy, allowing early return to work.[3] Arts et al.[4] in their randomized control trial (RCT) between open and microtubular discectomies concluded that both open and minimally invasive techniques had their own advantages and pitfalls. The minimally invasive discectomy was superior in terms of speed of recovery and outcome. However, patients’ scores in terms of visual analog scale (VAS) were better in the conventional cohort. Although, these differences were not clinically proven, both the techniques had similar results. Righesso et al.[5] in their RCT of comparison between open and micro-endoscopic techniques for discectomy found similar results at 2-year follow-up. Size of skin incision and length of hospital stay were statistically in favor of tubular discectomy, whereas surgery time and immediate postoperative wound pain faired better in the open cohort. Ryang et al.[6] randomized 60 patients between open and microdiscectomy and found no significant differences in outcome. The fact that evidence showed similar outcomes for both techniques in discectomy with the obvious advantages and excellent results encouraged the authors to extend their skill in tubular discectomy to more complex indications including central and large disc herniations.

Microtubular surgery in central/large disc herniation

Microtubular surgery is a challenge in central/large disc in achieving adequate decompression due to the morphology, location, and the technical capability of accessing the herniated fragments.[7] Hussein et al.[7] noted excellent long-term outcomes using tubular microdiscectomy in large uncontained lumbar disc herniations and opined that tubular microdiscectomy preserves the anatomy of the spine without compromising its stability, leading to decreased incidence of low back pain. According to symptomatology and magnetic resonance imaging location of fragment, the opposite side axilla as well as the shoulder of the nerve root and the anterior aspect of the dura are probed for hidden fragments by gradual wanding of tubular retractor [Figure 1].
Figure 1: Case illustration of microtubular discectomy in central disc herniation

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Microtubular surgery through translaminar approach in migrated disc herniation

Cranial or caudal migration poses a threat to the facet joint complex during extension of the laminar fenestration in the conventional open approach. This may eventually lead to instability.[8],[9],[10] The application of minimally invasive technique to the translaminar approach and the effectiveness of targeted approach has been well described.[11],[12] The tube is docked on the pars interarticularis flush to the pedicle. The docking over superior or inferior lamina depends on the direction of the migration. It is followed by laminotomy and easing out of the herniated disc [Figure 2A] and [B].[12]
Figure 2: (A) Preoperative images of case illustration of microtubular discectomy of migrated disc. (B) Postoperative images of case illustration of microtubular discectomy of migrated disc

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  Lumbar Canal Stenosis Top

The ability to perform a thorough unilateral over-the-top decompression through a small portal with preservation of the paraspinal muscles has shifted the paradigm toward microtubular decompression surgeries from their open counterparts.[13],[14],[15],[16],[17],[18]

Microtubular decompression in severe stenosis

Tubular decompression in simple/severe stenosis is relatively straightforward. Central and lateral recess stenosis can be decompressed using this technique with minimal bone removal. Care should be taken to keep the laminotomy parallel to the ipsilateral pars and to maintain a safe distance of at least 5mm from it to avoid postoperative iatrogenic instability [Figure 3]. In addition, an interesting recent study has highlighted the similarity in the outcomes of microtubular decompression in both extreme and non-extreme stenosis.[19]
Figure 3: Case illustration of microtubular decompression in severe stenosis

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Microtubular decompression in stenosis with degenerative spondylolisthesis

Surgical management of lumbar degenerative spondylolisthesis is a constant source of controversy, the treatment swinging from decompression alone to fusion.[20],[21],[22],[23] The authors developed a scoring system taking into consideration clinical, radiological and technical factors. This scoring system helped to classify degenerative spondylolisthesis into stable and unstable variety, furthermore aiding treatment decision [Figure 4A] and [B].
Figure 4: (A) Preoperative images of a case illustration of microtubular decompression in degenerative spondylolisthesis. (B) Three months postoperative images of a case illustration of microtubular decompression in degenerative spondylolisthesis

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Microtubular decompression in stenosis with degenerative scoliosis

The subgroup of patients with stable scoliosis and dominant radicular leg pain may benefit with a minimal access decompression. The indications for decompression alone include dominant leg pain without disabling back pain, stenosis in the central zone/lateral recess/extra-foraminal zone without foraminal stenosis, and an intact pars and facet joint as outlined by Berven et al.[24] Technical aspect, which should be kept in mind, is that the alignment of the C-arm should be parallel to the end plates of the level to be decompressed. Tube docking in these cases may be challenging due to osteophytosis and lack of differentiation of the facet joints. These patients also tend to have a narrow lamina and interlaminar window on the side of concavity. Microendoscopic decompression (MED) in these cases is technically demanding and requires a high level of expertise and should be attempted once the learning curve is achieved [Figure 5]. Nomura and Yoshida,[25] in their study on 480 patients who underwent microendoscopic decompression, considered 30 surgeries as the benchmark, following which the operative time and intraoperative blood loss reduced significantly. Sclafani and Kim,[26] in their systematic review of learning curve in various minimally invasive spine procedures, concluded that the learning curve for operative time and complications for the various minimally invasive procedures was between 20 and 30 cases. The most common complication reported was durotomy.
Figure 5: Case illustration of microtubular decompression in degenerative scoliosis

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Microtubular decompression in lumbar Intraspinal synovial cyst

It is a common belief among surgeons that a lumbar intraspinal synovial cyst (LISC) is associated with segmental instability, and fusion surgery is the only way out. The authors in their study have outlined the possibility to get away with MED in stable situations.[27] The trick is to decompress the LISC from the opposite side in a technique similar to over-the-top decompression and conserve most of the facet joint while avoiding instability [Figure 6].
Figure 6: Microtubular decompression in a case of lumbar intraspinal synovial cyst

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  Minimally Invasive Fusion Top


Advances in the design of the percutaneous pedicle screws, combined with the tubular retractor system developed by Foley and Smith,[1] led to the development of minimally invasive transforaminal lumbar interbody fusion (TLIF). The advantages include wide access to the spine by avoiding subperiosteal dissection, avoiding undue retraction, and thus reducing local muscle denervation and postoperative back pain and muscle spasm, minimal blood loss, cosmetic postoperative scars, tremendous reduction in infection rates, and the muscle fall back aiding in sealing off small dural tears (DTs) if any.[14],[28],[29],[30],[31] Vazan et al.,[32] in their review article comparing minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) and open TLIF, concluded that both techniques had similar outcomes with MIS-TLIF associated with higher intraoperative radiation doses, a shallow learning curve that included longer operating times and implant failures during the learning curve, which is acceptable for any surgeon learning a new art. However on the flipside, the pronounced benefits included significant reduction in blood loss, shorter hospital stay, and lower surgical site infection rates. Khan et al.,[33] in their meta-analysis, suggested that MIS-TLIF is associated with reduced blood loss and shorter hospital stay, decreased complications, and increased radiation exposure with similar outcomes when compared to the open counterparts, they also strongly advocated the need for further large multicentric RCTs as long-term outcomes were inconclusive. The need for further comprehensive studies was also mirrored in a review article by Karikari and Isaacs.[34] The North American Spine Society and American Association of Neurological Surgeons/Congress of Neurological Surgeons also recommend the need for further studies for clear and consistent definitions. They also do not outline any guideline, which grants superiority to any technique.[35] Authors in their study compared the outcomes of open TLIF with MIS-TLIF and concluded that quick recovery and early return to work are the hallmarks of MIS-TLIF with similar outcomes.[36]

MIS-TLIF in high-grade spondylolytic spondylolisthesis

Conventional open TLIF procedure has long been the surgery of choice for high-grade isthmic/spondylolytic spondylolisthesis. The challenge lies in successful reduction and fixation of the slip. Quraishi and Rampersaud[37] and Park and Foley[38] have described the feasibility and effectiveness of minimally invasive TLIF in high-grade spondylolisthesis. The methods of reducing the slip include postural reduction by proper positioning the patient, distractive reduction by using intra-discal shavers and translational reduction, using reduction screw extenders, has been well described by Park and Foley[38] and Scheer et al.[39] The authors attempt to attain reduction during positioning of the patient, which usually is sufficient, followed by the procedure [Figure 7A]–[C].
Figure 7: (A) Preoperative images of a case illustration of MIS-TLIF in high-grade spondylolisthesis. (B) Intraoperative images of a case illustration of MIS-TLIF in high-grade spondylolisthesis. (C) Postoperative images of a case illustration of MIS-TLIF in high-grade spondylolisthesis

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MIS-TLIF in failed back

Revision patients present a surgical challenge because of altered anatomical landmarks, avascular scars from previous surgery, and epidural fibrosis, which have been associated with increased risk of DTs, wound-related complications, and neural injury. Patients in these situations can potentially benefit from the decreased approach-related morbidity (dissection through scar tissue) provided by MIS-TLIF because of the unviolated intermuscular plane of Wiltse in prior midline open surgeries. Careful attention to the altered anatomy as a result of previous exposure is of paramount importance in limiting the concerns for potential neural injury. One of the crucial steps in approaching patients who had undergone previous wide laminectomy was the safe placement of the guidewire and working channel to avoid inadvertent dural penetration. The guidewire was directed more laterally on the facet to ensure that it was not near vital structures and previous iatrogenic bony defects. According to the authors’ published study, among the spectrum of failed backs, MIS-TLIF as an option is reasonable in recurrent disc herniation, infection, pseudarthrosis, hardware failure, flatback syndrome (opportunity of introduction of various sized lordotic cages and use of pre-contoured rods in minimally invasive spine (MIS) surgeries helps correct flatback syndrome), iatrogenic instability, or adjacent segment degeneration [Figure 8A]–[C].[40]
Figure 8: (A) First magnetic resonance imaging (MRI) of the case illustration of failed back. (B) MRI after recurrence. (C) Image after MIS-TLIF

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MIS-TLIF in adult lumbar degenerative scoliosis

Patients with adult degenerative scoliosis are usually the elderly with comorbidities, which may lead to postoperative complications. This fact is compounded in open procedures. The patients who underwent MIS-TLIF in our institution included patients with an unstable curve in standing and prone radiographs. The prerequisite for these cases includes accurate alignment of the C-arm parallel to the end plates of the vertebra to be fused for tube docking and screw insertion [Figure 9].
Figure 9: Case illustration of MIS-TLIF in adult degenerative scoliosis

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  Microtubular Surgery in Cervical Spine Top

Microtubular surgery is commonly performed for the treatment of lumbar spine disorder.[41],[42] But in the current scenario, there has been increasing use of tubular retractors in cervical spine. The indications of tubular retractors in cervical spine include posterior cervical foraminotomy, posterior cervical decompression, lateral mass instrumentation, posterior approach to intradural tumors, bony tumors, and anterior cervical discectomy. However, feasibility of microtubular surgery in revision surgery, gross kyphosis, and deformity correction of cervical spine has not been described yet.

Posterior cervical foraminotomy

Posterior cervical foraminotomy has long been used to address radicular pain arising from compression in the foramen, either bony stenosis or soft disc herniation.[43],[44],[45],[46] However, in central disc herniation or myelopathy from central canal stenosis, it is contraindicated. The technical shades of posterior foraminal surgery can be challenging for surgeons trained primarily in the anterior approach, mainly with concern to epidural bleeding in the prone position. Immediate postoperative outcome between open and minimally invasive methods seems to be comparable.[47] Comparative study by Kim and Kim[48] showed benefits of minimally invasive approach in reducing postoperative neck pain up to the first 4 weeks, but not beyond. Peto et al.,[49] in their study, have showed less neck pain even in the long term compared with an open approach group. Steinberg and German[50] showed no significant difference between minimally invasive posterior cervical foraminotomy and anterior cervical discectomy and fusion (ACDF) in terms of neck pain VAS score at the last follow-up. Hilton[51] has proved that posterior foraminotomy with tubular retractor gave excellent results with minimal muscle trauma as compared to open posterior foraminotomy. A newer cadaveric biomechanical study conducted by Brody et al.[52] suggested that one-sided foraminotomy does not alter the range of motion of the index segment and thus should not contribute for the change of cervical alignment and the development of adjacent segment disease as opposed to ACDF. Cho et al.[53] came to similar conclusion. The authors have also used tubular retractor to address radicular pain arising from compression in the foramen [Figure 10A] and [B].
Figure 10: (A) Preoperative image of C6-7 right-sided herniated nucleus pulposus. (B) Intraoperative images of skin incision with serial dilatation and tubular docking

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Microtubular excision of C2 osteoid osteoma

In an attempt to further advance minimally invasive approaches to the spine, tubular retractors with muscle splitting techniques have been applied to the treatment of intradural pathology and for the management of tumors of the spine. The surgical open exposure can disrupt muscle, ligamentous tissues, and bony elements important to stability.[54] However, minimally invasive procedure with tubular retractor minimizes muscle destruction and affords an adequate corridor to tumor resection. Campos et al.,[55] in their case report, have managed C2 body osteoid osteoma using an anterior approach via tubular retractors. Amendola et al.,[56] in their case report, have applied a new mini-invasive anterior approach technique via tubular retractors to manage C2 body osteoid osteoma, which was located superior to the dorsal aspect of the inferior end plate of C2. The authors have used tubular retractor in excision of a tumor located at lamina-lateral mass complex of C2 vertebrae through posterior approach [Figure 11A] and [B].[57]
Figure 11: (A) Preoperative axial T2-weighted magnetic resonance imaging and computed tomography scan showing a lesion in the lamina-lateral mass complex of C2. (B) Intraoperative images of final tubular docking and picture showing the lesion with the pinkish fleshy nidus (arrow)

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Anterior cervical spine surgery

There is limited literature on the use of minimal access tubular retractors to decompress and reconstruct the anterior cervical spine. Indication for this is cervical spondylotic myelopathy or cervical radiculopathy. The advantages of performing anterior cervical spine surgery using tubular retractors are as follows: it reduces the risk of iatrogenic injury to carotid and esophagus, minimizes tissue disruption, minimizes blood loss, reduces post-op pain, and betters cosmetic results.[58] But for this, it requires advanced manual skills and good experience with MIS techniques. Vergara and Timofeev[59] concluded that minimally invasive microscopic ACDF through tubular retractors was a feasible option and gave excellent results. Yao et al.[60] concluded that micro-endoscopic ACDF with a 2-cm port appeared to be safe and gave excellent results. The authors have used expanded tubular retractor in one case to execute C5 corpectomy and reconstruction with Titanium mesh cage (TMC) and in another case, they have used expanded tubular retractor for anterior reconstruction at C4-5 and at C5-6 level [Figure 12A]–[C] and [Figure 13A]–[C].[61]
Figure 12: (A) Preoperative image of sagittal and axial magnetic resonance imaging showing significant spinal cord compression posterior to the C5 body. (B) Intraoperative image showing the assembly, docking of tube, expansion of retractor for corpectomy, and placement of cage. (C) Postoperative X-ray

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Figure 13: (A) Preoperative image of sagittal and axial magnetic resonance imaging showing compression at C4-5 and C5-6. (B) Intraoperative images of anterior reconstruction at C4-5 and C5-6. (C) Postoperative images of anterior reconstruction at C4-5 and C5-6

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Expanding by shrinking the tubes from 18mm to 14 and 12 mm

The use of 16- and 18-mm tubes for the removal of disc herniations is well known and routine. With increasing experience of dealing with complex pathologies, the authors envisaged to incorporate 14 and further 12mm tubes in their armamentarium. A yet to be published study by the authors shows excellent outcomes with regard to patient satisfaction, surgery parameters, and complication profile with increasingly smaller size of tubular retractors. The authors suggest attaining expertise in the 16- and 18-mm tubular retractors first and transcending the learning curve before the use of smaller and more challenging tubular retractors. The trick is accurate localization of the tube, a thorough preoperative planning, and the use of thinner suction and slender bipolar cautery forceps [Figure 14].
Figure 14: Image of L5-S1 HNP and use of 12-mm METRX tube for discectomy

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  Three-Dimensional Navigation: How it has changed the Paradigm Top

MIS techniques go hand in hand with the use of intraoperative fluoroscopy. Increased radiation doses and availability of uniplanar images are the established drawbacks.[62],[63] Navigation-guided spine surgery is a promising technique that addresses many of these concerns. As such, the evolution of three-dimensional (3D) intraoperative image guidance (navigation) has paralleled the advances in MISS.

There are C-arm-based two-dimensional (2D) navigation systems, computed tomography (CT)-based navigation and presently improved by the ISO-C3D navigation system (Siremobil Iso-C 3D; Siemens Medical Solutions, Erlangen, Germany) and O-arm. Intraoperative CT-like images can be generated using 3D navigation and O-arm. Many of the disadvantages of CT-based and 2D C-arm-based navigation are eliminated using 3D navigation and O-arm.[64]

Applications in spine surgery

Traditional methods of pedicle screw instrumentation can result in misplacement rates as high as 30%.[65],[66],[67] For minimally invasive techniques, it is essential to optimize accuracy to avoid neurologic or vascular compromise. A meta-analysis by Shin et al.[68] showed that the risk of pedicle perforation may be significantly decreased by using computer-assisted navigation without increasing the operative time.

Cervical spine

Screw placement in the cervical spine is a challenge due to proximity of vascular and neural elements and smaller bony corridors available for instrumentation, especially in the upper cervical spine. Holly and Foley[69] showed that navigation increases the accuracy of pedicle screw placement and avoids vertebral artery injury. Navigation can be used for C1-2 fixation [Figure 15A] and [B], C2 and C7 pedicle screw placement, C1-2 trans-articular screw placement, and for lateral mass screws. The authors have used 3D navigation in excision of tumors located at posterior border of cervical vertebrae [Figure 16A] and [B].[70]
Figure 15: (A) Intraoperative image of attachment of patient reference array and localization with navigated probe. (B) Navigated image of C2 pedicle screw course

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Figure 16: (A) Navigation image of localization of osteoid osteoma using a probe. (B) Navigation image showing the extent of burring of tumor using a navigated burr and confirmation in C-arm

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Thoracic spine

Variability in the pedicle anatomy, proximity to vital neurovascular structures, organs, and poor visualization of fluoroscopic images can make instrumentation of thoracic spine challenging. Evidence of navigation in thoracic spine is limited; however, few reports suggest higher accuracy rates as compared to freehand techniques.[71]

Lumbar spine

There are multiple applications of navigation in lumbar spine, the most common being percutaneous pedicle screw placement and minimally invasive transforaminal lumbar interbody fusion [Figure 17A]. Bourgeois et al.[72] have noted in their study increased accuracy of pedicle screw placement and advantages of navigation in minimally invasive surgery. Authors have been consistently using navigation for dealing with complex cases such as use of navigated burr in over-the-top decompression in severe stenosis [Figure 17B], to calculate pedicle screw size in complex revision cases [Figure 17C], and to know the extent of filling of graft in the disc space before the placement of cage.
Figure 17: (A) Navigation set up of MIS-TLIF surgery. (B) Use of navigated burr to determine the extent of burring in over-the-top decompression. (C) Use of navigation in calculation of pedicle screw size in revision and complex cases

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Deformity/revision procedures

Navigation is increasingly used for complex procedures where the anatomy is altered or obscured. Larson et al.[73] showed an increase in pedicle screw placement accuracy in pediatric deformity population using navigation. Metz and Burch[74] suggested that navigation improved safety and efficacy in revision spine procedures. The authors have used 3D navigation in deformity correction surgeries, hemi-vertebrae excision, and degenerative scoliosis.

  Conclusion Top

The tubular retractor has changed the paradigm of spine surgery. Most of the spinal pathologies dealt in routine practice are focal in nature, and the conventional open approaches used to reach these pathologies come with collateral tissue damage, increasing the morbidity. The tubular retractors take the surgeon directly to the pathology with minimal morbidity and collateral damage to the tissues around the pathology. Initially pioneered for lumbar discectomy, the tube has gradually witnessed its applications in most degenerative, infective, traumatic neurosurgical etiologies as well as in spinal tumors. A combination of navigation and minimal access applications has revolutionized spinal surgery for the benefit of mankind.

However, one needs to be familiar with the open procedures before expanding the usage of minimally invasive techniques in all the pathologies. The tubular system has been shown to provide equivalent surgical results as the open techniques with the benefits of faster recovery, less blood loss, and reduced infection rates in retrospective cohort studies. Few studies have also shown increased operative time, increased exposure to radiation, and increased rates of recurrent disc with the use of tubular retractors. There is a need for high-quality randomized controlled trials to evaluate the proposed benefits of minimally invasive surgeries through tubular retractor system. At present, it would be appropriate to consider minimally invasive surgeries using tubular retractors as a viable option with lesser tissue damage and proposed benefits of faster recovery.

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Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17]


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