Expanding horizons of cervical endoscopic spine surgery: Important surgical landmarks and technical pearls

Jayesh Sardhara; Ashutosh Kumar

doi:10.4103/joss.joss_48_22

EDITORIAL

Year : 2022 | Volume : 9 | Issue : 4 | Page : 186-192

Expanding horizons of cervical endoscopic spine surgery: Important surgical landmarks and technical pearls

Jayesh Sardhara, Ashutosh Kumar
Department of Neurosurgery, Fortis Hospital, Mumbai, Maharashtra, India

Date of Submission	15-Oct-2022
Date of Acceptance	01-Nov-2022
Date of Web Publication	30-Dec-2022

Correspondence Address:
Jayesh Sardhara
Department of Neurosurgery, Fortis Hospital, Mulund, Mumbai - 400 078, Maharashtra
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/joss.joss_48_22

How to cite this article:
Sardhara J, Kumar A. Expanding horizons of cervical endoscopic spine surgery: Important surgical landmarks and technical pearls. J Spinal Surg 2022;9:186-92

How to cite this URL:
Sardhara J, Kumar A. Expanding horizons of cervical endoscopic spine surgery: Important surgical landmarks and technical pearls. J Spinal Surg [serial online] 2022 [cited 2023 Mar 21];9:186-92. Available from: http://www.jossworld.org/text.asp?2022/9/4/186/366324

Introduction

Endoscopic spine surgery (ESS) is a major evolutionary step toward targeted surgery and functional spine surgery. It has solved the very problem of minimally invasive spine surgery (MISS) of limited exposure by allowing the visualization of a wider field, higher magnification, resolution, and better illumination. With smaller incisions and a narrower trajectory, the collateral damage to the normal anatomical structures is significantly minimized. Three-dimensional high-resolution endoscopes, high-speed drills, irrigation pumps, and improved endoscopic systems have provided major impetus in making ESS a better alternative to existing techniques. Following initial utilization in the management of lumbar spine pathologies, most surgeons are now exploring its application in the cervical spine. At present, both endoscope-assisted and full endoscopic techniques are being employed to address myriad cervical pathologies.

Endoscopic Techniques and the Armamentarium

The existing endoscopic techniques for cervical pathologies can be divided into two broad categories: endoscope-assisted and pure endoscopic surgeries [Figure 1]. Endoscopic-assisted surgeries require special retractors that accommodate the endoscope and have separate working ports. All these retractor systems work on the basic principles of triangulation, with few modifications to make the instrument handling easier. These techniques have been superseded by pure endoscopic techniques.

Figure 1: Diagram showing different endoscopic procedures for cervical spine surgery. AECD: Anterior endoscopic cervical discectomy, PECD: Posterior endoscopic cervical discectomy, AECTcD: Anterior endoscopic cervical transcorporeal decompression, PECF: Posterior endoscopic cervical foraminotomy, CE-ULBD: Cervical endoscopic unilateral laminotomy for bilateral decompression

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Pure endoscopic surgery involves percutaneous insertion of the endoscopes with no retractor system. Based on the working port, they can be uniportal or biportal. Uniportal pure endoscopic techniques use endoscopes with built-in working channels. Whilst, in the biportal system, the instruments are inserted through a separate port requiring another stab incision. These procedures are further classified based on the approach-anterior or posterior.

Endoscopic Cervical Approaches: A Technical Evolution With Promising Results

The principle aim of MISS is to prevent collateral damage to normal anatomical structures while addressing the offending pathology responsible for the symptoms. The other benefits include shorter hospital stays, less postoperative pain, and lesser wound complications. Most studies comparing pure endoscopic approaches for cervical disc anterior endoscopic cervical discectomy, posterior full-endoscopic cervical discectomy, and anterior cervical discectomy and fusion (ACDF) concluded that operative time, intraoperative blood loss, postoperative recovery time, and need for pain medication were significantly lesser in the former. The clinical outcomes such as pain score and postoperative functional status were comparable between the two groups.^[1],[2]

The most common complications reported were dural tears (4.65%), transient hypesthesia (3.37%–4.65%), and swallowing difficulty (1.96%–3.70%). Other complications include hematoma formation, injury to recurrent laryngeal nerve, carotid injury, and postoperative surgical site infections.

Endoscopic ACDF is performed for patients with progressive neurological deficits and debilitating pain that is resistant to conservative modalities with evidence of spinal cord or nerve root compression on magnetic resonance imaging (MRI). Endoscopic ACDF led to improvement in clinical outcomes and showed similar fusion rates compared with the conventional ACDF in one-level cervical discogenic disorder with efficacy and safety in a short period.^[3] There was no significant difference in change of disc height and cervical lordosis at immediate postoperation and 6 months' follow-up^[4] Future studies with a longer follow-up period are needed to evaluate whether endoscopic fusion rate would influence the progression of degenerative changes. Endoscopic ACDF is one of the minimally invasive techniques which could replace a conventional open ACDF if the learning curve could be overcome.

With the evolution of minimally invasive techniques, there has been an improvisation in the techniques of posterior cervical discectomy and foraminotomy (PCDF) leading to a better functional outcome with a better acceptance. The procedure encompasses all the beneficial advantages of a minimally invasive technique like lesser muscle dissection, shorter hospital stay, less intraoperative blood loss, lesser postoperative pain, and a reduced infection rate.^[1],[2],[5] Soha A Alomar et al. concluded that the posterior approach had a lower complication rate and higher success rate for cervical radiculopathy due to degenerative disc disease in a systemic review and meta-analysis.^[6]

Anterior Cervical Endoscopic Approach: Surgical Anatomy and Technique

Dr. Jho described in 1996 microscopic anterior cervical foraminotomy where the transverse processes and uncovertebral joints were exposed and the decompression was performed with the gradual removal of the uncinate process to reach the nerve root.^[7],[8],[9] Endospine can also be used for anterior endoscopic cervical foraminotomy and partial vertebrectomy as described by Jho. This is indicated for soft or hard foraminal disc herniations. In elderly patients, the compressing disc is thin and hard. In such cases, anterior endoscopic foraminotomy can be easily extended to the midline or opposite side where the foramen begins.^[10],[11]

Surgical anatomy

An uncinate process is a hook-shaped process on the lateral borders of the superior surface of the third to the seventh cervical and first thoracic vertebrae. The uncovertebral joint or Luschka's joint is formed between the uncinate process below and the uncus above [Figure 2]a. A piece of thin cortical bone of the uncinate process is left to protect the vertebral artery until the posterior longitudinal ligament (PLL) is exposed. This lateral remnant of the uncinate process can also be fractured at the base after gentle dissection from the vertebral artery. Although the central disc and opposite side root can be decompressed using the lateral foraminotomy approach by angulating scope medially, it is not required for the central disc without radiculopathy. The entry point can be medial and foraminotomy may not be required in case of central disc herniation [Figure 2]b.

Figure 2: (a) The uncinate process projects upward from the superior surface of the vertebral body below as a lip, and the uncus projects downward from the inferior surface of the vertebral body above. (b) Entry points for resection of central disc herniation (square) and lateral foraminotomy (oval)

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Surgical technique

Two techniques for cervical endoscopic discectomy via anterior approach include discectomy with or without interbody fusion. The patient with unilateral cervical nerve root radiculopathy due to lateral soft disc herniation can be treated with endoscopic partial discectomy without fusion for motion preservation. For significant central disc prolapse, after complete discectomy and nerve root decompression, interbody fusion is necessary. The spinal endoscopic set required can be any percutaneous interlaminar spinal endoscopy set which is commonly used for lumbar spine surgery. The surgery is performed under general anesthesia. The patient is positioned supine with slight neck extension to facilitate the visualization of index disc space. The anterior neck area is cleansed with a cleaning solution and sterile drapes are placed. Using left-hand fingers, firmly pressing the anterior neck, the thyroid and trachea are displaced to contralateral side (with the middle and the ring finger) and the pulsatile carotid sheath ipsilateral side (using the index finger) until the prominence of the anterior disc to be treated was felt (using right-hand index finger), and create enough working space to insert instrument. After confirming the correct surgical level using an anteroposterior (AP) and lateral view of the C-arm, the surgeon passes a thin needle into the midline of the disc space gently. A 1.5 cm transverse incision is made in one of the creases of the neck. It is deepened between the carotid sheath and thyroid, working around the thin needle to allow the passage of serial working dilators over it to dissect visceral structures. The working sleeve is then installed on the segmented level under fluoroscopic control to conform to its correct placement in the midline and esophagus on the opposite side. The endoscope is inserted through the working sleeve docked in the midline between the longus colli muscles of either side.

Clear visualization with minimal bleeding during procedures is one of the prime advantages of endoscopic ACDF. Radiofrequency ablation is commonly used to ablate vessels to get a good visualization. The medial portion of the longus colli muscle is excised to expose the lateral part of the desired level. Part of the uncinate processes below and the uncus above is removed with a high-speed drill using diamond burrs of 3-mm tip to achieve anterior micro-foraminotomy. The PLL is incised and removed with a 1-mm Kerrison punch. Sub-ligamentous or an extruded disc herniation, if present, is removed. Using a 2 mm diamond bur and 1 and 2 mm Kerrison punch, disc, hypertrophic posterior osteophytes, as well as the uncovertebral joint are removed. Thus, decompressing the underlying nerve root under an endoscopic view. The PLL needs to be removed using a 2 mm diamond drill and 1 mm Kerrison punch to fully decompress the spinal canal. If fusion is planned, a 2 mm diamond drill is useful to remove the cartilage endplates and prepare the fusion bed. The height of the empty disc space is measured by a Kerrison punch and a cage size is chosen to restore the normal disc space height. A 4 mm cage holder is introduced into the endoscopic working channel to hold the cage and then gently endoscope is inserted into the surgical field. Thereafter, a cage filled with autograft or demineralized bone matrix is inserted under the visualization of the endoscope. Two small blade retractors are used to allow the surgeon to visualize the anterior vertebral body and discs before implantation of the polyetheretherketone Cage. C-arm is used to confirm the appropriate position and alignment of the cage. Any bleeding in the epidural space is controlled with bipolar cautery meticulously under the endoscopic view, and then, the working sleeve is removed. A suction drain is placed, and the fascial layer, subcutaneous layers, and skin are closed with a few sutures and surgical glue, leaving a minimal scar.

Posterior Cervical Endoscopic Approach: Surgical Anatomy and Technique

PCDF a procedure have been performed for decades. The advantages of the posterior approach to the disc are (a) It is a motion preserving nonfusion surgery; (b) Spinal surgeons are familiar with the approach; and, (c) There is avoidance of manipulation of anterior visceral structures. Thus, the posterior approach avoids damage to the trachea, esophagus, and recurrent laryngeal nerve.

Indications of the endoscopic posterior cervical lamino-foraminotomy and discectomy

Patient presenting with pure radiculopathy without myelopathy
Presence of one or two contiguous levels postero-lateral hard disc
Foraminal soft disc herniation
Foraminal stenosis due to osteophytes spurs/facet arthropathy
Multilevel foraminal stenosis without central stenosis
Persistent foraminal stenosis after anterior discectomy with fusion
Root compression where anterior approaches are contra-indicated – posttracheotomy, postradiotherapy, or the presence of cervicothoracic junction disc prolapse.

The presence of a broad, centrally situated disc is an absolute contraindication for this procedure, as is the presence of an ossified PLL (OPLL), significant kyphosis, and spinal instability.

Surgical anatomy

The difference between cervical and lumbar foramen anatomy is that the nerve root passes from above the pedicle of the same number of the vertebra, which means it is situated in the lower third of the foramen rather than the upper third as in the lumbar spine. Second, the vertebral artery is an important anatomical structure in the cervical spine that need to be taken care of. It is situated 5–6 mm lateral to the lateral disc margin corresponding to the lamino-facet junction posteriorly [Figure 3]. In posterior cervical endoscopic surgery through the interlaminar approach, identification of the “V” point is important [Figure 4]. The V-point is formed by the inferior margin of the cephalic lamina, the medial junction of the inferior and superior facet joints, and the superior margin of the caudal lamina. For foraminotomy and discectomy medial one-third of the facet joint can be drilled to expose and free the nerve root or expose the disc prolapse. The presence of a dural margin medial to the V-point provides adequate free epidural space thus reducing the dural injury and nerve root retraction during bone drilling and further decompression.

Figure 3: C3 vertebra showing the relative position of the vertebral artery in its foramina concerning the lamino-facet joint posteriorly and the lateral edge of the intervertebral disc

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Figure 4: Image showing the V-point (black dashed line) and its relationship to the lateral margin of the thecal sac and the nerve roots. AIVD: Anatomical inter V-point distance, TIDW: Transverse interdura width, SCW: Surgical critical width which can be positive (+) or negative (−)

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Anatomically, from above to downward, C2 to C4 level – the V point overlies the nerve root crossing; below it. However, at C5, C6, and C7 levels, the “V point” overlies the dura and the nerve root course will be more oblique, and a little bit away from the “V point.”^[12] However, the relationship is not constant and varies according to age, cervical levels, spinal curvature, and the degree of canal stenosis.

The dural margin at the levels C4-5 to C6-7, especially in patients over 70 years of age was found to have the dural margin located lateral to the V-point. As the degenerative changes progress with aging, loss of disc height and degenerative kyphotic changes reduce the spinal canal's AP diameter. Then, the compressed thecal sac is bulged to the bilateral side and induces the dura width increase. Hence, the evaluation of the preoperative imaging for a safe corridor should be individualized and the surgical approach needs to be custom-made for each patient. Facet joint width at C2/3 and C3/4 is avg. 11–12 mm, whereas at C4/5; C5/6; C6/7 it is 13–14 mm. 30%–50% facet can be safely drilled at each level.^[13]

The technique (posterior cervical endoscopic decompression for cervical spondylosis using Destandau's system)

Approximately 2–3 cm vertical skin incision, 1 cm lateral to the midline is made at the spinal level to be decompressed under lateral C-arm view. Subcutaneous tissue and fascia are cut with a knife underneath the skin incision. A further approach to the lamino-facet junction can be done by splitting the para-spinal muscles or it may be retracted laterally by separating it from the spinous process through subperiosteal dissection. The micro-endoscopic set and instruments commonly used for lumbar disc disease can be used for this procedure. Endoscopy system (Destandau's) is placed on the lamina and facet joints to be decompressed. Monopolar and bipolar cautery is used to remove any residual muscular and soft tissues overlying the lamina and facet joint. Lamina, facet joint, and interlaminar area are identified, and the V-point is defined. Unilateral laminectomy (superior lamina) is done using a high-speed drill to thin out the lamina. Kerrison rongeurs are used to remove thinned-out lamina. The endoscope is then turned medially and the base of the spinal process along with a small part of the opposite lamina is drilled to decompress the canal. Ligamentum flavum is left intact until all bony work was complete to prevent a dural tear. A small angled curette, nerve hook, or Kerrison rongeurs can be used to separate ligament flavum from the underlying dura. Adjacent cranial or caudal level decompression can be performed by pushing the endoscopy set cranially or caudally, respectively. Three-level pathologies can be decompressed using the same incision. Another skin incision needs to be added for more than three levels of compression.

To decompress the exiting nerve root and resect the herniated disc, the lamino-facet junction needs to be drilled at the V-point. Excessive drilling of the facet can be prevented by feeling the pedicle supero-laterally with a nerve hook or curved dissector. Once the lamino-facet junction is drilled, the nerve root can be identified. While working through the axilla or the shoulder of the nerve root depending upon the site of the pathology, the underlying disc can be decompressed. A similar approach is utilized in full endoscopic posterior cervical decompression using uniportal or biportal endoscopic systems, with even smaller incisions.

Illustrative Cases (Endoscopic Approaches For Cervical Spine Pathologies)

Cervical discectomy through the posterior endoscopic approach

A 28-year-old male patient with left side C6 radicular pain with no sensory-motor deficits [Figure 5]. The MRI was suggestive of C5-6 left paracentral disc herniation. Endoscopic posterior cervical discectomy using Destandau's system was done. Postoperatively, there was an improvement in pain with no complications.

Figure 5: The T2 weighted sagittal (a) And axial (b) Sections of MRI show C5-6 left paracentral disc herniation. Destandaus endoscopic system (c and d) was used and docking was confirmed in lateral C-arm view (e). The system allows bi-manual instrumentation (f). Intraoperative endoscopic view (g) Showing prolapsed disc (black arrow) just beneath the C6 nerve root (blue arrow) with well-fenestrated C5/C6 interlaminar window. MRI: Magnetic resonance imaging

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Endoscopic spinal intradural extramedullary tumor excision

45 years male presented with right hemiparesis for 8 months. The MRI was suggestive of cervical neurofibroma against the C5 vertebral body with extension to adjacent disc spaces [Figure 6]. The patient underwent posterior cervical endoscopic hemilaminectomy with complete resection of the lesion. There was an improvement in symptoms with no postoperative complications.

Figure 6: The MRI (a) Was suggestive of an intradural extramedullary lesion (neurofibroma). Complete excision (c) Was done using Destandau's endoscopic system with a 2 cm incision (d). The postoperative MRI (b) Complete tumor excision. MRI: Magnetic resonance imaging

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Limitations of endoscopic procedures for cervical spine

The steep learning curve is a major impediment to the adaptation of these techniques. Limited surgical fields and small instruments make the procedure technically challenging. Patient selection is also crucial in confirming good postoperative outcomes due to limited indications for these procedures. Results of endoscopic decompression for cervical OPLL or severe canal stenosis with cervical myelopathy are still questionable. For this indication, open approaches are still considered the gold standard. Older age, intramedullary T2 intensity changes on MRI, and longer duration of symptoms are associated with poor outcomes. Additionally, the presence of bony compressive elements and multiple-level compression limits the role of endoscopic surgery.

Conclusion

Presently, both endoscopic assisted and pure endoscopic procedures are being utilized as minimally invasive procedures for cervical spine pathologies including degenerative spondylosis, herniated intervertebral disc, and intra-dural extramedullary lesions. The clinical outcome is at par with open techniques, along with the benefit of minimally invasive procedures. The limited indications are expected to be broadened with the evolution of the instruments, endoscope systems, and techniques.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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