Endoscopic Spine Techniques: An Overview

32 Endoscopic Spine Techniques: An Overview

Nima Salari, Christopher Yeung, and Anthony T. Yeung

Abstract

Posterolateral endoscopic discectomy provides excellent access to the epidural space from pedicle to pedicle facilitating removal of herniated disc fragments. It is the least invasive visualized surgical procedure for treating lumbar disc herniations. Literature demonstrates equivalent or better results compared to standard posterior microscopic discectomy. It is an excellent minimally invasive surgical approach to many disc herniations. Ideal indications include foraminal/extraforaminal disc herniations, upper lumbar and lower thoracic herniations, revision cases, foraminal stenosis, and as a treatment of discitis. This chapter will discuss the historical development of the procedure, relevant literature with results, and indications and contraindications, and describe the step-by-step surgical technique.

Keywords: endoscopic discectomy, foraminoplasty, posterolateral discectomy, YESS, herniated disc, minimally invasive discectomy

32.1 Introduction

The pathogenesis of disc degeneration and herniation is complex and multifactorial, but surgical management for the condition has seen little change since the introduction of the operating microscope.¹^,² The microscopically assisted technique became the gold standard; however, it requires retraction of the dural tube and nerve, periosteal stripping of the muscle and ligaments, removal of laminar bone, and regional or general anesthesia. As outlined in previous chapters, tubular retractors utilize tissue dilation rather than cutting, and minimize the superficial tissue destruction, but the technique still requires the same amount of bone removal and neural manipulation as the standard microscopic posterior discectomy.³ This can cause muscle atrophy and scarring around the sensitive nerve roots even in a technically perfect operation.

The evolution of the surgical endoscope brought about significant change in many fields of medicine, predominantly in the realm of abdominal surgery and joint arthroscopy. Knee arthroscopy in many cases replaced the classic arthrotomy that was performed in the past. Adoption of endoscopy in spinal surgery has seen slower growth. In the early 1970s, Kambin, Gellman,⁴ and Hijikata⁵ separately defined posterolateral approaches for percutaneous central nucleotomy in the lumbar spine. The intervertebral disc space was later visualized with a modified arthroscope by Forst and Housmann.⁶ These developments along with Kambin’s anatomic description of the neural foramen for the purposes of posterolateral endoscopic access through the “triangular zone”⁷^,⁸ ( Fig. 32.1) became the cornerstones in the development of the endoscopic transforaminal approach.

Yeung⁹ introduced a rigid rod-lens, flow-integrated, multichannel, wide-angle operating spinal endoscope that allowed visualized access to the disc space. The endoscope configuration and the complementary instrument system with specialized slotted and bevel-ended tubular access cannulas allowed for same-field viewing of the intradiscal space, annular wall, and epidural space ( Fig. 32.2). The design allows for improved access to the posterior disc for visualized fragmentectomy, improved access to the undersurface of the superior articular facet for foraminoplasty, and protection of the neural structures by rotating the cannula.

Several commercially available systems have been introduced to the market (Richard Wolf GmbH, Knittlingen, Germany; Joimax GmbH, Karlsruhe, Germany; Karl Storz, Tuttlingen, Germany; Max-MoreSpine, Unterföhring, Germany) and the technique has seen some changes.

Fig. 32.1 The reader should be familiar with Kambin’s “triangular zone” as best seen during a transforaminal interbody fusion approach to the disc space. The traversing and exiting nerve roots constitute the medial and superior borders of the triangle, respectively, while the inferior border is lined by the superior end plate of the lower lumbar vertebra.

Fig. 32.2 The configuration of the endoscope and the bevel-ended tubular access cannulas allow for same-field viewing of the intradiscal space, posterior annular wall and longitudinal ligament, and epidural space. A, herniation; B, foraminal ligament (extension of ligamentum flavum); C, ligamentum flavum; D, posterior longitudinal ligament; E, beveled cannula; F, disc; G, annulus; H, traversing nerve root.

Imaging quality has improved over the years with higher definition cameras and monitors allowing for better visualization of the surgical field. Furthermore, the quality and assortment of instrumentation has seen refinement, with addition of holmium: yttrium aluminum garnet (Ho:YAG) laser, larger working channels, angled instruments, Kerrison rongeurs, and articulating reamers facilitating easier surgical access. Broader use of the technique has led to publication of multiple studies, which demonstrate the efficacy of the surgical approach.¹⁰^,¹¹^,¹²^,¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷

Quality studies suggest that outcomes are favorable in direct comparison to traditional microdiscectomy, all while minimizing approach-related morbidity. In their prospectively randomized clinical trial, Ruetten et al¹⁴ demonstrated benefits in posterolateral endoscopic surgery over microdiscectomy with similar patient satisfaction. The study cited shorter duration of operation time, more rapid rehabilitation, lower cost of care, and reduced trauma. Systematic reviews of the literature further this sentiment, indicating at least equally good outcomes for patients undergoing posterolateral endoscopic discectomy as compared to traditional microdiscectomy, although a long learning curve for this technique has been emphasized.¹⁰^,¹¹^,¹²^,¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷^,¹⁸ Prior experience with discography, epidural injections, and joint arthroscopy will help reduce the learning curve for the budding endoscopic spine surgeon.

32.2 Indications for Endoscopic Spine Techniques

Any intervertebral disc herniation contiguous with the disc space not sequestered and migrated is amenable to endoscopic disc excision. The sizes and types of herniations chosen by the surgeon are dependent on their skill and experience level. Perhaps the ideal lesion for the technique is the far lateral extraforaminal disc herniation. The approach accesses the disc through the foramen where the cannula is easily inserted at the herniation site. Other opportune circumstances include the following:

• Targeting upper lumbar and lower thoracic disc herniations.

• Recurrent disc herniations after a standard microdiscectomy.

• Posterior annular tears.

• Foraminal bony stenosis.

• Discitis.

• A novel approach for interbody fusion.

32.2.1 Herniations

Herniations in the upper lumbar segments require more aggressive laminotomies when approached posteriorly because of laminar shingling and overlap in relation to the disc space. Furthermore, more sagittal orientation of the facet joints may increase the chance for postoperative instability. Any potential destabilization is avoided via a posterolateral approach, and safe removal of disc herniations can also be achieved in the lower thoracic segments without the need to manipulate the spinal cord or conus medullaris.

The posterior laminotomy defect and epidural scarring add a level of difficulty and require more technical skill to achieve safe outcomes in cases of recurrent disc herniations. It is not uncommon for the formed scar tissue to limit the migration of the recurrent herniated disc fragment. This makes the posterolateral endoscopic approach more advantageous as it avoids the scar tissue and allows for safer access to the disc fragment.

Radiofrequency energy can be applied to annular tears under direct visualization to contract the collagen and ablate ingrown granulation tissue, neoangiogenesis, and sensitized nociceptors. This and the use of saline irrigation, which helps flush the neurotoxic chemicals and metabolites causing chemical irritation, can help reduce pain generated from this region. Frequently, interpositional nuclear tissue is seen within the fibers of the annular tear preventing the tear from healing. This tissue can be removed to allow the tear to heal, providing a minimally invasive alternative to a condition that may otherwise be treated with fusion or total disc replacement.

Endoscopic foraminoplasty can be readily achieved with bone trephines/rasps, specially designed articulating burrs, Kerrison rongeurs, and the side-firing Ho:YAG laser. The roof of the foramen is formed by the undersurface of the superior articular facet. This is easily visualized and accessed via the endoscope. The side-firing Ho:YAG laser and bone trephines strip the facet capsule and remove bone to enlarge the foraminal opening. Synovial cysts can also be visualized and removed.

32.2.2 Discitis

Discitis can be treated with posterolateral endoscopic discectomy and debridement. Current methods rely on needle aspiration, followed by prolonged antibiotic treatment. Needle aspirations are not as reliable as tissue samples from endoscopic debridement, and are often negative even in the face of bacterial discitis. Surgeons are often hesitant to perform open debridement because of the morbidity of the open approach, creation of dead space and devascularized tissue, and the concern for spreading the infection in the spinal canal. Endoscopic excisional biopsy and thorough debridement via the posterolateral portal has provided almost immediate pain relief and a much more reliable tissue sample for laboratory analysis and culture. Since only tissue dilation is used, no dead space is created that would allow the infection to spread.

32.2.3 Interbody Fusion

With the growing popularity of interbody fusion and development of expandable interbody implants for the purpose of spinal realignment, the posterolateral endoscopic technique has the potential to become the least invasive method to achieve these results. With the use of specialized flexible shavers and direct visualization of the interspace via the endoscope, a more efficient discectomy is affordable. Further, previously inaccessible levels such as an L5/S1 interspace become amenable to minimally invasive posterolateral fusion via the approach. Similarly, lateral access to other levels of the lumbar spine is easily gained without dilation through the iliopsoas muscle or excessive traction on the individual nerve roots and/or the sensitive nerve plexus.

32.3 Contraindications for Endoscopic Spine Techniques

Contraindications are relative and depend on the location of disc herniation, the patient’s anatomy, and surgeon experience. Sequestered herniations and highly migrated extruded herniations can be successfully treated from the posterolateral approach, but are more easily removed via a traditional posterior approach. Patients with a high iliac crest and a more horizontal sacral slope present a challenge for the posterolateral endoscopic approach. A steeper, more medialized trajectory is needed, making it more difficult to reach herniations in the posterior quadrant of the disc space. In degenerative scoliosis, access through the neuroforamen on the concave side of the curve presents yet another challenge. Although these barriers are not insurmountable for the experienced surgeon, the surgeons first learning the technique should attempt more accessible foraminal herniations. As they become more familiar with the technique and their endoscopic surgical skills improve, they can successfully treat more difficult-to-reach herniations. In order to overcome anatomic constraints at L5/S1, for example, the more experienced endoscopic spine surgeon will attempt to remove the ventral portion of the superior articular process to allow for a shallower approach trajectory to the posterior aspect of the disc space.

32.4 Preoperative Planning

A careful preoperative history, physical examination, and meticulous review of the plain radiographs and MRI are essential before attempting a posterolateral endoscopic discectomy regardless of the pathology being addressed. Attention to specific anatomic relationships is important to determine whether the approach is safe and feasible, and to ensure that there are no contraindications. Note the level of the iliac crest in relation to the disc space being accessed to determine the optimal needle trajectory. A high narrow pelvis may make it difficult to access the L5/S1 disc space. Furthermore, review the axial MRI images to evaluate the relationship of the lateral facets to the disc space and the location of retroperitoneal structures in order to obtain a better understanding of the planned trajectory ( Fig. 32.3). Also, severe degenerative scoliosis or the presence of spondylolisthesis may make the endoscopic procedure less predictable.

Some endoscopic spine surgeons may elect to perform their own transforaminal epidural steroid injections. As a diagnostic tool, it is invaluable as a selective nerve root block to isolate the pathology to a unilateral and singular level. It may also provide the patient with therapeutic relief of symptoms, if only for a short period of time. More importantly, it may serve as a “trial run” to determine the ease of endoscopic instrument access to the pathologic lesion.

32.4.1 Instrumentation

There are a number of endoscopic systems in clinical use today with similar instrumentation ( Fig. 32.4). At heart, they consist of an endoscope, video camera, light source with cable, a video processing unit, and a tower. The endoscopes typically employ a rigid rod-lens design connected to a body, which has a working channel and several attachments for irrigation fluid, suction, and a video source. The system used by the authors consists of the Yeung Endoscopic Spine Surgery System (YESS)/Vertebris system (Richard Wolf GmbH.) with the following instruments:

• Multichannel, 20-degree oval spinal endoscope with a 2.7-, 3.1-, or 4.1-mm working channel and integrated continuous irrigation (inflow and outflow) ports.

• Multichannel, 70-degree oval spinal endoscope.

• Access cannulas of 7 and 8 mm with various open slotted, beveled, and tapered tips.

Fig. 32.3 While posteroanterior and lateral fluoroscopic imaging should aid the surgeon in triangulating the tip of the needle to the desired position after the patient has been positioned, close attention should also be paid to preoperative imaging. This axial view shows proposed needle trajectory as it traverses the erector spinae (ES) in relation to the quadratus lumborum (QL), psoas muscle (P), and the peritoneal cavity. Axial MRI imaging should also allow the surgeon to estimate the distance of the skin entry point from the midline (L) and the angle of the needle trajectory off of the horizontal plane.

Fig. 32.4 Basic instrument set includes the endoscope with a working channel for discectomy and probing tools utilized under direct visualization.

• Guide wire and tissue dilator/obturator cannulated with a central channel and an eccentric channel to accommodate a needle for local annular anesthetic (eccentric channel) while simultaneously positioned over the guide wire (central channel).

• Specialized single and double action rongeurs for visualized fragmentectomy through the endoscope working channel.

• Larger straight and hinged rongeurs that fit through the access cannulas for biportal fragmentectomy and fluoroscopically guided uniportal discectomy.

• Cutting tenotomy type forceps to release annular fibers.

• Trephines for annulotomy and removal of bone for foraminal enlargement (foraminoplasty).

• Micro-rasps, curettes, and Penfield probes.

• Annulotomy knife.

• Flexible bipolar radiofrequency probe (Elliquence) for hemostasis, thermal contraction of the annular collagen, and thermal ablation of the annular nociceptors.

Adjunctive equipment includes the following:

• Straight and flexible suction-irrigation shavers for discectomy.

• Pump suction-aspirator to connect to the suction-irrigation shavers for stronger suction than standard wall suction.

• Side-firing Ho:YAG laser for fine tissue and bone vaporization/dissection.

• Endoscopic high-speed drill and alternatively an articulating burr for foraminoplasty.

• Fluid pump for consistent and continuous irrigation.