Posterolateral Endoscopic Lumbar Discectomy

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CHAPTER 59 Posterolateral Endoscopic Lumbar Discectomy

Posterolateral endoscopic lumbar surgery is a less invasive surgical procedure to address lumbar pathology in the disc and boney foramen. Like any surgical procedure, it is based on visual identification and exposure of the target pathology and adequate surgical tools to address the offending pathology. Modern day endoscopic technology allows for visualized discectomy and decompression of the traversing and exiting nerve roots from a percutaneous posterolateral/transforaminal approach. This is safe and equally efficacious to microscopic discectomy in properly selected patients.14 Recent advances also allow for bony decompression of foraminal stenosis.5,6

Advances in the ability to perform endoscopic discectomy have paralleled other specialties, yet percutaneous spinal surgery has not met with the same peer recognition as the other fields. This is due in part to the high success rate and relative low morbidity of the current gold standard, posterior microscopic lumbar discectomy. However, this approach still requires a 1-inch midline incision, significant muscle and ligament stripping, prolonged muscle retraction, partial facet and lamina resection, and both nerve root and dura retraction. This can weaken the muscular lumbar stabilizers, create instability and facet arthrosis, cause traction neuropraxia, promote epidural scarring, and make revision surgery more difficult.

Another barrier for more widespread adoption was the relative paucity of peer-reviewed literature, and critics noted that only a few authors were contributing to this body of literature. Recently, there have been many more published results of posterolateral endoscopic discectomy from around the world and the preponderance of evidence supports its efficacy.

Numerous other nonvisualized percutaneous techniques often get categorized and confused with posterolateral endoscopic lumbar discectomy. These include automated percutaneous lumbar discectomy (APLD), percutaneous laser discectomy, and percutaneous discectomy with the Dekompressor or Arthrocare wand (Coblation). These are all fluoroscopically guided nonvisualized procedures that access the disc via the same posterolateral approach as endoscopic lumbar surgery. The underlying principle of these procedures is that through central nucleus removal or ablation, intradiscal pressure can be substantially lowered. This was based on the work of Hirsh and his postulated relationship between intradiscal pressure, disc herniation, and low back pain. He hypothesized that lowering this pressure in an injured disc could be efficacious in the relief of sciatica.7 Multiple studies described decreases in intradiscal pressures of 50% or greater.810

The results of these types of indirect decompressive procedures have been similar with initial favorable reports. However, subsequent studies have shown varying degrees of success. The inability to consistently see the decompressed nerve or the targeted patho-anatomy has limited the use of these nonvisualized decompressive procedures.1114 It is unfortunate that these procedures, and their results, are mistaken for posterolateral endoscopic discectomy.

History

The basis for percutaneous lumbar disc procedures came from accepted posterolateral percutaneous biopsy techniques of the lumbar vertebrae. These procedures were initially performed with the use of a Craig needle to perform a posterolateral biopsy for neoplastic conditions.15,16

Minimal access surgery for lumbar disc herniation was first independently reported by Kambin and colleagues17 and Hijikata18 in 1975. The technique used a posterolateral approach to the foraminal zone of the disc bordered by the traversing nerve dorsally, the exiting nerve ventrally, and the endplate of the inferior vertebra caudally. The goal was to decompress nerve roots secondary to lumbar disc herniation by the “inside-out technique” of central and posterior nuclectomy and fragmentectomy. Advances in technique and instrumentation since Kambin, however, have allowed the surgeon to also enlarge the medial or lateral foramen by decompression of the lateral and ventral portion of the facet joint complex to reach the midline of the disc and the epidural space. Thus it is feasible to treat the full spectrum of disc herniations with advanced endoscopic instrumentation and techniques that can either target the extruded fragment directly or with a combination of the “inside-out technique.”19

The early efforts were limited to a nonvisualized central discectomy to achieve an indirect decompression of the nerve roots,17,18,20 but improvements in surgical equipment and technique evolved gradually over the next 30 years. In the past 10 years, the important major equipment improvements have included various-sized high-resolution rod lens operating endoscopes with variable-size working channels, beveled and slotted cannulas, flexible shavers and pituitary forceps, a bipolar flexible high-frequency/low-temperature radiofrequency (RF) electrode, multidirectional Holmium Yttrium-Aluminum-Garnet lasers, and high-speed diamond burrs and motorized shavers to decompress the foramen.19 An improved fluoroscopically guided approach method introduced by Yeung and reported by Tsou2123 outlined a consistent and safe technique for entry into all lumbar posterior disc spaces including the L5-S1 level. This specific technique has been termed selective endoscopic discectomy (SED) but can be classified under the more general descriptive term of posterolateral endoscopic lumbar discectomy (PELD) that other authors describe.

These refinements have enhanced the capabilities of foraminal endoscopic discectomy to deliver surgical results similar to the results obtainable by traditional transcanal approaches for treating common lumbar disc herniations.14

Minimal access posterolateral endoscopic intradiscal visualization with the available operating tools has introduced new operative capabilities. That includes foraminal decompression for more central access of disc herniations and selective nuclectomy and annuloplasty performed intradiscally. The process of foraminal decompression also decompresses the lateral recess in lateral recess stenosis and mild central canal stenosis, a common late sequela of lumbar discectomy.

Anatomy

Posterolateral endoscopic lumbar surgery is performed through what has been named the triangular working zone, or Kambin’s triangle (Fig. 59–1). This triangular zone is defined as a safe zone in the posterolateral annulus between the exiting and traversing nerve roots. The exiting nerve root forms the anterior border of the triangular zone as it exits under the cephalad pedicle. The superior endplate of the caudal vertebral body forms the inferior border and the articular process and superior articulating facet of the caudal vertebra form the posterior border. The working zone is bordered medially by the traversing nerve root and dura. From cadaveric measurements it was determined that cannulas ranging from 4 mm to 10 mm could be safely used in the triangular working zone.2427 A thorough understanding of the three-dimensional anatomy is necessary to understand and perform posterior percutaneous lumbar surgery.

Endoscopic Lumbar Discectomy

Endoscopic surgery developed out of fluoroscopically guided percutaneous procedures that initially used a working cannula with modified instruments designed for disc removal. The first surgeon credited with percutaneous nucleotomy was Hijikata in 1975.18 The evolution of endoscopic techniques followed a series of transitions. Initially, an arthroscope was used to inspect the disc and annulus intermittently through the cannula while the mechanical nuclectomy was done under fluoroscopic guidance. The introduction of a biportal approach allowed for direct visualization of instruments introduced through a cannula inserted into the disc from the opposite posterolateral portal. The later development of an operating spine scope with a working channel allowed for surgical removal of disc material and visualization of foraminal anatomy under direct visualization via a uniportal approach.

Parviz Kambin performed the first true endoscopic lumbar procedures. The arthroscope was at first used intermittently through the working cannula. At certain stages of the procedure such as perforating the disc in the triangular working zone, the arthroscope would be placed in the cannula. The nonworking channel scope was used for identification of the annulus and periannular structures. The basis was to see that the nerve was not in the way before advancing the cannula. Once the cannula was safely within the disc, the nucleotome, an arthroscopic shaver, and pituitary rongeurs were passed through the cannula to perform mechanical disc removal. The majority of the procedure was only fluoroscopically visualized.17 Kambin reported an 88% success rate in his first 100 patients.28,29

The early endoscopic procedures were limited by the absence of a working channel arthroscope. This led Kambin to the development of a biportal technique in which the scope was inserted on one side and the working cannula on the opposite side. Kambin’s indications for a biportal approach included large subligamentous herniations, extraligamentous herniations, and arthroscopic interbody fusion.26 In later studies Kambin reports results from both uniportal and biportal procedures together. Overall results ranged from 85% to 92% satisfactory results at a minimum 2-year follow-up. There was no differentiation made between the results of uniportal versus biportal approaches.3032

Kambin’s first prototype of the working channel scope was not fully developed and was not successfully marketed. The problems with the initial scope included fragility, limited degree of angulation for the working instruments, and the inability to establish sufficient inflow or outflow for adequate visualization.33 Anthony Yeung developed the first working channel endoscope to become widely available. The scope was developed in 1997 and was approved for use by the U.S. Food and Drug Administration in March 1998. The Yeung Endoscopic Spine Surgery (YESS) system (Richard Wolf Surgical Instruments, Vernon Hills, Ill.) modified the scope by adding multichannel integrated irrigation, specialized beveled cannulas, a two-hole obturator, and newly designed discectomy tools that allowed for constant real-time visualization with a uniportal technique.34 (Fig. 59–2)

image

FIGURE 59–2 The Yeung Endoscopic Spine Surgery system.

(Courtesy Richard Wolf Surgical Instruments, Vernon Hills, Ill.)

Another major change, which allowed for advancement in the field of endoscopic spinal surgery, was the emphasis on placement of the cannula closer to the epidural space and the base of the targeted disc herniation. This enabled surgeons to target extruded herniations in addition to contained herniations. Previous percutaneous modalities all focused on entry through Kambin’s triangle and working within the center of the disc with the cannula anchored inside the annulus. The cannula was advanced past the annulus and remained there under fluoroscopic control. Mathews’ transforaminal approach for microdiscectomy allowed for routine visualization of the epidural space and greater access to the traversing nerve root.35

The development of a working channel scope and use of the transforaminal approach using beveled and slotted cannulas enhanced endoscopic lumbar surgery. Using this approach, surgeons can operate under full visualization throughout most of the procedure and follow the neural structures into the epidural space. The specialized cannulas provide greater access to pathology and help protect and retract sensitive anatomy such as the exiting nerve and dorsal root ganglion. The working channel also allowed the passage of high-speed burrs for bone removal and direct foraminal enlargement and decompression of foraminal stenosis (foraminoplasty) (Fig. 59–3).

Indications/Contraindications

Current indications for the use of an endoscopic posterolateral approach to the lumbar spine include foraminal and far-lateral disc herniations, contained central and paracentral disc herniations, small nonsequestered extruded disc herniations, recurrent herniations, symptomatic annular tears, synovial cysts, biopsy and débridement of discitis, decompression of foraminal stenosis with or without spondylolisthesis, visualized total nuclectomy (before nucleus replacement), visualized discectomy, and endplate preparation before interbody fusion.

Perhaps the ideal lesions for posterolateral selective endoscopic discectomy are the foraminal and extraforaminal disc herniations. The cannula inserts directly at the herniation site, and the exiting nerve is routinely visualized and protected. This approach requires less manipulation of the exiting nerve root than the paramedian posterior approach.

Any herniation contiguous with the disc space not sequestered and migrated is amenable to endoscopic disc excision if the boney anatomy permits an unobstructed approach. This uses an “inside-out” technique where the herniation is grasped from its base within the disc space, pulled back into the working intradiscal cavity, and removed via the cannula. The size and types of herniations chosen by the surgeon for endoscopic excision will depend on the skill and experience of the surgeon. Certainly, all contained disc herniations are appropriate for endoscopic decompression. With experience, extruded herniations can be routinely addressed. This approach is especially attractive for recurrent herniations after a traditional posterior approach because the surgeon can avoid the scar tissue from the previous surgery.

Radiofrequency energy can be applied to the annular tears under direct visualization to contract the collagen and ablate ingrown granulation tissue, neoangiogenesis, and sensitized nociceptors.36 Frequently interpositional nuclear tissue is seen within the fibers of the annular tear, preventing the tear from healing. This tissue can then be removed to allow the tear to heal.

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