Endoscopic Spinal Surgery Kai-Uwe Lewandrowski, Sang-Ho Lee, Menno Iprenburg
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Spinal endoscopy: historical perspectivesChapter 1

Kai-Uwe Lewandrowski
 
INTRODUCTION
Surgical decompression of neural elements and stabilization of unstable spinal motion segments have been the main goals of spinal surgery regardless of what type of technologies are used to achieve these goals. Often, this requires extensive exposure and stripping of soft tissues, which in turn may devitalize and degenerate the very structures, the integrity of which is paramount to maintaining a healthy spinal motion segment. Problems such as postlaminectomy instability and epidural fibrosis have long been recognized as some of the potential follow-up problems that could arise from traditional open spinal surgery.1–3 Other well-recognized problems include disruption of vascular supply and denervation of paraspinal muscles with resultant decreased trunk strength, and chronic pain syndromes that at least in part arise from extensive spinal exposures.4
At 10 years, the cumulative rate of development of adjacent level disease in both the cervical and the lumbar spine, in previously healthy spinal motion segments adjacent to fusions, has been reported to be as high as 25%. This is not a small number and recognition of this problem has prompted surgeons to look for alternative ways to accomplish the two basic goals of each spinal surgical procedure: neural element decompression and stabilization of unstable motion segments.5–8
From the patient's point of view, reduction of blood loss and surgical time, with rapid recovery and return to work, is a clear advantage that nowadays is being openly discussed. With the advent of the internet, social media hubs, and blogs, and the overall availability of educational information, patients have become much more educated, inquisitive, at times critical, and hopeful that their specific problem can be solved with less aggressive procedures. From a surgeon's point of view, these advantages are no less important because they seem to drive patient traffic into their offices, and to present a number of clinical upsides that can easily be communicated to patients, families, hospitals, insurance carriers, third party payers, and medical review boards. Nevertheless, the question remains whether these minimally invasive procedures will withstand the test of time and show at least a similar track record when it comes to long-term clinical outcomes. This is obviously the area where opinions diverge the most and where discussions are most controversial.
In this chapter, the author attempts to summarize, without any claim on completeness, how the current state-of-the-art endoscopic spinal surgery progressed from a simple discectomy procedure to an array of sophisticated methods that have largely evolved from advances in high-definition optics, computerized irrigation/suction systems, production of durable endoscopic instrumentation, and incorporation of technologies well proven in other medical areas such as radiofrequency ablation and lasers.
 
HISTORY OF LUMBAR ENDOSCOPIC SPINAL SURGERY
The first microdiscectomy procedures for radicular pain due to herniated disc were performed by Mixter and Barr in 1934. They reported on 19 patients who underwent laminectomy.9 The concept of a less aggressive decompression was first introduced by Hult, who performed nucleotomy through an extraperitoneal approach in 1951.10 In the 1960s, the concept of chemonucleolysis evolved after Lyman and Smith discovered that percutaneous injection of chymopapain could hydrolyze a herniated nucleus pulposus in a patient with sciatica due to the herniated disc.11
In 1973, Parvis Kambin introduced the concept of a transforaminal approach with the use of percutaneously placed Craig's cannulas through which he performed microdiscectomy in a nonvisualized fashion.12 Hijikata reported on nonvisualized psoterolateral percutaneous nucleotomy in 1975.13 William Friedman introduced the direct lateral approach for percutaneous nucleotomy in 1983 and reported that this procedure was associated with a higher rate of bowel injury.14 The introduction of a specially modified arthroscope into the intervertebral disc, and thus the first visualized microdiscectomy, was first reported by Forst and Hausman in 1983.15 The addition of a motorized shaver was described by Onik in 1985 which led to the coining of the term ‘automated percutaneous nucleotomy.’16
Kambin published his first ‘discoscopic views’ from within the disc in 1988 and later emphasized the importance of epidural visualization as well.17 One year later, Schreiber described the injection of indigo carmine dye into the disc to stain abnormal nucleus pulposus and annular fissures.18
Kambin first described the ‘safe’ or ‘working’ zone in 1990 as the triangle bordered by the exiting nerve root, the inferior endplate and superior articular process of the inferior vertebra, and medially by the traversing nerve root (Figure 1.1).19 Better understanding of the anatomy of the working triangle paved the way for introduction of larger working cannulas for introduction of more sophisticated instruments and endoscopes (Figure 1.2).20 Endoscopes with an angled optic were introduced by Schreiber in 1993, allowing dorsal vision around an annular tear.18 Kambin and Zhou demonstrated the use of a 30° endoscope, recognizing that lateral recess stenosis can hamper effectiveness of the procedure. In 1996, they demonstrated foraminoplasty via endoscopic removal of facet overhang, osteophytes, and annulectomy, using specialized forceps and trephines.20,21 Foley, Mathes, and Ditsworth furthered the field of endoscopic spinal surgery by popularizing the transforaminal approach in their clinical studies published between 1998 and 1999.22–24 In 1999, Yeung introduced the Yeung Endoscopic Spine System (YESS™) 2using a multichannel, wide-angled endoscope.25
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Figure 1.1: Surgical anatomy of the ‘safe zone’. The safe zone is formed by the lateral border of the exiting nerve root above, medially by the border of the traversing root or thecal sack, inferiorly by the endplate, and dorsally by the superior articular process of the inferior vertebral body. The safe zone is located within the axilla between the exiting and traversing nerve roots. (Redrawn from an original by Robert F. McLain in: Lewandrowski K-U, Yeung CA, Spoonamore MJ, McLain RF (eds). Minimally Invasive Spinal Fusion Techniques. 2008, Summit Communications).
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Figure 1.2: The ‘safe zone’ is entered by removing parts of the superior articular process of the inferior vertebral body, thus performing a foraminoplasty. (Redrawn from an original by Robert F. McLain in: Lewandrowski K-U, Yeung CA, Spoonamore MJ, McLain RF (eds). Minimally Invasive Spinal Fusion Techniques. 2008, Summit Communications).
In 2001, Knight et al. showed that endoscopic foraminoplasty with a side firing Ho:YAG (holium:yttrium–aluminum–garnet) laser can be effective in neural element decompression.26 The advent of lasers also stimulated electrothermal annuloplasty for low back pain, which was described by Tsou and Yeung in 2002.27
More contemporary systems were introduced by Antony Yeung in 2003 with the launch of the YESS, which was designed around the transforaminal endoscopic approach for intradiscal and epiduroscopic procedures.28 Yeung et al. describe the utility of provocative intraoperative discography, thermal discoplasty and annuloplasty, and annular resection for creation of an annular window to perform foraminoplasty with the use of abrasive drills, burrs, and lasers. Bipolar electrofrequency probes were introduced by Tsou who performed a thermal electroannuloplasty for chronic discogenic low back pain. This technique was done on the direct visualization targeting disc nucleus and annular fissures.29
Another leap forward was achieved by Ruetten et al. who dealt with the problem of poor visualization of the epidural space, with the popularization of the direct lateral approach and uniportal use of a foraminoscope.30 Hoogland and Schubert dealt with the problem in an alternative way by describing foraminoplasty with transforaminal reamers in 2005.31 This technique made it easier to gain access to sequestered disc fragments that migrated in locations far distant from the interspace. This problem was further analyzed by Lee, in 2006, who found that patients with severe canal and lateral recess stenosis had less favorable clinical outcomes as a result of a higher risk for remnant disc fragments responsible for persistent clinical symptoms.32
Lee et al. also pioneered the definition and application of a classification system for the location of herniated disc by dividing them into near-migrated (zone 2 and zone 3), and upward (zone 1) or downward (zone 4) far-migrated disc fragments.33 The author's own clinical experience underlines the importance of the use of radiographic classification systems for both herniated disc and spinal stenosis. The utility of a radiographic classification system for foraminal and lateral recess stenosis is demonstrated in Chapter 22 of this text, where division of the neuroforamen into entry, mid-, and exit zones has been shown to be helpful when stratifying patients and selecting appropriate surgical candidates.
 
HISTORY OF CERVICAL ENDOSCOPIC SPINAL SURGERY
The first to report on percutaneous cervical discectomy in 1989 was most likely Tajima et al.,34 and Gastambide (1993)35 independently reported on manually removing the central portion of a cervical disc without removal of the posterior longitudinal ligament under fluoroscopic guidance. This process produced an indirect decompression. Algara et al. developed an automated percutaneous cervical discectomy procedure in 1993.36 Herman also reported on automated nonendoscopic discectomy 1 year later.37 Bonati (1991),38 Sieber (1993),39 and Hellinger (1994)40 reported on the utility of laser percutaneous cervical discectomy. Lee et al. introduced the combined use of percutaneous manual and laser discectomy in 1993 and later popularized the concept of ‘laser-assisted spinal endoscopy.’41 This system was based on a straight firing Ho:YAG laser that was introduced through an illuminated and irrigated 3-mm flexible cable. In 1994, Zweifel published on experimental laser disc surgery, pointing out that the Ho:YAG laser was the safest but most effective laser for tissue ablation while minimizing thermal damage to surrounding tissues. Chymopapain has been used in the mid-1990s but was later abandoned because of catastrophic clinical complications.42
Another technological break was achieved with the introduction of a 0°, 4-mm endoscope with a 1.9-mm working channel (Figure 1.3). Surgeons at the Wooridul Spine Hospital in Seoul, South Korea took advantage of improved endoscopic visualization, and a large working channel.43 Ahn et al. reported that 88.3% of their 111 percutaneous anterior cervical discectomy patients improved at a mean follow-up of 49.9 months. Loss of mean disc height was later analyzed in a smaller series of 36 patients and was limited to 11.2%, suggesting that sagittal alignment could be maintained without development of postoperative segmental instability or spontaneous fusion with the use of the percutaneous anterior cervical discectomy procedure.443
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Figure 1.3: Anterior 20° cervical endoscopic system with instruments (asap Endosystems GmbH, Umkirch, Germany).
 
BRIEF CHRONOLOGICAL SYNOPSIS OF CLINICAL OUTCOME STUDIES
Until recently, randomized prospective trials comparing the traditional open versus the endoscopically performed lumbar microdiscectomy procedure were unavailable. Earlier studies, however, suggested that successful outcomes can be achieved, e.g. Choi et al. reported a 92% success rate with their own extraforaminal fragmentectomy technique. In their 2007 study, they reported on 41 patients in whom soft extraforaminal disc herniations were treated in such a way with a more medialized trajectory.45 In the same year, Lee et al. demonstrated high clinical success rates with downward migrated disc fragments (91.8%), in upward migrated disc fragments (88.9%), in near-migrated disc fragments (97%), and slightly less favorable clinical results with far-migrated disc fragments (78.9%).32,33 The type of herniation is obviously the hardest to reach and demands proficient surgical skills. Ruetten et al. published results of 463 patients treated with the endoscopic transforaminal discectomy procedure.47
In 2009, Ruetten et al. published the results on surgical treatment for lumbar lateral recess stenosis using the full endoscopic and interlaminar approach versus conventional microsurgical technique. This prospective randomized controlled trial on 161 patients showed similar clinical results in the ‘full endoscopic group’ and the microsurgical group when analyzing the German version of the North American Spine Society instrument and the Oswestry low back pain disability questionnaire.48
In the cervical area, Chiu reported outcomes on 200 patients whom he treated with percutaneous microdecompressive endoscopic cervical discectomy, with a side-firing Ho:YAG laser. At 25 months of average follow-up he reported a 94.5% success rate in the absence of major clinical complications.49
 
THE EVOLUTION OF LASERS IN LUMBAR MICRODISCECTOMY
Lasers have always been very attractive for surgeons when applied in minimally invasive procedures due to the ability to deliver a large amount of energy through a small fiber in a very focused small area. This has first been demonstrated by Peter Ascher who employed a neodymium:yttrium–aluminum–garnet (Nd:YAG) laser through an 18-gauge needle that was introduced fluoroscopically into the intervertebral disc. 50 He ablated intradiscal tissue in short bursts to avoid heating of adjacent tissues, thereby vaporizing tissue that was allowed to escape through the needle. This procedure was ideally suitable for an outpatient setting – as the patient was discharged, the needle was withdrawn, and the puncture wound covered with a small Band-Aid.
Many subsequent authors demonstrated the utility of different types of lasers including the Ho:YAG which was compared with the Nd:YAG laser in a clinical trial conducted by Quigley et al. in 1991.51 They concluded that the Ho:YAG laser was the best for compromising between efficacy of absorption and convenience of fiberoptic delivery at that time. In 1990, Davis et al. described a 85% success rate in a study on 40 patients who underwent laser discectomy using the potassium titanic phosphate (KTP 532-nm) laser.52 Only 6 of the 40 patients required revision with open discectomy procedures because of clinical failures. In 1995, Casper et al. described the use of the side-firing Ho:YAG laser53 which was also later employed by Yeung et al.54 At 1-year follow-up, Casper et al. reported an 84% success rate.53 In the same year, Siebert et al. reported an 78% success rate on 100 patients with a mean follow-up of 17 months who were treated with the Nd:YAG laser.55
Mayer et al. was the first to suggest the combined use of an endoscope with laser ablation through an endoscopically introduced fiber. Large clinical trials followed and were very supportive of the clinical use of lasers for removal of herniated disc.56 Hellinger reported in 1999 on more than 2500 patients whom he treated with the use of the Ascher technique.57 He reported the success rate of 80% over a 13-year period. One year later, Yeung et al. reported an 84% success rate on more than 500 patients whom he treated with the KTP laser.54
 
RADIOFREQUENCY ABLATION
High-frequency radiofrequency (RF) ablation has found several applications in neurosurgery, endoscopic spine, orthopedic and pain management. High-frequency RF with low temperatures has been employed for tissue dissection (monopolar) and coagulating mode (mono- and bipolar). For spinal endoscopy, the Trigger-Flex Bipolar System (Elliquence, New York, USA) has been developed to accomplish targeted application and precise tissue ablation (Figure 1.4). The Trigger-Flex Bipolar System is compatible with all working channel spinal endoscopes and is used for hemostasis, shrinkage, or ablative effects in soft tissue to dissect them off a herniated disc.
RF ablation of tissues is well accepted in other areas such as plastic surgery, oral maxillofacial surgery, and dental procedures. These devices have found their way into spinal surgery for thermal ablation of disc tissue. With further miniaturization and reduced acquisition costs, they now present an attractive alternative to lasers which in most cases are more costly and cumbersome, and impose certain safety issues for patients, surgeons, and supporting staff alike.
The utility of high-frequency RF with low-temperature tissue ablation has been investigated in at least one study. In 2004, Tsou et al. retrospectively reviewed 113 consecutive patients with a minimum postoperative follow-up of 2 years. Patients were treated for discogenic low back pain:294
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Figure 1.4: (a) Trigger-Flex Bipolar System (Elliquence, NY, USA) introduced through the central working channel for tissue ablation. (b) Squeezing the hand piece will flex the tip: the probe is connected to a generator.
Using the surgeon assessment method, 17 patients (15%) had excellent results, 32 patients (28.3%) had good results, 34 patients (30.1%) had fair results and 30 patients (26.5%) had poor results. Of the 30 patients in the poor result group, 12 reported either no improvement or worsening, and refused further surgical treatment. Of the remaining 18 patients in the poor group, 8 had spinal fusion, 3 had laminectomy and 7 had repeat spinal endoscopic surgery. The patient-based questionnaire yielded similar percentages in each category. However, only 73.5% of the 113 patients returned the survey questionnaire. There were no aborted procedures, unexpected hemorrhage, device-related complications, neurologic deficits, perioperative deaths or late instability.
The authors concluded that the treatment interrupted the purported annular defect pain sensitization process.
Nowadays, high-frequency RF with low-temperature tissue ablation is an integral part of spinal endoscopy, and is most useful when controlling bleeding and shrinking tissue to facilitate decompression.
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