Endoscopic Procedures on the Spine

This book aims to familiarize readers with the overall scope of endoscopic surgeries for the treatment of various types of spinal disease. State of the art techniques for minimally invasive endoscopic procedures to the cervical, thoracic, and lumbar spine are precisely described. The coverage includes cutting-edge endoscopic solutions for spinal canal stenosis or instability and low back pain. All technical aspects are explained in detail, and the text is complemented by many helpful illustrations. A further key feature is the provision of accompanying surgical videos, which will be of value to both novice and experienced surgeons. As a result of recent technological advances, minimally invasive endoscopic procedures are now being used for the treatment of patients with spinal problems in various institutes across the world. It can be anticipated that, in the near future, these procedures will be regarded as mainstream in spine surgery. The authors hope that this book will motivate the reader to participate in this trend, which promises important benefits for patients.

• Language: English
• Publisher: Springer
• Release date: Sep 3, 2019
• ISBN: 9789811039058

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© Springer Nature Singapore Pte Ltd. 2020

J.-S. Kim et al. (eds.)Endoscopic Procedures on the Spinehttps://doi.org/10.1007/978-981-10-3905-8_1

1. Spinal Endoscopy: Historical Review and Current Applications

C. Birkenmaier¹  

(1)

Department of Orthopedics, Physical Medicine and Rehabilitation—University of Munich (LMU), Munich, Germany

C. Birkenmaier

Email: [e-mail]

Keywords

Spinal endoscopyEndoscopic discectomyTerminologyHistoryArthroscopy

1.1 Nomenclature and Terminology

The term endoscopy implies the use of a thin, tubular and coaxial surgical instrument that contains image transmission, illumination, and frequently also irrigation and a working channel. Such an instrument is placed into the surgical field via a small stab incision and by means of tissue dilation. The image is produced by a camera at the end of the optical system and transmitted to a monitor. In the spine and different to endoscopy of preformed body cavities, the very limited surgical space is constantly irrigated to maintain visibility, to control bleeding, to cool tissue when radiofrequency or laser are being used, and to wash out surgical debris.

These specific features distinguish true endoscopy (or full endoscopy as termed by Ruetten) from tubular microendoscopy, where a small retractor or working tube is placed and surgery is performed in the dry and with standard microsurgical instruments under camera vision. Examples for the latter technique could be the Storz Destandau system or the more recently developed Storz Easy-Go system.

Another synonym for full endoscopy that is commonly used in the Asian literature is working channel endoscopy, which stresses the fact that such modern coaxial endoscopes contain an instrument channel beyond the rod lens, the illumination, and the irrigation channel.

Frequently used technical descriptions in the context of endoscopy are percutaneous or minimally invasive. However, these terms are not truly meaningful since all surgery (apart from superficial dermatological surgery) is in principle percutaneous and since no generally accepted definition of minimal invasiveness exists. Provided that the term endoscopic is used precisely and appropriately, no further qualifying adjectives should be required to explain the nature of the surgical approach and the type of surgical endoscope used.

Another conceptual problem tends to be the implied but not spelled-out inclusion of one specific anatomic approach into the name of a surgical technique. A very good example would be the acronym PELD for percutaneous endoscopic lumbar discectomy. PELD typically implies that the traditional transforaminal approach is used. However, many pathologies that can be treated by means of transforaminal PELD can equally or sometimes even better be addressed using an interlaminar or in certain cases a transosseous (burr hole) approach.

This terminological imprecision tends to be further complicated by the indiscriminate use of the term discectomy, which is not what microscopic or endoscopic spine surgeons perform these days. Probably the only surgical techniques that actually do achieve an almost complete discectomy are the ALIF procedure or a total lumbar disc replacement (TDR). With spinal endoscopy, sequestrations, disc fragments, or herniations are extracted under direct vision and the acronyms and terms we use should reflect that.

In the same line of thinking, the terms foraminoplasty or annuloplasty really do not confer a precise image of what is being done during an operation and we should all aim at being as precise and anatomically correct as possible when describing and naming surgical procedures.

1.2 Brief History of General Endoscopy and Arthroscopy

It has been a longstanding desire of researchers, medical doctors, and other curious individuals to look inside the human body and its cavities. The word endoscopy is derived from two Greek roots: ἔνδον (éndon) = inside and σκοπεῖν (skopein) = to observe.

As for modern medical applications, Philipp Bozzini in the early nineteenth century was the pioneer who first invented a candle-illuminated device to inspect ears, urethra, and rectum [1]. In 1853, the French physician Desormeaux developed a more advanced device for very similar applications and for the first time the term endoscope was documented in the 1855 proceedings of the French Academy of Sciences [2]. Desormeaux also spent significant effort into propagating the technology and therefore is known as the father of endoscopy.

But it required the invention of the electric light bulb (Edison 1879), of more advanced rod lens systems (Hopkins 1960), and of the CCD camera (Boyle and Smith 1970) to truly make these early endoscopes anywhere nearly as useful as we know them to be today.

However, even before the introduction of CCD cameras into medicine, Kenji Tagaki and Masaki Watanabe from Japan developed a series of ever better arthroscopes, first for veterinary use, but after the second world war increasingly also for human use and in 1950, the first human knee joint was arthroscopically examined. Based on their experience with 300 patients, Watanabe, Takeda, and Ikeuchi published the first Atlas of Arthroscopy in 1957 [3]. It is not by chance that Watanabe is known as the father of arthroscopy and since spinal endoscopy derives itself from arthroscopy, he may very well also be seen as a grandfather of spinal endoscopy.

1.3 The Development of Spinal Endoscopy

Initially, the lumbar spine with its rather common pathology disc herniation was the target of the se new percutaneous approaches. The first of these approaches to lumbar disc herniations, however, were blind procedures in terms of direct visualization, since neither Kambin nor Hijikata [4] used endoscopes in their early work in the 1970s. In the following period of innovation, APLD (automated percutaneous lumbar discectomy) [5] became the in-procedure and this technique also led to a patent. The major disadvantage of not having visual control was soon recognized, though, and only a few years after the first optical images from within a lumbar disc had been published [6], the procedure that we nowadays know as discography was inaugurated by Kambin [7] as well as by Schreiber et al. [8]. This fluoroscopy- and contrast-controlled injection of indigo carmine into the disc continues to be one of the most valuable steps in improving intraoperative accuracy and anatomic identification of the surgical target under endoscopic view.

While interest in blind percutaneous procedures with the purpose of disc volume reduction continued with the focus of interest shifting from APLD towards laser decompression [9], the surgical desire for full visual control, advanced technical accuracy, and precise surgical targeting in a parallel development pushed the advancement from arthroscopy to spinal endoscopy. Probably one particularly interesting early paper in this sense was the report on endoscopically guided laser application on non-sequestrated disc herniations in 6 patients by Mayer et al. [10]. They termed their new technique PELD (percutaneous endoscopic laser discectomy), an acronym that nowadays mostly is used for an endoscopic surgical technique. In 2001, Knight published his experience on endoscopy-guided foraminal nerve root decompression and used the term foraminoplasty for his technique [11].

An important step in the development of spinal endoscopy with respect to the original transforaminal approach was the anatomic definition of the safe working zone (also known as Kambin’s triangle) between the descending, exiting nerve root as the antero-superior limitation, the ascending facet as the posterior limitation, and the lateral border of the superior endplate of a motion segments’ inferior vertebra as the inferior limitation by Kambin and Zhou [12].

This safe entry zone into the disc, the colorization of nucleus material with indigo carmine together with improved endoscopes and working tools inaugurated the first phase of major global interest in spinal endoscopy—at the time termed percutaneous arthroscopic disc surgery.

The knowledge concerning the anatomy of the safe triangle and tools to trim the anterior aspect of the ascending facet also permitted for larger endoscopes and cannulas to be employed, which made surgical decompression more efficient.

Initially, bilateral biportal access was used—much like in knee arthroscopy. When Schreiber first used an angled optical system, visibility of the posterior annulus region with these early intradiscal (all inside and inside-out strategies) was significantly improved [8]. Kambin et al. published on their experience on 59 patients operated on with the biportal technique and on 116 patients operated on with the more modern, unilateral and uniportal technique [13].

Yeung did major work on improving the devices available with his YESS system, from which several current endoscopic systems are derived and published on a large (albeit uncontrolled) personal series with posterolateral transforaminal endoscopic decompression of disc herniations and lateral recess stenosis [14, 15].

Based on the pioneering work described above, a more differentiated and specific approach to spinal pathologies became possible while at the same time, MRI diagnostics had become more readily available in the developed world. The primary intradiscal approach (in-out-technique) had been abandoned by most surgeons and disc extrusions, free sequestrations, and migrated fragments had become the targets of visually controlled surgery. In 2005, Schubert and Hoogland published their results with a large series (2-year-FU on 558 of 611 patients, no controls) of lumbar disc herniations, operated on by transforaminal endoscopy [16]. During the same period, variations of the original transforaminal approach were developed and the osteoclastic widening of the foraminal passage enabled more directional variety when entering the canal [17]. These developments in turn necessitated a more anatomically specific and approach-oriented classification of the pathologies to be treated by spinal endoscopy and the paper by Lee et al. was seminal in this process [18]. The same group also published on the technical specificities when addressing extraforaminal herniations [19]. Ruetten et al. expanded the panel of practically usable endoscopic approaches to the lumbar spine by describing the far-lateral transforaminal approach [20] as well as by adding the interlaminar lumbar approach in analogy to the traditional microsurgical approach to the lumbar spinal canal [21].

While non-visualized (only controlled by fluoroscopy) percutaneous cervical procedures (lasers, mechanical decompression) were attempted early, cervical endoscopy lagged behind lumbar endoscopy mostly because of the lack of suitable endoscopic systems. Only after the turn of the millennium did smaller caliber and shorter coaxial systems with good optics, illumination, and a reasonable working channel become available. Prior to that, Fontanella had started to use a 4.6 mm working cannula through which he worked with rigid or flexible endoscopes for visualization and with microsurgical instruments. He published his personal series of 171 patients who underwent anterior and posterior cervical disc surgeries in this fashion [22]. It is to the credit of the surgeons from Seoul’s Wooridul Spine Hospital that the first series of percutaneous endoscopic cervical discectomy (PECD) via the anterior approach and using a working channel endoscope was published [23]. The posterior interlaminar approach to cervical pathology (in analogy to the microsurgical Frykholm procedure, [24]) was published in 2007 by Ruetten et al. [25].

Already in the early years of spinal endoscopy, Leu et al. pioneered techniques for endoscopic lumbar interbody fusions [26, 27]. In those early series, the stabilization required was obtained with a transpedicular external fixator, which most likely was the main reason why interest in this approach subsided again. In 2004, Gastambide began the endoscopic transforaminal placement of specially designed titanium cages without additional fixation, but reported a considerable complication rate [28].

1.4 Currently Available Evidence from Controlled Studies

The past decade has seen several high-quality controlled and randomized-controlled studies that compared endoscopic surgery with standard, microsurgical procedures for cervical and for lumbar pathologies. Most of these studies have been analyzed and discussed for a 2013 review article [29].

The pathologies treated in these controlled comparisons were:

Primary cervical disc herniations with radiculopathy (posterior endoscopic foraminotomy vs. ACDF) [30]

Primary lumbar disc herniations (transforaminal or interlaminar endoscopic sequestrectomy vs. microsurgical sequestrectomy) [31]

Recurrent lumbar disc herniations (transforaminal or interlaminar endoscopic revision surgery vs. microsurgical revision surgery) [32]

Recurrent lumbar disc herniations (transforaminal endoscopic revision surgery vs. microsurgical revision surgery) [33]

Cervical disc herniations with radiculopathy (anterior endoscopic decompression vs. ACDF) [34]

Lumbar lateral recess stenosis (interlaminar endoscopic decompression vs. microsurgical decompression) [35]

Lumbar central canal stenosis (bilateral interlaminar endoscopic decompression vs. bilateral microsurgical decompression) [36]

The majority of these studies report 2 years of follow-up with clinical outcomes that are largely equivalent to those with microsurgical standard procedures and with fewer and fewer serious complications in the endoscopy group. There was a tendency towards higher reoperation rates with endoscopy in some studies, despite the fact that these RCTs uniformly were performed by experts in the field [31, 33]. Other short-term benefits of endoscopy were less blood loss, shorter operation times, shorter hospital stays/faster return to work, and less postoperative pain.

No long-term outcomes in comparison to microsurgery (e.g., in relation to progression to fusion or to adjacent segment degeneration) have been reported from these trials as of yet.

1.5 Current Clinical Applications of Spinal Endoscopy

In the lumbar spine, disc herniations, recurrent herniations, and migrated sequestrations are routinely being addressed by transforaminal or interlaminar endoscopic techniques. Foraminal stenoses and zygapophyseal cysts are frequently treated by spinal endoscopy. There also is an increasing body of literature showing that the decompression of lumbar central spinal canal stenosis can very well be accomplished by endoscopy.

There currently appears to be interest in performing lumbar and iliosacral medial branch and dorsal branch ablations under endoscopic vision as opposed to the traditional fluoroscopy-supported techniques.

In the cervical spine, the anterior transdiscal as well as the posterior interlaminar approaches for the endoscopic treatment of disc herniations and foraminal stenoses are firmly established. One recent case report describes a further evolution of the transcorporeal microsurgical approach originally described by Choi [37, 38]. The authors passed an endoscope through the burr hole and performed the extraction of a migrated disc herniation and direct endoscopic control [39]. In contrast to the lumbar spine, there is no relevant published work on the endoscopic treatment of spinal canal stenoses with associated myelomalacia. The same applies to stenoses caused by a calcified PLL.

In the thoracic spine, the endoscopic approaches and techniques that are routine in the lumbar and in the cervical spine are much less standardized and established. In addition, there is a crossover between these techniques and microsurgery as well as with the established, video-assisted surgical techniques that have long been employed for the treatment of fractures, infections, and the anterior release in scoliosis surgery. The relevant endoscopic publications in that arena therefore are mostly case series. With symptomatic disc herniations and stenoses being frequent in the cervical and lumbar spine while remaining comparatively rare in the thoracic spine, this is most likely not to change very soon.

In addition to the approaches and techniques mentioned above, there is a body of published experience with transnasal and transoral endoscopic approaches to the upper cervical spine and to the craniocervical junction. Again, these are typically case reports or small case series on pathologies ranging from tumors to infections, degeneration, and inflammatory conditions. Overall, these techniques represent a transition between classic spinal endoscopy and ENT endoscopy.

As far as surgical instruments are concerned, articulated high-speed burrs, probes, and rongeurs enlarge the actual working space that can be reached within the visual field of an endoscope. Slightly larger systems with a wider working channel have made the endoscopic treatment of lumbar central canal stenosis more efficient and less time-consuming.

In terms of tissue ablation and tissue modulation, side-firing lasers maintain a strong position in those countries, where billing and reimbursement structures allow for the considerable cost of these systems to be recovered. Alternatively, the radiofrequency probes used for hemostasis are often also capable of shrinking, modulating, and ablating soft tissues, but cannot vaporize bone.

Despite all efforts, endoscopic lumbar interbody fusion has so far not been able to establish itself as a viable alternative to open or mini-open techniques and this for a number of reasons. The transforaminal endoscopic approach—even when performed bilaterally—entails size limitations for surgical tools, interbody cages, and bone grafting. Cages with a small footprint, limited cage expandability, difficulty in performing a complete evacuation of the nucleus, and an optimal preparation of the endplates all contribute to a lesser reconstruction of disc space height, a higher chance for subsidence, and/or insufficient fusion. Since currently much attention is given to lordosis reconstruction in the context of lumbar fusions, endoscopic transforaminal lumbar fusion is facing an uphill battle.

1.6 Outlook

One of the greatest perceived limitations of spinal endoscopy (and for that matter of endoscopy in principle) is the current lack of true 3-dimensional vision and hence of a precise appreciation for the depth of the visual field.

It is probable that some surgeons consider this a greater problem than others and it is also likely that the capabilities of a human brain to 3-D-navigate within a 2-D-image vary significantly between individuals. Another factor is certainly the type of training received during residency and fellowship: Someone who has professionally grown up using an operating microscope will possibly find the 2-dimensional space of an endoscopic image less easy to conquer than another surgeon who has routinely arthroscoped knees, shoulders, and other joints before becoming a spinal specialist.

Within the coming years, however, this technological limitation should increasingly be overcome by the current developments in advanced stereoscopic ultra-HD cameras and suitable optics. These will deliver a true 3-dimensional view from within the spinal canal while preserving a key advantage of endoscopy, which is to have the surgeon’s eye right next to the pathology and to avoid the typical problem of deep, narrow operating fields that limit the usable angle of vision for microscopes. This will probably represent the fall of the last relevant technical barrier for a wider acceptance of spinal endoscopy, also outside the countries that have led the way for decades now.

It appears likely that the endoscopic treatment of lumbar spinal canal stenoses and disc hernations will expand further. After all, symptomatic lumbar spinal canal stenoses and disc herniations together constitute a large portion of lumbar degenerative conditions requiring treatment, and the group of patients in need of surgical treatment for these conditions is getting older, more comorbid, and more obese in many industrialized countries. With faster operations, shorter hospital stays, the option of performing many of these procedures under conscious sedation, and with obesity being no obstacle to endoscopic techniques, the current period might constitute a historical turning point in the relative popularity of microsurgical and endoscopic approaches.

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© Springer Nature Singapore Pte Ltd. 2020

J.-S. Kim et al. (eds.)Endoscopic Procedures on the Spinehttps://doi.org/10.1007/978-981-10-3905-8_2

2. Currently Available Equipment Details in the Market

Dirk Goethel¹  

(1)

RIWOspine GmbH, Knittlingen, Germany

Dirk Goethel

Email: [e-mail]

Keywords

DiscoscopesEndoscopic discectomy equipmentEndoscopic decompression equipmentRadiofrequency surgeryEndoscopic fluid management

2.1 Fundamentals of Development

Performing precise surgical procedures is determined by the interaction between the individual personal skills of the surgeons and the functionality of the medical equipment. The extremely demanding requirements for quality, safety, and reproducibility of results require the subjective influencing factors to be reduced to a minimum and integration of maximum functionality and ergonomic design within the medical equipment. The development and implementation of standardized surgical procedures is one of the basic requirements for quality assurance in medicine and also forms the platform for development of medical devices and instruments. Each new development needs to be benchmarked against the criteria of quality, safety, and reproducibility. These standards need to be achieved and at least partly improved. Validation of these results is a basic requirement for successful dissemination of new surgical techniques and their development to a new standard.

2.2 From Microscope to Endoscope

Anatomical structures need to be navigated in order to reach the spine through surgical access ports, and distances of approximately 10–25 cm need to be bridged optically and mechanically. Since precise manipulations are carried out close to sensitive structures, it makes sense to use optical imaging technologies during operations to improve the quality of visualization. This is primarily necessary if surgical access ports are to be miniaturized for minimally invasive techniques . The development of these methods is therefore significantly bound up with the development of new technologies for optical visualization while operations are being carried out. The surgical microscope succeeded in significantly improving direct intraoperative depth visualization for surgeons due to the optically enlarged and 3-dimensional display. However, the source of image generation outside the surgical area and most bimanual coaxial instrumentation must be carried out in the limited field of vision of the microscope (Fig. 2.1).

../images/437056_1_En_2_Chapter/437056_1_En_2_Fig1_HTML.png

Fig. 2.1

Microsurgical technique

There are therefore limits to minimization of the diameters of surgical tubes. This gave rise to the idea that the source of image generation could be relocated to the intraoperative area by means of an endoscope fixed in the surgical tube (Fig. 2.2). The working instruments are used in this process as in microsurgical procedures. Simultaneous application of two instruments is frequently necessary, since, e.g., a suction instrument is also used in parallel when bleeding occurs. An improvement to intraoperative visualization is possible in microendoscopic procedures under certain conditions but not a further reduction in the diameter of the surgical access port. The loss of 3-dimensional imaging by comparison with the microscope does not appear to be a disadvantage owing to the short distance between the endoscope tip and the anatomical structures. The necessity for a miniaturized surgical access port while also being able to deploy instruments during an operation already led to the development of a full-endoscopic technique (Fig. 2.3) in other surgical disciplines such as urology (cystoscope) [1] at the beginning of the nineteenth century. At the beginning of the 1990s, the first endoscope and instrument systems were presented for lumbar discectomies (Fig. 2.4) [3–5].

../images/437056_1_En_2_Chapter/437056_1_En_2_Fig2_HTML.png

Fig. 2.2

Microendoscopic (endoscopically assisted) technique

../images/437056_1_En_2_Chapter/437056_1_En_2_Fig3_HTML.png

Fig. 2.3

Full-endoscopic technique

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Fig. 2.4

YESS endoscope [2]

In contrast to the microsurgical and microendoscopic technique , each instruments is inserted one after the other through the working channel of the endoscope in the full- endoscopic technique with direct endoscopic visualization. The endoscope is articulated at the distal end (usually by 25°) and permits visualization round the corner. Rotating the endoscope permits visualization of a large intraoperative area. Permanent irrigation and aspiration of isotonic saline solution during the operation permits optimum vision at the surgical site. The full- endoscopic procedure achieves a significant reduction in the diameter of the surgical access port (7–10 mm) for spinal decompression. Instruments with a different design have to be used in a different surgical technique in order to achieve at least the same functionality, safety, and efficiency [6–8]. This requires comprehensive training in all cases.

2.3 Endoscopic Visualization

The quality of full-endoscopic visualization is determined by the combination of all components of the imaging system (endoscope, endoscopic camera, monitor) and the light-transmitting system (light source, light cable, endoscope). Quality is always based on the weakest link in the chain due to the concatenated structure of the system. Endoscopic camera systems currently available can record and transfer images in full HD quality (resolution 1024 × 728 pixels) up to 4 K (resolution 3840 × 2160 pixels). However, these high-resolution images can only be transmitted with endoscopes that have rigid rod-lens image systems (Fig. 2.5).

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Fig. 2.5

Components of rigid endoscopes [9]

The maximum resolution for image transmission in endoscopes with flexible or semi-flexible image guide is defined by the number of light fibers (usually 30,000–50,000) of the image guide and can therefore not achieve the optical quality of the camera. The primary objective in the development of endoscopic surgical systems for the spine should always be displayed in maximum resolution because this can significantly influence the success of the operation and safety for the patient. LED light projectors are generally used to generate endoscopic illumination. The light is input through a flexible fiberglass light cable into the endoscope and then transmitted through the endoscope to the distal end. Figure 2.6 shows an endoscopic workplace which also includes a radiofrequency and motor system alongside video equipment (endoscopic camera, light source, monitor, documentation unit). Standardization of full-endoscopic techniques and their clinical validation was an important milestone in the definition of requirements for the equipment. Alongside functionality and ergonomic design, universal application for maximum efficiency was also intended as a top priority.

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Fig. 2.6

Endoscopic workstation for spine surgery [10, 11]

2.4 Endoscopes and Access Systems

2.4.1 Endoscopes and Working Sleeves for Lumbar and Thoracic Applications

Lateral and posterolateral transforaminal, extraforaminal, and interlaminar access ports have meanwhile been standardized and now define the type and dimension of instrument set used in a full-endoscopic procedure using endoscopes on the basis of the indication spectrum [6–8, 12–15]. Effective bone resection specifically requires application of burrs with a diameter of >4 mm and it is important to take the anatomical relationships into account for the access port [16, 17]. Table 2.1 shows a fundamental orientation for selection of the endoscope and the working sleeve.

Table 2.1

Summary of geometric requirements for endoscope and access system depending on lumbar indication and surgical access port

In summary three different systems are recommended (Figs. 2.7, 2.8, and 2.9) for performance of all lumbar and thoracic indications on the basis of ergonomic requirements for all systems, universal usability, and minimization of system components for efficiency enhancement [17–19].

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Fig. 2.7

Full-endoscopic surgical system for transforaminal and extraforaminal access ports and the indications lumbar disc herniation and lateral spinal canal stenosis [10, 11]

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Fig. 2.8

Full-endoscopic surgical system for interlaminar access ports and the indications lumbar disc herniation and lateral spinal canal stenosis [10, 11]

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Fig. 2.9

Full-endoscopic surgical system for interlaminar access ports and the indication central spinal canal stenosis [10, 11]

In principle, all indications and access ports can be performed by using working sleeves with oblique distal end. Other versions of shape at the distal end are supplied for special indications and to meet the personal preferences of surgeons.

Spinal cannula sets for transforaminal and extraforaminal access ports are supplied. They comprise cannulas and guide wire in different lengths and diameters. The dilation of these access ports is generally carried out in a single stage (Fig. 2.10a) or optionally in a sequential process with several dilation steps (Fig. 2.10b) with the guide wire. In the interlaminar approach, the dilator is inserted directly through the stab incision as far as the ligamentum flavum without a guide wire.

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Fig. 2.10

Dilators, optionally (a) for one-step dilation or (b) sequential [10, 11]

2.4.2 Endoscopes and Working Sleeves for Cervical Applications

The anterior and posterior surgical access ports have meanwhile been clinically validated in several studies [6, 8, 20]. However, the requirements for the endoscope and sleeve system are completely different in the two systems. They are defined by anatomical and technical procedural details. The anterior access port is implemented as a transdiscal access port. The cervical disc height (approx. 4 mm) is regarded as a limit value for dimensioning the access system in order to penetrate to the posterior part of the disc as atraumatically as possible [6–8]. On the other hand, the instrumentation needs to adequately guarantee all the necessary functions for a surgical system such as radiofrequency ablation and coagulation, manual and motorized tissue and bone removal. This requires the use of instruments with a diameter of 2.5 mm (Fig. 2.11). If an assessment of this nature is to be carried out, interventions on the cervical spine are even more risky and require extremely precise application of the instruments. Maximum quality for endoscopic imaging is therefore all the more important. At the moment, this can only be achieved with rod-lens endoscopes. Figure 2.12 shows a concept for the anterior use on the cervical spine, which enables the requirements described to be fulfilled.

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Fig. 2.11

Presentation of the principle of a full-endoscopic surgical system to provide the anterior access port to the cervical spine on the basis of the anatomical and technical requirements [10, 11]

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Fig. 2.12

Full-endoscopic surgical system for anterior cervical access port [10, 11]

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Fig. 2.13

Full-endoscopic surgical system for posterior cervical access port [10, 11]

The system requirements for a posterior surgical system (Fig. 2.13) result from the need to penetrate the soft tissue structures to reach the spine with minimum traumatization, since the problem of soft tissue bleeding in conventional keyhole foraminotomy has been adequately described. Furthermore, precise bone resection should be possible on the basis of the anatomical relations. Table 2.2 summarizes the requirements.

Table 2.2

Summary of geometric requirements for endoscope and access system for cervical full-endoscopic applications

2.5 Fluid Management

The application of irrigation fluid in full-endoscopic surgical techniques needs to be exclusively for purposes of visualization and not for dilation as in arthroscopic methods. For this reason, a continuous inflow and outflow must be ensured (open system). In physical terms, this always involves a pressure increase in this system if the inflow is bigger than the outflow, or the outflow is completely closed. In this case, the in situ pressure then increases either to the value corresponding to the preset value at a pressure-controlled pump or in the case of hydrostatic irrigation to the difference between the height of the patient and the height of the fluid reservoir (Fig. 2.14).

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Fig. 2.14

Pump-controlled irrigation [10, 11]

Table 2.3 shows the intraoperative pressure values that can be generated for different height differences if no free outflow is guaranteed (closed system).

Table 2.3

Intraoperative pressure values depending on the height of the water column in hydrostatic irrigation with closed outflow

If dimensioning is not correct and irrigation systems are used, the irrigation fluid can lead to a critical pressure increase in the spinal canal and to compression of neural structures with corresponding symptoms. Studies have already demonstrated that spread of the fluid in the spinal canal during lumbar applications can lead to pressure increases in the cervical spine. It has been shown that patients can suffer from headaches and neck pain if there are intraspinal pressures of approximately 70 mm Hg [21]. This critical pressure can already be reached under unfavorable outflow conditions with a water column of less than 100 cm (Table 2.3). On the other hand, a high flow rate for irrigation fluid is generated as a result of high pressure values in hydrostatic irrigation. This ensures continuous removal of blood and tissue particles and hence provides good endoscopic visualization. As a result, the high flow rate also exerts impacts on shortening the surgical time. The conflict between high flow rate and maximally low pressure increase in the spinal canal can be solved either by appropriate dimensioning of the inflow and outflow system in the endoscope and working sleeve or by using a special pump system. This must guarantee that either the outflow is not obstructed by tissue and bone particles and permits more outflow than inflow at all times or the pump stops the irrigation immediately if the outflow is blocked. Figure 2.15a, b shows standard versions of dimensioning for inflow and outflow in the marketplace.

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Fig. 2.15

Fluid management for standard full-endoscopic systems in the marketplace, (a) inflow and outflow through separate channels in the endoscope, (b) inflow through irrigation channel, large outflow channel in the space between oval endoscope cross section and round working sleeve [10, 11]

The endoscopes and working sleeves can prevent a critical pressure increase in the spinal canal if the irrigation system is correctly dimensioned as in Fig. 2.15b.

Pump systems are now also supplied with special spine modes which guarantee this certainty against an unwanted pressure increase at all times. These pumps are not pressure regulated as is generally the case in arthroscopy pumps. They are flow controlled (Fig. 2.14). Automatic identification of the individually connected endoscope sleeve systems enables the flow rate to be varied using intelligent software control, without triggering an intraspinal pressure increase.

2.6 Instruments for Radiofrequency Surgery

The coagulation functionality is indispensable for a fully adequate surgical system and is crucial for safety. Adequately functioning tissue ablation is also necessary in many full-endoscopic indications for soft tissue and bone dissections. Radiofrequency systems in the bipolar application form are generally linked to actively articulatable electrodes for this purpose in order to achieve the full field of view generated by the 25° articulated telescope subject to the straight working channel of the endoscope (Fig. 2.16).

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Fig. 2.16

4 MHz radiofrequency device and actively articulatable bipolar electrode for coagulation and ablation [10, 11]

It is particularly important to highlight the working frequency of the radiofrequency device in this document. The concept of radiofrequency is commonly used in a broadband frequency range of approximately 300 kHz to 4 MHz. However, the behavior of biological tissue varies significantly when electricity flows through it within this radiofrequency. When electricity flows in the lower frequency range (300 kHz), the tissue warms up significantly more than in the upper range (4 MHz) [22]. The physical basis for this is provided on the one hand by the fact that the specific electrical resistance of biological tissue falls with increasing frequency of the electric current and on the other hand the physical laws Ohm’s law and Joule´s law, which generally describe the generation of heat during the flow of electricity [23]. Nerve tissue heats up, e.g., at 4 MHz only approximately half as much as at 300 kHz in a distance of 2.5 mm from the electrode tip (see Fig. 2.17) [24]. Full-endoscopic techniques