18 Principles of Endoscopic Techniques to the
Thoracic and Lumbar Spine
G.M. McCullen, A.A. Criscitiello, H.A. Yuan
18.1
Terminology
This chapter describes the principles of endoscopic surgical techniques of the thoracic and lumbar spine.
Endoscopes are rigid (straight or angled) or flexible systems that provide visualization, light, and magnifi- cation to anatomical areas thereby avoiding larger open incisions. Current spinal endoscopic exposures in- clude: (1) posterolateral (arthroscopic microdiscecto- my, AMD) and interlaminar (microendoscopic discec- tomy, MED; Medtronic Sofamor Danek, Memphis, TN) approaches for lumbar discectomy and neural decom- pression; (2) transperitoneal and retroperitoneal lapa- roscopic techniques for lumbar interbody fusions; (3) lateral and prone thoracoscopic methods for anterior release in scoliotic and kyphotic deformity, discectomy for decompression/fusion, and anterior thoracic in- strumentation; and (4) lumbar epiduroscopy for lysis of adhesions in pain management.
18.2
Surgical Principle
The principal purpose of these minimally invasive en- doscopic techniques is to approach the spine through portals rather than larger skin incisions. At the target site, the same operative procedure is performed using an endoscopic approach as is performed using an open approach, the difference being a smaller, less invasive access. Benefits include decreased soft tissue distur- bance leading to lesser postoperative scarring, pain, and reduced ultimate healing time.
18.3 History
In 1807, in Frankfurt, Germany, Bozzini was the first re- corded individual to use an endoscope. Known as the
“Lichtleiter”, this device used candle illumination to examine body orifices [7]. Lens and light amplification improvements followed. In 1901, Ott used a cystoscope
to visualize structures within the pelvis [38]. Kelling, in 1902, was the first to induce pneumoperitoneum in dogs [25]. Oxygen, followed by carbon dioxide, was used for insufflation. In 1938, Veress developed the in- sufflation needle that bears his names and is still in use today.
Throughout the 1920s, Jacobaeus, in Sweden, was the first to perform both laparoscopic and thoracosco- pic procedures in humans [19, 20]. He used a cysto- scope and a heated platinum lighting loop. Intrapleural pneumolysis was performed on patients with tubercu- losis.
A “myeloscope” was first used to visualize the spinal cord in 1932 [6]. In 1938, a myeloscope was used to view the dorsal nerve roots of the cauda equina and was as- sociated with a high rate of morbidity [40]. In 1946, as- piration biopsies of the disc space were performed in patients with sciatica [30]. Craig utilized the postero- lateral approach to obtain vertebral body specimens through a cannula to protect the surrounding anatomi- cal structures [9]. Discography was introduced by Smith in 1964, subsequently leading to the injection of chymopapain [50]. In 1973, Kambin modified Craig’s instruments to perform an indirect percutaneous canal decompression through a posterolateral extracanal ap- proach [22]. He subsequently coined the term “triangu- lar working zone” (the optimal portal entry area: inferi- or to the exiting nerve, lateral to the traversing nerve, and superior to the caudal adjacent vertebral body) through which a 6.5-mm cannula can be positioned to avoid injury to the surrounding neurological struc- tures [23, 24]. In 1975, Hijikata developed instruments for percutaneous nucleotomy [16]. Hausman, in 1983, used a nucleoscope to assess for the presence of re- tained fragments after open discectomy [15]. In 1991, Schreiber and Leu were the first to carry out a biportal percutaneous discoscopy [49].
With improvements in medical management of tu-
berculosis, closed biopsy techniques, and general anes-
thesia for open techniques, interest in thoracic endo-
scopic approaches had waned from 1960 to 1990. In the
early 1990s, renewed interest was experienced in thora-
coscopy for the inspection and treatment of pleural dis-
eases and for endoscopic pulmonary resection. During
these procedures, the excellent visualization of the tho- racic spine was recognized.
Thoracoscopic spine procedures began with the drainage of an intervertebral disc abscess [31, 42]. The majority of thoracoscopic procedures are performed in the lateral decubitus position which requires a dual lu- men endotracheal tube for selective lung ventilation.
Indications include: anterior release of large (greater than 80°) and fixed (corrects to less than 60° with push- prone views) curves; Scheuermann’s kyphosis greater than 90° which fails to correct to less than 50° with hy- perextension over a bump; anterior fusion in skeletal immaturity to decrease the incidence of postoperative crankshaft; and decompressive discectomy and corpec- tomy. Endoscopic anterior instrumentation has been developed. The problems encountered include difficul- ties performing compression or distraction and rod ro- tation.
The recent introduction of the prone position for thoracoscopic spinal procedures offers benefits includ- ing a more familiar orientation, gravity-assisted retrac- tion, gravity-assisted correction of kyphosis, the elimi- nation of the need for repositioning, and the use of a standard single-lumen endotracheal tube [27, 52]. Si- multaneous posterior exposure and prone thoracosco- pic release as been reported [29].
In 1991, Obenchain and Cloyd described laparo- scopic lumbar discectomies [37]. Transperitoneal lapa- roscopy is performed in a supine position accessing L3- 4, L4-5, and L5-S1. Laparoscopic instrumentation with BAK cylindrical interbody devices (Sulzer Spine Tech, Minneapolis, MN) was first reported in 1995 [57]. Ret- roperitoneal, lateral disc exposure can be used for ac- cess to L4-5 and above [5]. Thalgott has described a bal- loon-assisted endoscopic retroperitoneal gasless (BERG) technique allowing the use of conventional in- struments and avoiding the complications of carbon dioxide insufflation [53]. Lateral endoscopic retroperi- toneoscopy has been described with an apparently re- duced risk of small bowel adhesions and autonomic plexus dysfunction [34]. Performed in the lateral decu- bitus position, the intra-abdominal contents “fall away” from the spine.
Midline, posterior, interlaminar lumbar endoscopy (MED) was proposed and developed by Foley and Smith [12]. A tubular retraction system can be used with either an endoscope or a microscope. The tube can be angled to allow bilateral bony and ligamentous de- compression under the midline while preserving the supraspinous and interspinous ligaments and the con- tralateral musculature [39].
Endoscopy within the spinal canal, “epiduroscopy”
with navigation of the flexible scope via the hiatus sac- ralis, has seen some clinical interest and early applica- tion [46]. Determining the underlying pathology in chronic pain syndrome has often proved elusive. Mor-
phological changes have been identified primarily in the form of epidural adhesions that may or may not be relevant to the generation of pain. Lysis of adhesions with mechanical instruments or a holmium:YAG laser and direct administration of medications can be per- formed [32, 46].
18.4
Technical Equipment
The endoscope consists of optical fibers and a light source. Each fiber in the coherent bundle delivers a sep- arate piece of visual information to a camera and a vid- eo-integrated system. The camera processes the multi- ple image components into picture elements that are called “pixels”. To increase picture quality and clarity, the number of optical fibers and pixels would have to be increased. Given the size constraints of an endoscope, an increase in the number of optical fibers would re- quire a decrease in fiber size. However, if the fiber be- comes too small, the capacity to transmit light is signif- icantly impeded. Presently, the maximum number of pixels in a camera system given the size constraints of the straight 10-mm-diameter thoracic or lumbar endo- scope is 30,000. Zero and 30°-angled scopes are most commonly used. Flexible scopes, for intradiscal and in- tracanal navigation, contain pull wires to allow bend- ing and steering capability. Some endoscopes contain suction and irrigation ports. Within the epiduroscope, the imaging bundle diameter is 1.2 mm with 10,000 camera pixels with visualization that is not always opti- mal.
Imaging advances have assisted minimally invasive strategies. Fluoroscopy is utilized in laparoscopic and posterolateral and interlaminar lumbar endoscopic procedures. In laparoscopic interbody fusions, the ex- act midline of the disc must be identified using a true AP fluoroscopic image with symmetrical pedicles and flat endplates. Radiation safety precautions should be followed to minimize the risks while working under fluoroscopy. Total exposure time should be kept to less than 1 min, and image memory rather than continuous fluoroscopy should be used. To decrease scatter, the beam should be collimated. Lead of at least 0.5 mm thickness should cover the chest, abdomen, thyroid, gonads, marrow organs, hands, and eyes. Total whole body exposure should be less than or equal to 5 rem or 1 – 1.7 min/case [47].
Frameless stereotaxy, developed in 1992, was initial-
ly designed for intracranial use. The technique links the
anatomy to a preoperatively acquired image. In endo-
scopic approaches, navigational systems have been dif-
ficult to apply because of problems with registration
(precisely correlating anatomical landmarks with im-
age reference points). External landmarks are not reli-
able as implanted fiducials for registration. A frame, at- tached to a percutaneously placed pedicle screw can serve as a stable, fixed reference. The frame of reference is placed percutaneously and a CT scan is subsequently performed. Registration, using the geometry of the frame as fiducials, has been successful when used with endoscopic spine surgery [2, 3].
Intraoperative nerve monitoring can assess for nerve compression or irritability. Mechanically elicited EMG activity recorded in the muscles innervated by the lumbar nerve roots can alert the surgeon to nerve prox- imity.
18.5 Advantages
The advantages of endoscopic over traditional tech- niques include diminished pain, improved healing, and enhanced visualization. The entire operating team is able to watch the monitor during the procedure.
Using posterolateral AMD, local anesthesia with in- travenous sedation is possible. However, not all patient are able to tolerate the prone lying position for the length of time required for the surgery. The minimal dissection of the posterior paraspinal muscles de- creases postoperative pain and narcotic use. In addi- tion, by avoiding direct canal entry, there is a decreased epidural vein disruption and decreased perineural scarring [8]. Lastly, should reherniation occur, prefer- ential migration of the disc material through the pos- terolateral arthroscopic portal area might be less likely to cause neurological impingement.
With thoracoscopy, it is possible to visualize from T4 to L1 and thoracoscopic right or left approaches are possible. Compared to open procedures, thoracoscopic techniques cause less acute and chronic postoperative pain and intercostal neuralgia with improved pulmo- nary function [10, 36]. In addition, improved shoulder girdle strength and range-of-motion [36], decreased cost, and reduced hospital stay have been reported with the thoracoscopic technique [10, 14].
In retroperitoneal endoscopy, the peritoneum is left intact decreasing the postoperative complications re- lated to manipulation of the bowel and disruption of the peritoneum. During these approaches, the intact peritoneum serves as a retractor aiding in the control of the bowel.
18.6
Disadvantages
Spinal endoscopic procedures are technically demand- ing, and require a dedicated effort to safely overcome the “learning curve.” The vascular or thoracic surgeon
and the spine surgeon should train together in the labo- ratory before performing live surgery on humans. The surgeon should always be prepared to convert the case to an open procedure with open laparotomy and thora- cotomy instruments and vascular instruments close at hand.
Lateral thoracoscopy requires a double-lumen en- dotracheal tube and high airway pressures. Tube dis- lodgement and tracheal tears are possible complica- tions. When approached from the convex side of a sco- liotic curve, single-lung ventilation must occur in the smaller lung on the concave side of the curve. Large scoliotic curves (greater than 90°) result in a smaller chest cavity limiting the space available to perform the endoscopic procedure [36]. Patients with right idio- pathic scoliosis have a more posterior aorta [51]. An open approach allows for a circumferential exposure of the spine to place a finger around the side opposite to protect the far-side vasculature during placement of screws. With thoracoscopic fusion, such protection is not possible.
Prone thoracoscopy uses double lung ventilation with decreased tidal volumes and increased respiratory rate. There is less anesthetic preparation time with prone versus lateral thoracoscopy [27,52]. Postopera- tive oxygen requirements are decreased with double- lung versus single-lung ventilation [52]. The lateral po- sition must be used for discectomy above T4 using an axillary portal anterior to the pectoralis major.
In transperitoneal laparoscopy, insufflation is re- quired for visualization. In order to maintain pneumo- peritoneum, the use of suction is limited. Carbon diox- ide insufflation can cause elevation of the mean arterial pressure and hypercapnia (secondary to increased CO
2absorption and decreased diaphragm movements) and CO
2embolism. Despite a Trendelenburg positioning and the use of multiple ports, the small bowel remains a problem. Vascular mobilization can be difficult. Rou- tine preoperative magnetic resonance imaging or CT scanning can be used to classify vascular anatomy [28].
The iliolumbar vein, should be identified, mobilized, and ligated for exposure to the L4-5 level. If the bifurca- tion of the great vessels is above the L4-5 disc space, a laparoscopic approach to L4-5 is technically easier.
With lateral retroperitoneal laparoscopy, the psoas is often very large. A muscle splitting approach through the psoas may lead to injury of the genitofemoral nerve or elements of the lumbosacral plexus.
In AMD, the L5-S1 is difficult to approach, particu- larly in the male patient with a high-riding iliac crest.
18.7 Indications
These are no different than for open procedures.
18.8
Contraindications
Previous operative interventions may create scarring which effects tissue mobilization and visualization.
Laparoscopic procedures are unable to visualize the neural elements and are unable to address spinal canal stenosis. Fusion for internal disc derangement with tall discs is a relative contraindication as it is more difficult to obtain adequate disc distraction. The larger inter- body devices that would be required for fusion of tall disc spaces cannot be delivered laparoscopically.
Thoracoscopic procedures are usually contraindi- cated in those patients who have undergone multiple anterior thoracic procedures with expected scarring and adhesions. Patients with neuromuscular deformity and a history of pneumonia or empyema may have thick pleural adhesions. Those patients with restrictive lung disease will be unable to tolerate single-lung venti- lation.
Arthroscopic lumbar microdiscectomy is not rec- ommended when disc fragments have migrated or in cases of cauda equina. Obesity represents a relative contraindication, as arthroscopic cannulas might have insufficient length.
18.9
Complications
Lateral thoracoscopy requires single-lung ventilation.
Correct placement of the double-lumen endotracheal tube followed by confirmation with fiberoptic bron- choscopy is necessary. The tube can be dislodged when turning the patient from the supine to the lateral posi- tion. Intercostal neuralgia after thoracoscopy is not un- common, occurring in approximately 7 % of patients [33]. Softer, flexible trocars have helped reduce the de- velopment of intercostal neuralgia.
Perforation of the diaphragm and parenchymal lung injury are best avoided by directly visualizing the in- struments when introduced into the chest cavity. The sixth or seventh intercostal space is the safest region for entry for the first thoracic port. All subsequent port placements should be performed under direct visuali- zation. With endoscopic instrumentation, screw pull- out at the cephalic screw is usually the result of poor screw placement and unicortical purchase. Tension pneumothorax secondary to over advancement of a guide wire during instrumentation has been reported [45].
Laparoscopic complications include vascular and peritoneal/visceral injuries. In a study comparing lapa- roscopic versus mini-open approach, the complication rate was 20 % in laparoscopic versus 4 % in mini-open [56]. Sixteen percent of the laparoscopic approaches
have been considered “inadequate”, allowing one rath- er than two cages to be placed [56]. Approximately 10 % of laparoscopic procedures require conversion to open for repair of vessel lacerations or to close tears in the peritoneum [11, 43]. During laparoscopy, the insuffla- tion pressure should be decreased to 10 mm Hg or less during stages within the case to check for areas of ve- nous bleeding that could otherwise go unrecognized at case completion. Retrograde ejaculation rate among males is high after laparoscopy: 16 – 25 % [11, 28] com- pared to a 6 % rate with mini-open [21]. Avoiding monopolar electrocautery and limiting the degree of dissection along the left side of the aorta and the left ili- ac artery may help to minimize the risk of ejaculatory dysfunction [28]. Ureteral injury has been reported [13]. During transperitoneal laparoscopy, the sigmoid colon mesentery is approached from the right. The right ureter, traveling over the right iliac artery, must be identified before making the posterior peritoneum incision. In lateral endoscopic transpsoas approaches, a 30 % rate of transient paresthesias in the groin/thigh region has been reported [4].
After AMD, 16 % of patients may experience moder- ate to severe hyperpathia secondary to dorsal root gan- glia irritation from mechanical pressure of the cannula or local space-occupying fluid extravasation within the triangular working zone [41]. This complication occurs more commonly in procedures lasting over 90 min [41]. Typically, the symptoms are transient and im- prove with administration of a steroid with a tapering dose.
18.10
Conclusions and Critical Evaluation
Thoracoscopic procedures have been compared to open procedures in clinical and laboratory studies.
Thoracoscopic discectomy for release/fusion is equal to the open technique in the percentage of disc removal (76 % for open, 68 % for thoracoscopic) [18] and in the adequacy of the biomechanical release [54]. In scoliosis anterior release/fusion, the percent curve correction, blood loss, and complication rate are similar when comparing open and endoscopic methods [17, 36, 52].
The endoscopic technique was 28 % more expensive, reflecting the expensive disposable tools [35]. Thora- coscopic release procedures require a 50 % longer oper- ating time compared to open thoracotomy [51]. The
“learning curve” demonstrates improvement in operat-
ing times with early thoracoscopic release taking
29 min/disc level, improving to 22 min/level with expe-
rience [35]. Thoracic disc excision for radicular and
myelopathic patients have demonstrated a 70 % clinical
success with a mean operative time of 173 min, blood
loss of 259 cc, and average hospital stay of 4 days [1].
There is no significant difference between mini-lap- arotomy versus laparoscopic approach when compar- ing analgesia requirements, time to resuming oral in- take, or the length of hospitalization [44, 56]. The com- plication rate was significantly higher in the laparo- scopic group, 20 % versus 4 % [56]. Laparoscopy cost more ($1,374/case on average) [44]. Laparoscopic oper- ative time averages 167 min for single level and 215 min for multiple levels [28]. Average blood loss is 124 cc [28].
Posterolateral AMD has not reached “main stream”
use within the spine surgery community. The tech- nique continues to have vigorous advocates whose out- comes are similar to open microdiscectomy. A good to excellent outcome has been reported in 85 – 90 % of pa- tients and poor outcomes in 10 %, [24, 55] with a com- plication rate of 3.5 % after AMD [55].
Comparing MED and traditional open techniques for spinal canal decompression, one study reported 109 min/level average operating time for MED (versus 88 min/level for open). MED patients required an aver- age 42-h postoperative stay (versus 94 h) and resulted in 68 cc blood loss (versus 193 cc) [26]. Less mechani- cally elicited nerve irritation was recorded on EMG monitoring with the MED technique [48]. Endoscopic spinal procedures are a relatively recent addition to the spine surgeons armamentarium. The techniques offer the surgeon enhanced visualization of the operative target site with less skin, soft tissue, and muscle disrup- tion. While there are definite benefits, these procedures are technically challenging and there are associated risks (Tables 18.1 – 18.3).
As new modalities are developed, care should be di- rected to prevent inventing new indications to justify the technique. The core indications for surgical inter- vention should not change and should remain rooted in basic surgical principals. Expect and prepare for a
Table 18.1. Thoracoscopic spine summary Improved visualization
Less tissue dissection to accomplish approach Similar discectomy extent and release capability when compared to open thoracotomy
Large (greater than 90°) scoliotic curves create smaller available “working space”
Unable to perform a circumferential exposure for far-side tissue protection
Difficult but improving anterior instrumentation Lateral positioning
Double-lumen endotracheal tube Single-lung ventilation
Prone positioning Double-lung ventilation
Simultaneous anterior/posterior procedures
Table 18.2. Laparoscopic spine summary Anterior interbody fusion
Requires CO2insufflation Elevated mean arterial pressure Hypercapnia
Embolism
Unrecognized venous bleeding No direct canal decompressive capability Interbody graft size/shape limitations
Experience assisted the development of mini-open laparo- tomy techniques
Prone
Transperitoneal L4-5 and L5-S1 Vessel mobilization Retrograde ejaculation Ureter injury
Lateral
Retroperitoneal
L3-4 and more cephalic levels
Psoas, genitofemoral, and lumbosacral plexus injuries
Table 18.3. Lumbar posterior decompressive endoscopic sum- mary
Posterolateral AMD
Similar outcomes as microdiscectomy Minimize epidural dissection and scarring Hyperpathia, dorsal root ganglia irritation Not recommended:
Migrated disc fragments Cauda equina
Degenerative osteophyte formation with lateral recess stenosis
Interlaminar MED
Bilateral decompression through a unilateral approach
“learning curve.” Endoscopic technology will continue to evolve through merging with biomedical advance- ments in robotics and image guidance systems.
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