Endoscope in MISS: How to Adopt and Change

10 Endoscope in MISS: How to Adopt and Change

Albert E. Telfeian

Summary

In this chapter, we review the key features in targeting, technology, and technique necessary to perform endoscopic lumbar spine surgery using a working channel endoscope. Step-by-step descriptions for how to target and treat lumbar pathology through an interlaminar or transforaminal approach are provided in the text and figures.

Keywords: endoscopic lumbar discectomy transforaminal interlaminar working channel endoscope Kambin’s triangle

10.1 Introduction

Endoscopic spine surgery is spine surgery that utilizes an endoscope for visualization. The technique discussed here involves the use of a working channel rigid endoscope. The term “endoscopic spine surgery” indicates a method of visualization rather than a surgical procedure. Lumbar spine surgical procedures, such as discectomy, laminectomy, and fusion, can be performed with visualization by the naked eye, loupes, microscope, or endoscope. When an endoscope is used, the size of the retractor is such that (often a tube is of the size of a number 2 pencil or smaller), it can be placed through a different approach made possible because of the size and accessibility of these very small ports to small spaces. Learning endoscopic spine surgery, therefore, involves much more than becoming familiar with a different method of visualization (think loupes vs. microscope for a lumbar discectomy), it means adapting to an entirely different mode of targeting, technology, and technique.

Minimally invasive spine surgery that utilizes a tubular retractor and a camera with light source attached is known as endoscopic spine surgery, but the tubes used for these procedures are typically 16 mm or greater in diameter and, for the most part, utilize an approach that is similar to non-endoscopic versions of the same procedures. In this chapter, we will discuss endoscopic spine surgery performed through an approximately 7-mm working channel endoscope that can be used for both transforaminal and interlaminar approaches.

Understanding the principles of the targeting, technology, and technique, practicing the technique in a course, and observing a surgeon performing endoscopic spine surgical techniques are good steps in learning to practice these techniques.

10.2 Target

10.2.1 Kambin’s Triangle

For transforaminal or interlaminar lumbar endoscopic surgery, the anatomic target is Kambin’s triangle. In 1972, Kambin introduced endoscopic intervertebral discectomy by posterolateral approach, defining Kambin’s triangle as the site to approach the intervertebral disc.1 Kambin’s triangle is defined as a right triangle over the dorsolateral disc where the hypotenuse is the exiting nerve root, the base (width) is the superior border of the caudal vertebra, and the height is the dura/traversing nerve root. Fig. 10.1 is photograph of a cadaveric specimen of the L5-S1 neural foramen with the facet removed depicting the anatomical landmarks of Kambin’s triangle.² The anatomical specimen illustrates the point that the widest area of Kambin’s triangle is its base which runs along the superior endplate of the inferior vertebra. The safest target point then to avoid injuring the exiting nerve is to aim for the medial wall of the inferior pedicle to address most foraminal pathology. The distance between the exiting nerve and the inferior pedicle is about 18 mm at the medial wall of the pedicle versus 10 to 11 mm at the lateral wall of the pedicle.² Kambin’s triangle represents the “safe zone” for avoiding the exiting and traversing nerve roots. For both the transforaminal and interlaminar approaches, Kambin’s triangle works as a “landing zone” for the endoscope so that most foraminal pathologies can be visualized from this position. The order for most endoscopic procedures is to first target and access using fluoroscopic guidance and second, once access has been established, begin visualization with the endoscope identifying normal and pathological anatomy.

Fig. 10.1 Cadaveric demonstration of the working triangle (Kambin’s triangle) in the L5-S1 neural foramen. The working triangle is the triangle between the exiting and the traversing nerve roots above the superior margin of the inferior pedicle.

10.2.2 Foraminal Window

The foramen is bounded by the superior articulating process (SAP) and inferior articulating process of the facet joint superiorly, the pedicles laterally, and the disc and vertebral bodies inferiorly. With loss of disc height or coronal scoliosis, the pedicle-to-pedicle distance and foraminal window narrow in width. With overgrowth of the facet, the foramen can narrow in height. Degenerative disease can cause extreme lateral widening and narrowing of the foramen that makes accessing medial canal pathology from a transforaminal route almost impossible; however, interlaminar and contralateral interlaminar approaches then become more feasible for accessing more medial canal pathologies.

10.2.3 Upper Lumbar versus Lower Lumbar

At L5-S1, the iliac crest makes a direct transforaminal approach almost impossible (transiliac crest approaches have been reported). A superior starting point and oblique trajectory become necessary then at L5-S1. This trajectory makes accessing medial superior foraminal pathology difficult.

In the upper lumbar spine as opposed to the lower lumbar spine, the thecal sac widens relative to the bony canal. At L5-S1, the thecal sac ends in an anteroposterior (AP) dimension at the medial wall of the pedicle. At L1–2, the thecal sac ends in an AP dimension at the midpoint of the pedicle. Targeting the medial pedicle wall at L1–2 can potentially lead to dural or neural injury. Special attention to the retroperitoneum also needs to be paid for upper lumbar pathology because the kidneys can be injured if a too lateral approach is taken. In general, for transforaminal approaches, a starting point at 12 to 16 cm off midline is used at L5-S1 and 8 to 10 cm off midline for the upper lumbar segments.

10.2.4 Superior Articulating Process

One of the biggest advances in transforaminal endoscopic spine surgery, arguably, was the addition of circular reamers to remove a portion of the ventral SAP to open the foraminal window for safe targeting and accessing foraminal and canal pathologies. Targeting for maximizing SAP removal using reamers then requires the surgeon to essentially hit and “walk off” the SAP during needle targeting. “Hugging” the SAP during targeting allows for maximal SAP removal, maximal opening for the foraminal window, and maximal access to canal pathology.

10.3 Pathologies Treated

•Herniated discs: Endoscopic spine surgery is an excellent technique for treating lumbar disc herniations. Far-lateral, paracentral, central, and extruded disc herniations are all accessible, but most surgeons start with foraminal disc herniations because they are the most accessible. Far-lateral disc herniations are also very accessible, but these tend to be directly under the exiting nerve root which can add a degree of difficulty to the surgical procedure.

•Stenosis: Foraminal stenosis is treatable with endoscopic drills from both interlaminar and transforaminal approaches. New larger endoscopes with larger working channels for bigger drills and Kerrison punches are now available for treating central stenosis.

•Facet cysts: Facet cysts are treated endoscopically by experienced endoscopic spine surgeons but do not make good “first cases” because they are often adherent to nerves and dura.

•Complex spine problems: Since transforaminal endoscopic spine surgery uses an approach that is different from traditional spine surgery techniques, it can provide an elegant salvage approach for complex spine problems. In the literature there are reports of treating complications from kyphoplasty cement leakage,3 endplate fractures from artificial disc surgery⁴ and lateral fusion surgery,⁵ failed lateral recess decompression after fusion,⁶ as well as adjacent segment disease.⁷

10.4 Technology

The idea for transforaminal endoscopic spine surgery arose in the 1970s and 1980s from surgeons who thought to apply orthopaedic arthroscopic techniques to spine pathology. Several technological advancements were critical to the reemergence of the technique in the following century: working channel endoscopes with high-definition cameras, continuous irrigation, and specialized instruments for disc and bone removal.

High-definition cameras, rigid fiber optics, continuous irrigation, and radiofrequency cauterization work together to provide incredible visualization to endoscopic spine surgeons. Compared to microscopic surgery where the lens and light source for visualization are about 50 cm away from pathology, putting the lens and light source directly at the target pathology creates a significant opportunity for improved visualization.

Surgical instruments available for endoscopic spine procedures are the similar to those used in open procedures (except smaller): drills, Kerrison punches, graspers, chisels, radiofrequency probes for cautery, and lasers.

Endoscopic spine fusion is an area exploding with commercial interest. Instruments and implants are in current development to (1) navigate the anatomical constraints of Kambin’s triangle, (2) decompress disc and foraminal pathologies, and (3) restore foraminal height and provide a substrate for subsequent fusion. The percutaneous nature of this technique makes awake, outpatient spinal fusion a future reality.

Larger working channel endoscopes are available that are 1-cm wide with a 6-mm working channel. These endoscopes are now used to perform awake multilevel cervical and lumbar laminectomies⁸^,⁹ through a single 1-cm incision. The large diameter working channel can accommodate drills and Kerrison punches of significantly larger size making larger amounts of bone removal feasible and fast.

10.5 Technique: Step-by-Step

10.5.1 Transforaminal Lumbar

•Position the patient either prone on radiolucent Wilson or Kambin frame or in lateral position with the knees flexed (Fig. 10.2).

•Anesthesia is typically light sedation with Versed and fentanyl. Lidocaine with epinephrine is used for local anesthesia. Patient should be awake enough to respond if he or she feels shooting pain in the legs.

•Targeting is performed with AP and lateral fluoroscopy to determine the skin access point. General rule of thumb is a starting point of 12 cm off midline for L5-S1 pathology, 11 cm off midline for L4–5 pathology, 10 cm off midline for L3–4 pathology, etc. For wider patients the distances are further and for thinner patients the distances are smaller.

•A spinal needle (18 gauge, 25 cm) is used to target the top of the superior endplate of the inferior vertebral body touching the endplate on lateral view and at the medial wall of the inferior pedicle on AP view (Fig. 10.3). A transisthmus approach is used to avoid the exiting nerve and maximize the amount of removal of the ventral portion of the SAP with the reamers (Fig. 10.2).

•A Kirschner wire (K-wire) is placed in the needle. A 5-mm stab incision is made over the needle. The needle is removed while pushing in on the K-wire so not to dislodge it. Sequential dilators are placed over the K-wire to dilate the muscle. All but the smallest dilators are removed and reaming begins. Small, medium, and large reamers are used over small, medium, and large dilators. Sequential reaming tends to lead to more effective bony removal and is less painful for the patient (Fig. 10.2).

•A beveled tubular retractor is then placed over the dilators and its position is confirmed on AP and lateral fluoroscopy. The beveled dilator should be laying bevel down on the disc in the epidural space (not in the disc) on lateral view and in the foramen and canal on AP view.

•The working channel endoscope is introduced with irrigation on and the foraminal contents should be visible (Fig. 10.4 and Fig. 10.5). The ventral portion of the SAP and pedicle are the constant landmarks in this part of the procedure. For far-lateral disc pathologies, the endoscope is held upside down to visualize the exiting nerve.