Endoscopic Foraminal Approach to the Lumbar Spine

Fig. 52.1

(a) Illustration of spine at L5–S1, right-sided view with the patient in the prone position. Kambin’s triangular working zone is the site of surgical access for posterolateral endoscopic discectomy. It is defined as a triangular zone bordered by the superior facet of the inferior vertebra and traversing nerve root dorsally, the exiting nerve root ventrally, and the superior endplate of the inferior vertebra caudally. In foraminal decompression, the foramen from pedicle to pedicle can be reached by manipulating and protecting the exiting and traversing nerve with various configured access cannulas. (Adapted with permission from Yeung AT, Yeung CA: Posterolateral selective endoscopic discectomy: The YESS technique, in Kim DH, Fessler RG, Regan JJ, eds: Endoscopic Spine Surgery and Instrumentation: Percutaneous Procedures, New York, NY, Thieme Medical Publishers, Inc, 2005.) (b) Cadaver dissection photograph showing anatomy of the left posterolateral foraminal area from L2–S1 (blue hubbed needles are inserted into the disk). Only in the L5–S1 disk space is access to the spinal canal restricted because of the pelvis and the relatively wide facet (gray hubbed needle in the L5–S1 disk). High lumbar disk herniations from L1 to L3 are easier to reach endoscopically through the posterolateral foraminal portal due to the significant posterior overlap of the lamina encountered in a posterior approach. L4–L5 provides ample room for either approach. Note the furcal nerve branches entering the psoas muscle. These furcal nerves are frequently present in the foramen, adjacent to the foraminal ligament (the lateral extent of the ligamentum flavum). It is sometimes difficult to differentiate the ligament from a furcal nerve

The indications for this surgical approach expanded after improvements in endoscopic instrumentation began with the development of a rigid multichannel spinal endoscope with a 2.7 mm working channel by Anthony Yeung in 1993 (Fig. 52.2). This allowed targeted mechanical discectomy under constant endoscopic visualization. It also allowed the surgeon to safely navigate the entire foramen and epidural space to remove foraminal, extraforaminal, and extruded central and paracentral herniations.

Fig. 52.2

Illustration of a multichannel operative endoscope (the Yeung Endoscopic Spine Surgery [YESS] system, Richard Wolf Medical Instruments Corp, Vernon Hills, IL). The rigid spinal endoscope is designed with an operative working channel for insertion of tools, multichannel irrigation, and a cannula system that exposes patho-anatomy and protects spinal nerves. (Adapted with permission from Yeung AT, Yeung, CA: Advances in endoscopic disc and spine surgery: foraminal approach, in Szabó Z, ed. Surgical Technology International XI. San Francisco, CA, Universal Medical Press, Inc, 2003: 255-263—Fig 5 p 259)

Because the posterolateral approach accesses the disc through the foramen, foraminal and extraforaminal herniations are ideal indications. The posterolateral endoscopic lumbar discectomy approach is also advantageous for targeting recurrent disc herniations after a standard posterior discectomy, upper lumbar and lower thoracic herniations, posterior annular tears, discitis, and foraminal bony stenosis.

The posterolateral foraminal approach avoids the posterior epidural scar tissue in a recurrent herniation and is not more difficult than a standard first time discectomy. Typically the old scar tissue can limit the migration of the recurrent herniation and it is easily accessible.

Upper lumbar herniations require more aggressive laminotomies when approached posteriorly due to the increased overlap of the lamina in relationship to the disc space. The facet joints are also more sagitally oriented and thus there is a higher chance for postoperative instability with the traditional posterior approach. The posterolateral approach avoids any potential boney destabilization and since the iliac crest does not limit the trajectory of the approach at these levels, one can start as lateral as needed to access the herniation with a more shallow approach to the disc. Lower thoracic herniations can be safely removed with the advantage of not requiring any manipulation or retraction of the spinal cord or conus.

Symptomatic annular tears are often treated with fusion or total disc replacement, but posterior lateral endoscopic discectomy and thermal treatment of single quadrant radial annular tears is a minimally invasive alternative that can often shrink and seal chemically sensitized tears enough to delay the larger reconstructive surgery. Nucleus pulposus tissue interposed within the annular tear can prevent the annulus from healing. This interposed nucleus pulposus is removed along with the inflamed granulation tissue to allow the annular fibers to reconnect and potentially heal. Sometimes the thermal treatment actually seals the tear if there are enough intact annular layers, but if the tear is large, one can only debride the margins and hope it scars back together (Fig. 52.3a–c). The sensitized nerve endings in the granulation tissue and tear are denatured with the thermal laser and radiofrequency treatment, partially denervating the posterior annulus and reducing its pain stimulus. The saline irrigation also flushes out the neurotoxic chemicals and metabolites that can cause chemical irritation.

Fig. 52.3

(a) Sagittal T2 MRI of the lumbar spine showing a posterior high intensity zone (HIZ) at L5–S1 which represents an annular tear. (b) Endoscopic intradiscal view of an annular tear. Note the inflamed red granulation tissue within the annular fibers. (c) After thermal treatment with the bipolar radiofrequency probe, the granulation tissue has been ablated and removed. The annular fibers are now in a better situation to heal and scar together

In discitis, this technique can obtain a good tissue sample for biopsy and culture. It also accomplishes a thorough debridement and wash out of the disc space without creating any surgical dead space for the infection to spread.

Endoscopic trephines, rasps, burrs, Kerrisons, and laser allow targeted boney removal of the ventral portion of the superior articular facet and vertebral body osteophytes to treat foraminal stenosis. This approach directly accesses the area of stenosis.

Contraindications

Endoscopic removal of disk herniation is only limited by the accessibility of endoscopic instruments to the herniation site. Contraindications are relative and depend on the location of disc herniation, the patient’s anatomy, and surgeon experience. Sequestered herniations and highly migrated extruded herniations can be successfully treated from the posterolateral approach, but are more easily removed by a posterior transcanal approach. The surgical approach to L5–S1 is more difficult in patients with high iliac crests (above the L4–L5 disc space on lateral X-rays) and a horizontal L5–S1 disc space since this forces the approach to be steeper, making it more difficult to reach the herniation in the posterior quadrant of the disc. A centrally located herniation at L5–S1 is also difficult to access since one needs a fairly shallow approach to access the base of the herniation. Degenerative scoliosis can make surgical access through the foramen difficult on the concave side. These are not insurmountable barriers to the experienced endoscopic surgeon. However, surgeons learning the technique should start by operating on foraminal and contained paracentral herniations. Then as they become more familiar with the foraminal anatomy and their endoscopic surgical skills improve, they can successfully treat the herniations that are more difficult to reach. For example, advanced techniques to overcome anatomic constraints at L5–S1 and foraminal stenosis at the scoliosis concavity include removal of the ventral portion of the superior articular process to allow a shallower approach trajectory and more central access to the posterior disc pathology. A biportal approach allows larger more flexible rongeurs to reach the herniation through the accessory contralateral portal while visualizing it from the main portal.

Alternative Treatments

Microscopic lumbar discectomy via the posterior approach is considered the gold standard and is the main alternative. Unfortunately there are a lot of other percutaneous discectomy techniques that are confused with and often categorized with posterolateral endoscopic lumbar discectomy, but are entirely different. These procedures include automated percutaneous lumbar discectomy (APLD), percutaneous disc decompression, various indirect percutaneous “laser” discectomy techniques, nucleoplasty (coblation), and intradiscal electrothermal therapy (IDET). These aforementioned techniques are fluoroscopically guided, non-visualized procedures that theoretically treat disc herniations by removing nucleus material centrally and thus indirectly decompressing the disc herniation. They do not directly target or remove the herniated portion of the disc and nerve root decompression cannot be verified during these procedures. Their indications are limited to contained herniations.

Posterolateral endoscopic lumbar discectomy is like any other typical “surgical procedure” and is based on direct surgical exposure, visualization of the target pathology, and direct removal of the offending pathology. Laser and radiofrequency bipolar probes are only adjunctive tools used to fine tune the discectomy, control hemostasis, and remove boney osteophytes.

Technique(s)

Setup/Exposure

Proper OR setup requires a radiolucent table with an antilordotic frame, one C-arm, and a tower with the usual monitor for endoscopic viewing. The patient is placed prone on the antilordotic frame with the arms away from the side of the body. Care is taken to line up the patient with the C-arm to ensure a perfect posterior–anterior and lateral view for fluoroscopic imaging. The surgical level must be centered to avoid parallax error. The imaging/video equipment, instrument table, and operating room personnel are positioned in relation to the surgeon as shown (Fig. 52.4). Although some surgeons utilize the lateral position, the prone position is preferred as it allows easier visual orientation of the video image in relation to the patient and more ergonomic manipulation of the operating instruments. The prone position also allows a biportal (bilateral) approach for real time visualization of larger and flexible working instruments from this accessory cannula while the operating scope simultaneously directs smaller instruments through its operating channel during discectomy.

Fig. 52.4

Illustration of the operating room setup. The patient is in the prone position with the anesthesiologist or anesthetist at the head of the operating table and the surgeon and nurse at the patient’s left for a left sided herniation. (Adapted with permission from Yeung AT, Yeung CA: Posterolateral selective endoscopic discectomy: The YESS technique, in Kim DH, Fessler RG, Regan JJ, eds: Endoscopic Spine Surgery and Instrumentation: Percutaneous Procedures, New York, NY, Thieme Medical Publishers, Inc, 2005)

Local anesthetic and IV sedation with Versed and Fentanyl are the preferred choice for anesthesia versus general anesthesia. This allows for real time nerve monitoring utilizing the patient’s pain response to avoid any injury to the exiting or traversing nerve root. One-half percent lidocaine is the preferred local anesthetic since this can anesthetize the area enough to avoid pain, but does not prevent a painful response when the nerve roots are stimulated. The anesthesiologist should avoid using Propofol for IV sedation since this can induce general anesthesia and prevent the patient from responding to a maneuver that could cause a nerve root injury.

Instruments/Equipment

There are a few endoscopic systems in clinical use today with similar instrumentation, but we will only describe the one used by the authors. The Yeung Endoscopic Spine Surgery System (YESS)/Vertebris system (Richard Wolf Medical Instruments Corp, Vernon Hills, IL) consists of the following instruments (Fig. 52.2).

Multichannel, 20° oval spinal endoscope with either a 2.7, 3.1, or 4.1 mm working channel and integrated continuous irrigation (inflow and outflow) ports
7 and 8 mm access cannulas with various open slotted, beveled, and tapered tips
Guide wire and tissue dilator/obturator cannulated with a central channel and eccentric channel to accommodate a needle for local annular anesthetic (eccentric channel) while simultaneously positioned over the guide wire (central channel)
Specialized single and double action rongeurs for visualized fragmentectomy through the endoscope working channel
Larger straight and hinged rongeurs that fit through the access cannulas for biportal fragmentectomy and fluoroscopically guided uniportal discectomy
Cutting tenotomy type forceps to release annular fibers
Trephines for annulotomy and removal of bone for foraminal enlargement (foraminoplasty)
Micro rasps, curettes, and penfield probes
Annulotomy knife
Flexible bipolar radiofrequency probe (Elliquence, Oceanside, NY) for hemostasis, thermal contraction of the annular collagen, and thermal ablation of the annular nociceptors

Adjunctive equipment

Straight and flexible suction-irrigation shavers for discectomy
Pump suction-aspirator to connect to the suction-irrigation shavers for stronger suction than standard wall suction
Side firing Holmium-YAG laser for fine tissue and bone vaporization/dissection
Endoscopic high speed drill for foraminoplasty
Fluid pump for consistent and continuous irrigation

Procedure(s)

Protocol for Optimal Needle Placement

Optimal needle placement is critical as all subsequent instrumentation follows this trajectory. The needle entry point typically starts about 10–13 cm from the midline and is positioned to allow entry into the disc parallel to the endplates to allow intradiscal positioning without damaging the endplates. The patient’s body habitus will determine just how far lateral from the midline one will have to start. A good estimate can be made by laying a metal rod transversely on the patients back and marking a point 1 in lateral to the point where the rod does not touch the skin. After determining the lateral extent of the incision site, you will then check a lateral X-ray and position the incision in line with the disc inclination.

To obtain the most accurate needle placement customized to the patients’ individual body habitus, a thin metal rod is utilized as a radio-opaque marker and ruler to draw lines on the skin to mark surface topography for guidance in free hand biplane C-arm needle placement. These surface markings help identify and target three key landmarks for needle placement: the anatomic disc center, the annular foraminal window (centered within the medial and lateral borders of the pedicles), and the skin window (needle entry point/skin incision).