Summary of Key Points
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Less invasive techniques have been well refined for the performance of lumbar discectomy.
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Options include transforaminal and extraforaminal approaches to the disc; visualization may be accomplished via operating microscope or endoscope.
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Outcomes are excellent and comparable to open procedures.
Minimal Access Lumbar Discectomy
Lumbar discectomy has become the most common neurosurgical procedure in the United States, with nearly 300,000 procedures performed each year. Herniated lumbar discs and resultant radiculopathy lead to approximately 15 million physician visits per year and have created a financial burden on society exceeding $50 billion annually.
Historical Review
The operative treatment of lumbar disc disease has challenged spine surgeons since the first reported case of Dandy in 1929. The operating microscope revolutionized the operation. It improved the ability to visualize the neural elements and disc material, decreased surgical morbidity, and decreased incision size. Yasargil popularized the operating microscope in the mid-1960s, although it was not until the 1970s that the first publications by Yasargil and Caspar began to appear separately. In 1978 Williams reported on 532 patients who had undergone lumbar microdiscectomy through an intralaminar approach. These publications detailed the usefulness of the microscope and the appearance of lumbar microdiscectomy.
Since these early descriptions, surgeons have sought to decrease the incision size and iatrogenic morbidity associated with the operation. Faubert and Caspar in 1991 reported the use of a muscular retractor system rather than subperiosteal dissection to facilitate visualization of smaller operative corridors. The endoscope was also applied for the treatment of spine pathology.
True minimally invasive lumbar microdiscectomy was first described by Foley and Smith in 1997. They reported the use of a microendoscopic discectomy system that entailed the use of tubular dilators to facilitate muscle sparing, a tubular retractor system, and an endoscope coupled with microsurgical techniques and instrumentation. This approach (microendoscopic discectomy) revolutionized minimal access spine surgery and paved the way for minimally invasive surgery (MIS) laminectomy and fusion techniques. The goal of these MIS approaches is to achieve clinical outcomes similar to those of standard approaches yet minimize the iatrogenic injury encountered during the approach to the spine.
This chapter reviews current concepts in minimal access lumbar discectomy. The focus will in large part be on microscopic discectomy, but we will review percutaneous endoscopic discectomy for extraforaminal herniations and other new modalities that may be applied in lumbar disc surgery.
Microsurgical (Microlumbar) Discectomy
General Principles
Microscopic magnification, illumination, and three-dimensional vision have unquestionably increased the accuracy of surgery and reduced tissue trauma.
From a technical standpoint, the microsurgical discectomy technique requires only a small incision with minimum paravertebral muscle dissection. Extradural fat, facets, and laminae can usually be preserved. The technique requires a blunt paravertebral muscle-splitting approach. Evidence has suggested that the approach is characterized by less postoperative pain, shorter hospitalization, and faster return to work. The subperiosteal approach, by contrast, requires a larger incision and the detachment of the tendinous insertions of the paraspinal muscles and their retraction from the spinous process. The paravertebral muscles are rich in proprioceptors and may be injured when retracted. There are reports on the correlation between denervation and retraction-ischemia of the muscles and postoperative pain.
The microsurgical approach to a herniated lumbar disc entails several modifications of the standard approach: surgical planning, positioning of the patient, and intraoperative imaging. Some of these modifications may appear as disadvantages to those surgeons not experienced with microsurgery. The surgical corridor to the target area is limited, so the localization of the skin incision has to be determined precisely. Once the skin incision has been placed, there is no way of altering the approach other than by enlarging the incision. The approach uses the same instruments that are used in standard lumbar discectomy but have been modified for use through small tubular retractors. The instruments are usually bayoneted and are of a dark color to reduce glare from the light source. A high-speed drill with a long, tapered, and gradually bent tip is designed to be used through these tubular retractors.
Patient Positioning
The patient is positioned prone on a radiolucent spine table such as the Jackson table. We prefer to place the patient’s knees and legs in a sling with the hips flexed rather than on flat boards with the knees and legs extended. This placement increases the interlaminar space and optimizes access (personal experience).
Surgical Technique
Step 1: Localization
The lumbar spine area is prepped and draped in a standard fashion. We prefer to insert a spine needle in the midline at the desired surgical level. This is confirmed on lateral fluoroscopy. The needle tip should point to the disc space. On the basis of the location of the disc space, a vertical paramedian incision is then made through the skin and the fascia one finger-breadth from the midline toward the side of pathology. The size of the incision is dependent on the size of tubular retractor to use (typically, 14 to 19 mm). Generally, the incision should be slightly larger than the working tube.
Step 2: Dilator Insertion
The smallest dilator is then inserted through the incision and is docked on the inferior aspect of the cranial lamina ( Fig. 91-1 ). That is the L4 lamina for an L4-5 disc herniation. This is confirmed with lateral fluoroscopy. Remember that the edge of the lamina is caudal to the disc space. The anatomy should be palpated with the dilator, and a three-dimensional image of the anatomy should be formed in the surgeon’s mind. The inferior edge of the lamina is determined as well as the facet/lamina junction. The dilator may then be used to clear soft tissue from the lamina and medial facet. Care should be taken not to allow the dilator to slip into the intralaminar space.
Step 3: Sequential Dilator and Tubular Retraction Insertion
Sequentially place the second, third, and fourth dilators over the initial dilator down to the lamina, and then place the working channel (tubular retractor) over the final dilator ( Fig. 91-2 ). We do not check fluoroscopy after each dilator placed but do so after the last is secured. Continued soft tissue is dissected from the lamina during subsequent dilator placement. The length of the final working tubular retractor is determined from markings on the largest dilator. The length and width of the tube are determined, and the tube is placed over the dilator to dock on the edge of the lamina. Fluoroscopy is used to verify placement of the tube ( Fig. 91-3 ). We then direct the distal end of the tube somewhat medially.
The tube is then fixed to an arm, which is then attached to the operating table ( Fig. 91-4 ). Once it has been attached, the dilators are removed and a corridor is established percutaneously to the lamina and interlaminar space. We place a Penfield no. 4 under the edge of the lamina to confirm correct level localization on the lateral image ( Fig. 91-5 ) and also confirm medial-lateral position on the anteroposterior image.
Step 4: Soft Tissue Removal and Laminar Identification
At this point, the operating room microscope or endoscope is brought into the field to provide illumination and magnification. Soft tissue usually will need to be removed from the laminae by using a Bovie with an extended tip and rongeur. The inferior (caudal) edge of the lamina should be identified as well as the medial facet joint ( Fig. 91-6 ). Visualization of the fibers of the facet capsule ensure that one does not inadvertently enter the joint or remove too much of the joint and cause potential instability.
If an optimal view is not obtained, the tubular retractor may be angled in any direction. This may be accomplished with the largest dilator. It is critical to keep downward pressure on the tubular retractor before moving, thus preventing soft tissue from creeping under the tubular retractor and obstructing the operative view. It is crucial to remove all soft tissue that is exposed in the operative corridor to maximize the working space within the tubular retractor.
Step 5: Hemilaminotomy and Flavectomy
A small laminotomy or facetectomy may be performed with a high-speed drill and match-stick bit. Alternatively, a Kerrison rongeur may be used. The ligamentum flavum is then opened to expose the traversing nerve root and dura mater. This may be performed in multiple ways. We prefer to use an angled curette to access the subligamentous region and remove the remaining ligament with a rongeur.
Step 6: Nerve Root Exploration
The dura and traversing nerve root are then identified. The traversing root is retracted medially by using a Penfield dissector or Love-style retractor. If necessary, the epidural vessels may be bipolar cauterized and divided to identify the disc space.
Step 7: Discectomy and Root Decompression
Once the disc space is visualized, the disc material is removed as for any standard discectomy. We prefer to only remove herniated disc material. If an annulotomy is required, a small one is made in a horizontal fashion (medial/lateral) with a no. 11 blade or a sheathed microknife ( Fig. 91-7 ).
Step 8: Closure
Finally, loosen the flexible arm, and remove the tubular retractor slowly. Any bleeding in the paraspinal musculature may be controlled with bipolar forceps.
The fascia is then approximated with one or two interrupted absorbable sutures. The dermal tissue may be closed with interrupted absorbable sutures, and the skin is closed with a running subcuticular absorbable stitch and an adhesive.
Patients are urged to begin ambulating immediately and are discharged within 24 hours, either the same day or the following morning.
Microendoscopic Discectomy for Extraforaminal Lumbar Disc Herniations
Spine endoscopy has been widely used to treat patients with cervical, thoracic, and lumbar disorders safely and effectively. The most common application has been in the lumbar spine, specifically lumbar discectomy.
General Principles
Extraforaminal lumbar disc herniations (EFDHs), otherwise known as far lateral lumbar disc herniations, are relatively rare and make up 1% to 12% of all lumbar disc herniations. The surgical treatment of EFDHs is more complex than that of the more common dorsolateral or central disc herniation, owing to an increased risk of nerve root injury, postoperative instability from extensive facetectomy, or inadequate decompression.
The microendoscopic approach for EFDH can further reduce surgical morbidity by preserving the facet joint stability, providing less chance of nerve root injury while still achieving similar or better outcomes. Despite these advantages, the surgeon faces new challenges. The technique takes surgery from direct line of sight with an open retractor system to one in which surgery is performed through a tubular retractor with visualization of the operative bed on a video monitor placed in front of the surgeon. This requires specialized training and has resulted in a shallow learning curve that must be overcome for proficiency with the procedure.
Anesthesia
We prefer to use general anesthesia for microendoscopic discectomy. The operative time for this procedure, especially early in a surgeon’s experience, may be prolonged. Use of a general anesthetic will ensure the patient’s and surgeon’s comfort during the procedure.
Patient Positioning
The patient is positioned prone on a radiolucent operating room table, such as a Jackson table, with the spine flexed. We typically utilize a sling for the legs to optimize interlaminar space and optimize access.
Surgical Technique
Step 1: Disinfection and Localization
The lumbar spine area is prepped and draped in the usual fashion. Fluoroscopy is draped and brought into the operative field, and lateral imaging is performed. A spine needle is inserted into the midline at the level of the affected disc. This needle should aim directly down to the superior end plate of the inferior vertebral body—that is, the superior end plate of the L5 vertebral body for an L4-5 far lateral disc herniation. A set of landmarks may then be used to direct tubular retractor placement. An anteroposterior fluoroscopic image is used next. A horizontal line may be drawn along the caudal edge of the rostral transverse process (L4 in our example), and a second line may be drawn along the superior end plate of the caudal vertebral body (L5). A vertical line may be drawn between these horizontal lines approximately 4.5 cm lateral to the midline on the symptomatic side. This will mark the lateral incision needed for retractor placement as well as the cranial/caudal boundaries.
Step 2: Dilator Insertion
Remove the spine needle, and make a 15- to 22-mm (length determined by the retractor system that is used) vertical skin incision along the vertical mark. The incision length has to match the diameter of the respective tubular retractor, although we typically make the incision a few millimeters longer than the tube diameter. The skin and underlying fascia are incised. The first dilator is directed through the fascial incision to dock on the caudal transverse process, at the junction of the lateral facet, transverse process, and pars interarticularis junction. This requires medial angulation toward the spine. This is confirmed by using lateral fluoroscopy. This first dilator is then used to clear soft tissue from the transverse process, pars, and lateral facet joint.
Step 3: Sequential Dilator and Tubular Retraction Insertion
Insert the sequential dilators over the initial one, followed by the tubular retractor. Secure the flexible arm to the table, attach it firmly to the tubular retractor 180 degrees away from the surgeon, and then remove the sequential dilators to establish a tubular operative corridor. The appropriate positioning is confirmed by fluoroscopy.
Step 4: Endoscope Insertion
Insert the endoscope into the tubular retractor. The endoscope can be placed anywhere within the 360-degree periphery of the tube and can be retracted or extended for variable magnification. This is somewhat limited by the specific endoscope system that is used. The endoscope should initially be placed in the most retracted position to avoid contact with soft tissue. Blotching the endoscope with soft tissue will dramatically reduce visualization, especially clarity. If this occurs, remove the endoscope from the tubular retractor, and clean the lens using antifog solution and gauze.
Step 5: Focus and Image Orientation
Surgical focusing and orientation are extremely important. To help in this regard, the endoscopic image orientation should be adjusted such that the medial anatomy will be on the top of the video monitor (12 o’clock) and the lateral anatomy on the bottom (6 o’clock). A sucker tip can be placed laterally inside the tube to help guide the surgeon regarding lateral and medial orientation.
Step 6: Soft Tissue Removal
Clear the soft tissue from the base of the transverse process and pars interarticularis using an insulated Bovie electrocautery and small pituitary rongeur. This should permit clear visualization of the bony landmarks.
The lower half of the foramen is normally filled with fatty tissue. Small veins coming from the paravertebral plexus cross the foramen to join the epidural veins. The lumbar segmental arteries usually do not cross the foraminal working area. In the case of a disc lesion, this lower part is filled with disc tissue or protruded anulus material.
Coagulate the pars artery, if present, with the bipolar forceps, and divide it with microscissors. Separate soft tissue from the undersurface of the pars, using small, angled microcurettes. This maneuver detaches the medial edge of the intertransverse ligament from the pars and allows for entry into the neuroforamen.
Step 7: Nerve Root Exploration and Decompression
Remove bone from along the inferomedial aspect of the transverse process and the most lateral aspect of the pars with an angled Kerrison rongeur or high-speed drill. This maneuver opens the lateral aspect of the neuroforamen, allowing palpation of the pedicle with a nerve hook or ball-tip probe and straightforward identification of the exiting nerve root as it travels around the pedicle.
When the exiting nerve root has been definitively identified at the level of the pedicle, dissect laterally and caudally along the root, following its caudal course toward the disc by wanding the tubular retractor. If an overhanging articular process is encountered (secondary to coexisting facet hypertrophy), remove the lateral margin of the articular process with the drill or Kerrison rongeur, further exposing the distal course of the nerve root.
Identify the dorsal root ganglion, which makes up the enlargement of the exiting nerve root just lateral and inferior to the neuroforamen. Treat this structure gently, as excessive manipulation of the dorsal root ganglion can produce significant postoperative pain.
Typically, the nerve and ganglion are pushed laterally and cranially by the free disc fragment. Usually, removal of the fragment alone is sufficient for nerve root decompression. But if necessary, enter the interspace for further disc removal. Finally, reexplore the root to confirm that it has been fully decompressed.
Step 8: Closure
Last, irrigate the wound, loosen the flexible arm, and remove the tubular retractor slowly. Any bleeding in the paraspinal musculature may be controlled with the bipolar cautery. Approximate the fascia with one or two interrupted absorbable sutures, close the subcutaneous tissue in an inverted manner, and, finally, approximate the skin edges with a subcutaneous suture and adhesive. Patients are urged to begin ambulating immediately and are discharged within 24 hours, either the same day or the following morning.
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Timing of Surgery Following Spinal Cord Injury
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