Historical Review

The operative treatment of lumbar disc disease has challenged spine surgeons since the first reported case of Dandy in 1929.⁴ 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.⁵ Yasargil popularized the operating microscope in the mid-1960s, although it was not until the 1970s that the first publications by Yasargil⁶ and Caspar began to appear separately.⁷ In 1978 Williams reported on 532 patients who had undergone lumbar microdiscectomy through an intralaminar approach.⁸ 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 system⁹ rather than subperiosteal dissection to facilitate visualization of smaller operative corridors. The endoscope was also applied for the treatment of spine pathology.¹⁰

True minimally invasive lumbar microdiscectomy was first described by Foley and Smith¹¹ 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.

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. Recent evidence has suggested that the approach is characterized by less postoperative pain, shorter hospitalization, and faster return to work.¹² 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.¹²

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 very limited, so the localization of the skin incision has to be determined very 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 2: Dilator Insertion

The smallest dilator is then inserted through the incision and is docked on the inferior aspect of the cranial lamina (Fig. 81-1). 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.

FIGURE 81-1 The smallest dilator has been inserted through a 17-mm skin incision and is docked on the inferior aspect of the cranial lamina (L4 for L4-5 discectomy).

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. 81-2). 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. 81-3). We then direct the distal end of the tube somewhat medially.

FIGURE 81-2 Following placement of the initial dilator, the other dilators are placed, one over the other, until the final working diameter is reached. Fluoroscopy is used to verify placement, and finally, the working port may be placed over the last dilator.

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FIGURE 81-3 Fluoroscopy is used to verify tube placement.

The tube is then fixed to an arm, which is then attached to the operating table (Fig. 81-4). Once it has been attached, the dilators are removed and a corridor is established percutanously 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. 81-5) and also confirm medial-lateral position on the anteroposterior image.

FIGURE 81-4 Demonstration of the port being situated through the muscle-splitting approach and docked on the lamina immediately above the disc herniation. The port is then attached to the table.

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FIGURE 81-5 A, Fluoroscopy is then used to verify final positioning prior to beginning the laminotomy. B, We place a Penfield no. 4 under the lamina and check both a lateral and an anteroposterior image to verify level localization.

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. 81-6). 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.

FIGURE 81-6 Once the port is in place and the soft tissue has been cleared, the surgeon should have a clear view of the inferior edge of the lamina and the medial facet joint.

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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 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 anulotomy is required, a small one is made in a horizontal fashion (medial/lateral) with a no. 11 blade or a sheathed microknife (Fig. 81-7).

FIGURE 81-7 Once an anulotomy has been made, the offending disc fragment is removed through the port.

(Copyright Cleveland Clinic Foundation.)

General Principles

Extraforaminal lumbar disc herniations (EFDH), otherwise known as far lateral lumbar disc herniations, are relatively rare and make up 1% to 12% of all lumbar disc herniations.^13,14 The surgical treatment of EFDH 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, and/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 had resulted in a shallow learning curve that must be overcome for proficiency with the procedure.^11,15

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

Historical Review

Percutaneous discectomy promised to change the field of lumbar spine surgery when it was introduced in the late 1970s. Kambin et al.^16,17 and Hijikata¹⁸ separately reported the efficacy of this procedure, that is, percutaneous nucleotomy.

In 1985, Onik et al.¹⁹ reported the technique of automated percutaneous discectomy (APD). This procedure consisted of the insertion of a 2-mm probe into the disc. The device was then able to mechanically facilitate the removal of disc material.

Shortly thereafter, in the late 1980s, Choy et al.²⁰ introduced percutaneous laser discectomy (PLD). This modification utilized an approach similar to that of APD but used laser energy to remove disc material.

In the 1990s, the intradiscal electrothermal anuloplasty (IDET) procedure was developed by Saal and Saal.^21,22

The procedure consisted of a percutaneous approach to the site of pathology similar to the approach used by other procedures, such as APD and PLD. The unique feature of the IDET procedure is that it used a navigational catheter with a temperature-controlled thermal resistive coil to heat and absorb the disc material.

Evidence of the superiority of such minimally invasive techniques compared with microdiscectomy remains unclear; this is attributed to the lack of high-quality studies.²³

Therefore, the percutaneous procedures are highly dependent on patient selection. Patient selection and limited pathology have probably been the single largest factor in preventing the more widespread use of these procedures.

Patient Selection

As was stated previously, appropriate patient selection is the single most important factor with regard to favorable outcome. As in all procedures for disc pathology, candidate patients are those with radiculopathy with little to no back pain. Confirmatory physical examination findings should also be sought, such as a positive straight-leg raise sign. As will all surgical procedures, patients with vague or equivocal symptoms are not candidates for these percutaneous techniques.

In addition, a minimum 6-week course of conservative treatment should be attempted, which may include anti-inflammatory nonsteroidal medications, physical therapy, epidural steroid injections, and other modalities as appropriate.

Radiographic criteria are extremely important in considering percutaneous discectomy. These procedures are appropriate only for patients with a contained disc demonstrated on MRI. This is defined as disc material that is contained by either the anulus fibrosus or the posterior longitudinal ligament. An unfavorable outcome will likely be seen if the procedure is performed on patients with free or extruded discs. In addition, patients with disc herniations compromising more than 50% of the spinal canal with significant thecal sac compression should not be treated by those procedures.

Other radiographic contraindications include spinal stenosis, lateral recess stenosis, and calcified disc herniations.

Needle Placement

The major component of any percutaneous technique or disc decompression is needle placement. The initial needle for essentially all of the aforementioned procedures is passed through the Kambin triangular zone, which is located between the traversing and exiting nerves. We recommend biplanar fluoroscopy for safe passage.

Surgical Technique

The patient is placed prone on a radiolucent spine frame, with the arm away from the side of the body. Care is taken to line up the patient with the C-arm to ensure perfect posteroanterior and lateral views. The spinous process should be centered between the pedicles on the AP view and the end plates parallel in the lateral view.

The sedation is kept light to allow patient feedback. This permits an alteration of trajectory if nerve irritation is encountered. The patient’s lumbar region is prepped and draped in the usual fashion. Local anesthetic is infiltrated into the skin and subcutaneous tissue as well.

The fluoroscopy unit is positioned such that an oblique view of the spine is obtained; the gantry angle should be oriented such that the superior articular process (SAP) of the inferior vertebral body crosses the intervertebral disc and divides it into one third medial to the SAP and two thirds lateral to the SAP for the L4-5 and L5-S1 discs. A ratio of half and half is used for the more cephalad lumbar discs.

The fluoroscopic view of the most superior and inferior aspect of each end plate should be superimposed such that the introducer needle can be positioned perpendicular to the disc or parallel with the gantry angle. When this view cannot be obtained, the patient must be repositioned, the cephalocaudal tilt of the C-arm must change, or the entry point of the needle must be altered to correct the malalignment.

Thereafter, a 17-gauge introducer needle is advanced from approximately 8 cm laterally from the midline, using an oblique fluoroscopic projection.

The needle is aimed at the Kambin safe triangle. This triangular working zone is bordered ventrally by the exiting root, inferiorly by the proximal end plate of the lower lumbar segment, and medially by the traversing root and the dural sac. The floor of the triangular working zone is occupied by the intervertebral disc, the vertebral end plate, and the dorsal boundary of the adjacent vertebra²⁴ (Fig. 81-8).

FIGURE 81-8 The Kambin triangle is defined ventrally by the existing nerve root, inferiorly by the proximal end plate of the lower lumbar segment, and medially by the traversing root and dura. The floor is occupied by the intervertebral disc, the end plate, and the dorsal boundary of the adjacent vertebra.

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It is important that the introducer needle be positioned parallel to the vertebral end plate to avoid injury to the end plate. Moreover, the needle should not be placed too lateral (ventral) to the SAP.

A tactile resistance and gritty crunching are encountered when the needle first enters the anulus, and the fluoroscope is then repositioned in a posteroanterior projection. Care should be taken not to advance the needle beyond the disc margins, and if there is any confusion about the position of the needle tip during advancement, the position should be checked fluoroscopically in two orthogonal planes.

The patient may report transient localized back pain as the needle penetrates the anulus. Radicular symptoms are not expected and may indicate a needle position that is too close to the transversing root. The needle position is checked in the posteroanterior projection, confirming the tip position just inside the anulus. Under lateral fluoroscopy, the introducer needle is then advanced minimally to achieve positioning in the nucleus pulposus in the ventral half of the disc. Optimal positioning is with the needle tip between a 12 o’clock and a 3 o’clock position (Fig. 81-9).

FIGURE 81-9 The needle must be placed in the optimal position in the nucleus pulposus, with the needle tip between a 12 o’clock and a 3 o’clock position as illustrated.