Laser Discectomy

Updated: Aug 17, 2015
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: Erik D Schraga, MD  more...
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Overview

Overview

Background

Chronic low back pain is one of the major chronic debilitating conditions involving tremendous loss of money, work, and quality time. Lasers are used in different fields of medicine and confer unique advantages. In the treatment of lumbar disc disease, they are useful and advantageous. Laser discectomy is an outpatient procedure with one-step insertion of a needle into the disc space. Disc material is not removed; instead, nucleus pulposus is burned by the laser. Laser discectomy is minimally invasive, cost-effective, and free of postoperative pain syndromes, and it is starting to be more widely used at various centers.

The rapid acceptance of minimally invasive surgery in the United States has occurred largely without statistical proof of its superiority over traditional methods. All members of the healthcare field now see the need for valid outcome studies supporting the efficacy of new treatment techniques. Percutaneous laser disc decompression (PLDD) will gain wide acceptance only if it is demonstrated statistically to be a safe and effective alternative treatment for lumbar disc herniation.

Epiduroscopic laser neural decompression is considered an effective treatment alternative for chronic refractory low back and/or lower extremity pain, including lumbar disc herniation, lumbar spinal stenosis, and failed back surgery syndrome that cannot be alleviated with existing noninvasive conservative treatment. [1]

PLDD performed with computed tomographic (CT) and fluoroscopic guidance appears to be a safe and cost-effective treatment for herniated intervertebral discs and is being used with increasing frequency. It is minimally invasive, can be performed in an outpatient setting, requires no general anesthesia, results in no scarring or spinal instability, shortens to rehabilitation time, is repeatable, and does not preclude open surgery should that become necessary.

Various laser wavelengths have been used, but no consensus exists regarding which is most efficacious. Good candidates for this procedure have a classic clinical syndrome and neuroimaging evidence.

In cases of ruptured posterior longitudinal ligament (ie, epidural leak of contrast medium in discography), PLDD is not indicated. Indications for the operation first of all depend on the clinical symptoms, but the success of the operation depends on the discographic findings.

Laser-assisted posterior cervical foraminotomy and discectomy is an efficacious surgical option for treating lateral cervical disc herniation. The pinpoint accuracy of the laser scalpel facilitates sophisticated decompression within a limited surgical field and may reduce the risk of intraoperative bleeding and neural damage. [2]

Indications

This minimally invasive technique can be performed in patients who need surgical intervention for disc herniation (see the image below) with leg pain from radiculopathy. Patient selection, and especially disk morphology, are the two most important factors determining the choice of the technique.

Disc herniation classification. A: Normal disc ana Disc herniation classification. A: Normal disc anatomy demonstrating nucleus pulposus (NP) and annular margin (AM). B: Disc protrusion, with NP penetrating asymmetrically through annular fibers but confined within the AM. C: Disc extrusion with NP extending beyond the AM. D: Disc sequestration, with nuclear fragment separated from extruded disc.

Exclusion criteria include stenosis or facet hypertrophy and disc fragment, though a review from Knight et al described its use in foraminoplasty. [3] Relative contraindications are progressive neurologic deficit, involvement in workers' compensation cases, and previous surgery at the same disc level.

In general, the herniation must have continuity with the parent disc; rupture of the annulus is not a contraindication. All patients must be considered on an individual basis.

Criteria for inclusion are undergoing continuing change. Although the optimal candidate, as previously described, is one who has an untreated single-level herniation with limited migration or sequestration of free fragments, a study from Ahn et al showed the procedure to be effective for recurrent disc herniations in some selected cases. [4] What is unacceptable now may, with modifications, become acceptable in the future. During this early stage of PLDD, not adopting a fixed position is important.

Technical considerations

The aim of PLDD is to vaporize a small portion of the nucleus pulposus of an intervertebral disc, thereby reducing the volume of a diseased disc and the pressure within it.

A small amount of tissue is excised from the center or nuclear part of the disc, which is believed to exert an effect on a noncontiguous portion of nucleus that is protruding through the annulus fibrosus and abutting an exiting nerve root. First described by Hijikata in relation to the percutaneous discectomy method, the central cavity created by the laser is believed to allow the nuclear protrusion to move back within the disc. [5] A small change in disc nucleus volume can exert disproportionately large changes on the disc.

Yonezawa et al first demonstrated significant alterations in intradiscal pressure in response to vertical load after neodymium (Nd):yttrium-aluminum-garnet (YAG) laser treatment. Their study also reported the equivalency of laser to aggressive manual curettage. [6] Choy and Altman reported greater than 50% reduction of intradiscal pressure in response to load following treatment with 1000 J of Nd:YAG laser energy. [7] Prodoehl et al reported similar results using 1200 J from the holmium (Ho):YAG laser.

No specimen is available to weigh after laser discectomy; therefore, the amount of disc removed can only be approximated. By calculating the geometry of the laser tract, Choy and Altman estimated that 1000 J of Nd:YAG laser energy vaporized 98.52 mg of disc. [7] Lane et al, who compared the effectiveness of 1200 J each of carbon dioxide, argon, and Ho:YAG laser energy, reported that Ho:YAG was superior, ablating 2.4 g of disc tissue. By comparison, a clinical trial of automated percutaneous discectomy reported removal of 2-7 g of disc tissue with a suction cutting device. Quigley's group compared an automated device, Nd:YAG laser, and Ho:YAG laser and clearly demonstrated the superiority of the automated device in removing the greatest mass of tissue. [8]

Outcomes

Laser discectomy has been used for many years; however, there is a paucity of randomized clinical trials. On the basis of US Preventive Services Task Force criteria, the indicated level of evidence for percutaneous lumbar laser disc decompression is limited for short- and long-term relief.

Reviews by Singh et al and Manchikanti et al revealed limited evidence for percutaneous lumbar laser disc decompression. Automated percutaneous mechanical lumbar discectomy may provide appropriate relief in properly selected patients with contained lumbar disc herniation. [9, 10]

The most extensive experience in the literature was published by Choy and Ascher, who used an Nd:YAG laser. [11] They observed 333 patients for a mean duration of 26 months. The success rate was 78.4% (as measured by a good or fair response) according to MacNab.

Siebert reported on his first 100 patients treated with Nd:YAG. [12] The success rate was 78% at mean follow-up point of 17 months.

Davis reported an 85% success rate with the potassium titanyl phosphate (KTP) laser, with success rate defined as minimal discomfort and the ability to return to gainful employment (follow-up duration was not specified). [13]

Yeung reported preliminary assessment of more than 1000 patients whose herniated lumbar discs were treated with KTP laser. The reported success rate (good or excellent results) was 84%. No specifics were supplied. [14]

Sherk et al used a Ho:YAG laser in a comparison of laser discectomy and conservative treatment. [15, 16] No differences were noted between treated and control groups. They concluded that laser discectomy is a safe procedure that appears to be effective in relieving symptoms in some patients. The author uses a Ho:YAG laser, and successful results are approximately 80% (comparable to those of other investigators).

In another study from India by Agarwal, Ho:LADD (laser-assisted disc decompression) is a very cost-effective and minimally invasive procedure with patient mobilization immediately after the surgery. [17]

According to Kramer, the best clinical results were found in discographic stages 7 and 8. [18] In cases of epidural leak of contrast medium and in cases of total degeneration, the clinical results were significantly poor (stages 6 and 9).

The literature now includes 23 well-documented cases of erectile dysfunction caused by spinal cord disc herniation. PLDD is a minimally invasive procedure that that can be used to treat such herniation.

Singh et al reviewed 38 research reports published between 1986 and 2005 for intradiscal disease therapy classification, surgical intervention, and treatment outcomes (neurologic status, pain scores, and ambulation). Their results revealed that the surgical literature on the management of intradiscal disease continues to be limited, and arthrodesis continues to be the primary treatment modality in most patients. [19] Newer treatment options including laser discectomy have shown promising results with regards to symptomatic relief and early return to function.

Provocative discography is recommended prior to the percutaneous lumbar disc decompression. Besides discectomy, laser has been used by Knight et al for endoscopic foraminoplasty as well. [3]

Ishiwata et al have performed a study on MRI-guided percutaneous laser disc decompression for lumbar disc herniation. They have suggested that the middle zone in the targeted disk space seems to be a favorable target to obtain better clinical outcomes. [20]

In a Cochrane database review by Gibson et al, microdiscectomy gave broadly comparable results to open discectomy. [21] Surgical discectomy for carefully selected patients with sciatica due to lumbar disc prolapse provides faster relief from the acute attack than conservative management. The evidence on other minimally invasive techniques remains unclear (with the exception of chemonucleolysis using chymopapain, which is no longer widely available).

In a study done in the Netherlands by Schenk et al on routine management of lumbar disc herniation, minimally invasive techniques were expected to be less effective, with higher recurrence rates but less postoperative low back pain. [22] Most surgeons allowed early mobilization but appeared to give conservative advice in resumption of work.

Brouwer et al performed a randomized, controlled trial comparing PLDD with conventional treatment for lumbar disc herniation. [23]  In terms of the primary outcome (Roland-Morris Disability Questionnaire), they found a strategy of PLDD, followed by surgery if needed, to be noninferior to surgery at 1 year.

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Periprocedural Care

Equipment

Although numerous laser wave lengths have been used in both the experimental and clinical setting, no consensus exists regarding selection of laser, treatment duration, or energy requirements. The following are the various kinds of lasers currently used.

Neodymium:yttrium-aluminum-garnet laser

Ascher and Choy et al performed the first neodymium (Nd):yttrium-aluminum-garnet (YAG) laser discectomy in the mid-1980s. [11] Their procedure consisted of fluoroscopically guided insertion of a needle into the disc space to be treated and threading of a thin laser fiber through the needle into the disc space. Activation of the laser with delivery of approximately 1200 J (in short bursts to avoid heating the adjacent tissues) into the disc cavitated the nucleus and ablated a small amount of tissue. The products of vaporization (steam and carbon particles) were allowed to escape through the spinal needle surrounding the laser fiber. At the end of the procedure, the needle site was covered with an adhesive bandage, and the patient was discharged.

These investigators postulated that removal of even a small volume of tissue from the disc resulted in a large drop in intradiscal pressure. They believed that this may be the mechanism responsible for prompt and marked pain relief in patients who were treated for radiculopathy secondary to degenerative disc protrusion and contained herniations. They suggested that the procedure would not be useful for patients with uncontained herniations or sequestered disc fragments outside the disc space loose in the spinal canal. Ascher, Choy, and others have performed this procedure in more than 1000 patients, with long-term pain relief reported in 70-80%. The procedure is appealing in that it is performed on an outpatient basis with conscious sedation.

PLDD with a 1.06 Nd:YAG laser has been approved by the US Food and Drug Administration (FDA). Generally, laser discectomy is believed to be equivalent to other percutaneous discectomy procedures, such as chemonucleolysis and automated percutaneous lumbar discectomy (APLD) using a reciprocating suction cutter.

Potassium titanyl phosphate laser

The crystal of potassium, titanyl, and phosphate (KTP) produces laser light that is lime-green. This laser employs fiber optics and is directed easily into disc space through a spinal needle. Davis first used KTP laser for laser discectomy and reported results essentially the same as those described by Ascher, Choy, and others. [13] In early experience, the procedure was found to be safe and effective, and the FDA subsequently approved the KTP laser for this application. Manufacturers subsequently developed side-firing probes, which make it possible to point the laser energy in almost any direction, minimizing the risk of injury to structures anterior to the spinal column (eg, aorta, vena cava, and iliac vessels).

Holmium:yttrium-aluminum-garnet laser

The holmium (Ho):YAG laser has its wavelength in the midinfrared range, a range that is absorbed well by water. It is fiberoptic. An effective dose of energy can be introduced into the disc via fibers introduced percutaneously through a needle or catheter. The Ho:YAG laser is a pulsed laser, in contrast to the continuous-wave near-infrared lasers, and therefore has the theoretic advantage of producing minimal amounts of heat in adjacent tissues.

With a pulse width of approximately 250 msec at 10 Hz and 1.6 J per pulse, virtually no temperature rise is noted in adjacent tissues. When 1200 J of Ho:YAG laser energy was introduced into the disc through a 400 µm fiber with the same parameters, it consistently produced a 2 cm × 1.5 cm × 1 cm defect in the nucleus pulposus. The defect can be localized precisely in the disc by means of fluoroscopic needle guidance. The defect should be in the posterior quadrant just anterior to the site of herniation.

Early experience revealed the procedure to be safe and effective (as were Nd:YAG and KTP laser procedures), sufficiently so to justify FDA approval for marketing of this application.

In testing various lasers (including carbon dioxide lasers in continuous wave and pulse mode; erbium:YAG; Nd:YAG 1318 µm and 1064 µm; argon; Ho:YAG; and excimer), Choy in 1995 found the greatest efficiency in the carbon dioxide laser in continuous wave and pulse mode and the lowest efficiency in the argon laser. [11] Data on the Ho:YAG laser were unreliable because of the early generation of laser tested. The Nd:YAG was second only to the carbon dioxide laser, and because the latter has no waveguide, the authors deemed the Nd:YAG the laser of choice for PLDD.

Patient preparation

All percutaneous methods rely on the posterolateral approach to the disc as described by Day. [24] Use local anesthetic supplemented with light sedation to avoid inadvertent root injury.

The injection procedure can be performed in an operating room or in a special procedure room of a radiology department, provided that the necessary equipment, anesthesia, emergency cart, and trained personnel are available.

The prone or lateral decubitus position is satisfactory if the patient can be positioned properly and stabilized to afford a lateral approach to the disc space. Radiation exposure of the patient in a typical procedure is equivalent to that encountered in a five-view lumbosacral spine series.

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Technique

Laser discectomy

Needle placement

After sterile skin preparation, as for any surgical procedure, drape the area.

Identify the disc space with the help of a C-arm fluoroscope. Disc margins are made clear by craniocaudal movement of the fluoro tube. At this time, rotate the fluoro tube obliquely to bring the superior articular process to the midline.

Introduce an 18-gauge 7-in. needle immediately anterior to the superior articular process and superior to the transverse process via a triangular safe zone. Advance the needle in 1- to 2-cm increments in a "stop and look and go" process, so that the needle's course can readily be changed if it is found not to be directed properly.

View the progress of needle advancement in anteroposterior and lateral projections with the C-arm fluoroscope, which must be of sufficient strength and quality to give a clear view of the area. Upon completion, the needle tip should be at the center of the disc upon completion. In most patients, the entry points in the skin for treating either the L4-L5 or the L5-S1 disc space are at the level of the iliac crest (very close to each other). The rubbery texture of the annulus is easily felt with the tip of the 18-gauge needle.

Fluoroscopy precautions include the wearing of lead aprons by all personnel in the procedure and operating rooms. Wearing lead gloves and avoiding exposing the operator's hands also reduces radiation exposure.

Despite proper precautions, the use of fluoroscopy during minimally invasive laser microdiscectomy exposes the operator to significantly higher levels of radiation than open microdiscectomy does. [25]

Laser application

Once the needle has reached the annulus, advance it through the annulus and into the nucleus pulposus for a distance of approximately 1 cm. Then mark the fiber to prevent penetration of the tip more than 1 cm beyond the end of the needle.

Owing to differences in absorption, energy requirements and rates of application also differ among lasers. Choy and Ascher reported using a neodymium (Nd):yttrium-aluminum-garnet (YAG) laser as 20 W of continuous energy delivered in 1-sec pulses with 1-sec pauses until 1000-1850 J was delivered. [11] Davis used a potassium titanyl phosphate (KTP) laser as 10-15 W of continuous energy in 0.5-sec pulses with 0.5-sec pauses for a few minutes. [13] The commercial KTP laser is designed to deliver up to 1250 J before it shuts down automatically, and it allows another 300 J to be administered before it issues a warning. Sherk et al used the holmium (Ho):YAG laser in the pulsed mode at 10 Hz. [15, 16]

The great importance of correct needle placement with appropriate radiologic monitoring is emphasized. The needle tip must be just past the annulus, and the needle must be parallel to the disc axis, preferably halfway between the superior and inferior endplates.

Complications

Discitis is the only documented complication of laser discectomy. In 1993, Choy's group tabulated the world experience with laser discectomy, reproting two cases of discitis.

Subchondral marrow abnormalities may occur in the vertebral endplates after Ho:YAG laser discectomy. Possible causative mechanisms include thermal injury and photoacoustic shock. However, these changes probably do not affect surgical outcomes and appear to resolve over time.

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