Laser Diskectomy

Laser diskectomy (discectomy) is an outpatient procedure with one-step insertion of a needle into the disk space. Disk material is not removed; instead, nucleus pulposus is burned by the laser. Laser diskectomy is minimally invasive, cost-effective,[1] and free of postoperative pain syndromes, and it has come to be more widely used at various centers.

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 disk disease, they are useful and advantageous.

The rapid acceptance of minimally invasive surgery in the United States has occurred in many cases without statistical proof of its superiority over traditional methods. All members of the healthcare field see the need for valid outcome studies supporting the efficacy of new treatment techniques. Whether the benefits of laser spine surgery necessarily outweigh the risks remains controversial.[2] To gain wide acceptance, percutaneous laser disk decompression (PLDD) must be demonstrated statistically to be a safe and effective alternative treatment for lumbar disk herniation.

Epiduroscopic laser neural decompression is considered an effective treatment alternative for chronic refractory low-back or lower-extremity pain, including lumbar disk herniation, lumbar spinal stenosis, and failed back surgery syndrome that cannot be alleviated with existing noninvasive conservative treatment.[3, 4, 5]

PLDD performed with computed tomographic (CT) and fluoroscopic guidance appears to be a safe and cost-effective treatment for herniated intervertebral disks and is being used with increasing frequency.[6, 7] It is minimally invasive, can be performed in an outpatient setting, requires no general anesthesia, results in no scarring or spinal instability, shortens the rehabilitation time, is repeatable, and does not preclude open surgery should that become necessary. PLDD has also been performed with ultrasonographic (US) guidance for cervical disk herniation and pain.[8, 9]

Various laser wavelengths have been used, but there is no consensus as to which is most efficacious.[10] 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 diskography), 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 diskographic findings.

Laser-assisted posterior cervical foraminotomy with diskectomy is an efficacious surgical option for treating lateral cervical disk 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.[11]

This minimally invasive technique can be performed in patients who need surgical intervention for disk 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.

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

Criteria for inclusion are evolving. 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 disk herniations in some selected cases.[12]  What has been unacceptable may, with modifications, become acceptable in the future. At this stage in the development of PLDD, it is advisable not to adopt a fixed position.

Exclusion criteria for this procedure include stenosis or facet hypertrophy and disk fragment, though a review from Knight et al described its use in foraminoplasty.[13]  Relative contraindications are progressive neurologic deficit, involvement in workers' compensation cases, and previous surgery at the same disk level.

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

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

A small amount of tissue is excised from the center or nuclear part of the disk, which is believed to exert an effect on a noncontiguous portion of nucleus that is protruding through the anulus fibrosus and abutting an exiting nerve root. First described by Hijikata in relation to the percutaneous diskectomy method, the central cavity created by the laser is believed to allow the nuclear protrusion to move back within the disk.[14]  A small change in disk nucleus volume can exert disproportionately large changes on the disk.

Yonezawa et al first demonstrated significant alterations in intradiskal pressure in response to vertical load after neodymium (Nd):yttrium-aluminum-garnet (YAG) laser treatment.[15] Their study also reported the equivalence of laser to aggressive manual curettage. Choy and Altman reported a greater than 50% reduction of intradiskal pressure in response to load following treatment with 1000 J of Nd:YAG laser energy.[16]  Prodoehl et al reported similar results using 1200 J from the holmium (Ho):YAG laser.

No specimen is available to weigh after laser diskectomy; therefore, the amount of disk 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 disk.[16]  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 disk tissue.

By comparison, a clinical trial of automated percutaneous diskectomy reported removal of 2-7 g of disk 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.[17]

Laser diskectomy 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 lumbar PLDD has been limited with respect tor short- and long-term relief.

Reviews by Singh et al and Manchikanti et al revealed limited evidence for lumbar PLDD. Automated percutaneous mechanical lumbar diskectomy may provide appropriate relief in properly selected patients with contained lumbar disk herniation.[18, 19]

An extensive experience was published by Choy and Ascher, who used an Nd:YAG laser.[20]  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.[21]  The success rate was 78% at a mean follow-up point of 17 months.

Davis reported an 85% success rate with the potassium titanyl phosphate (KTP) laser, with success defined as minimal discomfort and the ability to return to gainful employment (follow-up duration was not specified).[22]

Yeung reported preliminary assessment of more than 1000 patients whose herniated lumbar disks were treated with a KTP laser. The reported success rate (good or excellent results) was 84%. No specifics were supplied.[23]

Sherk et al used a Ho:YAG laser in a comparison of laser diskectomy and conservative treatment.[24, 25]  No differences were noted between treatment and control groups. They concluded that laser diskectomy is a safe procedure that appears to be effective in relieving symptoms in some patients. The author uses a Ho:YAG laser, with a success rate of approximately 80% (comparable to those of other investigators).

In another study from India by Agarwal, Ho:LADD (laser-assisted disk decompression) was found to be a very cost-effective and minimally invasive procedure with patient mobilization immediately after the surgery.[26]

According to Kramer, the best clinical results were found in diskographic stages 7 and 8.[27]  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 includes more than 20 well-documented cases of erectile dysfunction caused by spinal cord disk 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 intradiskal 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 intradiskal disease continues to be limited, and arthrodesis continues to be the primary treatment modality in most patients.[28]  Newer treatment options, including laser diskectomy, have shown promising results with regard to symptomatic relief and early return to function.

Provocative diskography is recommended prior to the PLDD. Besides diskectomy, laser has been used by Knight et al for endoscopic foraminoplasty as well.[13]

Ishiwata et al performed a study on magnetic resonance imaging (MRI)-guided PLDD for lumbar disk herniation. They suggested that the middle zone in the targeted disk space seems to be a favorable target to obtain better clinical outcomes.[29]

In a Cochrane database review by Gibson et al, microdiskectomy yielded results broadly comparable to those of open diskectomy.[30]  Surgical diskectomy for carefully selected patients with sciatica due to lumbar disk prolapse provides faster relief from the acute attack than conservative management. The evidence on other minimally invasive techniques is less clear (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 disk herniation, minimally invasive techniques were expected to be less effective, with higher recurrence rates but less postoperative low back pain.[31]  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 disk herniation.[32]  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.

In a retrospective review examining results in 65 patients who underwent percutaneous lumbar laser diskectomy, Patel et al documented a reduction in the average visual analogue scale (VAS) pain score at 2 weeks after the procedure (from 7.6 to 3.7); the VAS score remained below the preprocedural level at 6 weeks (4.3), 3-6 months (4.1), and 12 months (4.2).[33]  Neuritis occurred in four cases (two of which were treated pharmacologically) and resolved in all four.

Although numerous laser wavelengths have been used for laser diskectomy (discectomy) in both experimental and clinical settings, no consensus has been established regarding selection of laser, treatment duration, or energy requirements. The following kinds of lasers are currently used.

Neodymium:yttrium-aluminum-garnet laser

Ascher and Choy et al performed the first neodymium (Nd):yttrium-aluminum-garnet (YAG) laser diskectomy in the mid-1980s.[20]  Their procedure consisted of fluoroscopically guided insertion of a needle into the disk space to be treated and threading of a thin laser fiber through the needle into the disk space.

Activation of the laser with delivery of approximately 1200 J (in short bursts to avoid heating the adjacent tissues) into the disk cavitated the nucleus and ablated a small amount of tissue.[20] 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 disk resulted in a large drop in intradiskal pressure.[20] They believed that this might be the mechanism responsible for prompt and marked pain relief in patients who were treated for radiculopathy secondary to degenerative disk protrusion and contained herniations. They suggested that the procedure would not be useful for patients with uncontained herniations or sequestered disk fragments outside the disk 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.

Percutaneous laser disk decompression (PLDD) with a 1.06 Nd:YAG laser has been approved by the US Food and Drug Administration (FDA). Generally, laser diskectomy is believed to be equivalent to other percutaneous diskectomy procedures, such as chemonucleolysis and automated percutaneous lumbar diskectomy (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 disk space through a spinal needle. Davis first used KTP laser for laser diskectomy and reported results essentially the same as those described by Ascher, Choy, and others.[22]

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 middle of the infrared range, a range that is absorbed well by water. It is fiberoptic. An effective dose of energy can be introduced into the disk 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 theoretical advantage of producing minimal amounts of heat in adjacent tissues.

With a pulse width of approximately 250 ms 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 disk 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 disk 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.[20]  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.

All percutaneous methods rely on the posterolateral approach to the disk as described by Day.[34]  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 disk space. Radiation exposure of the patient in a typical procedure is equivalent to that encountered in a five-view lumbosacral spine series.

Needle placement

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

Identify the disk space with the help of a C-arm fluoroscope. Disk 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 disk. In most patients, the entry points in the skin for treating either the L4-L5 or the L5-S1 disk space are at the level of the iliac crest (very close to each other). The rubbery texture of the anulus 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.

Even with proper precautions, the use of fluoroscopy during minimally invasive laser microdiskectomy exposes the operator to significantly higher levels of radiation than open microdiskectomy does.[35]

Ultrasonography (US) has also been used to guide needle placement in laser diskectomy for cervical disk herniation and pain.[8, 9]

Laser application

Once the needle has reached the anulus, advance it through the anulus 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, as illustrated by the following examples:

• Choy and Ascher reported using a neodymium (Nd):yttrium-aluminum-garnet (YAG) laser as 20 W of continuous energy delivered in 1-second pulses with 1-second pauses until 1000-1850 J was delivered ^[20]
• Davis used a potassium titanyl phosphate (KTP) laser as 10-15 W of continuous energy in 0.5-second pulses with 0.5-second pauses for a few minutes ^[22] ; 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 ^{[24, 25]}

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

In 1993, Choy's group tabulated the world experience with laser diskectomy up to that point, reporting two cases of diskitis.

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

In a study evaluating the effects of Ho:YAG laser ablation on postoperative low back pain and functional status after transforaminal endoscopic lumbar diskectomy, Li et al found that the only complication related to laser use was a burning sensation in the ipsilateral lower limb during the thermal procedure.[36]

A network meta-analysis by Wei et al compared the complications of the following eight surgical interventions for lumbar disk herniation[37] :

• Automated percutaneous lumbar diskectomy (APLD)
• Chemonucleolysis (CN)
• Microdiskectomy (MD)
• Microendoscopic diskectomy (MED)
• Open diskectomy (OD)
• Percutaneous endoscopic lumbar diskectomy (PELD)
• Percutaneous laser disk decompression (PLDD)
• Tubular diskectomy (TD)

In terms of complications, reoperation, operation time, and blood loss, the safest procedures for lumbar disk herniation were TD, PELD, PLDD, and MED.[37] PELD was associated with lower intraoperative complication rates, and PLDD as associated with lower postoperative complication rates.