Equipment
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.
Patient Preparation
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.
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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.
