Microscopic discectomy has been a gold standard of treatment in patients with herniated lumbar disc diseases resulting in radiculopathy. It needs to dissect muscles and make a bony work including facetectomy which may cause postoperative undesirable results such as postoperative back pain, wound infection and instability to lumbar spine^13,15,26).

Minimally invasive procedures, such as chemonucleolysis, nucleoplasty, percutaneous laser disc decompression (PLDD), intradiscal electrothermal therapy (IDET), decompressor, etc., have been recently introduced and performed to minimize procedure related muscle and ligament injury^{2,8,9,11,17,19,22,27,29)}. Their clinical outcomes and benefits did not reach the outcomes of microscopic discectomy and might cause complications which were not easy to deal³²⁾. Radiofrequency treatment is inaccurate and difficult to point out the lesioning area which can be related to high recurrence rate²⁸⁾. Laser treatment modality also has unsatisfactory clinical result and relapse rate because enough energy can not transfer to lesion area because of their conductivity and directionality^4,27).

Percutaneous plasma disc coagulation therapy (PDCT) was invented to correct these weak points. PDCT uses laser source called plasma light that the rays generated in the module are concentrated at the end of dome-shaped fiber and do not travel linearly. PDCT can provide sufficient energy and transfer it to the lesion area without damage to surrounding soft and neural tissues.

This is a prospective study of clinical outcomes of PDCT in patients with herniated lumbar disc disease (HLD) to evaluate the safety and efficacy in its clinical application and usefulness as a reliable alternative to microscopic discectomy.

Forty-six patients were enrolled in this study. This study consisted of 29 men and 17 women whose mean age was 37.2 years (range : 16-59). Symptom duration ranged from 6 weeks to 15 weeks (mean 8.5 weeks). The mean procedure time was 33 minutes. All patients were discharged right after the procedure. All the patients were periodically followed up in the outpatient clinic after the procedure. Median follow-up period was 21 months (range 6 to 36 months). There was no complication related to the procedure during the period.

The mean pre-PDCT VAS score was 7.47 (range 0 to 10). VAS score was decreased down to 2.37 right after the procedure and well maintained until final follow-up. The mean post-PDCT VAS score was 1.5 at final follow-up. This difference between pre-PDCT and post-PDCT VAS score was statistically significant (p<0.001) by paired t-test (Fig. 2).

The results in MacNab's criteria were excellent in 26 patients, good in 15 patients, fair in 3 patients and poor in 2 patients (Fig. 3). Forty-one patients (89.1%) showed excellent and good results in MacNab's criteria right after the procedure and well maintained until final follow-up. Three patients with fair outcome had 50% reduction of radiculopathy after procedure and had been taking pain medications. Two patients with poor outcome showed no improvement after the procedure and needed to convert to open discectomy.

We checked intervertebral disc degeneration of index level using Pfirrmann's grading system. Pfirrmann's grades were 14 patients in grade 3 and 32 patients in grade 4 before the procedure. MRI were done at 1 month after the procedure in all patients to check post-PDCT change. Fourteen patients showed decreased severity of disc herniation at the index level after PDCT (Fig. 4). The degree of disc herniation had no change in 32 patients. There was one case of spondylodiscitis which was well treated with antibiotics.

In general, patients with HLD can be managed with conservative treatments. Decompression surgery should be considered for patients who experience neurologic deterioration during the period of conservative treatment. Microdiscectomy has been widely performed as a gold standard treatment²⁵⁾. Microdiscectomy can be performed in any type of disc herniation which is extruded or protruded. Microdiscectomy provides good clinical outcome in patient with HLD. However, the complication rate of lumbar discectomy has been reported as 2-14%^18,31), and injury of normal spinal ligament and muscle structures at the index level is inevitable. In addition, excessive removal of the nucleus may induce collapsed disc space^25), which may cause undesirable results sometimes. Especially, There is sometimes a possibility that microcxdiscectomy can be an overtreatment for protruded and not ruptured HLD with moderate or severe degree. Partial removal of nucleus with minimal injury of surrounding normal ligament and muscle structures has been shown to decompress herniated disc, to relieve pressure on nerve roots and to maintain disc height²⁰⁾. Lumbar transforaminal epidural steroid injection has showed the short-term relief of radicular pain but long-term relief in a few studies³⁾. Moreover one study showed that patients treated with PDD had significantly reduced pain and better quality of life scores than those treated using repeated transforaminal epidural steroid injection¹⁴⁾.

Minimally invasive procedures have been developed to minimize the occurrence of morbidity related to open surgery. Advantages of all minimally invasive procedures are small incision, less muscle and ligament injury, no need for general anesthesia, and short hospital stay. However, each procedure has limitations and weak points such as inadequate decompression, rigid cannula, and difficulty in usage. Also, there are only few procedures which are available for the patients with HLD to alleviate radiculopathy^8,11). PDD for symptomatic contained cervical disc herniation showed good results more than conservative treatments⁵⁾. In patients with HLD, there is evidence that early intervention including surgery provides for a better short-term relief of radicular pain as compared to prolonged conservative care^16), and PDCT outcomes showed same tendency as early surgery respect to improvement of VAS pain score. Moreover, minimally invasive procedures can be a good treatment modality in patients who are not available for open surgery because of their poor general conditions or who have an antipathy to open surgery.

PDCT can be a one of minimally invasive treatment option for HLD refractory to conservative treatment. Clinical improvement in minimally invasive treatments using laser energy is based upon laser-induced evaporation of water within the disc; this results in a very slight decrease in disc size due to water loss. Because the intervertebral disc is essentially a closed hydraulic system, a small decrease in volume leads to a significantly larger decrease of intradiscal pressure; in vitro experiments confirm this^{10,11,27,29,32)}. Laser energy is applied through the fiber, resulting in vaporization of nucleus pulposus contents^27,32). Short term decrease in pressure is due to evaporation of water content within the nucleus pulposus; long term effects are thought to be due to protein denaturation, which limits the ability of the nucleus to reabsorb additional water and increase a tension of the disc tissue^4,7,27). This mechanism hypothetically results in a more even distribution of weight across the intervertebral disc^7,27).

There is no clear consensus regarding the most effective and safest laser or the ideal wavelength that should be used. Most lasers provide 1200 J of energy in a pulsatile fashion. High energy laser carries the risk of tissue burns, but low energy lasers may be insufficient to induce adequate vaporization. Lasers near the infrared region currently used in PLDD include neodymium : yttrium-aluminum-garnet laser (Nd : YAG), holmium : yttrium-aluminum-garnet laser (Ho : YAG), and diode laser. Lasers with visible green radiation include double-frequency Nd : YAG laser and potassium-titanyl-phosphate laser. Most lasers use a 3 mm outer cannula combined with a fiberoptic viewing cable²⁹⁾. PLDD uses directional laser beam energy that can be accumulated and penetrate anterior structure of disc which can cause injury of anterior longitudinal ligament, bowels, nerve roots, and end-plates, but cannot provide sufficient energy to disc itself.

PDCT was designed to correct and improve this directional property of laser in 2006. It uses plasma laser. The major difference of the plasma light from conventional laser is that the rays generated in the module are concentrated at the end of the fiber and do not travel linearly forward (Fig. 5). According to our experimental study for the temperature measurement inside the disc using 8-channel automatic temperature meter, the tissues 3 mm away from the fiber tip which radiates plasma light whose directionality was 5% or less remained at the temperature not higher than 40℃. Therefore, a 6 mm diameter fire-sphere is created around fiber tip which means coagulation area or lesioning area (Fig. 1). The plasma light without directionality creates fire-sphere and provides sufficient effect with the least output power because all the energy is concentrated at the tip of the fiber. Even though energy output is excessive, the surrounding tissues including nerve root are safe. Three lesions which are made by fire-sphere are communicated each other and the sufficient decompression of intradiscal volume can be achieved. Chen et al.⁶⁾ reported that the change in intradiscal pressure after nucleoplasty was negligible in older and degenerative discs, whereas intradiscal pressure was markedly reduced in younger and healthy discs in a cadaver study.

For avoiding the thermal damage of end plate, preservation of disc height and water content of nucleus pulposus may be very important factor in PDCT because it was easy to position the fiber tip in the middle of disc space in patients with well-maintained height of disc. In order to check these two factors, we have used Pfirrmann's grading system. We selected the patients with grade 3 and grade 4 disc degeneration. HLD with Pfirrmann's grade 1 and grade 2 disc degeneration is rare. Pfirrmann's grade 5 is not feasible for PDCT.

Success rates of previous PLDD using conventional laser have been reported vary from 56% to 87% and complications including procedure-related intraoperative neural injury have been described from 2.6% to 8%³⁰⁾. Sporadic cases of thermal injury to the cauda equina, disc herniation, and osteonecrosis of the vertebral endplates following IDET and nucleoplasty have been reported^1,12,21). Transient nerve injury appears to be the most common complication after these procedures. In this study, there was one case of spondylodiscitis related to PDCT during the follow-up period. Spondylodiscitis is a well-recognized complication of diagnostic discography, with an overall incidence of 1% to 4%²³⁾. Complication rate of PDCT may be similar to that of discogram.

The results of this study indicate that PDCT is a safe and effective percutaneous treatment for the HLD patients with symptomatic radiculopathy between unsuccessful conservative therapy and other operative methods. In addition, PDCT is useful for the selective patient with mild to moderate disc degeneration. Further studies on PDCT in comparison with other previously known procedures are needed. Strict control of inclusion criteria could prevent misuse of PDCT and bring about long-term successful results.