Discussion

Data provided by studies on the natural history of lumbar disc herniation and radiculopathy indicate that large and migrated herniations tend to decrease in volume to a greater extent than protrusions or small contained herniations which have less tendency to spontaneous regression. There are several treatment approaches for patients with nerve root compression due to a herniated disc.7 8

The success of open surgery for lumbosacral disc herniation is approximately 93–98% on short term evaluation but 5–7 years later it significantly decreases (75–80%). The so-called failed back surgery syndrome is caused by scar tissue or recurring hernia.9 10

Over the past decades, there has been increased interest in developing minimally invasive techniques for the treatment of disc herniations and chronic discogenic pain. This trend may be related to concerns relative to surgical trauma, potential complications of operative interventions and questionable efficacy in relieving discogenic pain.11–13 This has led to the emergence of different minimally invasive techniques such as percutaneous laser discectomy, intradiscal electrothermic therapy, percutaneous endoscopic discectomy and percutaneous nucleoplasty. Because nucleoplasty uses coblation technology with a non-heat driven ablation process, it produces minimal damage, minimal thermal penetration and localized effect. Chen et al have reported that there was no evidence of direct mechanical or thermal damage to the surrounding tissues in an experimental study using coblation of nucleus pulposus.4 5

The main goal of percutaneous procedures, other than effective treatment, is safety. While open surgery is effective, it has well known disadvantages, including epidural scarring, damage to bone, denervation of paraspinal muscles with consequent lumbar instability, long postoperative inactivity and the frequent ‘failed back surgery syndrome’.14

The concept of nucleoplasty is based on the principle that in an enclosed space a reduction in volume, even partial, confers a much greater reduction in pressure; this leads to decreased pressure on the nerve root and relief of sciatica, even without a radiographically evident reduction in total disc volume. After weeks or months, the partial vacuum causes the protruded portion of the nucleus pulposus (or other disc material) to move away from the nerve root back towards the centre of the disc, pushed by partially intact fibers and ligaments of the outer annulus; this process, along with regeneration of a more fibrous nucleus pulposus, favors restoration of the inner fibers of the annulus and decreases the tendency to further protrusion towards the spinal canal.15 16 The success of the procedure depends to a great extent on selecting lesions to treat: the protruding nucleus pulposus must be at least partially contained by the external fibers of the disc, without a large extrusion or migrated or sequestrated fragments. Such contained lesions are often circumferential bulges or protrusions which appear broad on axial MRI or CT.17 18 As MRI and CT do not usually enable distinction of a contained from an uncontained prolapse, in doubtful cases discography may help in assessing annular tears and extruded lesions. Discography may also show the size of the ‘neck’ connecting the protruded part of the disc with the central nucleus pulposus: the wider the connection, the more likely efficient transmission of pressure towards the centre of the disc.19 20

Nucleoplasty uses coblation (controlled ablation) technology with RF energy, providing controlled and highly localized ablation, resulting in rapid tissue removal with preservation of adjacent tissues. The proposed suggestion in this technique is that a small change in volume produces a large change in pressure; thus pain reduction may also arise from reduced intradiscal pressure. The only component of pain being treated is the leg pain caused by radicular compression.21 22

This technique has minimized the invasive nature of surgery and helped avoid or decrease complications such as fibrosis and infection linked to open surgery. The advantages of nucleoplasty are the percutaneous approach, outpatient procedure, local anesthesia or monitored anesthesia care and very short procedure time. Hence the patient can return to normal daily activities in just a few days.23–25

Our experience with nucleoplasty has been favorable, as reflected in our patients' VAS scores, analgesic consumption and ODI. The mean VAS score decreased from 8.2 to 1.1, 2.6, 1.7, 1.5 and 1.3 at the 2 week, 1 month, 3 month, 6 month and 1 year evaluations, respectively (p=0.001). ODI decreased from 62.2 preoperatively to 26.6, 13.6, 9.6 and 9.6 at the 1 month, 3 month, 6 month and 1 year follow-ups, respectively (p=0.001). Likewise, analgesic consumption was reduced or stopped in 64% of patients 2 weeks postoperatively and in 78%, 82%, 90% and 90% at 1 month, 3 months, 6 months and 1 year, respectively.

There were four patients who had persistent pain and underwent conventional microdiscectomy. There were no intraoperative complications. Five cases had postoperative discitis which cleared completely clinically and radiologically within 2 months without sequelae, and a good result at 6 months in four of them. One patient had to undergo operative instrumental fusion at the affected level.

From our experience, it was noted that the incidence of infection increases when the number of performed channels is more than six in a single level. It also increases when performing ablation near the endplates. The cases which developed discitis were among those done early in the study, denoting the significance of the surgeon's learning curve. Some authors believe that a decrease in disc height of more than 50% is a contraindication as the wand is too close to the endplates.20 26

Based on initial data, nucleoplasty appears to be a promising treatment for contained disc herniation with radiculopathy. Clinical studies using nucleoplasty have reported varying success, depending on the inclusion criteria. The results in these clinical reports are total resolution of leg pain in 70% of cases and patient satisfaction in approximately 80% after 6 months.3 11 27 28

Some authors have reported similar good results using the nucleoplasty technique in their patients. Sharps and Isaac treated 65 patients with low back and leg pain and reported that the procedure resulted in an overall 80% success rate.2 Singh et al reported on 67 patients with a similar etiology; the percentage of patients reporting improvement was 79% at 6 months.3 Our patients had improvement of, on average, 6.7 points at 6 months and 6.9 points at 1 year, in terms of VAS scores, with substantial reduction of analgesic consumption at the latest follow-up. Comparing the results of this study with previous studies, it is evident that strict inclusion criteria provided better results in all improvement parameters, not overall success rate. Despite technically successful procedures, four patients underwent microdiscectomy because of intractable pain. This failure rate is similar to those of other studies.

Cohen et al reported on seven patients who underwent nucleoplasty where only one patient reported >50% reduction in pain score. The authors mentioned that half of their patients had annular tears and that they had not formally measured the degree of herniation, and some of their patients had herniations extending more than 5 mm. They suggested that nucleoplasty should be done only in patients with small contained disc herniations and annular integrity.24 Indeed, our encouraging results are most probably due to strict patient selection criteria, including those mentioned by Cohen et al; patients with large or extruded disc herniations, with disc height <50% and with evident annular disintegration will not benefit from nucleoplasty and should not be treated with this technique.

This prospective study demonstrated a statistically significant improvement in VAS pain scores and functional status and a reduction in medication intake in a group of patients with radicular pain who failed conservative treatment. Moreover, we did not offer this procedure to patients with a history of open disc surgery at suspected levels, as these patients are considered poor surgical candidates and have historically been a challenging population to treat. The results of this study are similar to those reported by Alo et al in 2004. In his study, Alo used a Dekompressor 1.5 mm percutaneous discectomy probe to mechanically debulk the disc material, allowing for a reduction in intradiscal pressure. Although Alo et al used a different technology, they achieved the same goal as we did in our study using nucleoplasty.29 The mechanisms underlying the successes of both procedures are postulated to be related to disc remodeling, which results in volume reduction with a subsequent decrease in intradiscal pressure and a concomitant reduction in release of inflammatory mediators.30–32