Introduction

Diagnosis and treatment of lumbar discogenic pain remains difficult. It may account for one third of the patients with lower back pain. The mechanism of discogenic pain is still unclear, the clinical presentation can vary, and magnetic resonance imaging (MRI) may only suggest the presence of internal disc disruption. Provocative discography can provide unique information about the morphology of the disc and remains the only diagnostic test that can relate changes observed on imaging tests and the patient’s pain.

Minimal invasive treatments such as intradiscal biacuplasty and intradiscal electrothermal therapy (IDET) seem to be more efficacious, less invasive alternatives to currently available surgical options. They are cost-effective and may cause fewer side effects. However, the true therapeutic value of these therapies has yet to be established. More basic science and clinical studies are needed to give an insight on mechanisms of pain relief and to prove the clinical efficacy of such minimally invasive treatments. One thing that is clear, however, is that careful patient selection, based on the present data, significantly improves the successes of these procedures.

A handful of lumbar percutaneous disc decompression procedures are used as minimally invasive approaches to treat back and leg pain caused by contained disc herniation. The clinical outcomes have been generally favorable and complication rates low. However, more research is needed to identify the properly selected patients for a specific disc decompression technique.

Low back pain remains one of the biggest resource-consuming problems in medicine. At least 40% of the U.S. population at one time or another will use medical resources for the treatment of low back pain. Frequent sources of mechanical lower back pains are myofascial, discogenic, and facetogenic, from sacroiliac joint, compression fractures, and lumbar canal stenosis.^1,2

Low back pain is the one of the most common causes of lost work time in the United States,¹ and discogenic pain is one of the main causes of chronic lower back pain.³

It is the aim of this chapter to briefly review new and developing interventional and minimally invasive spinal treatments for discogenic low back (Figs. 18-1 to 18-3) and leg pain caused by contained disc herniation. Also, a simple algorithm is offered in Fig. 18-4 adopted and modified for discogenic back pain⁴ and should only be used as a rough intervention guide. This chapter highlights some interesting, novel interventional therapeutic approaches and is not intended to be a complete guide for the treatment of patients with discogenic lower back pain. A comprehensive approach with involvement of multiple specialties and adjunct therapies, such as physical therapy and occupational interventions, are frequently required to produce significant improvement in functional capacity and pain scores of patients with chronic lower back pain.

Fig. 18-1 Figs. 18-1 to 18-3 show fluoroscopic views of the final electrode positions during three different intervertebral disc heating procedures used for the treatment of discogenic pain head to head with schematic drawings of the ideal electrode placement. All three fluoroscopic views are anterior-posterior and the schematic drawings are illustrated transverse cuts through the targeted disc.

DiscTRODE (ValleyLab, Boulder, CO) A, DiscTRODE electrode properly positioned across the posterior annulus. A second probe visible on the right side is a temperature probe. B, Schematic drawing shows proper position of the radiofrequency electrode and temperature probe within the posterior annulus.

Fig. 18-2 Intradiscal electrothermal therapy (IDET) resistive coil is shown within the intervertebral disc. A, Anteroposterior fluoroscopic view of the properly positioned IDET coil. B, Schematic of the IDET coil proper positioning at interface between the annulus and nucleus. Note a limited temperature spread around the positioned coil.

Fig. 18-3 Bipolar intradiscal biacuplasty probes within the intervertebral disc. A, Anteroposterior fluoroscopic view of two biacuplasty probes within the intervertebral disc and away from vertebral endplates. B, Schematic transaction through the lumbar spine at the level of the intervertebral disc. Shown are two cooled electrodes for biacuplasty and their approximated positioning within posterior annulus of the lumbar disc. Using such electrodes, appropriate heat distribution is achieved across the posterior annulus without causing injury to posterior neural elements.

Fig. 18-4 A proposed simplified algorithm for the treatment of discogenic pain. After provocative or analgesic discography, minimally invasive options are those of annuloplasty or intradiscal injections. DMSO, dimethylsulfoxide; IDD, intervertebral disc disease; IDET, intradiscal electrothermal therapy; RF, radiofrequency.

Discogenic Lower Back Pain

When evaluating patients with the main complaint of long-lasting low back pain, with or without leg pain, it is necessary to investigate the pain generator causing debilitation. More typical features of discogenic source of pain include unrelenting nociceptive low back discomfort or groin or leg pain that worsens with axial loading that improves with recumbency. These signs and reported symptoms alone are usually inadequate to confirm an accurate diagnosis.^1–4 Although MRIs are helpful in visualizing such pathology as disc degeneration, desiccation, high intensity zones, and loss of disc height, these changes frequently correlate poorly with clinical findings and the presence of chronic pain, leaving open critical questions of causality.^1–4 Many practitioners use provocative or analgesic diagnostic discography as a way to substantiate their clinical diagnosis of discogenic pain. Provocative or analgesic discography is the only available method to relate anatomical abnormalities seen on MRIs of the lumbar spine with clinically observed lower back pain. However, the predictive value of this test is repeatedly questioned, mainly as a consequence of potentially high false-positive rates.^5–7

After provisional diagnosis of discogenic pain is introduced, an effective treatment is desired. Several commonly used minimally invasive intradiscal therapies involve careful heating of the annulus fibrosus (so-called annuloplasty procedures) (Fig. 18-4). Historically, such therapeutic modalities have been used regardless of the unclear relationship between positive therapeutic effects and absence of the histological changes expected within the annulus of the disc after heat is used.^8–12 Currently, denervation of the annulus by heat destruction of the nociceptors is a plausible mechanism of pain relief. There is no evidence that collagen fibers in the annulus are significantly affected by denaturation and coalescence, possibly suggesting that the collagen alteration is an additional therapeutic mechanism for pain relief.^9–12 The minimally invasive approach, low cost, and relative simplicity of these procedures are the key advantages compared with surgical procedures such as lumbar fusion and disc replacement. IDET (Smith and Nephews, London, UK), DiscTRODE (Valleylab, Boulder, CO), and intradiscal biacuplasty (Baylis Medical, Montreal, Canada) (Figs. 18-1 to 18-3) are several annuloplasty methods using heat to treat discogenic pain.

Mechanisms of Pain Relief by Annuloplasty

Dehydration of the intervertebral disc and loss of nuclear material with increasing age are associated with disc degeneration. Consequent delamination and tearing of the lamellar layers are just physical changes that can be associated with biochemical and cellular changes within the disc. Inside the degenerating disc, production of inflammatory cytokines, including tumor necrosis factor-α (TNF-α), nitric oxide, and matrix metalloproteinases are greatly altered.^13,14 Neural elements that are normally limited to the outer third of the annulus penetrate farther into the degenerated disc along the vasculature and fissures.^15–18 Immunohistochemical studies have shown that such nerves in growth is of nociceptive origin (C- and A-δ fibers) and likely responsible for transmitting pain responses.^14,17 Elimination of these nociceptors may disrupt the transmission of pain signals.

Thermal annular procedures were developed in an effort to provide minimally invasive delivery of thermal energy to the affected disc via a resistive heating coil (IDET) or an RF catheter (biacuplasty, Kimberly Clark, Atlanta, GA; DiscTRODE) to denervate nociceptive fibers and coagulate collagenous tissues in the annulus. However, scientific evidence to support either mechanism of action is lacking.

During the application of RF, alternating flow of electrical current causes ions in the tissue to move back and forth. This alternating movement by the ions causes molecular vibration within the tissue and results in frictional heating.^19,20 This effect is called ionic heating, and it can lead to thermal injury of the cells when tissue temperature reaches greater than 42° C.²¹ The extent of cellular damage usually depends on the amount of temperature and duration of heating.²² Increase in tissue temperature is a function of current density, or the amount of current per unit area. Current density is greatest at the proximity of the electrode and decreases with increasing distance from the electrode. However, by increasing the power output, current density around the electrode is increased, and thus the lesion size produced by ionic heating is limited by the current density.

One method of increasing lesion size or volume is by cooling the RF electrode internally. This technique was initially developed for tumor and cardiac ablation^23–25 and is currently used in intradiscal biacuplasty procedure.^26–28 Cooled RF probes have hollow lumens that extend to the tip of the electrode. The cooling fluid circulates in a closed loop through the hollow lumens to the tip of the electrode and back to a pump. The coolant acts as a heat sink that removes heat from the tissue adjacent to the electrode. Consequently, larger lesion volumes can be produced by increasing power deposition and the duration at which current is delivered without causing tissue charring around the electrode.²³ A larger lesion volume can be produced by using two internally cooled RF electrodes in a bipolar arrangement at the lower temperature.

Intradiscal Electrothermal Therapy

IDET technology (Figs. 18-2 and 18-4) relies on elongated resistive coil of very small diameter to deliver surrounding heat over the limited area of the posterior annulus. Possible mechanisms of pain relief were discussed above. The only difference between the IDET and other disc annuloplasty procedures is that the temperatures attained during the IDET are very high just around the electrode itself, and they dissipate relatively quickly at 2 to 4 mm radius away from the coil. The IDET procedure requires from the proceduralist a relatively long learning curve, and although it seems relatively easy to position resistive coil within the posterior annulus of the disc, multiple attempts may be required or it may be necessary to place another coil from the opposite side of the posterolateral disc to achieve optimal position within the interface between the annulus and nucleus (Fig. 18-2). This may contribute to further damage of the intervertebral disc, and sometimes placement of the tip of the coil within the posterior annular fissure may extend too close to the posterior edge of the disc. Indications for IDET include persistent discogenic low back pain despite comprehensive conservative treatments, including physical therapy, a directed home exercise program, and fluoroscopically guided epidural corticosteroid injections. The Saal brothers, inventors of the IDET catheter,^29–31 used initially some additional criteria for the selection of patients, which include those with normal neurological examination results, negative results on straight-leg raise test, absence of any inflammatory arthritic or nonspinal condition that may impersonate lumbar pain, and the absence of prior surgery at the symptomatic intervertebral disc level.^29–31 Provocative discography should replicate the concordant pain at low disc pressurization at up to three intervertebral disc levels. The above selection criteria disparities used in subsequent studies evaluating the effectiveness of IDET are thought to account for divergence seen in clinical results (Table 18-1).^29–43

The IDET results seem to improve if additional patient selection criteria are used.^33,41 Multilevel disc degeneration in patients with discogenic pain was an important predictor of treatment failure compared with a group of patients with one or two degenerated discs as shown on the MRI. Unfortunately, single disc level disease is less frequent, and the majority of the patients present with discogenic pain and multilevel degeneration present on MRI.⁴¹ Overweight patients⁴⁴ and patients receiving workers’ compensation benefits^40,45 represent additional patient subsets that have a low probability of achieving desired results from IDET.

Other Annuloplasty and Nucleoplasty Procedures

IDET is not the only minimally invasive annuloplasty procedure (Fig. 18-4). The DiscTRODE is a radiofrequency (RF) method in which heat is applied to the posterior annulus. This treatment is generally termed percutaneous intradiscal RF thermocoagulation.^46,47 Kvarstein et al⁴⁶ used appropriate inclusion criteria, which listed disc height reduction less than 30% and disc protrusion of less than 4 mm, as well as positive one-level pain provocation discography. A disappointing performance resulted because patients reported only modest or no improvements in pain scores and functional capacity.^46,47 Furthermore, the mean reduction of Oswestry Disability Index scores did not reach statistical significance when compared with baseline.⁴⁶ This technology proved to be unsuccessful in improving functional capacity and visual analog score (VAS) versus IDET during another study in which strict patient selection criteria were used.⁴⁷

Intradiscal Biacuplasty

Intradiscal biacuplasty is the latest minimally invasive posterior annulus heating technique (Fig. 18-4). This technology uses bipolar cooled RF electrodes called transdiscal electrodes (Kimberly Clark, Atlanta, GA). Reviewing the pain scores and functional capacity improvement ratings in patients with discogenic pain, biacuplasty is comparable or better than other minimally invasive annuloplasty methods.^48–52 Internally cooling electrodes provides for even heating over the wider area of the posterior annulus (Fig. 18-3, B).^26–28

The procedure itself is fluoroscopy guided with the patient lying in the prone position. Electrodes are inserted bilaterally in the posterior annulus of the intervertebral disc as shown in Fig. 18-3, B. The generator controls delivery of RF energy by monitoring the temperature measured by a thermocoupler near the tip of the electrode. The temperature increases gradually over a period of 7 to 8 minutes to 50° C with final heating for another 7 minutes. During this time, the patient should be awake and communicating with the physician to decrease the probability of neurological injury.

Currently, clinical biacuplasty data from two case series of eight and 15 patients are available for critical review. Both studies demonstrated significant pain relief after the disc biacuplasty procedure at 3, 6, and 12 months.^50–52 European case series suggested improvement in pain scores greater than 50% at 3 months with general good patient satisfaction. A U.S. pilot study involving 15 patients described reduction in the median VAS pain score from 7 to 3 cm at 6 and 12 months of follow-up, respectively; improvement in Oswestry Disability Index from 23.3 to 16.5 points; and significant increase in the Short Form 36 Physical Functioning scores (Table 18-1).^50,52 The sham, prospective randomized study is currently being conducted, and data may be available as soon as mid-2011. Intradiscal biacuplasty may offer several advantages over the earlier techniques. There is negligible disruption to the native tissue architecture, and thus the biomechanics of the spine is likely unchanged, and the relative ease of electrode placement abolishes the need to thread a long-heating catheter (e.g., IDET).

Complications of Annuloplasty Procedures

The incidence of various complications related to annuloplasty could be as high as 10%.^53,54 If the RF electrode or resistive coil is positioned in the close proximity of the neural elements, high temperatures delivered may cause nerve injury possibly manifested as a radicular pain or transient palsy. Transient radiculopathy with the resolution in less than 6 weeks and, rarely, motor deficit with prominent foot drop were previously reported after the IDET procedure.⁵⁴

Catheter breakage,⁵⁴ vertebral osteonecrosis,⁵⁵ and cauda equina⁵⁶ syndrome all have been reported as rare complications of the IDET procedure. The duration of back pain, obesity, smoking, history of leg pain, and diabetes may not be associated with the higher incidence of complications.⁵³ Compared with nucleoplasty (disc decompressive procedure) alone, the frequency of the complications was not higher in patients who received IDET combined with nucleoplasty procedure.⁵⁷

Discitis is rare complication of any intradiscal procedure.^58–62 Appropriate timing of intravenous antibiotic seems to be effective in preventing discitis after provocative discography and any minimally invasive intradiscal procedure.^58–62 The incidence of disc herniation after annuloplasty could be as high as 0.3%, and it was speculated to be caused by thermally mediated loss of tensile strength of the collagen fibers.⁶³ At least one case report documented disc herniation with clear increase in the size of disc protrusion after IDET procedure.^53,54

Mechanisms of Disc Herniation and Pain Relief from Percutaneous Disc Decompression

A herniated disc can cause radicular pain or referred pain in the extremity involved. Whereas radicular pain follows appropriate dermatomal area, referred pain can be elsewhere in the extremity. With an internal disc disruption, nucleus of the disc has altered weight-bearing loads and could cause a change in shape or complete disruption of the annular fibers, which in turn may produce contained disc herniation or extrusion of the disc. Nerve root compression can result from either of those two mechanical events (Fig. 18-5).⁶⁴

Fig. 18-5 Two basic types of intervertebral disc herniation: protrusion is characterized by the fact that the greatest distance, in any plane, between the edges of disc material beyond the disc space is less than the distance between the edges of the disc base in the same plane (A). Extrusion is present if any one distance between the edges of the disc material beyond the disc space is greater than the distance between the edges of the base in the same plane (B).

Occasionally, radicular or referred pain in the extremity can be significant with or without significant mechanical pathology as described above. This is because various inflammatory mediators are present in the intravertebral disc, including phospholipase A₂, prostaglandin E₂, interleukin-1α, interleukin-1β, interleukin-6, TNF-α, and nitric oxide.⁶⁵ Exposure of the neural structures to the nuclear material, therefore, may cause chemical painful radiculitis. MRI remains the modality of choice in diagnosing lumbar disc herniations. Intervertebral disc can be well described, as well as the surrounding nerves and bony structures.

Assumption that protruded but contained disc herniation may exert pressure on a nerve root and possibly dorsal root ganglion provided the basis for intradiscal percutaneous disc decompression. Simply, removal of the small amount of the nuclear material from the disc with contained herniation and with absent transannular fissure, or RF within the nucleus, can provide rather precipitous decrease in intradiscal pressure and partial retraction of the herniation away from the nerve. Such a decrease in intradiscal pressure is less likely if the elasticity of the disc is not preserved and the outer annulus is damaged containing high-grade (Dallas 5) fissure.

Therefore, the ideal candidate for percutaneous, minimally invasive intradiscal disc decompression is someone with maintained height of the disc (>50%), radicular pain correlating with imaging findings, leg pain more than back pain, and clearly contained disc herniation. Those who are not candidates for such procedures are patients with extruded disc herniation, progressive neurological motor deficits, cauda equina syndrome, and overly calcified disc herniations. Also, the presence of any spinal stenosis needs to be closely evaluated.

Complications of Percutaneous Decompressive Procedures

At least one study found a statistically significant higher prevalence of leg pain and increased weakness in patients who received nucleoplasty compared with those receiving just conservative treatment. However, the most common side effect was soreness at the site of the catheter insertion.⁷⁶ Although side effects with the Dekompressor are rare, so is the volume of the patients reported receiving this procedure (at least when compared with the number of patients in studies on nucleoplasty). The probe break within the disc nucleus has been described where the tip of the probe had to be removed surgically.⁷⁷

Conclusion

Discogenic pain continues to be a debilitating condition that represents a major source of chronic low back pain. At this time, evidence for the overall effectiveness of minimally invasive intradiscal procedures for the treatment of discogenic pain is deficient. However, continued studies provide evidence that the RF annuloplasties can be beneficial to selected subpopulation of patients. DiscTRODE annuloplasty and conventional nuclear RF seem to be ineffective in improving functional capacity in patients with discogenic back pain. IDET and intradiscal biacuplasty types of annuloplasty may produce positive therapeutic effect in highly selected patient groups. More work is ahead of us to clearly determine if certain disc decompression procedures can provide long-term pain relief during randomized, sham-controlled studies.