Minimally Invasive Intradiscal Procedures for the Treatment of Discogenic Lower Back and Leg Pain

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Chapter 18 Minimally Invasive Intradiscal Procedures for the Treatment of Discogenic Lower Back and Leg Pain

Leonardo Kapural, Dawn A. Sparks

Chapter Overview

Chapter Synopsis: Diagnosis and treatment of lumbar discogenic pain remains a challenge. It may account for one third of patients with lower back pain. The mechanism of discogenic pain remains unclear, 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 the changes observed on imaging tests and the patient’s pain. Minimally invasive treatments such as intradiscal biacuplasty or intradiscal electrothermal therapy are likely better alternatives to the currently available surgical options. They are cost-effective and may cause fewer side effects. However, the value of most of these therapies has yet to be established. More basic science and clinical studies are needed 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 success of these procedures.

Percutaneous, minimally invasive intradiscal decompression procedures may be used to relieve pain from a herniated disc; several of these procedures are also considered. As in all interventional therapies for pain, attention to patient selection can vastly improve the odds of success.

Important Points:

Better selection criteria improve results of annuloplasty and disc decompression procedures for lower back and discogenic leg pain.

Patients with evidence of one or two levels of disc degeneration on MRI and one or two levels positive on provocative discography are desired candidates for annuloplasty.

Outcomes of the percutaneous disc decompression procedures were largely positive when used for the treatment of contained lumbar disc herniations. However, more randomized, prospective studies are needed to confirm their effectiveness.

Clinical Pearls:

Optimal patient positioning, which includes correction of lumbar lordosis using either a soft roll or pillow placed under the mid-abdomen, will facilitate needle placement for any of the intradiscal procedures.

During provocative discography, excessive amounts of local anesthetic injected deep, closer to the disc and foramina just prior to intradiscal needle placement, may decrease the ability of patient and operator to detect the nerve root impalement.

During intradiscal biacuplasty, although the temperature is set to 50° C on the radiofrequency generator, tissue temperature reaches about 70° C because of distal ionic heating. During this time, the patient should be awake and communicate with the physician.

Clinical Pitfalls:

Puncturing an intervertebral disc with a needle may potentially lead to progressive disc disruption. Greater progression of degenerative disc disease has been suggested in post-discography discs, and it seems to be worse in patients who had larger diameter needles inserted in their intervertebral discs.

Serious but rare complications include discitis, spinal abscesses, and vertebral osteomyelitis. Other neurological complications, such as cauda equina and nerve root damage, may be exclusively caused by misplacement of trocars, probes, or heating elements.

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.