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12 Articles in Volume 12, Issue #5
A-Delta Pain Fiber Nerve Conduction Study Benefits Patients With Spinal Pain
Chronic Pain Management of the Noncompliant Patient
Clinical Applications of Radiofrequency Lesioning for Back and Neck Pain
Current Understanding and Management Of Medication-overuse Headache
Fibromyalgia: An Overview of Etiology and Non-pharmaceutical Treatment Options
June 2012 Pain Research Updates
Junk The Term Narcotics—Call Them Opioids
Managing Adverse Drug Effects in Pain: Focus on Muscle Relaxants
Music Therapy for Pain Management
Perioperative Pain Management in the Opioid-tolerant Elderly Patient: Case Challenge
Practical Tips in the Treatment Of Osteoarthritis of the Knee
Sudden, Unexpected Death in Chronic Pain Patients

Clinical Applications of Radiofrequency Lesioning for Back and Neck Pain

Continuous and pulsed radiofrequency lesioning can be effective in treating cervical, lumbar, and sacroiliac spinal pain.

Radiofrequency (RF) neuroablation, or lesioning, is a target-specific, safe, and effective treatment used to prevent nociceptive signals from reaching the central nervous system, thereby providing long-lasting pain relief. The procedure has been used successfully as a treatment for a variety of conditions including facet-mediated pain, radiculopathies, and sacroiliac (SI) joint dysfunction. This article reviews the difference between continuous and pulsed RF lesioning, and explores the clinical evidence for their use in the treatment of back and neck pain.

What Is RF Lesioning?
The widespread use of RF current for the treatment of spinal pain began in 1980, when Sluijter and Metha introduced a 22-gauge cannula through which a thermocouple probe could be inserted.1,2 The smaller electrode meant that the procedure could be performed percutaneously on a conscious patient without causing much discomfort. This development was important because it allowed the patient to be monitored for complications. Shortly after the introduction of the Sluijter-Metha cannula (SMK) needle, a series of studies was published on the use of RF current for the treatment of facet joint pain, discogenic pain, SI joint pain, and sympathetically mediated pain.2-11 RF lesioning has since supplanted the use of other neurolytics (particularly chemical neurolytics), largely because of the highly focused nature of RF lesions.

Continuous vs Pulsed RF Lesioning
Radiofrequency energy can be applied either continuously or as pulsed currents. Continuous RF current generates heat in the tissue surrounding the electrode. On a pathologic level, the heat results in wallerian degeneration of the targeted nerves,12-15 while on a physiologic level, the current destroys all fiber types within a nerve and is not selective for any one fiber type.16-18 Coagulation occurs in a small, distinct oval pattern around the active tip of the needle—extending a distance of about 1.6 needle widths. Little coagulation occurs distal to the tip.

Additionally, studies have shown the volume of the lesion increases in relation to increasing tissue temperature, the duration of coagulation, and the dimensions of the active tip. For example, the size of the lesion increases proportional to an increase of temperature until the tissue temperature reaches 90oC; after this point, there is a risk of charring the tissue, which may cause cavitation and possible sterile abscess formation. Likewise, as the time of lesioning is prolonged, the volume of coagulation increases. Maximal size is achieved at 90 seconds; and at 60 seconds, 94% of maximal size is obtained. Similarly, a greater coagulation occurs with larger gauge active tips. These studies support the conclusion that optimal coagulation occurs when the tissue is treated for 60 to 90 seconds at 90oC with an 18- to 20-gauge needle. The placement of the active tip of the needle should be parallel to the nerve to allow greatest coagulation to occur; additionally, as exact placement of the nerve may vary from patient to patient, multiple lesioning should be performed to account for varied anatomy.

In contrast to continuous RF, pulsed RF (PRF) lesioning does not depend on heat to provide the therapeutic effect; rather, it uses the electrical field produced by the alternating current. Studies have shown that this electrical field can produce similar palliative effects resulting from a continuous RF lesion; although, an exact reasoning as to what occurs to produce such an effect is not fully understood.1,2 During PRF, intervals of short bursts of current lasting 20 milliseconds followed by a quiet phase of 480 milliseconds produce an intense electrical field while keeping the tissue temperature below neurolytic levels. Because temperature during PRF lesioning will not cause coagulation, PRF lesioning can be applied to the dorsal root ganglion (DRG) of a nerve to treat radiculopathies. The greatest electrical field occurs distal to the active tip and is greatest when voltage and current are as high as possible without tissue temperature exceeding 42 to 45oC (neurolytic level). Therefore, needle placement should be perpendicular to the DRG.

Lumbar Medial Branch RF
RF lesioning is gaining acceptance as an effective treatment option for the management of facet joint pain when more conservative approaches fail to provide symptomatic relief. Patients with facet joint pain commonly present with a deep, aching sensation in the low back that radiates in a nondermatomal pattern to the buttocks, the posterior or anterior thigh above the knee, the groin, and the hip. These patients often report morning stiffness. Younger patients may report that the pain followed some type of trauma, but older patients report an insidious onset. Although the diagnosis is more common in patients older than 65 years, it cannot be made solely on the basis of history, physical examination, or laboratory studies—such as radiographs.1,16,19,20 However, certain clinical features have been found to predict a positive response to medial branch block. These include pain relieved by lying down and meeting four of the following six characteristics: age greater than 65 years and back pain not exacerbated by forward flexion, rising from flexion, hyperextension, extension and rotation, or coughing.1,16,19

Mechanical pain must be distinguished from radicular pain. Radicular pain travels in a narrow band in the affected extremity. The pain is typically described as shooting or lancing, rather than dull or aching. It has both a deep and superficial quality, in that the patient feels both a deep and cutaneous sensation in the affected extremity. This pain is more often felt below, rather than above, the knee.21 Among patients with a mechanical cause of pain, the severity of the lower extremity pain mirrors that of the back pain; it never occurs independent of back pain. When attempting to distinguish between these two causes of pain, it is helpful to quantify the percentage of pain in the back versus that in the lower extremity. Of the pain in the lower extremity, one must distinguish between the percentage of pain above the knee and that below it.

Upon physical examination, the patient may report focal tenderness over the facet joints, and extension or lateral side bending may increase the pain.16,22-26 Patients with only facet joint pain have a normal neurologic examination. Imaging studies may show a normal-looking facet joint, although some patients show degenerative changes of the discs and facet hypertrophy.3,16,25,26

The diagnosis is complicated by the lack of direct correlation between clinical findings and response to a medial branch block.19,20,27,28 The medial branch procedure involves placing a small amount (0.3 mL) of local anesthetic on the targeted nerves and quantifying the amount of pain relief reported by the patient.16,29 Diagnoses based on a single medial branch block are not considered valid because of the high false-positive response rate, which can be as high as 40%.16 The outcome of an RF procedure relies on the results of a properly performed series of two medial branch blocks. The procedure is indicated if the patient reports greater than 80% relief after each of two medial branch procedures, provided the pain is emanating from the facet joint alone. However, because a given patient may have more than one cause of back pain, some investigators have suggested that greater than 50% pain relief is an adequate criterion. Other investigators have suggested that complete pain relief in a distinct topographic area is adequate to constitute a positive response.16 The target specificity of the medial branch procedure was established by Dreyfuss et al, who showed that, with properly placed needles, injected contrast dye incorporated the medial branch nerves without spreading to the adjacent spinal nerve.30 The blocks were also shown to have both face validity and construct validity and are therefore predictive of a positive outcome for a properly performed RF procedure.

Efficacy of RF Lesioning
Bogduk et al wrote an excellent review on the lumbar medial branch neurotomy procedure.29 In that review, the investigators studied six randomized controlled trials and pointed out that to evaluate the outcome of any procedure, one must first assess whether the procedure was performed properly—that is, in a manner expected to produce the desired result. They further stated that, of the six randomized controlled trials performed to date, three should not be considered as evidence, based on improper patient selection (patients not selected based on positive response to two correctly performed medial branch blocks) or improper surgical technique (electrodes not correctly aligned parallel to nerve). Although the remaining three trials were suboptimal in terms of patient selection or proper anatomic technique, all showed positive results when compared with placebo. In addition, three descriptive studies were published that used proper patient selection and anatomic technique, and all three showed positive outcomes. These investigators believed that when these results were “pooled,” they presented strong evidence supporting efficacy of the procedure. Table 1 presents a summary the results of the best studies performed to date.

Callout: Differences Between Continuous and Pulsed RF Energy

Lumbar DRG Procedure
As noted earlier, the indication for PRF is neuropathic pain that is confined to the distribution of a known nerve.2,31-33 The specific indication for PRF treatment of the DRG is radicular pain or radiculopathy that is completely but temporarily relieved by transforaminal injection of local anesthetic performed on two separate occasions. The local anesthetic injections are performed diagnostically to identify the location of the origin of the pain and to confirm the nerve levels involved. The procedure has been used for both acute and chronic radicular pain and radiculopathy.32-42

Some investigators studied the efficacy of PRF lesioning of the DRG by targeting the lumbar, thoracic, or cervical spine. Most of these studies were prospective uncontrolled trials or retrospective studies, and one was a randomized controlled trial. Each of the four prospective uncontrolled trials concluded that PRF lesioning of the DRG was a safe and effective pain treatment, and each of the five retrospective studies reported similarly positive results. These data are summarized in Table 2.

Although the studies appear promising, none included a control group, and most reported only relatively short-term efficacy. To date, only one double-blind, randomized, placebo-controlled trial of PRF lesioning has been conducted, and that trial studied 23 patients with chronic cervicobrachial pain for 6 months.34 Patients underwent either PRF lesioning (n=11) or sham lesioning (n=12) at the C5-C7 nerve levels. At 3 months, significantly more patients in the treatment group (83%) than in the control group (33%) reported at least 50% improvement in global perceived effect, an effect that was also maintained at 6 months. Similarly, at 3 months, significantly more treatment-group patients (82%) than control-group patients (25%) reported at least a 20-point decrease in visual analog scale (VAS) score, although the effect was not maintained.

This study has been criticized because the recruitment challenges limited its statistical power; the two study groups were not comparable in terms of average age and baseline VAS scores, and the effect was not maintained at 6 months. Despite these shortcomings, this study is important because it is the first prospective controlled trial to show a treatment effect.Table: Radiofrequency of the Lumbar Medial Branch

Martin et al proposed that the efficacy of PRF lesioning of the DRG is directly related to the proximity of the RF electrode to the targeted neural structure and the amount of delivered current.43 These investigators recommended using a stimulation voltage between 0.1 and 0.3 volts to position the electrode properly. They also suggested that higher current delivery (150 to 200 mA) improves outcomes.

Considering the preponderance of the evidence, it appears that PRF does indeed have a clinical effect for the treatment of radicular pain. Further research is required to bolster the data presented here and to prove the long-term utility of the procedure.

Cervical Medial Branch RF
Neck pain is thought to result from tearing of the joint capsule, which allows microscopic movement of the joint surfaces and causes inflammation and pain.44 The two most commonly injured joints are the C2-C3 joint and the C5-C6 joint.45 Pain emanating from the C2-C3 facet joint commonly causes posterior occipital headaches. This pain is often described as a unilateral headache located at the base of the skull and sometimes radiating to the forehead. Pain in the C5-C6 facet joint often radiates to the inferior aspect of the trapezius muscle and scapular area.Table: Radiofrequency of the Dorsal Root Ganglia

The goals of RF neurotomy of the cervical medial branches are to reduce afferent nociceptive signals from the facet joints and to provide palliative relief. Because pain emanating from a specific facet joint is difficult to localize, treatment is usually performed on three medial branches or two facet joints.

Patients with facet joint pain commonly present with a deep, aching sensation in the neck, punctuated by sharp shooting sensations with certain types of movements. They may complain of increased pain with flexion, extension, rotation, or lateral side bending of the head. The pain is most often bilateral, exacerbated by movement, and relieved by rest. Younger patients may report a traumatic event causing a whiplash injury, but older patients more often report an insidious onset of the pain. The pain refers in a nondermatomal pattern into the occipital area or forehead, shoulder, and upper back. Physical examination may reveal focal tenderness or spasm, with no sensory or motor deficits.42,43

Cervical facet joint pain cannot be definitively diagnosed by history, physical examination, or the results of imaging studies, nor is a single medial branch block considered to be a valid method of confirming the diagnosis.23,46-48Dwyer et al49,50 mapped pain referral patterns by injecting saline solution into the joints of normal volunteers. The researchers then used these data to predict the segmental location of the pain.

When Is RF Lesioning Indicated In Neck Pain?
For patients with neck pain, the indication for RF lesioning is pain that has persisted for more than 3 months and has not responded to conservative therapy. The patient must report relief after diagnostic blocks, but the amount of relief is controversial. Traditionally, patients must report greater than 80% pain relief on two separate occasions in response to medial branch blocks.16 However, a study on patients with cervical facet pain showed no difference in outcome of the RF procedure in patients reporting 50% relief and those reporting 80%.51 Based on this study, for patients with cervical facet joint pain, 50% reduction in pain after medial branch block may be adequate to indicate the need for treatment.

In a double-blind, randomized, controlled study comparing cervical medial branch RF lesioning with a sham treatment, Lord et al found that patients in the treatment group experienced statistically significant improvement in pain when compared with the control group (median time to recurrence of pain was 263 days and 8 days (P=0.04), respectively).52 Patients with C2-C3 joint pain were excluded from the study because preliminary data indicated that RF treatment was difficult at that level. However, subsequent research demonstrated that C2-C3 joint pain could be successfully treated by RF neurotomy of the third occipital nerve.53 In a follow-up to the study by Lord et al, 63% of patients reported complete pain relief for an average of 421 days.54 Finally, a study by Schofferman and Kine demonstrated that when pain recurred following RF neurotomy, repeat treatment was an effective, long-term solution.55

Sacroiliac Joint RF
Patients with SI joint pain are an important part of a pain physician’s practice. The SI joint is the primary source of pain in 10% to 25% of patients presenting with back pain,56 as well as in 32% of patients who undergo lumbosacral fusion.57,58 The symptoms of SI joint pain may be similar to those seen in patients with facet joint abnormalities (eg, low back and buttock pain referring to the leg); however, some important differences exist. Pain originating from the SI joint is typically unilateral. It is always felt low in the back and never above the L5 vertebral level. Although pain that is felt entirely above L5 cannot be emanating from the SI joint, pain below L5 can originate from several different spinal structures because the typical radiation pattern is into the low back and buttocks. For example, referral patterns from facet and discogenic pain overlap with those from the SI joint. Pain from the SI joint can refer to the buttocks, back of the thigh, knee, and even the lateral calf and foot, thus making it difficult to distinguish SI joint pain from SI radicular pain.

An important historical feature that can help distinguish radicular from radiating mechanical pain is that radicular pain is located almost entirely in the lower extremity and does not worsen with activity (Table 3). Lower extremity pain associated with a mechanical cause is severe only when the back pain is severe; it never occurs independently of back pain. For these reasons, when taking the history of a patient complaining of back pain, one should always ask what percentage of the pain is in the back versus in the lower extremity and what percentage of the lower extremity pain is above the knee versus below it. Patients with SI joint pain typically react to abrupt movements with pain. They may also feel increased pain during lower extremity loading, such as when standing on one leg. Seemingly innocuous movements, such as turning over in bed, may also induce pain. Patients with SI joint pain may report that they unload the painful side when sitting; however, they should not report neurologic symptoms, such as paresthesias, numbness, or weakness.

Table: Mechanical Pain vs Radicular Pain

Examination usually detects focal tenderness over the joint, and the findings that appear to correlate most closely with a positive diagnosis are pain below L5 and single-finger pointing by the patient to the posterior superior iliac spine when he or she is asked where the pain is located. These findings have been shown to have a positive predictive value of 60%.59 Clinical suspicion of SI joint intra-articular or ligament pain may be confirmed by differential, fluoroscopically guided, interosseous ligament, or intra-articular injection of local anesthetic, with or without steroid.

When to Use RF Lesioning for Low Back Pain
The indications for SI joint RF lesioning are back pain below the L5 level for the past 3 months that has failed to respond to conservative therapy. The patient must report a positive response (ie, >80% relief) to SI joint injections on two occasions to be considered a candidate for an SI joint RF procedure. Contraindications include local or systemic bacterial infection, bleeding diathesis, and possible pregnancy.

Efficacy of RF Lesioning for Low Back Pain
Approaches to RF lesioning of the SI joint include intra-articular, cooled-probe RF ablation, bipolar or monopolar strip lesions, and a combination of ligamentous and neural RF ablation. This discussion focuses on cooled-probe RF ablation and bipolar or monopolar strip lesions.

Cooled-probe RF
Cooled-probe RF ablation is a relatively new method of treating SI joint pain that can increase lesion size by a factor of 8. To date, its use has been published in two papers. The first described a randomized, placebo-controlled study of 28 patients with SI joint pain confirmed by a single intra-articular diagnostic block.60 The study compared sham and cooled-probe denervation of the S1-S3 lateral branches, with conventional lesions performed at L4 and L5 medial branches. Patients in the treatment group reported significant improvement in pain (a reduction by 60%, 60%, and 57%, at 1, 3, and 6 months, respectively [P<0.001]) compared with the patients in the placebo group, none of whom reported significant improvement. Patients in the treatment group also reported improvement in functional capacity and medication usage. The other article described a retrospective case series including 27 patients with SI joint pain confirmed using dual diagnostic blocks.61 Thirteen of the patients (50%) reported at least a 50% decrease in pain 3 to 4 months following treatment.

Strip Lesion
Strip lesions are another relatively new method of treating SI joint pain. The technique was used in a prospective observational study that included nine patients with SI joint pain confirmed by local anesthetic joint and lateral branch nerve blocks.62 The strip lesions were created adjacent to the lateral dorsal foraminal aperture, with conventional monopolar lesions at the L5 dorsal ramus. Eight of the nine patients were satisfied with the treatment, and 78%, 67%, 67%, 89%, and 67% reported being very satisfied at 1, 3, 6, 9, and 12 months, respectively. Median improvement in pain intensity was 4.1 on a 10-point rating scale, and reduction in disability was 17.8 on the Oswestry Disability Index.

Conclusion
RF lesioning is an effective way to provide pain relief to patients suffering from chronic pain. Its palliative effects allow for patients to resume normal activities and regain quality of life. Thanks to pioneering studies by Bogduk, Lord, Govind, Dreyfuss, and others, proper anatomic targets for the lumbar medial branch procedure were identified and were used to devise the optimal means of destroying the nerves. This research helped to confirm the efficacy of the procedure. Through experimentation with the use of continuous RF, the PRF mode was developed, thus allowing the treatment of targets for which heat is contraindicated.

As is often the case during the development of a treatment, no single theory has been able to explain the mechanism of action for PRF. However, clinical data support the notion that, when PRF is properly used to treat well-selected patients, it is an effective tool for some types of chronic pain syndromes (most notably radicular pain and peripheral neuropathies). These patients in particular are often refractory to medication and, in the absence of PRF, may require more expensive and invasive treatments (eg, spinal cord stimulation). To date, most studies show only short-term efficacy (approximately 3 months). Further research is needed to determine the best methods of applying PRF for longer-term pain relief.

Last updated on: April 15, 2015
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