A Prospective Outcome Study on the Effects of Facet Joint Radiofrequency Denervation on Pain, Analgesic Intake, Disability, Satisfaction, Cost, and Employment

Article Outline

• Abstract
• Methods
  • Subjects
  • Intervention
  • Outcome Measures
    • Pain severity, frequency, bothersomeness, and analgesic use
    • Disability
    • Satisfaction
    • Costs
    • Employment
    • Complications
    • Analysis
• Results
• Discussion
  • Study Limitations
• Conclusions
• References
• Copyright

Abstract 

Burnham RS, Holitski S, Dinu I. A prospective outcome study on the effects of facet joint radiofrequency denervation on pain, analgesic intake, disability, satisfaction, cost, and employment.

Objective

To assess the effect of radiofrequency denervation (RFD) on patients with chronic low back pain (LBP) of facet joint origin.

Design

Prospective cohort study.

Setting

Interventional pain management program.

Participants

Consecutive subjects (N=44; 101 facet joints) over 2 years with chronic refractory mechanical LBP of facet origin established by 2 local anesthetic blocks (medial branch ± intra-articular) resulting in more than 50% pain relief.

Intervention

RFD of the symptomatic lumbar facet joints.

Main Outcome Measures

Self-reported pain intensity, frequency, bothersomeness, analgesic intake, satisfaction, disability, back pain–related costs, and employment twice prior to and at 1, 3, 6, 9, and 12 months post-RFD.

Results

Post-RFD, significant improvements in pain, analgesic requirement, satisfaction, disability, and direct costs occurred. They peaked at 3 to 6 months and gradually diminished thereafter. Satisfaction with medical care and living with current symptoms improved similarly. Overall, satisfaction with the RFD procedure was high, and no complications were reported.

Conclusions

RFD provides safe and significant short-term improvement in pain, analgesic requirements, function, satisfaction, and direct costs in patients with chronic LBP of facet origin.

Key Words: Outcome assessment (health care), Rehabilitation

List of Abbreviations: LBP, low back pain, NRS, numerical rating scale, NSAID, nonsteroidal anti-inflammatory drug, RCT, randomized controlled trial, RFD, radiofrequency denervation, VAS, visual analog scale

PHYSIATRISTS, PAIN MANAGEMENT physicians, and interdisciplinary teams are commonly faced with the challenge of treating patients with chronic mechanical LBP. Typically, a functional restoration approach to treatment is undertaken in which physical and psychologic impairments and functional disabilities are identified, quantified, and rehabilitated. Analgesic medication management is sometimes also used. Although this approach is helpful for many, some patients with chronic LBP experience no improvement in pain or function despite the best rehabilitation efforts. Others experience activity related pain aggravation that impedes functional restoration progress and success. In such cases, precise localization and selective treatment of the pain generating spinal structure could conceivably improve pain control, minimize analgesic requirements, reduce disability, enhance patient satisfaction, and reduce the financial burden borne by the patient in order to manage their back pain. One structure of the spine that can generate pain and is assessable to localized treatment is the facet (zygapophysial) joint. According to local anesthetic block criteria, the prevalence of chronic lumbar facet joint origin pain ranges between 15% in younger patients to as high as 40% in older patients.¹, ²

Although commonly performed, the evidence basis for RFD of lumbar facet joints is controversial. One notable yet small prospective outcome study adhered to strict inclusion criteria and an optimal procedural technique and reported 60% of patients obtaining at least 90% relief at 12 months and 87% obtaining at least 60% relief at 12 months.³ Recently, a larger prospective clinical audit using similar selection and treatment criteria reported 68% of patients experiencing good (>50%) to excellent (>80%) pain relief lasting from 6 to 24 months.⁴ Five RCTs exist in the literature and vary considerably in terms of subject selection criteria, outcome measures, follow-up duration, procedure technique, and results. Two demonstrated positive benefit⁵, ⁶ and 3 found little or no benefit over sham procedure.⁷, ⁸, ⁹

The outcome variables reported in the cited studies are limited, in most cases, to measures of pain and disability. A couple of studies also measured analgesic use and quality of life. In all cases, outcome measurements were recorded once prior to the procedure and then at varying intervals and durations postprocedure. No previous studies have recorded preprocedure outcomes on more than 1 occasion in order to assess stability of the painful low back condition. Despite being part of a core set of questions recommended for LBP-related clinical, quality improvement, and research work, no previous studies have evaluated the effect of facet joint RFD on patient satisfaction.¹⁰ Cost comparison studies of various treatments available for chronic LBP have indicated that percutaneous minimally invasive procedures, including facet RFD, are less expensive.¹¹ However, no literature exists evaluating their impact on back pain–related costs after the procedure. Change of employment status affects back pain–related costs and is of particular interest to the sponsor of the study. The David Thompson Health Region of Alberta, Canada, started its RFD program 4 years ago. Like Gofeld et al,⁴ we wanted to perform a prospective clinical audit to assess the effectiveness of the procedure. Additionally, we wanted to assess its effect on more domains than just pain and disability. This audit was conducted over the first 2 years of the program.

The purpose of this investigation was to evaluate the effectiveness of RFD of the lumbar facet joints on pain, analgesic intake, disability, patient satisfaction, back pain–related costs, and employment status in the context of a clinical audit of a new RFD program. The research hypotheses were that RFD of symptomatic lumbar facet joints would decrease pain, analgesic intake, patient dissatisfaction, back pain–related costs, and unemployment.

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Methods 

Subjects 

After receiving ethical approval from the University of Alberta Health Ethics Review Board, consecutive patients seen for interventional facet joint pain management during the first 2 years of the program operation (2003–2005) were invited to participate if they fit the following criteria: LBP for longer than 6 months; no clinical or investigative evidence of back pain secondary to tumor, infection, viscerogenic, inflammatory, or neurologic (radiculopathy or stenosis) sources; spine pain refractory to conventional noninvasive treatment; more than 50% back pain relief with 2 fluoroscopically guided diagnostic facet joint blocks (intra-articular or medial branch blocks; at least 1 had to be a medial branch block) using a long-acting and short-acting local anesthetic (.75mL/medial branch; 1mL/intra-articular facet); greater than 18 years of age; no contraindication to spinal injection such as local or systemic infection, coagulopathy, or local anesthetic allergy; and Beck Depression Inventory score less than 8.¹² Every patient accepted the invitation to enroll in the study, and all but 1 completed the full 12 months of follow-up. All subjects provided written, informed consent to participate in the study.

Intervention 

Under sterile technique, local anesthesia, and fluoroscopic guidance, the medial branch nerves innervating the symptomatic facet joint, as identified by the diagnostic blocks, were lesioned. The first burn was performed by passing a 21-gauge 10-mm exposed active curved tip radiofrequency electrode^a down the beam of the image intensifier (angulated approximately 20° caudad and oblique) to the junction of the superior articular and transverse processes. The electrode was advanced parallel to the long axis of the nerve to the superior medial aspect of the transverse process but not into the intervertebral foramen. For the L5 posterior ramus, the electrode was placed at the junction of the S1 superior articular process and the sacral ala. The electrode position was checked in the anterior-posterior, lateral, and oblique views. Motor stimulation of 2Hz was applied to ensure multifidus muscle without leg myotomal twitching occurred. A 90-second burn at 80°C was created using a radiofrequency generator.^a Second and third burns were performed with the electrode respectively positioned approximately 1mm laterally and 1mm superomedially from the first burn site. After the procedure, ice was applied to the procedure site for 15 to 20 minutes. The subject was examined to ensure that no radicular injury had occurred. Discharge instructions included encouragement to resume their core stabilization exercise program that had been provided at an earlier visit, once the postprocedure discomfort settled.

Outcome Measures 

Subjects completed a questionnaire on 2 occasions prior to their facet joint RFD procedure to establish their baseline status. This was done at the time of recruitment and just prior to the procedure (mean time ± SD between baseline assessments, 2.3±1.4mo). The same questionnaire was completed at 1, 3, 6, 9, and 12 months postprocedure. The questionnaires were completed by the subjects and were either mailed or faxed back to the research assistant. The questionnaire included the core set of instruments for clinical researchers recommended in 1997 by a multinational group of spine research experts exploring domains of pain severity, frequency, and bothersomeness; disability; and satisfaction.¹⁰ These instruments were selected because of their ease-of-use; clinical relevance; and documented reliability, validity, and responsiveness. Questions were added to gain information about analgesic use, employment, direct/indirect costs, and perceived complications. Overall, the questions explored the domains of pain, analgesic use, disability, satisfaction, costs, and employment as described.

Pain severity, frequency, bothersomeness, and analgesic use 

For pain severity, a numerical rating scale score was obtained by asking the following question: “On a scale of 0–10 (0 being no pain and 10 being excruciating pain), what was your average back/leg pain level over the past week?” To quantify pain frequency, the following questions were asked: “During the past week, how often have you suffered back pain?” and “During the past week, how often have you suffered leg pain?” with possible responses being none of the time, a little of the time, some of the time, a good bit of the time, most of the time, and all of the time.¹⁰ For bothersomeness, the following questions were asked: “During the past week, how bothersome on average has your back pain been?” and “During the past week, how bothersome on average has your leg pain been?” with possible responses being not at all, slightly, somewhat, moderately, very, or extremely bothersome.¹⁰ An additional question was asked pertaining to analgesic intake during the prior week with ordinal response options as follows: none, occasional acetaminophen or NSAID, daily acetaminophen or NSAID, occasional oral opioid/narcotic, daily oral opioid/narcotic, and injected opioid/narcotic.

Disability 

The average level of disability for the week was quantified using the Oswestry Disability Questionnaire.¹⁰

Satisfaction 

Three questions regarding satisfaction were asked: “If you had to spend the rest of your life with the back pain you have now, how would you feel about it?”¹⁰; “Over the course of treatment for your back pain, how satisfied have you been with your overall medical care?”¹⁰; and “How satisfied are you with the results of your radiofrequency procedure?” Possible response options included very satisfied, somewhat satisfied, neither satisfied nor dissatisfied, somewhat dissatisfied, and very dissatisfied.

Costs 

Both direct and indirect costs relating to LBP care that were or could potentially be borne directly by the subject were estimated. In Canada, we have socialized health care. No attempt was made to calculate government covered costs of hospitalization, investigations, or emergency department visits. Direct costs were calculated by asking the subject to describe the type and number of any of the following treatments/services received for their LBP in the previous month: physician office visits, chiropractic treatments, physiotherapy treatments, and treatments from other allied health practitioners (massage, acupuncture, psychology, and so forth). Inasmuch as the cost of each of these services is variably covered by private or public insurance, a typical cost per visit/treatment for each of the disciplines was used to calculate a monthly cost. For the cost of prescription and nonprescription medications, assistive devices (braces, walking aids, and so forth), and transportation related to back pain management, subjects reported their personal expenditure (before private insurance reimbursement). Indirect costs incurred by the subject for the previous month were also reported including the difference in income that month compared with a typical month when they did not have chronic LBP (compensation or insurance payments excluded), and costs incurred that month from hiring someone to complete any of their employment or domestic responsibilities they could not perform because of their back pain. The costs were reported in Canadian dollars.

Employment 

The subjects were asked if they were working at that time. If so, they reported the number of hours worked in the previous month and the number of pain-related absentee days.

Complications 

Finally, they were asked to describe any adverse reactions or complications they had experience as a result of the facet joint RFD procedure.

Analysis 

To assess changes in various outcome measures by facet joint RFD, we fitted a regression model for each outcome measure (except cost and employment) with the following mean structure:

where, for i^th subject's j^th month post-RFD (j=0 if pre-RFD), Post_ij is an indicator of post-RFD (1 if j>0, 0 otherwise), Month_ij equals j, and parameters β₀, β₁, and β₂ correspond to, respectively, the average outcome level in the pre-RFD period, the average (immediate) change of the outcome level because of RFD, and the average linear change (slope) of the outcome level over 1 year post-RFD. For the outcome measures of pain severity and disability, our regression models were linear models, where the β parameters captured average values of their corresponding quantities in the same units as these continuous outcomes. For the outcome measures of pain frequency and bothersomeness, medication use, and satisfaction, our regression models were proportional odds models.¹³ These analyses were appropriate for assessing changes in the ordinal categorical outcomes, where the β parameters captured changes in average log odds of responding with a worse outcome level. Statistical inference was performed based on these regression models, taking into account correlation among the repeated measures of each patient over time. This was accomplished by adjusting the standard error estimates of the β-parameter estimates for the correlation using a generalized estimating equation.¹⁴ Repeated-measures analysis of variance was used to evaluate the changes in direct and indirect back pain–related costs, hours worked, and absentee days at the times before and after the RFD.

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Results 

Forty-four subjects participated (23 men, 21 women; average age, 52±10y; range, 35–75y). One hundred and 1 facet joints were treated with RFD. Fifty-five were at L5/S1, 37 at L4/5, 7 at L3/4, and 2 at L1/2. No significant differences were found between the 2 pre-RFD times for any of the outcome measures. The results of the facet joint RFD procedure are summarized in table 1.

Table 1. Effect of Lumbar Facet Joint Radiofrequency Denervation on Pain, Analgesic Intake, Disability, Satisfaction, and Cost

Pain intensity dropped significantly post-RFD. The pain relief was maximal at 3 months and relatively stable for at least 6 months. By 9 months post-RFD, pain intensity started to rise significantly. In terms of percentage pain relief, 43%, 57%, 39%, 30%, and 20% of subjects experienced more than 50% relief at 1, 3, 6, 9, and 12 months post-RFD, respectively. Pain frequency and bothersomeness followed a similar pattern. The magnitude of pain frequency and bothersomeness improvement was greater in the low back than in the legs. Analgesic consumption dropped significantly post-RFD and remained stable at the reduced level for the entire 12 months.

Changes in disability followed the same pattern as pain intensity. Specifically, there was a significant drop post-RFD that peaked at 3 months, and after 6 months, a significant rise in disability was seen.

Overall, satisfaction post-RFD also improved. The improved satisfaction with the medical care the subjects had received for their chronic low back condition remained stable throughout the 12-month follow-up period. In contrast, the improved level of satisfaction living with their current level of pain post-RFD demonstrated a significant reduction after 6 months. In terms of satisfaction with the RFD procedure itself, the median response was somewhat satisfied, and this remained stable throughout the 12-month follow-up period. Described in percentages, 66%, 82%, 80%, 77%, and 82% were either somewhat or very satisfied with the facet RFD at 1, 3, 6, 9, and 12 months postprocedure, respectively.

There was a modest yet significant decrease in back pain–related direct costs post-RFD that lasted between 6 and 9 months. Sixty-nine percent of the reduction came from reduced medication costs. There was a statistically insignificant trend to decreasing indirect and overall costs. Ninety-three percent of the indirect cost savings came from reduced loss of employment income. Sixteen of the 44 subjects were unemployed prior to the facet joint RFD. At 3 months postprocedure, 2 of the subjects became employed, and by 6 months postprocedure, an additional 2 acquired employment. Therefore, 4 (25%) of 16 of the unemployed subjects became employed within 6 months of the procedure. The new employment was part time in all cases. After the procedure, there was a significant increase in the number of hours worked and a significant decrease in the number of pain-related absentee days in the prior month. No complications or adverse reactions were reported.

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Discussion 

The purpose of this investigation was 2-fold. First, because our RFD program was new, a clinical audit was undertaken in order to evaluate the effectiveness of the procedures and to compare our results with those described in the literature. Second, we wanted to explore the effect of this procedure not only on pain and disability but also analgesic use, satisfaction, cost, and employment. Our hypothesis was that RFD would beneficially affect all of these domains. Overall, the hypothesis was supported, although the procedure benefit in terms of costs was limited to direct costs.

Study Limitations 

One limitation of the study is the lack of a control group. However, outcome measures were administered twice prior to intervention with an average of 2.3 months separating the pre-RFD assessments. No significant interval changes in any of the outcome measures were found. In a limited sense, this within-subject design allowed the subjects to function as their own controls. It is acknowledged that a few months of back pain stability cannot be extrapolated to mean that the condition would be stable for an entire year. However, it does make it less likely that the post-RFD changes relate to a natural history of improvement over time. Inasmuch as consecutive subjects participated in this, the risk of selection bias is minimal.

The magnitude of pain intensity reduction in our study (NRS drop of ∼3.5) was greater than that described in the 2 positive RCTs in the literature. Compared with the sham procedure group, Gallagher et al⁵ found the facet RFD group to experience a statistically significant mean drop in VAS score of 1.7cm and 0.7cm at 1 and 6 months postprocedure, respectively. van Kleef et al⁶ found a mean VAS score drop of 2.4cm in the facet RFD group compared with 0.4cm in the sham group at 2 months postprocedure. The mean magnitude of pain relief achieved in our study exceeds the threshold of clinical significance (>2 of 10 or >30% reduction).¹⁵ However, compared with the 2 previously cited quality prospective cohort studies, both the magnitude and duration of pain relief in our study were less. The reason for this is uncertain but may reflect our relaxed selection criteria. We included subjects if they had more than 50% pain relief with 2 separate local anesthetic blocks (medial branch with an injectate volume of 0.75mL or intra-articular using an injectate volume of 1.0mL). Such criteria are commonly used in clinical practice, and some suggest that they minimize the risk of unnecessarily depriving patients who would benefit from the procedure.¹⁶ In contrast, the studies by Dreyfuss,³ Gofeld,⁴ and colleagues required more than 70% to 80% relief using only medial branch blocks and an injectate volume of 0.5mL. Additionally, the pharmacologic duration of action criteria recommended for comparative blocks (lidocaine>1h and bupivacaine>3h of relief) were not strictly adhered to in our study. Our program has now adopted more rigid selection criteria. However, it is interesting that, although the strict selection criteria adhered to by Dreyfuss³ and Gofeld⁴ are commonly advocated and have face and content validity, no study to date has formally evaluated whether selection criteria based on comparative block type, pain relief magnitude, or duration predict RFD outcome (predictive criterion validity). Only van Kleef et al⁶ alluded to a statistical relationship between “patients who reported themselves free of pain after diagnostic nerve block showing a higher rate of success,”^(p1941) but they did not elaborate.

In addition to the NRS of pain intensity, we also included measures of pain frequency and bothersomeness for both the low back and legs using a 6-point Likert scale. All of these measures demonstrated significant pain reduction after facet joint RFD. Pain frequency and bothersomeness of the low back responded to RFD more than that of the legs. Based on the magnitude of the slope change by RFD and post-RFD, the NRS of pain intensity appears more responsive than pain frequency or bothersomeness. This finding is in contrast to a recent investigation on responsiveness of pain measures for chronic whiplash that found pain bothersomeness to be more responsive than pain intensity measures. However, they used an 11-point NRS for both pain intensity and bothersomeness, which may explain the difference.¹⁷

Concordant with the reduction in pain was a reduction of analgesic intake. Reduced medication costs accounted for the greatest portion of the significant direct cost savings found in this study. We found no significant reduction of indirect costs or overall costs after facet joint RFD, although there was a trend toward reduced costs. The major indirect costs related to lost wages. Twenty-five percent of unemployed subjects in the study returned to work after facet joint RFD. However, this resulted in a limited impact on wage loss, not only because the percentage was low, but also because the subjects returned to part time work. It is possible that a higher return to work rate and a higher proportion of full time work could be achieved if an occupational/vocational rehabilitation program was instituted after the procedure.

The magnitude of the reduced disability level documented postfacet joint RFD is not only statistically but clinically significant, at least at 1 and 3 months postprocedure.¹⁷ After 6 months, disability level increased significantly. It is possible that the benefit of the procedure could be prolonged with adherence to a customized low back fitness program. Although all of the subjects enrolled in the study had been assessed and provided a customized home back exercise program emphasizing core stabilization, hip girdle muscle flexibility, and aerobic fitness, and optimizing body composition, exercise compliance was not monitored or enforced.

Overall, satisfaction improved after facet joint RFD. There was a significant improvement with the satisfaction relating to medical care received for their back pain condition that remained stable for the entire year postprocedure. Satisfaction with the current level of pain improved but was incomplete and did deteriorate after 6 months. Regardless, there was a high satisfaction rate with the RFD procedure throughout the entire follow-up duration. Most of the subjects have subsequently returned for a repeat procedure at their request. No complications have yet been encountered after the RFD procedures.

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Conclusions 

This prospective cohort study suggests that, in selected patients with chronic LBP, facet joint RFD results in significant short-term reductions in pain, analgesic intake, disability, dissatisfaction, back care–related direct costs, and time lost from work. The procedure appears to be safe and to have a high satisfaction rate. Further research including RCTs of lumbar facet RFD using strict selection criteria, an optimized procedural technique, and comprehensive outcome measures is recommended.

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