OUP user menu

Can Topical Anesthetic Reduce the Pain Associated with Diagnostic Blocks of the Lumbosacral Spine?

Isaiah J. Day BSc, Connie F. Kent RN, Robert S. Burnham MSc, MD, FRCPC
DOI: http://dx.doi.org/10.1111/j.1526-4637.2008.00474.x 675-679 First published online: 1 September 2008

Abstract

Objective. To evaluate the effectiveness of a topical local anesthetic cream (5% liposomal lidocaine) in reducing needle-induced pain in patients investigated for suspected zygapophysial (z-joint) or sacroiliac (SI) joint pain.

Design. Triple-blinded randomized controlled trial.

Setting. Interventional fluoroscopy suite.

Study Population. Eighteen patients presenting with chronic mechanical low back pain.

Interventions. Thirty minutes prior to diagnostic z- or SI joint blocks, equivalent amounts of topical 5% liposomal lidocaine cream was applied to one side of the low back and a placebo cream to the other. The treatment side and injection order were randomized and the patient, injectionist, and data recorder were blinded.

Outcome Measures. The subjects provided numerical rating scores of pain intensity immediately following each phase of the injection (skin penetration, deep, overall). Scores were analyzed with dependent t-tests.

Results. The injection associated pain was significantly less during the skin penetration phase on the side of the local anesthetic vs the placebo cream (3.0/10 vs 4.2/10; P = 0.002). No significant differences were found during the deep phase or for the injection procedure overall.

Conclusions. Five percent liposomal lidocaine cream significantly reduces the pain associated with the skin penetration phase of lumbosacral diagnostic blocks but does not change the pain associated with the deep phase or the injection procedure overall. Its usefulness for this application is questionable.

  • Topical
  • Anesthetic
  • Lodocaine
  • Zygapophysial
  • Sacroiliac

Introduction

Zygapophysial joint (z-joint) medial branch blocks, intra-articular injections, and sacroiliac (SI) joint lateral branch blocks are procedures designed to localize pain ostensibly arising from the z- and SI joints. An increasing number of spine care physicians are using these interventions as part of their diagnostic workup of chronic mechanical spine pain. These procedures require the penetration of skin, subcutaneous fat, and deep muscle tissue, and injection over nerve, periosteum, and joint capsule typically using a 22- or 25-gauge spinal needle. Interventional spinal injections may involve numerous injection sites and are associated with some discomfort to the patient. These injections can result in local muscle spasm or movement of the patient, both of which can increase the difficulty and duration of the procedure. False-positive rates as high as 40% are a major confounder in the diagnostic process [1]. Contributing to this may be the inadvertent treatment of the myofascial component of spine pain as a result of local anesthetic injection of skin and subcutaneous tissue, a strategy used by some interventionalists to minimize the discomfort of the z-joint intervention [2]. An effective and practical topical local anesthetic, applied prior to a spinal injection, may reduce procedural pain, duration, and difficulty, and eliminate the need for injected superficial anesthesia, thus decreasing the chance of a false-positive response.

Currently, topical anesthetics are rarely used for spinal injections. This is probably because long application times are required before maximal analgesia is reached and their effectiveness has not been established for spinal injection. Eutectic mixture of local anesthetics (EMLA) has been the most frequently used preparation for dermal anesthesia. EMLA consists of a eutectic mixture of 5% lidocaine and prilocaine. It has well-documented analgesic effects for percutaneous procedures such as venipuncture, intravenous catheter insertion, skin biopsy, skin grafting, subcutaneous, and even intramuscular injections [3,4]. It requires 60-minute application time under an occlusive dressing to achieve maximal anesthesia and penetrates to a depth of 3–5 mm. The duration of analgesia is typically 15–60 minutes.

Lidocaine (4 or 5%) in a liposomal delivery system has been formulated more recently and offers the advantage of a quicker onset of action and sustained release. A 30-minute application of 5% liposomal lidocaine is equal to EMLA in analgesic effectiveness for venipuncture and intravenous catheter insertion [5–7]. A recent study found that intravenous cannulation in children was more successful, less painful, and quicker at the site pretreated with liposomal lidocaine compared with the placebo [8].

This study evaluates the hypothesis that topical 5% liposomal lidocaine (Maxilene, RGR Pharma, Windwor, Ontario, Canada) applied 30 minutes prior to diagnostic z-joint or SI joint blocks reduces procedural pain. The pain was assessed separately at three phases of the injection procedure (skin penetration, deep phase, and the overall procedure).

Methods

After obtaining approval from the University of Alberta Health Research Ethics Board, subjects were recruited from the corresponding author's interventional pain management practice. The subjects were interviewed and examined to ensure they were receiving diagnostic lumbosacral spine joint blocks at the same segmental levels bilaterally for chronic mechanical spine pain. The subjects were excluded if they were minors, cognitively impaired, allergic to local anesthetic, taking anticoagulants, suffering from systemic infection, or subject to language difficulties. Subjects who satisfied the inclusion and exclusion criteria received a verbal briefing regarding the study and were then provided a written explanation in lay terms with an informed consent portion. They were encouraged to avoid taking analgesic medications for 24 hours prior to their procedure. None of the subjects were sedated for the procedure and no superficial anesthesia was injected. All of the injections were performed at the lumbosacral spine. Each subject was randomized by coin toss to determine which side was to receive the active topical anesthetic cream or placebo cream. Both creams had identical consistency and smell. The cream was applied by an assistant, blinded to the study's protocol and allocation. Five grams of cream was measured and applied to the lower back in an area from the spinous processes in the midline to 3 in. lateral of the midline, superiorly to the lower costal margin and inferiorly to the sacrococcygeal joint level. The inactive cream was applied in a similar fashion on the contralateral side. The creams were occluded using a plastic dressing. After 30 minutes, the dressing, 5% liposomal lidocaine, and placebo creams were removed. The physician performing the spinal injections and the procedure room nurses who recorded the subjects' pain ratings were blinded to which side was treated with the active and inactive agents. The same number and type of interventional injection was performed on each side of the spine using the same gauge needle (25 or 22), injectate substance, and volume. The side to side injection order was randomized by the procedure room nurses by coin toss. The procedural pain was quantified at three separate times during the injection. The initial measurement or “skin penetration phase” involved the needle piercing the skin into the subcutaneous fat. The “deep phase” involved the needle advancing from the subcutaneous fat, through muscle down to the vertebral level and performing the injection of contrast followed by local anesthetic. Immediately following each phase of the injection, the physician asked the subject for a rating of pain for that phase using a verbal numerical rating scale between 0 and 10 (0 = no pain; 10 = worst imaginable pain). At the completion of each injection, the subject was then asked to provide an “overall” pain rating of the injection (from needle insertion to removal) using the same scale. The procedure room nurse recorded the ratings throughout the procedure.

Results

A total of 38 pairs of injections were performed on 18 subjects. The injections were performed bilaterally and ipsi-segmentally. The location and number of paired structures injected were L3 medial branch (9); L4 medial branch (12); L5 dorsal ramus (10); SI lateral branch (2); S2 lateral branch (2); S3 lateral branch (2); and L5/S1 z-joints (1). Assuming a moderate effect size from the treatment, 38 dependant pairs of injections would provide a statistical power of 0.8 [9] (moderate effect size defined as the difference between the treatment and placebo group means divided by standard deviation = 0.5). The computer program Statistica (StatSoft, Tutsa, OK) was used to analyze the results. Data were analyzed using paired t-tests. Bonferroni's correction for multiple tests adjusted the significance level to P < 0.016. As demonstrated in Table 1, procedure-associated pain showed significant reduction during only the skin penetration phase on the side of the local anesthetic cream. No significant difference was found during the deep phase or for the procedure overall.

View this table:
Table 1

Procedural pain at various phases of diagnostic lumbosacral joint blocks with and without topical lidocaine cream

Phase of Injection5% Liposomal Lidocaine NRS Mean (SD)Placebo NRS Mean (SD)t ValueP Value
Skin penetration3.0 (2.0)4.2 (2.8) 3.220.003
Deep3.9 (2.5)3.9 (2.5)−0.130.901
Overall4.0 (2.3)4.4 (2.4) 0.910.368
  • NRS = numerical rating scale; SD = standard deviation.

Discussion

The development of more effective pain reduction techniques for interventional spinal injections is more important to both patients and physicians. The ideal topical anesthetic would provide quick and significant procedural pain relief yet not affect the diagnostic capability of the procedure. The purpose of this study was to determine whether 5% liposomal lidocaine, a topical anesthetic with a quicker onset of action than the more commonly used EMLA, is effective in reducing procedural pain associated with the diagnostic blocks of the lumbosacral spine in patients presenting with chronic mechanical low back pain.

Five percent liposomal lidocaine provided significant relief during the initial skin penetration phase of the injection only. Our study found that 5% liposomal lidocaine does not provide analgesia for the deep phase of the injection. This is understandable in that electron microscopic observations have documented the maximal depth of penetration of liposome encapsulations of local anesthetic to be 3–5 mm (into the dermis) [10]. This is in contrast with one report of topical EMLA cream reducing perceived pain from both needle puncture and a 1-in. deep intramuscular injection of 3 mL of sterile saline through a 23-gauge needle into the deltoid muscle of adults [4]. Another investigator found that EMLA cream decreased perceived pain with needle electromyographic percutaneous muscle insertions, but only at the forearm and not over the thenar eminence [11]. The authors proposed that the thicker skin of the hand decreased the penetration and effectiveness of the topical local anesthetic. It is possible that the skin of the low back in our subjects was thicker and more resistant to local anesthetic penetration than the skin overlying the deltoid muscle of the study conducted by Himelstein et al. [4]. The deep phase of the diagnostic block procedure involves advancing and positioning the needle under fluoroscopy, injection of contrast, possible repositioning followed by injection of local anesthetic. The deep phase may have been refractory to the analgesic effects of the topical local anesthetic because it lasts as long as minutes, whereas the superficial phase rarely lasts longer than a second. The injection site during the deep phase is also in areas rich with nociciptors such as the periosteum and capsule [1]. The prolonged discomfort of the deep phase of the injection probably overwhelmed the brief modest skin penetration phase analgesia provided by the topical local anesthetic resulting in the subjects' perception that the 5% liposomal lidocaine did not impact the pain of the procedure overall.

These results prompt possible future research in this area. Strategies to accelerate the onset of action, and increase the magnitude and depth of anesthesia may enhance the usefulness and effectiveness of prespinal injection transdermal local anesthetic use. The major barrier to transdermal drug penetration is the stratum corneum (SC) layer of the skin. “Passive” methods to enhance SC penetration involve modifying the drug and/or its carrier—liposomal encapsulation being an example. Combining the therapeutic agent with a chemical penetration enhancer (i.e., dimethyl sulfoxide [12]), supersaturation systems, vesicles, and prodrugs are examples of other passive strategies [13]. “Active” strategies involve the use of external energy as a driving force to reduce the barrier nature of the SC. Examples that may be practical, because they can be administered in a matter of seconds, include jet injection laser radiation [14], or ultrasound with or without iontophoresis [15,16]. However, it would need to be determined whether or not the external energy and added depth of local anesthetic penetration resulting from these strategies, would have intrinsic analgesic effects (such as treating the myofascial pain component) that would add to the problem of false-positive z-joint medial branch block/injection responses.

This scope of this study was limited to diagnostic blocks of the lumbosacral spine. The findings and conclusions should not be assumed to be valid for cervical or thoracic spine diagnostic blocks.

Conclusion

Five percent liposomal lidocaine cream significantly reduces the pain associated with the skin penetration phase of diagnostic lumbosacral joint blocks but does not change the pain associated with the deep phase or the perception of overall procedural pain. In its present form and mode of delivery, 5% liposomal lidocaine cream is not a recommended method of reducing procedural pain associated with diagnostic lumbosacral joint blocks.

Acknowledgments

We gratefully acknowledge RGR Pharma (Windsor, Ontario, Canada) for supplying the topical anesthetic and placebo products, the funding source: Edmonton Orthopedic Research Fund, and Dr. Dryden of the Department of Pharmacology, University of Alberta, for his helpful insights.

References

View Abstract