Q: I know that injections are commonly done to relieve pain. Is this a legitimate evidence-based treatment method with some long-term benefits for the chronic pain patient?

A: A variety of needle-based and injection-based interventional therapies exist for chronic pain and this chapter examines the evidence behind these therapies. The chapter covers several needle therapies including acupuncture, local anesthetic used for muscle pain, cryotherapy, phenol, glycerol and dextrose solutions that are used for orofacial pain. Corticosteroid injections joint and perinerual injections will be discussed also, but botulinum toxin (BoNT) injections to control both muscle spasm control and chronic nerve pain will be covered in more detail in another chapter.

Q: I have heard about acupuncture for acute pain, what is its role in chronic pain?

A: Acupuncture encompasses a range of procedures including manual needling, electrical acupuncture, moxibustion, acupressure, heat, and laser stimulation of acupuncture points. Using a Chinese medical philosophy that disease occurs when there is a disruption of normal energy flow called Qi, over 2,000 acupuncture points arranged on “meridians” have been mapped representing channels of energy flow. The stimulation of these points corrects the imbalances of Qi. While the history of acupuncture is quite ancient, modern science has only evaluated its efficacy within the past few decades. For chronic pain acupuncture provides transient pain suppression at best. This approach may be useful in patients that are unable or unwilling to take medications. See research evidence cited below.

Q: What is the evidence basis for acupuncture used for chronic pain?

A: In 1990 a meta-analysis evaluated the efficacy of acupuncture as a treatment of chronic pain. The authors concluded that acupuncture as a therapy for chronic pain is at best, doubtful [1]. In 1997 a National Institutes of Health consensus conference examined the literature and offered a statement on the current evidence for using acupuncture [2]. This prestigious body concluded that “Although there have been many studies of its potential usefulness, many of these studies provide equivocal results because of design, sample size, and other factors”. It also concluded that acupuncture analgesia has been demonstrated in controlled laboratory studies to produce greater analgesia than appropriate placebos [3]. The mechanism of acupuncture has been hypothesized as counter-irritation analgesia and is essentially a brainstem mechanism in which a brief, intense stimulation of afferent nerve fibers induces a brainstem inhibitory control structures modulates pain response. This response activates both opioid and non-opioid systems. Unfortunately, the NIH conference did not comment on the efficacy of acupuncture for treating chronic pain disorders [4]. In 1999 and 2000, there were three systematic reviews of the literature published which assessed the efficacy of acupuncture (primarily manual needling) on chronic pain.

These three systematic reviews each dealt with a different disease group (fibromyalgia, chronic pain of all types, and low back pain) and each reached a different conclusion. The first review focused on fibromyalgia but it was not a Cochrane Library-based review [5]. It concluded that acupuncture was better than sham-acupuncture.

The second review focused on acupuncture for chronic pain (of all types) was also not a Cochrane Library [6]. It concluded that the available studies were not of sufficient methodological quality to offer an endorsement.

The third review focused on acupuncture for the management of acute and chronic low back pain and it was a Cochrane Library review [7]. It examined 11 clinical trials but stated that only two were of sufficiently high quality. It also concluded that current evidence was not of sufficient methodological quality to offer an endorsement. With regard to Orofacial pain, in 2007 an article described the short-term effect of acupuncture on myofascial pain patients after clenching [8]. VAS scores were used to rate the pain in 15 chronic myofascial pain patients using a single-blind, randomized, controlled, clinical trial with an independent observer. Subjects were randomly assigned into two groups (acupuncture [n=9]; sham-acupuncture [n=6]).

Acupuncture or sham acupuncture was administered at the Hegu Large Intestine 4 acupoint and facial-jaw pain was then induced/exacerbated by having subjects clench their teeth continuously for 2 minutes. An algometer invoked a mechanical pain stimulus to the jaw muscles, and the subject rated his/her pain level using a VAS score. Pain tolerance in the masticatory muscles increased significantly more with acupuncture than sham acupuncture. An additional study in 2007 examined the effect of acupuncture-like electrical stimulation on chronic tension-type headache using a randomized, double-blinded, placebo-controlled trial in 38 chronic tension-type headache patients [9]. These patients were randomized into: a treatment group and a placebo group. Pain duration, pain intensity were recorded on a 0 to 10 cm VAS, and the number of headache attacks and use of medication were recorded in a 2-week diary.

The treatment was a surface electrode attached to an electrical stimulator or a sham stimulator and they were instructed to use the device at home. Six acupoints were used in the treatment (bilateral EX-HN5, GB 20, LI 4) and treatment was to be applied for 3 minutes twice a day. Data was collected 2 weeks before treatment, at 2 and 4 week time point during treatment and at 2, 4 and 6 weeks after treatment. Although both pain duration and pain intensity decreased during treatment there were no significant group differences. The only group difference was for a decrease in analgesic use in the acupuncture group, but not the sham acupuncture group. To summarize, no definitive conclusions about acupuncture for chronic orofacial pain can be made.

The lack of quality data combined with recent studies of better quality has only suggested short-term and minimal effects from acupuncture overall. Until additional scientifically valid studies are published, acupuncture as a treatment for chronic orofacial pain may provide at best, transient pain relief. Of course, this may be an acceptable clinical strategy for some chronic pain sufferers and fortunately, the treatment is generally a low-risk procedure.

Q: To really test the efficacy of any treatment you need a placebo or “sham” treatment to compare it against. Has this been done?

A: Yes, several studies have examined if patients can tell the difference between a real acupuncture needling and a sham needling. See the abstract below.

Q: How does the data from the Kreiner et al study compare to prior research?

A: Actually, there is not much data to compare to, but below is a graphic showing self-reported pain levels in two groups of patients who received 3 different acupuncture or sham-acupuncture treatments over a 3 week period. The results show that initially the sham-acupuncture produced a similar transient lowering of pain (although not as much as real acupuncture) and by the 3rd week the pain reduction seen in the real-acupuncture group was more on the day of and for several days after the treatment. These data suggest both a real physiologic effect of acupuncture and that with repeated needling the patient who got sham treatment were probably no longer blind to the treatment they were receiving. Data from: Nabeta T, Kawakita K. Relief of chronic neck and shoulder pain by manual acupuncture to tender points–a sham-controlled randomized trial. Complement Ther Med. 2002 Dec;10(4):217-22.

Q: Is trigger point injections with local anesthetic similar or different from acupuncture and if different, why?

A: Injection of a local anesthetic is a common treatment for myofascial trigger points, and more recently, Botulinum toxin has been used and will be discussed elsewhere. Both acupuncture and trigger point injections are counter-stimulation techniques that provide a brief reduction in pain so in this sense they are similar. The local anesthetic injection into trigger points does not “cure the trigger point” but it does allow better stretching of the taut band in which the trigger point resides in and with time this may desensitize the trigger point[10]. Trigger point pathogenesis is covered elsewhere.

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Q: What is the evidence basis for trigger point injection used for chronic myofascial pain [11]?

A: Unfortunately, not a great deal of high-quality evidence on the efficacy for trigger point injections versus a control (sham injections) or comparison therapy (e.g. acupuncture) for myofascial pain exists. In 1981 a controlled randomized double-blind cross-over clinical trials examined the injection of bupivacaine 0.5%, etidocaine 1% or saline into trigger points in 15 patients with myofascial pain. Outcome measures were based on the patient’s subjective pain response to these injections 15 minutes, 24 hours, and 7 days after treatment. The authors concluded that trigger-point injections with bupivacaine and etidocaine were generally preferred over saline. In 1989 a prospective randomized, double-blind study evaluated 63 low-back pain subjects treated with one of 4 treatments (0.5% lidocaine, 0.5% lidocaine combined with a steroid, acupuncture, and vapocoolant spray with acupressure [12]. No significant difference was found between the different methods of treatment, and the authors concluded that injection of lidocaine is not the critical factor, since direct mechanical stimulus to the trigger-point seems to give an equal effect. In 2001 a review article examining the previous studies and others concluded that trigger point injections using anesthetic solutions were no better than injecting sterile saline or dry needling alone [13]. However, this finding does not mean that trigger points are placebo therapy and it might be better to conceptualized them as acupuncture like therapy, namely a treatment that induces a temporary pain suppression effect at best. This point of view is supported by a 1988 study which investigated the use of intravenous naloxone (an opioid receptor antagonist) given after trigger point injection therapy [14].

The double-blind, cross-over study included 10 patients with myofascial trigger point pain, and each received an injection of 0.25% bupivacaine which generally decreased their pain and increased range of motion. Following these injections, patients received either an intravenous infusion of naloxone (10 mg) or saline in a cross-over design. All improvements afforded by the trigger point injection therapy were significantly reversed with intravenous naloxone but not so with intravenous placebo. These results point to an endogenous opioid system as a mediator for the decreased pain and improved physical findings following the anesthetic injections. In 2007 a study reported on the efficacy of intramuscular and nerve root stimulation versus 0.5% lidocaine injection to trapezius muscle trigger points in 43 myofascial pain patients [15].

The subjects were divided into two groups and treatment was rendered on days 0, 7 and 14. The results show that intramuscular stimulation was more effective than trigger points using pain scale scores at all visits. Another 2007 study compared acupuncture needling versus 0.5% lidocaine injection of in upper trapezius muscle trigger points in 39 elderly myofascial pain patients [16].

The subjects were divided into two groups and all received treatment at days 0, 7 and 14 days and outcomes were assessed at 28 days. Both groups improved, but there was no significant difference in the reduction of pain between the two groups. In 2008, the effectiveness of injection therapy (e.g. corticosteroids or anesthetics) for low-back pain was examined in a recent meta-analysis. The patients on which these injections were used all had subacute or chronic low-back pain [17].

The study examined papers between 1999 and 2007 in multiple languages. They included only RCTs on the effects of injection therapy involving epidural, facet or local sites for subacute or chronic low-back pain. The authors concluded that there was no strong evidence for or against the use of any type of injection therapy. In summary the above data suggests that trigger point injection therapy using local anesthetic is best conceptualized as an acupuncture-like therapy, namely a treatment that induces a short-lived pain suppression effect.

Q: Can you summarize what the above review says about needle therapy for chronic orofacial pain?

A: At present no Cochrane study is available that examined needle and/or injection-based therapies for the treatment of chronic orofacial pain. However, a Cochrane style review cited earlier (Staal et al, 2009) examined the role of injection therapy for subacute and chronic low back pain. This study systematically reviewed randomized controlled trials (RCTs) that sought to determine if injection therapy is more effective than placebo or other treatments for patients with subacute or chronic low back pain. The authors discovered 18 eligible clinical trials (1179 participants) in their review. The injection sites varied from epidural sites and facet joints (i.e. intra-articular injections, peri-articular injections and nerve blocks) to local sites (i.e. tender-and trigger points). Overall, the results indicated that there is no strong evidence for or against the use of any type of injection therapy for back pain.

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