Chapter 113. Trigger Point Injections

Musculoskeletal pain is a significant health problem for the North American population.1–9 Such pain affects between 10% and 20% of the population and is a major cause of morbidity.1 It is estimated that approximately half of the chronic pain complaints result from a musculoskeletal origin.2 It is hypothesized that myofascial trigger point (MTrP) injections may alleviate much of this pain. It is imperative that the Emergency Physician perform a thorough history and physical examination, with an emphasis on the neurological and orthopedic examination to exclude other causes of musculoskeletal pain.3

The etiology and pathogenesis of MTrPs have yet to be elucidated. Likewise, the precise mechanism by which MTrP injections inactivate the trigger point is unknown. Researchers do agree that acute trauma or repetitive microtrauma appears to lead to the development of a MTrP.6 The risk for a MTrP is increased when other factors are present, including poor physical conditioning, poor posture, and prolonged bending.7 MTrPs mostly affect the muscle groups used to maintain posture (i.e., muscles of the neck, shoulders, and back). When the head and neck region is affected, the patient may present with a tension headache or temporomandibular joint pain.6

MTrPs are hyperirritable points located within a taut band of skeletal muscle or fascia.2 When these points are compressed, they may cause referred pain, local tenderness, and autonomic changes.2 Pain may be localized or diffuse. It can be described as burning, dull, sharp, or some combination of these. Autonomic changes associated with a MTrP include dizziness, edema at the site, lacrimation, piloerection, salivation, and tinnitus. The compression of a MTrP can further lead to muscle spasm, stiffness, shortening, and fatigue.1 This may progress to impaired muscle coordination, reduced muscle strength, and decreased range of motion.1

Diagnosis of MTrPs

The diagnosis of a MTrP relies on the following criteria: a tender spot with an underlying taught band, pain on palpation of the tender spot, and a local twitch response (i.e., a transient local contraction of skeletal muscle fibers in response to palpation or needling).3 While the data on clinical outcomes provide no definitive answer, the best outcomes appear to occur in patients who exhibit a local twitch response with palpation.4 The current literature provides no pathophysiologic explanation for this result. There are no laboratory, pathology, or radiology studies to identify or verify a MTrP.

Identifying the palpable, taut band is critical in locating the MTrP. The MTrP can be identified by flat palpation, snapping palpation, pincer palpation, and/or deep palpation. Flat palpation uses a fingertip to slide across the skin over the affected muscle to find the MTrP (Figure 113-1). The taut band may be felt under the sliding fingertip. Snapping palpation uses the tip of the index finger to pluck the skin in an attempt to feel the underlying taut band. This motion is similar to plucking a guitar string. Pincer palpation uses the dominant thumb and index finger to firmly grasp the skin and muscle as a unit and roll it to identify the taut band (Figure 113-2). Deep palpation can be used to identify a deep MTrP or a superficial MTrP in an obese patient. Use the tip of the index finger to press slowly and deeply to reproduce the patient's symptoms and identify the MTrP.

Studies have utilized a variety of injectant fluids and solutions during injections of MTrPs including sterile water, sterile saline, local anesthetic solutions, corticosteroid suspensions, ketorolac, and botulinum toxin.1 No specific fluid or solution has demonstrated a clearly superior clinical outcome. Rather, it appears that the optimal injectant fluid or solution varies by Physician preference. The duration of pain relief has been found to last longer than the duration of action of the injectant. A recent meta-analysis of eight randomized and controlled clinical trials examined the type of injectant used and the resulting effect on symptom relief.1 The authors concluded that the injection of either lidocaine or botulinum toxin provided greater symptom relief than placebo (i.e., dry needling alone). No particular injectant was more efficacious than any other injectant. This finding is consistent with the general medical literature on the topic, which is still in its infancy, and provides no clear indication of effectiveness. More research is required in this area.

Noninvasive MTrP Management

Numerous noninvasive techniques have been used to treat a MTrP.2,5,8 One of the more common techniques uses spray vapocoolant (e.g., ethyl chloride) in combination with passive muscle stretch to relax the taut band. Ischemic compression therapy is the application of pressure to the MTrP to produce ischemia and ablate the MTrP. Digital pressure is applied and increased until the taut band relaxes. A deep pressure or stroking massage can be used to stretch the affected muscle and relax the taut band. Physical therapy can stretch and relax the affected muscles. Transcutaneous electrical stimulation units with the electrodes placed over the MTrP can be used to stimulate and relax the underlying muscle. Ultrasound can transmit heat and vibration to a superficial MTrP with the goal of muscle relaxation.

MTrP injections have been advocated for points of muscle pain that are not assisted by noninvasive therapy such as ischemic compression therapy, massage, physical therapy, spray vapocoolant, transcutaneous electrical stimulation (TENS), and ultrasound.8 There is no emergent indication for a MTrP injection in the Emergency Department.

Contraindications to MTrP injections are similar to other injection procedures. This includes the presence of a local or systemic infection, malignancy, anticoagulation therapy, a bleeding disorder, or a dermatologic condition over the injection site.5 Relative contraindications include allergies to local anesthetic agents, patients with needle phobias, and uncooperative patients.

It is important to differentiate between a patient with one or more isolated MTrPs and fibromyalgia (Table 113-1). A patient with fibromyalgia can have multiple MTrPs. Do not perform MTrP injections in a patient with fibromyalgia. The injection may worsen their pain.

• Sterile gloves
• Povidone iodine or chlorhexidine solution
• Alcohol swabs
• Sterile gloves
• Gauze 4 × 4 squares
• 25 or 27 gauge, 1.5 in. needle for superficial trigger points
• 25 or 27 gauge, 2 in. needle for deeper trigger points
• 3 or 5 mL syringe
• Injection solutions:
  • Lidocaine without epinephrine
  • Bupivacaine without epinephrine
  • Sterile water
  • Sterile normal saline
  • Botulinum toxin A, 20 units or 0.4 mL (50 U/mL) (Botox, Allergan, Irvine, CA) diluted to 1 mL with normal saline
• Ultrasound machine with a 5 to 7.5 MHz probe
• Ultrasound gel

Explain the risks and benefits of the procedure to the patient and/or their representative. Obtain an informed consent, either signed or verbal, with adequate documentation to support the latter method. Place the patient in a comfortable position on a gurney with the MTrP(s) exposed. Ideally, the muscle with the MTrP(s) positioned so that it is relaxed. Identify the MTrP site(s). Clean the skin of any dirt and debris. Use ultrasound to ensure there are no neurologic, tendinous, or vascular structures in the area that can be injured by the MTrP injection. Mark the MTrP skin site with a pen. Apply povidone iodine or chlorhexidine solution over the injection site(s) and surrounding skin and allow it to dry. Follow aseptic technique for the injection procedure.

Prepare multiple 3 or 5 mL syringes armed with a 25 or 27 gauge needle and containing the injection solution. The editor recommends local anesthetic solution as the injectant in the Emergency Department. The number of syringes to prepare depends upon the number of MTrP sites to be injected and the volume injected at each site.

Injection Technique

Reidentify the MTrP site. Use the nondominant index and middle fingers to locate and isolate the MTrP or taught band (Figures 113-3A & B). Insert the needle into the skin approximately 1 cm away from the MTrP or taught band, at a 30° angle to the skin, and aimed at the MTrP or taut band. Advance the needle into the MTrP or taut band. Insert the needle briskly, but also in a controlled manner. Use a “fast in, fast out” approach to elicit a local twitch response when the tip of the needle hits the MTrP or taut band.8 Aspirate to ensure that the tip of the needle is not within a blood vessel. Inject the solution within the syringe.

Common practice is to inject between 0.5 and 2.0 mL total per MTrP.5 This volume can be injected into the one location of maximal tenderness or numerous sites in a fanlike pattern within the MTrP (Figure 113-4).9 Once the injection is completed, withdraw the needle to the skin surface but do not completely remove it from the skin. Allow the injection solution to work for up to a minute. Reinsert the needle into the MTrP in a fanlike pattern until the local twitch response is no longer elicited or resisting muscle tautness is no longer palpable.7 Completely withdraw the needle. Apply pressure over the injection site to prevent bleeding and hematoma formation. Instruct the patient to slowly and fully stretch the affected muscle group.8

Dry Needling

The technique of dry needling involves inserting a needle into multiple sites within the MTrP or taut band without injecting any fluid or solution. This is similar to acupuncture. Insert the needle as described above. Withdraw the needle until the tip is just below the skin surface. Redirect and reinsert the needle in a fanlike pattern into a different location within the MTrP or taut band. Continue this process several times until the local twitch response is no longer elicited or resisting muscle tautness is no longer palpable.7 Completely withdraw the needle. Apply pressure over the injection site to prevent bleeding and hematoma formation. Instruct the patient to slowly and fully stretch the affected muscle group.8

The patient should experience relief of their symptoms after the injection. Passively and actively stretch the affected muscle in a slow manner to stretch it out. Apply digital compression to the injection site, the MTrP, and the taut band. If symptoms are still present, repeat the procedure with local anesthetic solution or by dry needling. Observe the injection site and apply pressure to control any bleeding.

Apply a simple adhesive bandage over the injection site. Postinjection soreness is expected and can be managed with acetaminophen or nonsteroidal anti-inflammatory drugs. Encourage the patient to use the affected muscle through its full range of motion, but avoid strenuous activity for 1 to 3 days after the injection. Instruct the patient to return to the Emergency Department immediately if they develop fever, chills, swelling at the injection site, redness at the injection site, or any drainage from the injection site.

The complications are the same as any injection procedure, including infections and needle breakage. An allergic reaction to the injection fluid or solution is possible. Treat this as any other allergic reaction. A thorough history may prevent an allergic reaction to the injectate. Never aim the needle at an intercostal space to prevent an iatrogenic pneumothorax.7 Hematoma formation following injection can be minimized with proper technique and the application of pressure over the soft tissue after the needle is withdrawn.2 Never inject the patient when they are standing or sitting in a chair. Ensure that the patient is always on a gurney and the side rails are upright to prevent injury if the patient becomes vasovagal or experiences syncope. Injury and inadvertent injection to adjacent structures can be avoided by knowing the local anatomy and using ultrasonography before the injection to identify adjacent structures.

MTrP injections can be performed in the Emergency Department. They are simple, quick, and effective to manage a patient's pain. The efficacy of MTrP injections has not yet been established. However, MTrP injections may serve as part of a treatment plan to offer quick relief of myofascial pain when other noninvasive therapies have been unsuccessful.