Trigger Point Injection

Trigger point injections are an effective treatment modality for inactivating trigger points and providing prompt relief of symptoms from myofascial pain syndrome. ^[1]  Myofascial pain syndrome is a common painful muscle disorder characterized by myofascial trigger points. This syndrome is distinct from fibromyalgia syndrome, which involves multiple tender points, though the two pain syndromes may be concurrent.

Myofascial trigger points are a major cause of pain and dysfunction. ^[1]  They produce pain focally and in a referred pattern and often occur in conjunction with chronic musculoskeletal pain disorders. Various modalities for the treatment of trigger points include spray and stretch, ultrasound, manipulative therapy, and trigger point injections.

Not all trigger points require injection or needling. Many active trigger points will respond to physical therapy, especially in the early stages of trigger point formation. However, for chronic trigger points, trigger point injection and needling is an effective treatment. ^[2]

Trigger point injections are indicated for patients who have symptoms and examination findings consistent with active trigger points. Latent trigger points are clinically asymptomatic and do not require treatment. Trigger points should be limited in number and should be appropriate for injection.

Conditions involving widespread pain complaints, such as fibromyalgia or endocrine disorder, are not suitable for injections. Treatment is indicated for endocrine diagnoses or fibromyalgia before trigger point injections are considered. In addition, the finding of tenderness alone is not an indication for trigger point injection, because patients with fibromyalgia may also have myofascial pain trigger points.

When indications for injections are being considered, it is not always necessary to have the classical clinical examination findings of a taut band with local twitch response and referred pain pattern. Within the total clinical context, the finding of tender points in typical trigger point locations that coincide with the patient’s pain and a “jump sign” is sufficient to justify trigger point injections. ^[2]

Trigger points should not be injected in the presence of systemic or local infection. Injection of patients with bleeding disorders or patients on anticoagulation must be done with proper medical evaluation and control. Although bleeding may be increased in these patients, the risk of harmful bleeding remains very low.

Avoid injections in the pregnant patient or patients who feel or appear to be ill. Use precautions in patients who are at high risk for infection, including debilitated patients, patients with diabetes mellitus, or patients on steroids.

Pain from myofascial trigger points is often treated by needling, with or without injection, though the evidence is inconclusive on whether this is effective. A literature review examined seven studies that assessed the effects of dry needling. ^[3]  One study concluded that direct dry needling was superior to no intervention; two studies comparing direct dry needling to needling elsewhere in the muscle produced contradictory results; and four studies used a placebo control and were included in a meta-analysis.

Upon analysis of these studies, needling was not found to be significantly superior to placebo; however, marked statistical heterogeneity was present. ^[3]  Thus, this review found limited evidence deriving from only a single study that deep needling directly into myofascial trigger points has an overall treatment effect when compared with standardized care.

In a 2013 systematic review and meta-analysis of 12 randomized, controlled trials designed to assess the effectiveness of dry needling for upper-quarter myofascial pain (MPS), Kietrys et al reported the following findings ^[4] :

• Evidence from three studies of dry needling vs placebo suggested that dry needling could immediately decrease pain in patients with upper-quarter MPS; there was an overall effect in favor of dry needling
• Evidence from two studies of dry needling vs placebo suggested that dry needling could decrease pain after 4 weeks in patients with upper-quarter MPS; the impact of this decrease was limited by the wide confidence interval for the overall effect
• Studies of dry needling vs other treatments yielded highly heterogeneous results; evidence from two studies suggested that lidocaine injection may be more effective in reducing pain than dry needling at 4 weeks

On the basis of these findings, the authors of the meta-analysis recommended dry needling, as compared with sham or placebo, for decreasing pain immediately after treatment and at 4 weeks in patients with upper-quarter MPS. ^[4]

Several mechanisms have been suggested as possible explanations for the inactivation of trigger points by injection, including disruption of abnormal muscle fibers or nerve endings that make up the sensory and motor aspects of the feedback loop, which may be responsible for trigger point activity. Needling may cause a local release of intracellular potassium, which may depolarize and thus disrupt nerve conduction.

Injected fluid may dilute any nerve-sensitizing substances to reduce irritability and inactivate any neural feedback mechanisms. Procaine has a local vasodilatation effect that increases circulation at the trigger point, increasing the local removal of metabolites and increasing local energy supply. Further, a local anesthetic may interrupt feedback mechanisms between the trigger point and the central nervous system, limiting high frequency discharges transmitted by the nerve. Depending on the anesthetic, focal necrosis may destroy the trigger point. ^[5]