Residency · Residency · Chronic Pain Management

Trigger Point Injections

Introduction

Myofascial pain syndrome (MPS) is one of the most common causes of chronic musculoskeletal pain, affecting an estimated 85% of patients presenting to pain clinics at some point during their evaluation. Central to MPS is the myofascial trigger point (MTrP) — a hyperirritable spot within a taut band of skeletal muscle that is painful on compression and can produce characteristic referred pain patterns, motor dysfunction, and autonomic phenomena.

Pathophysiology of Myofascial Pain Syndrome

The Integrated Trigger Point Hypothesis

The prevailing model for trigger point formation is the integrated hypothesis proposed by Simons and Travell. According to this model, abnormal endplate activity leads to excessive acetylcholine release at the neuromuscular junction. This sustained sarcomere contraction creates a localized energy crisis with increased metabolic demand and reduced local blood flow. The resulting ischemia promotes the release of sensitizing substances — bradykinin, substance P, CGRP, serotonin, and prostaglandins — into the local milieu, which in turn sensitize peripheral nociceptors and lower their activation threshold. With prolonged peripheral input, central sensitization develops, producing referred pain and expanded receptive fields.

Active vs. Latent Trigger Points

Active trigger points spontaneously produce pain and referred pain patterns that the patient recognizes as their usual complaint. Latent trigger points, by contrast, are painful only on palpation and may restrict range of motion without causing spontaneous pain. Latent points can convert to active points under conditions of mechanical stress, postural dysfunction, emotional stress, or systemic illness.

<image>Cross-sectional anatomical illustration of a myofascial trigger point within the upper trapezius muscle, showing the taut band of contracted sarcomeres, surrounding normal muscle fibers, the motor endplate zone with excessive acetylcholine release, and the local biochemical milieu including sensitizing substances such as substance P, bradykinin, and CGRP, with color-coded regions indicating ischemia versus normal perfusion</image>

Trigger Point Identification

Clinical Examination Techniques

Accurate identification of trigger points requires systematic palpation skills. Flat palpation involves applying fingertip pressure perpendicular to the muscle fiber direction against an underlying bony structure. Pincer palpation involves grasping the taut band between the thumb and fingers, which works well for muscles like the sternocleidomastoid or latissimus dorsi. Snapping palpation involves rolling the fingertip across the taut band to elicit a local twitch response (LTR).

Diagnostic Criteria

The essential diagnostic features of a trigger point include a palpable taut band within the affected muscle, an exquisitely tender nodule within that taut band, patient recognition of the pain as their usual complaint (for active trigger points), referred pain in a characteristic pattern for that muscle, a local twitch response upon snapping palpation or needle insertion, and restricted range of motion with increased pain at end range.

Common Trigger Point Locations

The upper trapezius refers pain to the ipsilateral temporal region and angle of the jaw. The infraspinatus refers pain to the anterior shoulder and lateral arm. The quadratus lumborum refers pain to the iliac crest, hip, and buttock. The piriformis refers pain to the posterior hip and proximal thigh and may mimic sciatica. The sternocleidomastoid refers pain to the ipsilateral forehead, ear, and periorbital region.

<image>Posterior view anatomical diagram of a human body showing the most common trigger point locations marked with red dots in the upper trapezius, levator scapulae, infraspinatus, rhomboids, quadratus lumborum, gluteus medius, and piriformis muscles, with arrows indicating characteristic referred pain patterns radiating from each trigger point in distinct colors</image>

Injection Technique

Preparation and Patient Positioning

The patient should be positioned to allow optimal access to the target muscle with the muscle in a mildly stretched position. The trigger point location is marked after careful palpation, and the skin is cleaned with antiseptic solution (chlorhexidine or alcohol). A 22- to 25-gauge needle of appropriate length is selected — 1.5 inches for superficial muscles and a 3.5-inch spinal needle for deep muscles such as the quadratus lumborum or piriformis.

Local Anesthetic Injection

The trigger point is stabilized between two fingers using a pincer grip or flat palpation. The needle is inserted into the trigger point and a local twitch response is elicited. Then 0.5-1.0 mL of 0.25% bupivacaine or 1% lidocaine without epinephrine is injected. The needle is redirected in multiple directions (fanning technique) to disrupt the entire taut band. A successful injection typically produces multiple local twitch responses followed by relaxation of the taut band.

Dry Needling

Dry needling uses the same technique as injection but without any injectate. The mechanical disruption of the trigger point by the needle is considered the primary therapeutic mechanism. Either acupuncture needles (0.25 mm) or standard hypodermic needles may be used, and multiple rapid insertions (pistoning technique) are performed until local twitch responses cease.

Botulinum Toxin Injection

OnabotulinumtoxinA (Botox) at doses of 10-50 units per trigger point may be used for refractory cases that fail to respond to local anesthetic injections. Its mechanism directly addresses the pathophysiology of the energy crisis hypothesis by inhibiting acetylcholine release at the neuromuscular junction. Onset of action is delayed (3-7 days) with peak effect at 2-4 weeks, and duration of effect is typically 3-4 months.

<image>Step-by-step procedural illustration showing trigger point injection technique in the upper trapezius muscle, depicting four sequential panels: (1) pincer palpation identifying the taut band and trigger point nodule, (2) needle insertion at a 30-degree angle into the trigger point with fingers stabilizing the tissue, (3) fanning technique with needle redirected in multiple directions within the trigger point, and (4) post-injection cross-section showing disrupted taut band with local anesthetic diffusion around the treated area</image>

Evidence for Efficacy

Local Anesthetic vs. Dry Needling

A Cochrane review found limited evidence supporting dry needling for myofascial pain, with moderate short-term benefit. Comparative studies suggest no significant difference between dry needling and local anesthetic injection in terms of pain relief. The local twitch response during needling is the strongest predictor of successful treatment regardless of whether an injectate is used. Hong (1994) demonstrated that eliciting local twitch responses during injection was associated with significantly better outcomes.

Botulinum Toxin Evidence

Randomized controlled trials show mixed results for botulinum toxin in myofascial pain. A meta-analysis by Soares et al. (2012) found modest benefit over saline for cervicothoracic myofascial pain. Cost-effectiveness remains a concern given the expense relative to local anesthetic injection, and the best evidence supports its use in chronic, refractory myofascial pain with clearly identified trigger points.

Adjunctive Therapies

Trigger point injections should be combined with a comprehensive rehabilitation program including stretching, postural correction, and ergonomic modifications. The spray and stretch technique using vapocoolant spray with passive stretching is an effective non-invasive adjunct. Addressing perpetuating factors — sleep disturbance, vitamin D deficiency, hypothyroidism, and mechanical asymmetry — is essential for sustained improvement.

Complications

Pneumothorax is a risk with injections over the thorax, particularly in the scalene, upper trapezius near the lung apex, and serratus anterior muscles. Post-injection soreness is common and self-limited, typically lasting 24-72 hours. Vasovagal syncope can be mitigated by supine positioning and adequate hydration. Hematoma and infection are rare with proper aseptic technique. Needle breakage is avoided by not bending needles and never inserting them to the hub.

Clinical Pearls

The local twitch response is the single most important indicator that the needle is in the trigger point, and it correlates with treatment success. Always palpate for the taut band first, then locate the nodule within it — injecting tender areas without identifying the taut band yields poor results. Total local anesthetic volume should be limited to avoid myotoxicity: 0.5-1.0 mL per trigger point with a maximum of 5-6 points per session. Post-injection stretching within the first 24 hours significantly improves outcomes and reduces post-injection soreness. For trigger points overlying the thorax, use a tangential needle approach and avoid directing the needle toward the chest wall to minimize pneumothorax risk.

References

1. Simons DG, Travell JG, Simons LS. Travell & Simons' Myofascial Pain and Dysfunction: The Trigger Point Manual. 2nd ed. Baltimore: Williams & Wilkins; 1999.
2. Hong CZ. Lidocaine injection versus dry needling to myofascial trigger point: The importance of the local twitch response. Am J Phys Med Rehabil. 1994;73(4):256-263.
3. Soares A, Andriolo RB, Atallah AN, da Silva EM. Botulinum toxin for myofascial pain syndromes in adults. Cochrane Database Syst Rev. 2014;(7):CD007533.
4. Shah JP, Thaker N, Heimur J, Aredo JV, Sikdar S, Gerber LH. Myofascial trigger points then and now: A historical and scientific perspective. PM R. 2015;7(7):746-761.

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