Trigger Point Injection with Local Anesthetic

What Is Trigger Point Injection

Trigger point injection — also called wet needling — consists of inserting a fine needle into an active myofascial trigger point followed by injecting a small volume of local anesthetic (typically 1% lidocaine without vasoconstrictor) or, in some schools, 0.9% saline. The technique targets the palpable taut band within the involved muscle, where the muscle fiber is chronically contracted and generates referred pain when stimulated.

The difference compared with dry needling is objective: in dry needling, only the needle is used, without injection of any substance; in wet needling, the effect of the local anesthetic is added to the mechanical effect of the needle. In clinical practice, this difference is more debatable than it appears at first glance — systematic reviews show equivalent results in many outcomes — but the two response profiles diverge on specific points, such as patient tolerance and post-procedure pain.

The technique was formalized by Janet Travell and David Simons in the classic Myofascial Pain and Dysfunction: The Trigger Point Manual (1983), still a reference work today. In Brazil, the correct terminology is "pontos-gatilho" (hyphenated); the older spelling "ponto de gatilho" appears in older texts but does not correspond to the technical nomenclature currently adopted. The procedure is performed by physicians trained in pain medicine, physical medicine and rehabilitation, medical acupuncture, anesthesiology, or rheumatology.

Mechanism of Action

The effects of trigger point injection combine at least three fronts. The first is mechanical: the needle, when crossing the taut band, disorganizes the contracted fibers and may trigger the so-called local twitch response, interpreted as a sign of technical precision and an indicator of direct involvement of the dysfunctional motor endplate.

The second is the biochemical washout of the trigger point microenvironment. Microdialysis studies led by Shah et al. (Arch Phys Med Rehabil, 2008) demonstrated that the chemical environment of active trigger points is distinct from normal muscle tissue, with increased concentrations of substance P, CGRP, bradykinin, prostaglandins, and other mediators of peripheral sensitization. Local perfusion induced by the injection contributes to the mechanical removal of these mediators and to reduction of local nociceptive excitability.

The third is the transient anesthetic blockade of sensitized nerve fibers. The pharmacologic effect of lidocaine lasts a few hours, but clinical relief frequently extends days to weeks — which suggests that the injection interrupts a self-perpetuating cycle of peripheral and central sensitization driven by chronic referred pain. The duration of the effect is not proportional to the half-life of the anesthetic: the functional "reset" of the circuit is the outcome of interest.

Scientific Evidence

Evidence on trigger point injection is extensive in volume but heterogeneous in quality. The technique has accumulated decades of clinical use since its formalization by Travell and Simons, and most available trials have been run in small populations, with varying methodologic designs and poorly standardized protocols — which limits quantitative synthesis of results.

The microdialysis study by Shah et al. (Arch Phys Med Rehabil, 2008) is a reference for the mechanism: by demonstrating the altered biochemical profile of active trigger points and the modification of this profile after injection, it supported the washout hypothesis as an important component of the therapeutic effect. In terms of clinical outcomes, the meta-analysis by Ay et al. (2020) compared wet and dry needling in myofascial pain and found equivalent results in most pain and function outcomes, with small advantages for wet needling in reducing post-procedure pain at the first session.

Successive systematic reviews on trigger point injection in myofascial pain show consistent benefit over placebo in the short term, with high heterogeneity between studies. The older Cochrane review by Scott et al. (2014) on trigger point blocks in nonspecific low back pain concluded with insufficient evidence for a strong recommendation — and that reading remains valid in the absence of recent multicenter RCTs that have filled the gap. Brazilian guidelines specific to the technique have not yet been published; in practice, application is by analogy with international recommendations and clinical judgment.

In cervicogenic headache and myofascial pain syndrome in the cervical and lumbar regions, small RCTs and case series describe consistent pain reduction in about 40-60% of responder patients, with NNT estimated between 3 and 6 in selected populations — a favorable value, but derived from small samples and with wide variation by subgroup. For diffuse myofascial pain or pain superimposed on centralized syndromes (such as fibromyalgia), evidence is consistently weaker.

Indications

Appropriate indication for injection depends on two pillars: clear identification of active trigger points on palpation (with reproduction of the patient's referred pain pattern) and failure or insufficient response to a prior step of conservative treatment. The procedure is rarely indicated as a first measure; its role is to resolve persistent points after the initial approach with exercise, postural guidance, and simple analgesics.

How It Is Done and What to Expect

The session is performed in the office, with the patient positioned to expose the muscle group being treated and relax adjacent musculature (for example, prone for trapezius and paravertebrals, side-lying for quadratus lumborum, seated with support for SCM and scalenes). The physician performs skin antisepsis and identifies the taut band and active trigger points by digital palpation — the most time-consuming and outcome-decisive step.

The typical protocol involves 1 to 3 points per session, with 1% lidocaine without vasoconstrictor in a volume of 0.5 to 1 mL per point, using a fine needle (27G to 30G, compatible with muscle depth). The fanning technique — fan-shaped movement of the needle in several directions within the trigger point, without fully removing it from the skin — is widely used to increase coverage of the taut band. The presence of local twitch response during fanning confirms precision at the correct point.

The session lasts between 10 and 20 minutes. Immediately after, a sensation of local soreness is common for 24 to 72 hours in 40-60% of patients — an expected phenomenon, part of the therapeutic effect, and not a complication. The usual guidance is local warm compress, gentle stretching of the treated muscle, and a simple analgesic if needed. Reassessment typically occurs after 1-2 weeks, when continuation, point adjustment, or discontinuation is decided based on response.

Adverse Effects, Risks, and Contraindications

Trigger point injection has a favorable safety profile in the medical office, with a low rate of serious adverse events. Most complications are self-limited and directly related to mechanical needle trauma. The risk of pneumothorax at thoracic points, though rare, is real and should be discussed with the patient before sessions in the middle trapezius, rhomboids, scalenes, and other groups adjacent to the chest cavity.

Limitations and What Is Still Not Known

Despite wide clinical use, trigger point injection still faces standardization limits and questions the literature has not yet answered satisfactorily. One recurrent source of misunderstanding is the direct comparison between wet and dry needling — a discussion that, when properly contextualized, points more toward clinical preference than technical superiority.

Evidence Gaps

Main gaps include: (1) protocol heterogeneity across studies (substance, volume, number of points, interval between sessions), which makes robust meta-analyses difficult; (2) lack of standardization on the ideal number of sessions per series and the criterion for discontinuation due to non-response; (3) scarcity of recent direct comparative RCTs between wet and dry needling with standardized outcomes and adequate blinding; (4) absence of a Brazilian guideline specific to the technique, which leaves practice anchored in clinical consensus and adaptation of international literature.

There is also a relevant operational issue: post-injection soreness is frequent and, although expected, may limit some patients' adherence to the full protocol of a series. Clear communication about this effect before the procedure is an important part of management; absence of this guidance is often confused with "complication" and leads to early abandonment of treatments that could still respond well.

Relationship with Medical Acupuncture

Trigger point injection and medical acupuncture share the use of the needle as a clinical tool and act, to some extent, on the same neurophysiologic pain circuits. However, they differ in target, dominant mechanism, and response profile. Injection focuses on the specific myofascial trigger point, with a predominantly local mechanism (mechanical + anesthetic); medical acupuncture selects points based on neuroanatomic and traditional criteria, including motor points, dermatomal points, and points corresponding to nerve trunks, with a more distributed effect and a more pronounced central component.

In practice, the two techniques coexist and generally are not applied to the same point in the same session — there is local redundancy and a risk of over-stimulation. Sequential use is more common: for example, injecting 1-3 dominant trigger points in short series to "unblock" the region and then maintaining the patient on a course of medical acupuncture for central modulation and recurrence prevention. The initial choice depends on availability, cost, trigger point profile, and informed patient preference.

In short: the techniques are complementary, not competitive, and the choice in each case relies on clinical and operational criteria, not on methodologic dispute. For well-delimited trigger points with a focal referred pain pattern, injection tends to resolve with fewer sessions. For regional pictures with significant central participation (chronic headache, low back pain with a nociplastic component, myofascial pain superimposed on centralized syndromes), medical acupuncture offers greater capacity for broad modulation. Well-planned sequential combination, conducted by the physician, is usually the best strategy when both are available.

When to Seek Medical Help

The decision to consider trigger point injection starts with a structured medical evaluation of myofascial pain. The procedure is not first-line in most cases — its indication gains weight when adequate initial conservative treatment has not produced the expected response. At the same time, indefinitely postponing a potentially useful intervention is not good practice when clinical criteria are already met.