Changes in stiffness at active myofascial trigger points of the upper trapezius after dry needling in patients with chronic neck pain: a randomized controlled trial

This randomized controlled trial investigated the immediate effects of dry needling on myofascial trigger points of the upper trapezius muscle in patients with chronic neck pain. Myofascial trigger points are hypersensitive areas within taut muscle bands that cause local and referred pain and are commonly found in patients with neck pain. Dry needling has been widely used to treat these conditions, but its mechanisms of action are not yet fully understood. The researchers recruited 60 patients with chronic unilateral neck pain (minimum duration 3 months) who had at least one active trigger point in the upper trapezius.

Participants were randomized into two groups: 32 received real dry needling and 28 received placebo (sham) needling. Real needling used 0.25 mm x 25 mm needles inserted directly into the most symptomatic trigger point, with rapid in-and-out motions until a local twitch response was elicited. The placebo group received a visually identical procedure but using a telescoping device that did not penetrate the skin. The main outcomes were assessed before and 10 minutes after the interventions, including shear wave elastography to measure muscle stiffness and algometry to assess pressure pain threshold, both at the trigger point and at a control point located 3 cm laterally.

Surprisingly, the results showed that neither treatment (real or placebo) produced detectable changes in muscle stiffness, measured by both Young's modulus and shear wave velocity. This finding contradicts the expectation that dry needling would reduce muscle tension at trigger points. However, both groups showed significant improvements in pressure pain threshold at the trigger point site. The group receiving real needling also showed additional increases in pain threshold at the control point, suggesting a broader analgesic effect compared with placebo.

These results have important implications for understanding the mechanisms of dry needling. The fact that both real and placebo treatments reduced local pain sensitivity suggests that factors such as patient expectation, tactile stimulation, and other nonspecific effects can contribute significantly to the benefits clinically observed. The additional analgesic effect at the control point observed only in the real group indicates that genuine dry needling may activate broader pain modulation mechanisms, possibly involving the central nervous system. The absence of changes in muscle stiffness raises questions about whether changes in muscle tension are truly the primary mechanism of action of dry needling, as traditionally believed.

Other mechanisms, such as neurophysiologic pain modulation, may be more relevant to the therapeutic effects observed clinically. This study has several important limitations. Stiffness assessment was performed only in the longitudinal plane of the muscle fibers, which may not adequately capture three-dimensional changes in muscle tension. In addition, measurements were made only immediately after treatment, not allowing assessment of more durable effects.

The sample size, although adequate for the study's objectives, is still relatively small for detecting more subtle effects. Shear wave elastography, despite being an objective technique, has shown only moderate reliability in previous studies, which may limit its sensitivity to detect clinically relevant changes. For clinical practice, these results suggest that dry needling may be effective for immediate pain reduction at trigger points, but its benefits may not be directly related to changes in muscle stiffness detectable by ultrasound. This does not necessarily diminish the clinical efficacy of dry needling, but it suggests that our understanding of its mechanisms of action needs to be refined.