Dry needling has lasting analgesic effect in shoulder pain: a double-blind, sham-controlled trial

Myofascial pain syndrome (MPS) is one of the leading causes of chronic shoulder pain, affecting up to 95% of patients with this condition. Characterized by the presence of painful trigger points in taut muscle bands, MPS can cause local and referred pain, significantly limiting shoulder function. Dry needling has emerged as a promising technique for treating trigger points, but its actual efficacy and temporal pattern of action remained poorly clarified in adequately controlled studies. This randomized, double-blind, sham-controlled trial was conducted at the Hospital das Clínicas of the University of São Paulo, Brazil, between February 2015 and January 2016.

The researchers recruited 74 patients with chronic shoulder pain, randomizing 43 participants into two groups: active dry needling (n=20) and sham (n=21). All patients had myofascial pain syndrome with identifiable trigger points in the trapezius muscle. The protocol included a rigorous assessment at three time points: one week before the procedure (D0), on the day of needling (D7), and one week afterward (D14). During the baseline period, patients recorded their pain intensity daily.

Active needling consisted of inserting 0.25 x 40 mm needles directly into the trapezius trigger points, following the standardized Simons technique. The sham procedure involved superficial and parallel needle insertion, without penetrating the muscle or reaching the trigger point. Both procedures lasted exactly 20 seconds, and the pain intensity during the procedure was carefully controlled to maintain blinding. The results demonstrated superior efficacy of active dry needling.

The mean pain intensity decreased significantly from 6.30 ± 2.05 before treatment to 2.40 ± 2.45 one week after in the active group, compared with a smaller reduction in the sham group (from 6.04 ± 1.32 to 5.14 ± 1.49). The effect size was robust (Cohen's d = 1.34), with a number needed to treat of just 2.1 patients. Interestingly, the temporal pattern of benefits revealed that analgesic effects were not immediate, beginning only on the second day after the procedure and persisting for at least the seventh day. This finding suggests that the mechanisms of action of dry needling may go beyond simple mechanical inactivation of trigger points, possibly involving more complex neurophysiological processes that take days to establish.

The study also investigated sensory changes through quantitative sensory testing (QST) in three areas: the painful region of the trapezius, the contralateral mirror area, and a control area on the trunk. Active dry needling produced a significant reduction in the area of mechanical hyperalgesia (from 49.2 ± 37.4 cm² to 30.3 ± 28.5 cm² after one week), but this sensory improvement did not correlate directly with clinical pain relief. In addition to benefits in pain intensity, dry needling significantly improved pain interference with daily activities, mood, and sleep, as measured by the Brief Pain Inventory. Eighty percent of patients in the active group reported "significant improvement" versus only 33.3% in the sham group.

Safety was excellent, with only minor and transient adverse effects reported, such as mild local post-procedure pain in some patients. Blinding was effective, as patients were unable to correctly identify which treatment they had received. The clinical implications are substantial. The delayed onset of benefits (after 2 days) suggests that immediate post-needling assessments may underestimate its true efficacy.

The duration of benefits of at least one week indicates that weekly sessions could be more appropriate than daily protocols for maintenance treatment. Proposed mechanisms include not only local effects on trigger points but also central pain modulation through descending inhibitory pathways, release of endogenous opioids, and modulation of neurotransmitters such as serotonin. Limitations include the use of only one treatment session (whereas clinical practice generally employs multiple sessions), follow-up limited to one week (the total duration of benefits is unknown), and the monotherapeutic nature of the study (in real practice, dry needling is frequently combined with other modalities). This study provides robust evidence that dry needling is an effective intervention for chronic shoulder pain associated with myofascial pain syndrome, with clinically significant benefits that persist for at least one week after a single session.