Unravelling the mechanisms behind the short-term effects of dry needling: new insights from a mediation analysis with repeatedly measured mediators and outcomes

Objective
to explore the causal pathways underlying the short-term effects of deep dry needling (DDN) in people with chronic neck pain.
Design
explanatory longitudinal mediation analysis with repeatedly measured mediators and outcomes.
Setting
primary care setting.
Participants
128 patients with chronic neck pain.
Interventions
Participants were randomized in 2 groups; DDN of the neck muscles combined with stretching (N = 64) and stretching alone (N=64).
Outcome Measures(s)
Two outcomes (pain intensity and neck pain-related disability) and 3 candidate mediators (local pain pressure thresholds (PPTs), cervical range of motion (ROM) and neck muscle strength) were included. Pain intensity was also included as a competing mediator in the mediation analysis for disability. Mediators and outcomes were measured at three timepoints; post-intervention and 2- and 4-week follow-up. Age, gender and the baseline values of the outcome and mediators were included as pre-treatment mediator-outcome confounders.
Results
reductions in pain intensity strongly mediated the short-term effects of DDN on disability, from post-intervention to 4-week follow-up. In addition, the attenuation of local hypersensitivity (via increasing PPTs) moderately mediated reductions in pain intensity at each timepoint. On the other hand, gains in cervical ROM contributed to reducing neck pain-related disability. Changes in muscle strength did not lead to better outcomes.
Conclusion
this novel study demonstrated that DDN effect on neck pain-related disability is strongly driven by the analgesic effects of this physical therapy modality. Increasing PPTs and cervical ROM seem to be also part of the mechanisms behind DDN's effect.