Unraveling 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: Patients (N=128) with chronic neck pain.

Interventions: Participants were randomized into 2 groups; DDN of the neck muscles combined with stretching (n=64) and stretching alone (n=64).

Main outcome measures: Two outcomes (pain intensity and neck pain-related disability) and 3 candidate mediators (local pressure pain 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 3 time points: after intervention and at 2- and 4-week follow-up. Age, sex, and the baseline values of the outcome and mediators were included as pretreatment mediator-outcome confounders.

Results: Reductions in pain intensity strongly mediated the short-term effects of DDN on disability, from after intervention to 4-week follow-up. In addition, the attenuation of local hypersensitivity (via increasing PPTs) moderately mediated reductions in pain intensity at each time point. 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.

Conclusions: 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.