Neurophysiological Effects of Deep Dry Needling on Spinal Reflexes

Academic Background

Deep Dry Needling (DDN) is a commonly used method for treating muscle trigger points (TrPs), particularly in patients with neuromuscular pain and spasticity. Although DDN is widely used in clinical practice, its neurophysiological mechanisms are not yet fully understood. Trigger points are classified as active or latent, with latent trigger points not necessarily causing pain but potentially affecting muscle function, range of motion, and muscle fatigue. Therefore, studying the effects of DDN on spinal reflexes, especially in the treatment of latent trigger points, can help elucidate its neurophysiological effects and provide a theoretical basis for neurorehabilitation.

This study aimed to investigate the effects of DDN on spinal reflexes, particularly on the H-reflex (Hoffmann reflex) and reciprocal inhibition of the triceps surae. By examining how DDN modulates spinal reflexes, the study provides scientific evidence for the application of DDN in neurorehabilitation.

Source of the Paper

This paper was co-authored by Gretchen Seif, Alan M. Phipps, Joseph M. Donnelly, Blair H. S. Dellenbach, and Aiko K. Thompson. The authors are affiliated with the College of Health Professions at the Medical University of South Carolina, the Department of Health Sciences and Research, and the University of St. Augustine for Health Sciences. The paper was first published on December 20, 2024, in the Journal of Neurophysiology, with the DOI 10.1152/jn.00366.2024.

Research Process and Results

Research Process

The study recruited 17 healthy adults aged 22 to 57 years, none of whom had known neurological or orthopedic conditions, and all had latent trigger points in their medial gastrocnemius (MG). Measurements were taken at four time points: before DDN treatment, immediately after treatment, 90 minutes after treatment, and 72 hours after treatment. At each time point, the following metrics were measured: 1. H-reflex and M-wave: The maximum H-reflex (Hmax) and maximum M-wave (Mmax) of the triceps surae (including the soleus, medial gastrocnemius, and lateral gastrocnemius) were measured by electrically stimulating the posterior tibial nerve (PTN). 2. Reciprocal Inhibition: Reciprocal inhibition of the triceps surae was measured by electrically stimulating the common peroneal nerve (CPN). 3. Passive Ankle Range of Motion (ROM): Passive dorsiflexion range of motion of the ankle was measured using a standard goniometer.

The DDN treatment procedure was as follows: Participants lay supine with their legs slightly flexed and externally rotated. Researchers located latent trigger points in the MG through palpation and inserted a disposable stainless steel acupuncture needle into the trigger points until a local twitch response (LTR) was elicited. The needle was then moved up and down near the trigger point for 25-30 seconds until all LTRs disappeared.

Key Findings

1. Changes in M-wave: The study found that the Mmax amplitude of the medial gastrocnemius significantly decreased immediately after DDN treatment and at 90 minutes post-treatment (by 14% and 18%, respectively), but returned to pre-treatment levels by 72 hours. In contrast, the Mmax amplitudes of the soleus and lateral gastrocnemius did not change significantly. This indicates that DDN temporarily affects the neuromuscular connections of the treated muscle.

2. Changes in H-reflex: The Hmax amplitude of the triceps surae did not change significantly after DDN treatment, suggesting that DDN does not significantly affect the excitatory reflex pathways of the spinal cord.

3. Changes in Reciprocal Inhibition: Reciprocal inhibition of the soleus increased significantly immediately after treatment and at 72 hours post-treatment (by 30% and 36%, respectively), while reciprocal inhibition of the lateral gastrocnemius did not change significantly. This suggests that DDN may enhance inhibitory reflexes in the soleus by modulating inhibitory interneurons in the spinal cord.

4. Changes in Ankle Range of Motion: Passive dorsiflexion range of motion of the ankle increased significantly immediately after treatment and at 72 hours post-treatment (by 4 degrees and 3 degrees, respectively), but returned to pre-treatment levels at 90 minutes. This indicates that DDN may improve joint range of motion by altering muscle mechanics or neural regulation.

Conclusions and Significance

The study found that DDN temporarily affects the neuromuscular connections of the treated muscle (medial gastrocnemius), as evidenced by the temporary decrease in Mmax amplitude. Additionally, DDN enhanced reciprocal inhibition in the soleus, indicating its modulatory effect on spinal inhibitory pathways. These findings reveal the complex neurophysiological effects of DDN at the spinal level and provide theoretical support for its application in neurorehabilitation.

Research Highlights

1. Specific Effects: DDN specifically affected the Mmax amplitude of the treated muscle without impacting other muscles, indicating its localized action.
2. Modulation of Spinal Reflexes: DDN enhanced reciprocal inhibition in the soleus, demonstrating its regulatory effect on spinal inhibitory pathways.
3. Time-Dependent Effects: The effects of DDN on Mmax and reciprocal inhibition were time-dependent, suggesting that its mechanisms may involve multiple neurophysiological processes.

Other Valuable Information

The study also found that the effects of DDN on ankle range of motion followed a similar time course as changes in reciprocal inhibition, suggesting that both may be regulated by the same neurophysiological mechanisms. Furthermore, the temporary effects of DDN provide a therapeutic window for motor training immediately after treatment or at 72 hours post-treatment to maximize therapeutic outcomes.

Summary

Through a systematic experimental design, this study revealed the complex effects of DDN on spinal reflexes, providing important scientific evidence for its application in neurorehabilitation. Future research could further explore the effects of DDN in different clinical populations and compare it with other trigger point treatment methods to optimize its clinical application.