This blog post is largely derived from our podcast interview with Barbara Cagnie and supplemented with evidence from several studies. It is by no means a complete overview of the scientific literature on dry needling but aims to provide evidence for the topics discussed. Enjoy reading!
Dry needling is a technique that is mainly used by physiotherapists to treat myofascial pain. Dry needling is a thin filiform needle that is inserted into the muscle into a specific trigger point with the main aim of decreasing pain and restoring muscle function. Other treatment indications are neurological disorders and scar tissue. It’s very often compared to acupuncture, but the philosophy of using this technique is quite different. Acupuncture is based on traditional Chinese medicine, whereas dry needling should be seen as a tool within the toolbox of healthcare providers in the management of musculoskeletal pain.
Peripheral Physiological Effects of Dry Needling: The taut band
How does dry needling decrease pain and what are the physiological mechanisms behind it? Our podcast guest Barbara Cagnie published a paper on the physiological effects of dry needling (Cagnie et al. 2013) which makes for an interesting read. There, she mentions several effects, both peripheral and central. Most studies have investigated the peripheral effects of dry needling, but to understand the underlying mechanism of dry needling, it’s important to briefly describe the pathophysiology of the development of a trigger point. The most common hypothesis is the so-called integrated trigger point hypothesis, which was originally developed by Travell and Simons and then further expanded by Robert Gervin, Jan Dommerholt, and Jay Shah (Gervin et al. 2004).
According to this theory, a taut band develops due to muscle overload or trauma and there may be an inhibition of acetylcholinesterase. That’s an enzyme that breaks down acetylcholine, which results in an increase of acetylcholine in the synaptic cleft. As a result, high-frequency miniature end plate potentials occur, which can be determined experimentally with needle electromyography as spontaneous electrical activity. This increase in spontaneous electrical activity and acetylcholine leads to an increased release of calcium at the level of the sarcoplasmic reticulum. In turn, this causes the sustained contraction of the sarcomeres leading to the formation of the taut band. Studies on rats have demonstrated that dry needling at the exact trigger point may increase the release of acetylcholinesterase, which decreases the acetylcholine release as well as the spontaneous electrical activity of the muscle. As a consequence, there’s a relaxation of the muscle.
Gerwin et al. (2004) – Sorry for the bad resolution
Peripheral Physiological Effects of Dry Needling: Pain & Inflammation
A second effect is on pain and inflammation. Due to the sustained muscle contraction, there is a capillary constriction which leads to local ischemia. This results in decreased energy supply. On the other hand, due to the ongoing contraction, the muscle needs a lot of energy leading to a disbalance. The reduced energy supply in combination with the increased energy demand results in an energy crisis and as a result, inflammatory mediators such as bradykinin, prostaglandin, and serotonin are released stimulating the nociceptors. Activation of those nociceptors releases other neuropeptides such as substance P and calcitonine-gene-related peptides. These changes cause local pain upon palpation of the trigger point. A study on rabbits has demonstrated that dry needling may increase the beta-endorphin levels in the muscle itself and in serum, accompanied by a reduction in substance P levels of the muscle and at the dorsal root ganglion This is mainly the case when one dosage of dry needling is given. If however, dry needling is performed for several consecutive days, there seems to be also an increase in the number of hypoxic responsive proteins which may promote angiogenesis and increase the capillarity in the skeletal muscle (Hsieh et al. 2012).
Central Effects of Dry Needling: From Gate Control to Placebo
Lastly, there may be central effects of dry needling which have been underestimated or understudied until now with the main information coming from the acupuncture literature. To start, the gait control effect, which is supposed to mainly occur by using techniques such as winding or in situ, which are not pain provocative, may stimulate A-beta fibers (Chu et al. 2022). Other effects are the conditioned pain modulation and changes in skin conductance (Navarro-Santana et al. 2022) and heart rate frequency (Lázaro-Navas et al. 2021), but these results are rather contradictory. Lastly, as with all hands-on techniques we use within physiotherapy, you have the placebo effect, which may not be underestimated when you use dry needling. These neurophysiological effects may very well be responsible for the main effects of dry needling.
Identifying Trigger Points – A Challenge and main critique point on DN
According to the theory, trigger points can be distinguished into active and latent trigger points. Active trigger points can cause spontaneous pain at rest, during movement, or compression. They can lead to local pain and referred pain recognizable pain for the patient. Furthermore, a jump sign or a local twitch response may be elicited upon palpation or needling which is not present in latent trigger points. Latent trigger points are only sensitive to compression or movement not at rest. While a referred pain sensation may be elicited, it is not the recognizable pain of the patient. On top of that, active trigger points are associated with greater zones of referred pain and higher pain intensity than latent trigger points.
At the moment there is no consensus in the scientific literature regarding the reliability of manual palpation of trigger points. Several studies show only low to moderate inter- and intra-rater reliability (Lucas et al. 2009, Myburgh et al. 2008). However, other studies have shown good reliability (Rozenfeld et al. 2017, Rozenfeld et al. 2021, Sales do Nascimento et al. 2018). In a Delphi study by Fernández-de-las-Peñas et al. (2018) on diagnostic criteria of myofascial trigger points, 60 international experts identified a cluster of three diagnostic criteria as essential for the trigger point diagnosis:
- Identification of the taut band
- Identification of a hypersensitive spot
- Induction of referred pain.
Similar to other studies on palpation, it seems that reliability is poor for objective signs such as the taut band and local twitch response and higher(often moderate to substantial) for subjective signs such as tenderness and pain reproduction like summarized by Lucas et al. (2009).
The phenomenon of referred pain in trigger points
According to the convergence-projection theory referred pain is always referred from a region of low density of afferent input to a region of high density of afferent innervations. In concrete, this could be pain referral from a deep axial, structure with a low afferent nociceptive innervation such as a facet joint, referring pain to a distal structure such as the back of the leg, which has a high afferent nociceptive innervations. In muscles, which are all highly innervated, the mechanism has to be different. The most plausible explanation of referred pain in trigger points zooms in on the dorsal horn. Sustained nociceptive impulses from the muscle may activate NMDA receptors at the dorsal horn that are normally inactive. If activated by sustained nociceptive impulses they may activate other wide dynamic range neurons and activate silent synapses. In turn, this may lead to an expansion of the receptive fields which is the underlying theory of referred pain from trigger points. For example, the soleus muscle can refer pain to the sacroiliac joint. The explanation for this phenomenon is that:
- Nociceptors in the trigger points of the soleus induce local pain
- Sustained proprioceptive impulses are transferred to the spinal cord neurons at segments L5 and S1, which are the normal relay stations of the soleus muscle.
- Excitation spreads in the spinal cord activating the normally ineffective connections between the soleus muscle and the neurons below L5 & S1, so S2-S4, which innervate the SI Joint
- The patient may also experience pain in the sacroiliac joint.
The local twitch response – necessary for treatment success?
A local twitch response is a very brief, sometimes painful contraction of a taut band in the skeletal muscle that is elicited during dry needling, which can sometimes be elicited by manual palpation as well. Clinically, the impression is that the effect after dry needling is often better when a local twitch response is elicited. However, the twitch response is also blamed for post-needling soreness. A systematic review by Perreault et al. (2017) showed that eliciting a local twitch response does not correlate with changes in pain and disability. On the other hand, a recent systematic review by Fernández-de-las-Peñas et al. (2022) concluded that the twitch response was more effective in immediate pain reduction. They did not find an effect on disability or pressure pain sensitivity in spinal pain disorders associated with muscle TrPs.
Local twitch responses are mainly elicited when using the fast in, fast out technique, also called the Hong technique, where the needle is repeatedly moved up and down in the muscle. This technique is mainly used in patients with subacute or recurrent pain.
In patients with chronic pain, it’s better to use techniques that do not elicit local twitch responses to avoid post-needling soreness. In these cases, other techniques, such as needle winding or needling with needles left in place, or recommended.
Dry Needling in other conditions
Dry needling in tendons involves repeated penetration of the affected tendon, which is thought to disrupt the chronic degenerative process and encourage localized bleeding and fibroblastic proliferation (Stoychev et al. 2020). A systematic review by Krey et al. (2015) found that tendon needling improves patient-reported outcome measures in patients with tendinopathy. The authors included studies on lateral elbow tendinopathy, Achilles tendinopathy, and rotator cuff tendinopathy.
Furthermore, evidence is emerging for dry needling as an effective treatment in patients with neurological disorders, mainly in patients with stroke, where dry needling is used to work on the spasticity of patients in the lower limb and in the upper limb. It has been demonstrated that dry needling in those patients improves spasticity, decreases pain, and improves the range of motion (Bynum et al. 2020).
For the treatment of scar tissue, it is assumed that mechanical stress by inserting a needle into scar tissue stimulates fibroblasts and encourages the realignment of collagen bundles to the direction of stress. The evidence is scarce with studies differing regarding the delivery of dry needling or local acupuncture for scar treatment. While 9 out of 10 included studies in the review by Chmieleswska et al. (2024) resulted in a reduction of scar pain or other scar-related symptoms, multicentre, blinded, randomized, controlled studies on dry needling need to be performed to analyze their effect on scar formation, scar-related pain, and clinical symptoms.
The effectiveness of dry needling in MSK conditions
In the last couple of years, a lot of systematic reviews have been published on the effectiveness of dry needling in different regions of the body. An umbrella review by Chys et al. 2023 umbrella review looked at the evidence of clinical effects of dry needling on musculoskeletal disorders across all body regions. They showed that dry needling is superior to sham or no intervention, and equally effective to other interventions when it comes to pain reduction in the short term. Results on physical functioning outcomes such as improving range of motion, improving strength, and improving motor control are contradictory across body regions. Limited data is available for mid and long-term effects.
While dry needling has often been investigated as a solo treatment, more studies are looking to investigate at the additional value to interventions that are used in clinical practice. These studies have shown that there is an additional treatment effect when dry needling is with other physiotherapeutic interventions compared to those interventions in isolation. The strongest evidence for dry needling nowadays exists for neck pain showing the superiority of dry needling for the reduction of pain intensity in the short term.
Adverse Events of Dry Needling
Major adverse events have been described in the literature after dry needling, such as pneumothorax and excessive bleeding. A study by Boyce et al. 2020 collected information related to minor and major adverse events that occurred during more than 20,000 dry needling sessions performed by over 400 physical therapists. In 36% of the cases, minor adverse events, such as small bleeding, bruising, and pain during dry needling were reported.
Boyce et al. (2020)
In 20,000 dry needling sessions, 20 major events (<0,1%) were described. For this reason, following formal education to perform dry needling is essential to minimize the risk of these adverse events.
Boyce et al. (2020)
Needling versus manual pressure techniques
Dry needling is one option to maybe relieve a taut band. Manual pressure is another, safer, alternative. In the literature, several studies have compared manual pressure release to trigger point dry needling. Most of these studies could not demonstrate a difference between both techniques (de Meulemeester et al. 2017, Lew et al. 2021, Jorge Rodríguez-Jiménez et al. 2022) . However, most studies investigated the superficial muscles, which can be approached both manually and with dry needling. The question is whether deeper-lying muscles can be accessed with manual techniques. No study has yet investigated the difference between manual pressure release of deeper-lying muscles and dry needling. So for superficial muscles, there’s no difference based on the scientific literature. Clinically, the impression by many therapists is a superior effect of dry needling compared to manual pressure release.
Short-term effects
Dry needling mainly has a short-term effect. The question if short-term effects provide any therapeutic value at all makes for a whole other discussion.
For this reason, it should be seen as a tool in the early phase of treatment in order to create a condition to start exercise therapy or to start other therapies. Moreover, dry needling should not be seen as a standalone therapy. The problem in scientific research is that it’s very often investigated as a standalone treatment, but an increasing number of studies are investigating the additional effect of dry needling. The results – again – are mixed (Stieven et al. 2020, Para-García et al. 2022).
