Trigger-point dry needling is an invasive procedure where a fine needle or acupuncture needle is inserted into the skin and muscle. It is aimed at myofascial trigger points (MTrP) which are hyperirritable spots in skeletal muscle that are associated with a hypersensitive palpable nodule in a taut band.[1] Trigger point dry needling can be carried out at superficial or deep tissue level.
Trigger points are thought to be due to an excessive release of acetylcholine from selected motor endplates. They can be divided into Active and Latent myofascial trigger points.
Active trigger points can spontaneously trigger local or referred pain. They cause muscle weakness, restricted ROM and autonomic phenomena.
Latent trigger points do not cause pain unless they are stimulated. They may alter muscle activation patterns and contribute to restricted ROM.
Therefore both active and latent trigger points cause allodynia at the trigger point site and hyperalgesia away from the trigger point following applied pressure.[2]
The formation of trigger points is caused by the creation of a taut band within the muscle. This band is caused by excessive acetylcholine release from the motor endplate combined with inhibition of acetylcholine esterase and upregulation of nicotinic acetylcholine receptors.
Initially taut bands are produced as a normal protective, physiological measure in the presence of actual or potential muscle damage. They are thought to occur in response to unaccustomed eccentric or concentric loading, sustained postures and repetitive low load stress. However when sustained they contribute to sustained pain.
Pain caused by trigger points is due to hypoxia and decreased bloodflow within the trigger point. This leads to a decreased pH which activates the muscle nociceptors to restore homeostasis. This causes peripheral sensitization.
Trigger points are also involved in central sensitization. The mechanism remains unclear but trigger points maintain nocioceptive input into the dorsal horn and therefore contribute to central sensitization.
Mechanisms of Action
Dry needling has been shown to immediately increase pressure pain threshold and range of motion, decrease muscle tone, and decrease pain in patients with musculoskeletal conditions.[4] Its suggested mechanisms of action include:
Local Twitch Response: Dry needling can elicit ‘local twitch response’ which is an involunatary spinal reflex resulting in a localized contraction of the affected muscles that are being dry needled. Local twitch response can lead to alteration in the length and tension of muscles fibers and stimulate mechanoreceptors like A Beta fibers.[5]
Effects on Blood Flow: Sustained contraction of taut muscle bands in trigger points might cause local ischemia and hypoxia. Dry needling causes vasodialation in the small blood vessels leading to increased muscle blood flow and oxygenation.[5]
Neurophysiological effects: Dry needling may produces local and centeral nervous responses to restore hemostasis at the site of the trigger point which results in reduction in both centeral and peripheral sensitization to pain.[4]
Remote Effects: Dry needling of distal MTrP has been found to have analgesic effect on proximal MTrP. The literature has conflicting evidence regarding the contralateral effect.[5]
Placebo Effect
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