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. Trigger point dry needling can be carried out at superficial or deep tissue level.

Superficial dry-needling

This was developed by Peter Baldry. He recommended the insertion of needles to 5-10mm over a MTrP for 30 secs. Palpation of the MTrP then determined the level of response and whether needle stimulation was sufficient to alleviate MTrP pain. If not the need was re- inserted.

Trigger point model

The trigger point model is a dry needling technique that specifically targets myofascial trigger points. They 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. 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 blood flow 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 nociceptive input into the dorsal horn and therefore contribute to central sensitization.

Suggested mechanisms of effect:

Stimulation of a local twitch response (LTR)

Dry-needling of these myofascial trigger points via mechanical stimulation causes an analgesic effect. This mechanical stimulation causes a local twitch response (LTR). An LTR is an involuntary spinal cord reflex contraction of the muscle fibres in a taut band. Triggering an LTR has been shown to reduce the concentration of nociceptive substances in the chemical environment near myofascial trigger points.

Muscle regeneration

The needle may cause a small focal lesion which triggers satellite cell migration to the area which repair or replace damaged myofibers. This occurs 7-10 days after dry needling. It is unclear whether continued dry needling within this period may disrupt this process.

A localised stretch to the cytoskeletal structures

This stretch may allow sarcomeres to resume their resting length.

Electrical polarization of muscle and connective tissue

The mechanical pressure causes collagen fibres to intrinsically electrically polarize which triggers tissue remodelling.

The effectiveness of this treatment depends greatly on the skill of the therapist to accurately palpate myofascial trigger points as well as kinaesthetic awareness of the anatomical structures.

A Cochrane review (2005) of RCTs concluded that trigger point dry needling is beneficial for low back pain. It is suggested that dry-needling reduces/removes nociceptive input from trigger points, normalize synaptic efficacy and reduce peripheral and central
sensitization. Dry-needling can restore muscle activation and strength as well as range of motion (ROM). Dry-needling decreases pain in patients with chronic low back pain and in patients with hemiparetic upper limb post CVA.