• Active trigger points can spontaneously trigger local or referred pain. They cause muscle weakness, restricted ROMand 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 fibers 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 repairs 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 localized 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 fibers to intrinsically electrically polarize which triggers tissue remodeling.

Indication:

• Identification of myofascial trigger points in the muscle through palpation
• Deep dry needling reproduces the patient’s pattern of pain
• Identification of ‘Jump’ and ‘Shout’ sign on palpation on MTrP
• The minimum criteria for the diagnosis of myofascial trigger points are:
  1. Spot tenderness in a palpable band of skeletal muscle.
  2.  Subject recognition of pain with palpation.
  3. Clinical presentation.

Contraindications:

Absolute contraindications

DN therapy should be avoided in patients under the following circumstances:

1. In a patient with needle phobia.
2. Patient unwilling – fear, patient belief.
3. Unable to give consent – communication, cognitive, age-related factors.
4. Medical emergency or acute medical condition.
5. Over an area or limb with lymphedema as this may increase the risk of infection/cellulitis and the difficulty of fighting the infection if one should occur.
6. Inappropriate for any other reason.

Relative Contraindication:

1. Abnormal bleeding tendency
2. Compromised immune system
3. Vascular disease
4. Diabetes
5. Pregnancy
6. Children
7. Frail patients
8. Patients with epilepsy
9. Psychological status
10. Patient allergies
11. Patient medication
12. Unsuitable patient for any reason