Also called myofascial trigger points, trigger points are hyperirritable spots in skeletal muscle that are associated with palpable nodules in taut bands of muscle fibers. It is believed that palpable nodules are small contraction knots and a common cause of pain.
Pressing the trigger point may cause local tenderness, referred pain, or local twitch response.
The trigger points frequently cause pain that frequently radiates from these points of local tenderness to broader areas, sometimes quite faraway from these points. In spite of being accepted them as a different entity, enough diagnostic criteria and cause of there origin is not known
The term trigger point was coined in 1942 by Dr. Janet Travell.
A typical trigger point is said to have following characteristics
- Pain related to a discrete, irritable point in skeletal muscle or fascia, not caused by acute local trauma, inflammation, degeneration, neoplasm or infection.
- The painful point can be felt as a tumor or band in the muscle, and a twitch response/tenderness/referred pain can be elicited on stimulation of the trigger point.
- Palpation of the trigger point reproduces the patient’s complaint of pain
Not all trigger points may have these classical features though.
Pathophysiology Trigger Point
Exact mechanism is unknown.
The most recent proposed mechanism says that trigger points are muscle spindles, made over-active by adrenalin stimulation. These very short muscle fibers (< 1 cm in length) called intrafusal muscle fibers are activated by adrenalin via the sympathetic nervous system.
An event of muscular overload causes a prolonged release of calcium from the sarcoplasmic reticulum (storage unit for the muscle cell) which results in a sticking cells leading to a contracture with compression of capillaries and results in an increased local energy demand and local ischemia (loss of blood circulation) to the area. This energy crisis causes the release of chemicals that augment pain.
Trigger points may be of following types
Active & Latent
An active trigger point is one that actively refers pain either locally or to another location
A latent trigger point is one that exists, but does not yet refer pain actively. It may do so when pressure or strain is applied to the myoskeletal structure containing the trigger point.
Key & Satellites
A key trigger point is one that has a pain referral pattern along a nerve pathway that activates a latent trigger point on the pathway, or creates it.
A satellite trigger point is one which is activated by a key trigger point.
Successfully treating the key trigger point often will resolve the satellite and return it from being active to latent, or completely treating it too.
Primary & Secondary
A trigger point in many cases will biomechanically activate a secondary trigger point in another structure. The original trigger point is called primary trigger point.
Treating the primary trigger point does not treat the secondary trigger point.
What Activates A Trigger Point?
- Acute or chronic muscle overload
- Activation by other trigger points
- Psychological distress
- Direct trauma to the region
- Rradiculopathy ( Pain due to compression /trritation of nerve root
Where Can Trigger points Appear?
- Joint capsule
- Scar tissue.
Diagnosis of Trigger Point
Trigger points are diagnosed by clinical history and examination that includes manual palpation. Pain patterns and a taut band or hard nodule guide to the diagnosis. A twitch response can be felt in the muscle by running finger perpendicular to the muscle’s direction. Pressing on an affected muscle can often refer pain.
Treatment of Trigger Point
Treatment of trigger points involves manual massage, mechanical vibration, pulsed ultrasound, electrostimulation, ischemic compression, local anaesthetics/steroid injection, low Level Laser Therapy and stretching techniques that invoke reciprocal inhibition within the musculoskeletal system.
After trigger points have been deactivated, muscle and fascial stretching should be done by active/passive means stretching to be effective to prevent redevelopment.
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