Research Update

Myofascial Trigger Points : The Current Evidence

Physical Therapy in Sports 5 (2004) 1-12 Leesa K Huguenin

This literature review provides an overview of the current knowledge regarding the history, pathophysiology, mechanism of pain production and proposed treatment methods for myofascial trigger points (MTP) as isolated phenomenon, as opposed to those occurring in more generalised pain syndromes (eg. fibromyalgia, CRPS).

MTPs can be defined as localised areas of deep tenderness within a taut band of muscle. They exhibit a local twitch (fasciculation) or 'jump' sign (whole body movement) in response to digital pressure or dry needling. MTPs are able to produce referred pain either spontaneously or on digital compression. MTPs may be active or latent.

Active MTPs are those that may be responsible for a patient?s presenting symptoms and may be associated with weakness and paraesthesia.
Latent trigger points present with more shortening of muscle and pain occurs only on application of external pressure.

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Trigger points in the infraspinatous muscle also showing distribution of referred pain.

Examination Findings Palpation of an active trigger point will usually reproduce the patient's symptoms, whereas latent trigger points may produce sensations unassociated with presenting symptoms.

There is a lack of valid and reliable diagnostic criteria and identification of a MTP relies on finding a local tender point within a taut muscle band, reproduction of recognisable symptoms and a local twitch response to snapping palpation or needle insertion.

Pathogenesis There are two most widely accepted theories to explain MTP aetiology:

Energy Crisis Theory : This postulates that increased demand on muscles, macrotrauma or recurrent microtrauma causes prolonged shortening of sarcomes. This compromises circulation and the reduced oxygen supply leaves the cell unable to produce enough ATP to initiate active relaxation. Ischaemic by products of metabolism accumulate, which are in part responsible for pain produced by sensitisation and direct stimulation of sensory nerves.
Motor End Plate Hypothesis : EMG studies have found that trigger points contain minute loci that produce characteristic electrical activity. These loci are located at the motor end plate zone where the motor nerve synapses with the muscle cell. The endplate noise seen on EMG is thought to represent an increased rate of release of acetylcholine (ACH) from the nerve terminal, which results in action potentials being propagated a short distance along the cell membrane. This small amount of propagation, although not enough to cause muscle contraction, may be enough to activate a few contractile elements and be responsible for a degree of muscle shortening. Both theories have not been scientifically validated.

Clinical Precipitants of trigger point formation MTP's are thought to form in response to increased or altered muscle demands, such as muscle overload often seen in pre-season sports conditioning. It may also occur from postural errors in the workplace, proximal nerve compression and post trauma. They can also be influenced by descending factors such as stress and constitutional illness.

They should be considered when assessing for sources of pain in different clinical scenarios. Sedentary workers presenting with neck pain and headache may exhibit triggers in trapezius, long extensors and scalenes from prolonged muscle loading. Also patients with lumbar disc injury may exhibit MTPs in the quadratus lumborum, erectae spinae and gluteals.

Referral pain from trigger points also needs consideration, especially if a patient is not responding to more local treatment. MTPs are only relevant to a condition if they reproduce a recognisable pain.

Trigger Point Therapy This is divided into invasive and non-invasive techniques. Non-invasive techniques include stretching, transcutaneous electrical nerve stimulation, ultrasound and laser. Invasive techniques include local anaesthesia, botulin toxin and dry needling. Dry needling involves repeated advances of an acupuncture type needle into the muscle in the region of the trigger point, aiming to reproduce the patient's symptoms, visualise local twitch responses and achieve relief of muscle tension and pain.

Given that dry needling involves a localised noxious stimulation to the muscle, it is thought that central opioid release produces global reduction in pain perception by gating spinal cord pain impulse transmission, producing hypoalgesia at a spinal cord level.

More randomised controlled trials are required to validate efficacy and mechanism of many of the trigger point therapies.

At EMPC we have begun utilising dry needle therapy as an adjunct to treatment of musculoskeletal pain, with generally good anecdotal success. It is generally used when a patient's treatment has plateaued or active MTPs are not altering with other conservative therapies (massage, stretching, heat, electrotherapy).

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