Most of us will be familiar with the sensation of a ‘muscle knot’ in our upper trapezius muscle, that is the thick muscle running from our shoulder up to our neck. We often get tender points in the muscle here if our posture is less than optimal, when stressed or spending prolonged periods of time studying or working at a computer. These knots are known as trigger points. Just like us, animals can suffer from the effects of trigger points too. Fortunately, physiotherapy can help address both the root cause of trigger points as well as treating and relieving trigger points themselves.
Since the early 19th century, various clinicians have been studying myofascial pain syndromes. It was an American physician by the name of Janet Travell (1901-1997) who popularised the use of the term myofascial trigger point, confirming that each muscle in the body has its own unique trigger point pain referral pathway.
What is a trigger point?
A trigger point is an area of hypersensitivity in a muscle which can impulses or signals to the central nervous system through a process known as nociception, potentially giving rise to referred pain.
As described by Travell & Simons (1983) “localised musculoskeletal pain originating from a hyperirritable spot or trigger point with a taut band of skeletal muscle or muscle fascia”.
How does a physiotherapist identify a trigger point?
The trigger point is painful to palpate or compress
On palpation, a trigger point will feel like a nodule, tightness or band in the muscle
Often a ‘local twitch response’ is felt where the muscle twitches in response to applied pressure.
How do trigger points evolve - what happens in the muscle?
Although we are not entirely sure what exactly causes a trigger point to develop within a muscle, there are several physiological changes that do occur:
Localised ischemia or hypoxia – reduced blood flow in the muscle leads to reduced oxygen content in the muscle fibre
Chemical changes occur in the muscle where a substance called acetylcholine (which is normally released by a contracting muscle) continues to be released when the muscle is at rest
Inflammatory chemicals are released in the muscle fibres which may activate the nociceptive system, potentially leading to a pain experience if the nervous system perceives that the affected tissues are at risk of harm
Types of trigger points:
There are several different types of trigger points that have been identified in people – it is challenging difficult to identify all of these types of trigger points in animals as they cannot communicate the nature of their symptoms with us like humans can.
Active trigger points form when the nociceptors (‘danger’ detecting structures found throughout in the body) are sufficiently activated to cause pain to be produced by the nervous system, where this pain may be felt some distance away from the trigger point itself. Three types of active trigger points are found:
Key trigger points
These are trigger points in a muscle, or group of muscles, where nociceptors are primarily responsible for the stimulation of pain syndromes. The patient will recognise the pain provoked on palpation or compression of the trigger point.
Satellite trigger points
This trigger point is another point which is initiated by the key source or key trigger point. It may develop in the referral area of the key trigger point or in neighbouring muscle groups who become overloaded as a result of compensation of the weakened / shortened primary affected muscle group. For example, satellite trigger points may develop in the gluteal muscles, secondary to key trigger points in the spinal muscles in a case of back pain. Treating the key trigger point may inactivate the satellite trigger points.
Latent trigger points
A latent trigger point is one where the nociceptors have not been sufficiently stimulated or activated to cause spontaneous pain to be produced, however the trigger point is likely to be as painful on palpation as a key trigger point is. These are the points that surprise patients; “I never knew I was sore there!”
The following are some of the factors which are involved in the development of trigger point pain in muscle:
Ischaemia – reduced blood flow to a muscle due to muscle overload
Repetitive work – leading to muscle overload
Compression of motor nerves
Immobilisation of a joint (e.g. after being in a cast, sling)
Poor saddle or bridle fit in the horse or poor harness fit in the dog
How do we treat myofascial trigger points?
Some of the treatment modalities used by physiotherapists to relieve trigger points in both human and animals include the following:
TENS or transcutaneous nerve stimulation
Ischaemic compression or trigger point release therapy
Reflex inhibition techniques
Massage in combination with cryotherapy and stretching techniques
Most importantly – addressing the cause of the trigger point and manage this through education and movement therapy is key to both managing trigger points and in preventing their return.