A trigger point is defined by Drs. Janet Travell, M.D., and
David Simons, M.D., as a hyperirritable spot in a skeletal muscle that is
associated with a hypersensitive palpable nodule in a taut band (a “taut band”
is a tight area in a muscle). The spot is painful on compression and can give
rise to characteristic referred pain, referred tenderness, motor dysfunction,
and autonomic phenomena. This definition is from their excellent two-volume
book Myofascial Pain and Dysfunction: The
Trigger Point Manual.
Fig.1 Strumming across the fibers of a muscle to feel taut bands and following it to locate the TrP. From Travell and Simon's, Myofascial Pain and Dysfunction |
What this definition states is that a TrP in a muscle will be associated with a taut band within this muscle. If TrPs are present in a muscle and you or a practitioner strums across the fiber direction of that muscle, there will be a taut, ropy band that is present. Somewhere within this taut band, usually towards the central belly of the muscle, there will be a palpable nodule which is often exquisitely tender, especially with pressure applied (Fig.1). Usually a minimal amount of pressure will elicit this discomfort, if indeed it is not actively painful with no pressure. In fact, it might be this active pain that brings a patient in for evaluation.
The interesting thing about TrPs is that they have
characteristic referral patterns which are where the patient experiences the
pain (Fig. 2), either with pressure on the TrP, or, when very active, without. While
this pain is sometimes in the vicinity of the TrP, many times it can be quite a
distance away. This makes assessment and diagnosis somewhat tricky.
Fig.2 Gluteus Minimus TrP referral pattern which mimics pain from neural compression causing sciatica. This is sometimes referred to as pseudosciatica |
Motor dysfunction caused by trigger points often involves
how this muscle relates to its opposing muscle group (agonist-antagonist). Many
times, the presence of TrPs can cause a muscle to become inhibited and it will
not be able to perform its job effectively. This might be the case when this
muscle, along with certain movements, also helps stabilize a joint.
The last part of the definition refers to autonomic
dysfunction. Some TrPs can cause sweating, goosebumps, they can contribute to
digestive disturbances, and can even contribute to positional vertigo.
It is important to note that TrPs appear as a result of
muscle dysfunction and are not a precise anatomical aspect of a muscle. What I
mean by this is that in a healthy muscle, there will be no signs of TrPs. When
a muscle is overloaded due to repetitive use, injury, postural tension, stress,
and other reasons, TrPs can form. Many times these TrPs can then become a
chronic cause of pain.
Finally, while TrPs are very common, there are many other
sources of orthopedic pain which can also refer. Spinal nerve impingement,
vertebral joint syndromes, tendinopathies and many other conditions need to be
taken into account whenever evaluating pain experienced by a patient.
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