to obtain and, therefore, more commonly found in the extensor digitorum communis than in the infraspinatus muscle.
m
The degree of stimulation required to reproduce a patient's usual pain determines whether a trigger point is considered active or latentJ40 An active trigger point has a
lower pain threshold
than a latent trigger point. A trigger point is
considered active when normal physiological movements or postures cause pain, whereas a latent trigger point requires a significant amount of mechanical stimulation
to reproduce pain. Various authors have suggested methods to objectively quantify the amount of pressure required to elicit a painful response from a trigger point
using algometry or palpometry; however, it remains difficult to determine the distinguishing features of active and latent myofascial trigger points J4 U42 It is important
to realize that pressure algometry is influenced by nociceptors in the skin and subcutaneous tissuesJ4J
Both active and latent myofascial trigger points may cause dysfunction, including restrictions in range of motion and muscle weakness.l2I In patients with acute
myofascial pain, restrictions in range of motion are primarily due to shortening of muscle fibers, pain, and kinesiophobia. In chronic cases, soft tissue and joint
adhesions can further contribute to restrictions in range of motion.344 Muscle weakness without atrophy is often seen with myofascial pain syndrome. Muscle
weakness may be due to pain, restrictions in range of motion, kinesiophobia, inhibition of gamma motoneuron activity, or reflex inhibition of anterior horn cell
function as a result of painful sensory input.345,J46
tion of the trigger point can produce several autonomic phenomena (i.e., vascular effects, changes in skin temperature, and secretory, pilomotor, and trophic changes).
Trophic changes may lead to the development of so-called "satellite trigger points" in the area of referred pain305 Gunn considered the trophic changes essential to the
diagnosis and treatment of neuropathy304 Autonomic changes are not specific for myofascial pain syndrome, as most pain syndromes have an autonomic
component.J47
Muscle Pain Syndromes I 15
The diagnostic process must include the usual differential diagnostic considerations, and rule out other pathologicaI processes. For example, in the examination of a
patient with knee pain, the clinician should consider ligamentous, meniscal, and capsular injuries, patellofemoral joint dysfunction, bursitis, tendinitis, and arthritis,
but also appreciate referred pain patterns and the biomechanical implications of taut muscle bands and myofascial trigger points in the quadriceps, hamstrings, gluteals
and iliotibial band, adductors, and calf muscles34Ð After establishing the initial diagnosis of myofascial pain syndrome, the clinician must determine any mechanical,
systemic, or psychological perpetuating factors that may contribute to the formation or persistence of myofascial trigger points. Major mechanical factors to be
considered in the diagnosis and management of myofascial pain syndrome include anatomic variations and poor postures. Myofascial trigger points and taut bands
may also contribute to further mechanical dysfunction.
Mechanical dysfunction is one of the main problems of myofascial pain. Correcting mechanical dysfunction has become the main objective of Gunn's intramuscular
stimulation approach to myofascial pain syndrome.304 Physical therapists may use soft tissue mobilization as well to correct mechanical dysfunction. For example,
considering that knee joint motion is accompanied by simultaneous coactivation of the quadriceps and hamstrings muscles, any mechanical discrepancy in either
muscle group will affect the resultant joint motion and possibly influence joint stability. It is conceivable that a taut band in the semimembranosis muscle restricts the
mobility of the medial and, perhaps, even the lateral meniscus through its insertions. The semimembranosis muscle reinforces the posteromedial aspect of the knee
capsule. It can llex and internally rotate the tibia on the femur and pull the posterior horn of the mediaI meniscus posteriorly during flexion of the kneeJ49 Perhaps, a
semimembranosis muscle shortened by taut bands and myofascia I trigger points maintains the menisci in a relative posterior position
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