Posted by MERm on 12/7/2008, 7:11 am
UPDATE OF Myofascial Pain from Trigger Points
By Professor David Simons
ABSTRACT: Objectives: To review clinical literature concerning the prevalence, diagnostic criteria, and treatment of myofascial trigger points [TrPs] and to summarize a new understanding of their etiology.
Findings: In three studies, the prevalence of myofascial TrPs among patients
complaining of pain anywhere in the body ranged from 30% to 93%;
among patients with chronic craniofacial pain, 55%;
and for lumbogluteal pain, 21%.
Among four studies of interrater reliability for 5 TrP diagnostic characteristics, untrained experienced examiners achieved unsatisfactory mean kappa values of 0.35 and 0.38; trained inexperienced examiners a fair value of 0.49, and trained experienced examiners a good mean kappa of 0.74.
The highest mean kappa values were for spot tenderness, pain recognition, and palpable band [0.84-0.88]. A revision of previous injection technique more effectively inactivates the multiple active loci that are an essential part of a trigger point. Recent literature introduced two differing hypotheses for the basis of TrPs:
1. dysfunctional muscle spindles;
2. dysfunctional extrafusal neuromuscular junctions. Clinically TrPs are found in the endplate zone. Electrophysiological investigation of TrPs reveals phenomena which indicate that the electrical activity of active loci arises from dysfunctional extrafusal motor endplates rather than from muscle spindles.
Conclusions: Myofascial TrPs are a common cause of musculoskeletal pain. Reliable diagnostic examination requires both training and experience. Several considerations help one to decide which are the most suitable diagnostic criteria of myofascial TrPs under given circumstances. The characteristic electrical activity of myofascial TrPs most likely originates at dysfunctional endplates of extrafusal muscle fibers. This dysfunction appears to play a key role in the pathophysiology of TrPs.
Clinical features of myofascial trigger points
Recent advances in the understanding of the nature of myofascial TrPs help to explain the strange combination of motor and sensory features that TrPs present clinically.
Prevalence
In Unselected and Control Groups. The prevalence of musculoskeletal pain identified as localized myofascial pain was quite high 37% of males and 65% of females] in a randomly selected Danish population of 1504 people aged 30, 40, 50, and 60 years
One study reported examination of a relatively unselected "normal" population to determine the prevalence of myofascial TrPs in the shoulder-girdle muscles only. In this study, Sola and associates examined 100 male and 100 female Air Force airmen [mean age 19.5 years] who had been selected as healthy individuals for military service.
The investigators found focal tenderness indicative of latent TrPs in shoulder-girdle muscles in 54% of the females and 45% of the males.
Pain was referred from the TrP to its reference zone in 5% of these subjects. These subjects were not examined for taut bands.
A recent study of 269 unselected female student nurses (23) showed a similar high prevalence of TrPs in masticatory muscles. A TrP was identified by palpating a taut band for spot tenderness of sufficient sensitivity to cause a pain reaction (24).
No effort was made to distinguish active and latent TrPs, but a considerable number of TrPs were likely active because 28% of subjects were aware of pain in the temple area. In masticatory muscles, TrPs were found in 54% of right lateral pterygoid muscles, in 45% of right deep masseter, in 43% of right anterior temporalis, and in 40% of intraoral examinations of the right medial pterygoid muscle.
Among the neck muscles, TrPs were identified in 35% of the right splenius capitis muscles and in 33% of right upper trapezius muscles. The insertion of the right upper trapezius was also tender in 42% of those muscles with TrPs.
Enthesopathy of this muscle was common (23). Frohlich and Frohlich (25) examined 100 asymptomatic control subjects for latent TrPs in lumbogluteal muscles. They found latent TrPs in the following muscles: quadratus lumborum [45% of patients], gluteus medius [41a/o], iliopsoas [24%], gluteus minimus and piriformis [5%]. In Patient Groups. Individual reports of the prevalence of myofascial TrPs in patient populations are available and, together, indicate a high prevalence of this condition among individuals with a regional pain complaint.
In an internal medicine group practice (3), 54 of 172 patients presented with a pain complaint. Sixteen [30%] of the pain patients met the criteria for myofascial TrPs. Four of these sixteen patients had pain duration of less than 1 month, three a duration for 1 to 6 months, and nine had pain duration of more than 6 months.
A neurologist examining 96 subjects from a community pain medical center (2(,) found that 93% of them had at least part of their pain caused by myofascial TrPs, and in 74% myofascial TrPs were considered the primary cause of the pain. Among 283 consecutive admissions to a comprehensive pain center, a primary organic diagnosis of myofascial syndrome was assigned in 85% of cases (27).
A neurosurgeon and a physiatrist made this diagnosis independently, based upon physical examination "as described by Simons and Travell (28)."
Of 164 patients referred to a dental clinic for chronic head and neck pain of at least 6 months duration, 55% had the primary diagnosis of myofascial pain syndrome caused by active TrPs (29). Five lumbogluteal muscles of 97 patients complaining of pain in the locomotor system were examined in an orthopedic clinic (25). Forty-nine percent of the patients presented latent TrPs and 21% presented active TrPs in the piriformis muscle.
The wide range in prevalence of myofascial pain caused by TrPs is likely due in part to differences in the patient populations examined and in the degree of chronicity. Also critical are differences in the criteria selected to make the diagnosis of myofascial TrPs and differences in the training of the examiner. Few of these studies gave a detailed description of the diagnostic examinations employed. This summary does not include papers that used the general definition of myofascial pain syndrome.
Active myofascial TrPs are clearly very common and are a major source of musculoskeletal pain and dysfunction, but the poor agreement on appropriate diagnostic criteria must be resolved. This paper presents some useful guidelines.
The question arises, "How commonly do TrPs occur with other conditions?"
Data from six recent studies of four common diagnoses are summarized in Table 2. In every condition, myofascial TrPs made some contribution, often a major contribution, to the patients' pain. Granges and Littlejohn found that 68% of patients diagnosed as having fibromyalgia [FM] also had at least one TrP in the immediate vicinity of a designated tender point site; however, they found hat few of the positive tender point sites qualified as TrPs based on a tender spot in a taut band, or induced referred pain, or inducing pain recognized by the subject.
The Cranges and Littlejohn study is a different kind of study than those of Finestone and Gerwin . In the latter two studies, FM patients were examined for a TrP in any muscle that was indicated by the distribution of the patient's pain
Diagnostic Criteria.
The diagnosis of myofascial TrPs depends on the history and on its confirmation by physical examination.
There is poor agreement among authors as to the most appropriate diagnostic criteria. Numerous clinical features have been associated with myofascial TrPs, but only recently have interrater reliability studies been reported that give some guidelines. No satisfactory laboratory or imaging test is currently available for making the diagnosis of myofascial TrPs.
Clinical Features. Several clinical features are commonly associated with the diagnosis of myofascial TrPs (31); these include a confusing mixture of sensory and motor phenomena: History of spontaneous localized pain associated with acute overload or chronic overuse the muscle.
The mildest symptoms are caused by latent TrPs that cause no pain but cause some degree of functional disability. More severe involvement results in pain related to the position of the muscle or muscular activity. The most severe level involves intermittent or continuous pain at rest
The precise pattern of pain described by the patient is THE most valuable clue for finding where the TrP is located. Recognizing the pattern of pain as characteristic of a particular muscle tells the clinician where to look for the TrP or TrPs that are responsible for at least part of the patient's pain.
Palpable Band. A cord-like band of fibers is palpable in the involved muscle. This band helps to locate spot tenderness, but it may be inaccessible because of overlying muscles or thick [or tense] subcutaneous tissue. Its tendon attachment may evidence the spot tenderness of enthesopathy .
Spot Tenderness. This involves a VERY tender and VERY small spot which is found
in a palpable band when the band is accessible to palpation. The sensitivity of this spot [the TrP] is increased by increasing the tension on the muscle fibers of the taut band.
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