Myofascial Pain in Athletes Workup

No laboratory test or imaging technique is generally established as useful in the diagnosis of TrPs. ^{[5, 6]}

Three measurable phenomena help to objectively substantiate the presence of characteristic TrP phenomena, and all three are valuable as research tools. Two of them, surface electromyography (EMG) and ultrasonography, also have much potential for clinical application in the diagnosis and treatment of TrPs. ^{[5, 6]}  For example, in a randomized, controlled trial that included 33 patients with upper trapezius myofascial pain, low-intensity continuous ultrasound treatment produced a significant reduction in pain scores. ^[7]

In addition to EMG recording, ultrasonography provides a second way of substantiating and studying the LTR and it also has a strong potential for providing a much needed available imaging technique that could be widely used to objectively substantiate the clinical diagnosis of TrPs. ^{[6, 5, 8]}

This test would require the examiner to use the skill-demanding snapping palpation technique, or to insert a needle into the TrP, to elicit the twitch response. ^[9]

Surface electromyography

TrPs cause distortion or disruption of normal muscle function.

Functionally, the muscle with the TrP evidences a 3-fold problem: It exhibits increased responsiveness, delayed relaxation, and increased fatigability. Together, these effects increase muscle overload and reduce its work tolerance. In addition, the TrP can produce referred spasm and referred inhibition in other muscles.

With the recent appearance of online computer analysis of EMG amplitude and mean power spectral frequency, a few pioneer investigators have reported the effects of TrPs on muscle activity. The reports indicate that TrPs can influence the motor function of the muscle in which they occur and that their influence can be transmitted through the central nervous system to other muscles.

To date, the number of well-controlled studies to establish the clinical reliability and application of these observations is insufficient, but findings from the few reports of these TrP effects are promising.

The strong clinical effects of TrPs on sensation, as evidenced by TrP tenderness and referred pain, are well documented.

Strong cutaneous stimuli (eg, electric shocks) are well known to cause reflex motor effects (eg, flexion reflex). If the skin can modulate motor activity and if TrPs can modulate sensory activity, the fact that TrPs can also strongly affect motor activity should not be surprising. In fact, the motor effects of lips may be the most important influence they exert, because the motor dysfunction they produce may result in overload of other muscles and spread the TrP problem from muscle to muscle.

Accumulating evidence now indicates that the muscles targeted for referred spasm from TrPs also usually have TrPs themselves. These motor phenomena of TrPs deserve serious competent research investigation.

An increased responsiveness of some affected muscles is indicated by abnormally high amplitude of EMG activity when the muscle is voluntarily contracted and loaded. ^[10] Clinical evidence suggests that some muscles tend to be shortened and abnormally excitable, while others appear to be weak and inhibited.

Fatigability noted at EMG and in terms of work tolerance, of the trapezius muscle that had MTrPs is accelerated compared to a contralateral muscle that was pain-free. The EMG amplitude increased and median power frequency decreased significantly in the involved muscle compared to the uninvolved muscle. Both of these changes are characteristic of initial fatigue.

Median power frequency generally is accepted as a valid criterion of muscle fatigue. Delayed recovery following fatiguing exercise commonly is seen in patients with muscle-related cumulative trauma disorder (CTD). MTrPs were very common in the involved muscles in this group.

Delayed relaxation is commonly seen in muscle-overload work situations. This failure to relax is a common surface EMG finding during repetitive exercises of muscles with MTrPs.

In addition, the TrP can induce motor activity (eg, referred spasm) in other muscles.

Algometry

Sensitivity to pain in patients with TrPs can be measured as the pain threshold to electrical stimulation or applied pressure. The use of pressure algometry is most commonly reported.

Pressure algometry involves the induction of a specific pain level in response to a measured force perpendicularly applied to the skin. The following 3 endpoints are reported: (1) onset of local pain (ie, pressure pain threshold), (2) onset of referred pain (ie, referred pain threshold), and (3) intolerable pressure (ie, pain tolerance).

Most commonly, the pressure required to reach pain threshold is directly measured on a spring scale that is calibrated in kilograms, newtons, or rounds. Because the pressure is applied through a circular footplate, its diameter is a factor, and the actual measurement is stress (in kilograms per square centimeter) applied to skin.

For example, one of the most common algometers has a footplate area of 1 cm²; therefore, its meter, which provides readings in kilograms, is numerically the same as the number of kilograms per square centimeter, and no numeric conversion is needed.

Thermography

Thermograms can be recorded by using infrared radiometry or films of liquid crystal. Recording infrared radiation (ie, electronic thermography) with computer analysis provides a powerful tool for tile accurate rapid visualization of skin temperature changes over large areas of the body. This technique can demonstrate cutaneous reflex phenomena characteristic of MTrPs. The less expensive contact sheets of liquid crystal have limitations that make reliable interpretation of the findings considerably more difficult.

Each of these thermographic techniques is used to measure the skin surface temperature to a depth of only a few millimeters. The temperature changes correspond to changes in the circulation within, but not beneath, the skin. The endogenous cause of these temperature changes is usually sympathetic nervous system activity. Therefore, thermographic changes in skin temperature are comparable in meaning to changes in skin resistance or changes in sweat production. However, electronic infrared thermography is superior to these other two measures (ie, infrared radiometry or with films of liquid crystal) in convenience and in spatial as well as temporal resolution.

In summary, Fisher's research studies indicate that the finding a hot spot on the thermogram is not sufficient to identify a TrP beneath it. A similar temperature change can be expected in radiculopathy, articular dysfunction, enthesopathy, or local subcutaneous inflammation. The thermographic hot spot of a TrP is described as a discoid region 5 to 1 (3 cm in diameter, displaced slightly from directly over the TrP).

Procedures to confirm diagnosis of MPS

The first international symposium on myofascial pain and fibromyalgia was held in 1989. It marked one of the first meetings of the principal proponents of the 2 major muscle pain syndromes. In the proceedings of that symposium, Simons listed the clinical criteria for diagnosis of MPS. ^{[6, 5]}

• Clinical criteria for the diagnosis of MPS caused by active TrPs

  • To make the clinical diagnosis of MPS, the findings should include 5 major criteria and at least 1 of 3 minor criteria. The 5 major criteria include the following: ^{[6, 5]}

    • Regional pain complaint

    • Pain complaint or altered sensation in the expected distribution of referred pain from a MTrP

    • Taut band palpable in an accessible muscle

    • Exquisite spot tenderness at 1 point along the length of the taut band

    • Some degree of restricted range of motion, when measurable

  • The 3 minor criteria include the following:

    • Reproduction of clinical pain complaint, or altered sensation, by pressure on the tender spot

    • Elicitations of a local twitch response by transverse snapping palpation at the tender spot or by needle insertion into the tender spot in the taut band

    • Pain alleviated by elongating (stretching) the muscle or by injecting the tender spot (TrP)

  • Additional symptoms, such as weather sensitivity, sleep disturbance, and depression, often are present, but they are not diagnostic because they may be attributable to chronic, severe pain perpetuated by multiple mechanical and/or systemic perpetuating factors.

• The required features include regional pain, referred pain, or disturbed sensation in a predicted location; a taut band; a tender point along the taut band; and restricted range of motion.

• One of 3 of the following minor criteria also must be present:

  • Pain complaint reproduced by pressure on the tender spot

  • A local twitch response

  • Relief of the pain by stretching or injecting

• At the same time, Simons listed research criteria for the identification of TrPs. To qualify, the point must be exquisitely tender, located in a taut band of a muscle with restricted range of motion, refer pain when pressed or needled, and exhibit a twitch response when needled.