CHAPTER 197 Trigger-Point Injection

Myofascial pain is among the most common complaints for which patients seek care. In many cases, there is a defined, reproducible site of tenderness in the affected muscle, called a trigger point, that can be targeted for relief of pain and spasm. Trigger points (TrPs) may be effectively treated in the office through the TrP injection technique described here. Understanding TrP pathology and treatment can aid the clinician in addressing one of the most common and debilitating acute complaints encountered in the outpatient setting.

The term trigger point was coined by Dr. Janet Travell in 1942 to describe the clinical finding of a painful nodule in an indurated cord or “taut band” of muscle (Fig. 197-1). According to the American College of Rheumatology, TrPs should be painful to palpation with 4 kg of pressure, approximately the point at which the examiner’s fingernail would begin to blanch. The taut band of muscle fibers may respond during palpation or needle activation with a local twitch response (LTR). Although the LTR phenomenon is not always visible, when present this response predicts an effective response to TrP injection.

Figure 197-1 Trigger point complex in muscle. ATrP, attachment trigger point; CTrP, central trigger point.

(From Simons DG, Travell JG, Simons LS: Travell & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual, 2nd ed. Philadelphia, Lippincott Williams & Wilkins, 1999.)

It is thought that any one of the over 600 striated muscles in the human body can develop TrPs, although not all can be accessed by direct palpation. Examples of the most common TrPs are shown in Figure 197-2. TrPs can form in response to an acute event such as a sudden strain placed on an already contracted muscle, or in the context of insidious, repetitive strain. TrPs are commonly classified as “active” or “latent.” Active TrPs (Box 197-1) are symptomatic, causing pain, stiffness, decreased range of motion, and referred symptoms such as paresthesias or a disturbance in motor or autonomic function. The pain experienced by patients may be well localized or diffuse, ranging in character from a dull ache to sharp, burning, and debilitating. Motor dysfunction includes muscle weakness and easy fatigability as well as spasm of other muscles in the kinetic chain. Examples of autonomic dysfunction include abnormal sweating, lacrimation, and salivation, pilomotor disturbance, mild edema, imbalance, dizziness, and tinnitus. Palpation of active TrPs typically reproduces the patient’s symptoms. Latent TrPs may also cause stiffness and restriction of motion but are generally not noted by the patient to be painful until directly palpated by the examiner or when “unmasked” during the treatment of active TrPs.

Figure 197-2 Anterior, lateral, and posterior views of common trigger points.

(From Simons DG, Travell JG, Simons LS: Travell & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual, 2nd ed. Philadelphia, Lippincott Williams & Wilkins, 1999.)

Approximately 20% of patients with active TrPs also have fibromyalgia; it is important to differentiate this subset (Table 197-1) because patients with fibromyalgia usually have diffuse pain that may be better managed with systemic regimens and physical therapy as opposed to localized TrP injections. Performing a TrP injection in patients with fibromyalgia may actually worsen the pain. It should be noted that TrPs are frequently located near a bony prominence, moving part, or where a muscle or tissue slides, whereas the tender points associated with fibromyalgia are often located in an area where the tissue is not subject to any local stress.

TABLE 197-1 Myofascial Pain due to Trigger Points versus Fibromyalgia

* Widespread pain denotes pain that is bilateral and involving both the upper and lower body. Widespread pain must have been present for 3 months.

† Pain in at least 11 of the 18 specific tender points must be present. These tender points (bilateral) include the occiput (at suboccipital insertion), lower cervical spine (C5–C7 levels), trapezius (midpoint of upper border), supraspinatus (above scapular spine near medial border), second rib (at second costochondral junction), lateral epicondyle (2 cm distal to the epicondyle), gluteus (upper, outer quadrants of buttocks), greater trochanter (posterior to the trochanteric prominence), and knee (at the medial fat pad proximal to joint line).

Trigger-point injection may be performed quickly and effectively in the office setting to treat myofascial pain, producing immediate and often long-term results, especially when combined with complementary therapies such as physical therapy, exercise, massage, “spray and stretch,” or ergonomic retraining. TrP injection is thought to work by causing a temporary relaxation of the taut muscle, allowing for improved local perfusion, replenishment of the adenosine triphosphate (ATP) required to release actin–myosin chains, and clearance of noxious metabolites. In turn, this breaks the pain–tension cycle. Studies have demonstrated that it is the mechanical stimulation of the TrP by the needle that releases the muscle spasm, whereas the substance injected provides only adjuvant therapy. Response rates are similar regardless of the substance injected; whether it is saline, a steroid, a local anesthetic, or a paralytic agent such as botulinum toxin injected, none has proven to be more effective than “dry needling” alone. However, the latter two substances may produce longer-lasting results because of caustic damage to the muscle. Injection of local anesthetic offers the additional benefit of significantly reducing postprocedure pain compared with saline or dry needling, without adding undue risk to the procedure. Most authorities recommend the use of 0.25% to 1% lidocaine without epinephrine or 2% procaine diluted to 0.5% for TrP injections. We recommend against the use of steroids for TrP injection.

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