Injection of trigger points with a local anesthetic (with or without an added corticosteroid) is a relatively simple, cost-effective treatment that often produces an almost immediate decrease in pain. In addition, it can provide long-term pain relief and increased range of motion, thereby enabling patients to resume normal activities.
Trigger point injections are especially helpful in patients whose pain has proved refractory to such conservative approaches as massage, physical therapy with stretching, and cooling topical anesthetic sprays. They represent an alternative method of pain control that may reduce or eliminate dependence on pain medication. These injections can also be used to treat such conditions as myofascial pain syndrome, fibromyalgia, temporomandibular joint syndrome, tension, and migraine.
Here I discuss the indications for and contraindications to trigger point injections. I also describe the techniques I have found most effective.
Trigger points can develop in any of the body's 400 muscle groups, but they are typically found near bony attachments (Figure 1) and occur most often in the larger muscles of the shoulder and pelvic girdle. They represent a disruption of the sarcoplasmic reticulum of the muscle fiber.1 These sensitive, tender, or irritable areas or nodules can be identified by palpation.
Trigger points can arise as a result of strain, sprain, or repetitive use of a muscle; stress and muscle tension; or specific disorders, such as herniated and degenerative disks, pinched nerves, fractures, surgical incision healing sites, postural problems, scoliosis, and osteoarthritis. However, they need not be associated with any other neurologic or musculoskeletal disease. A trigger point can itself be a source of pain, or it can produce referred pain.
Three hypotheses have been proposed to explain the origin of trigger points:
The muscle-spindle explanation implicates a dysfunctional muscle spindle as the cause. Hubbard and Berkoff2 have shown that when intrafusal muscle fibers receive direct sympathetic stimulation, actively firing muscle fibers are found in trigger points, whereas adjacent muscle fibers remain electromyographically silent. The actively firing fibers contribute to excessive muscular contraction at the trigger points, which results in pain.
The energy-crisis theory of muscle metabolism proposes that the contracture of a taut muscle band may be associated with abnormal local release of calcium, which results in a focal abnormality in the muscle.3,4 This, in turn, produces actin-myosin contractile activity, which leads to the accumulation of serotonin, histamine, kinins, and prostaglandins. Local muscular acidity increases, and this stimulates the firing of nociceptors in the muscle, which causes local and referred pain.1
The motor-endplate hypothesis postulates that dysfunction in the region of the extrafusal motor endplate is a major cause of trigger point pain.3
These 3 proposed mechanisms are not mutually exclusive. Further investigation is needed to elucidate their roles in the pathogenesis of trigger point pain.
EFFICACY OF INJECTIONS: THE SUPPORTING EVIDENCE
Several studies have demonstrated the effectiveness of injections in relieving pain associated with trigger points. In 63 patients with low back strain, trigger point injection (either with or without local anesthetic and/or corticosteroid) provided symptomatic relief of low back pain.5 In 122 patients with chronic pelvic pain who were given trigger point injections of a local anesthetic, more than half experienced complete relief and only 13 needed surgery to relieve their pain. All the patients who received only abdominal wall injections had a successful response-ie, one that resulted in a decrease in the level of pain and disability that the patient deemed satisfactory; the rate of response to the injections of those with vaginal wall trigger points was 84.6%.6
In another study,patients with myofascial trigger points of the upper trapezium muscle who were treated with either trigger point injections or ultrasound therapy in combination with neck stretching exercises reported significantly greater reduction in the subjective intensity of their pain, a higher pressure pain threshold, and greater range of motion than those treated with neck stretching exercises alone.7
FOR WHICH PATIENTS?
Trigger point injections are indicated for patients whose pain symptoms can be localized by palpation. You should be able to locate both the trigger point itself (also known as the "point of maximum tenderness") and the corresponding "area of pain reference," which is usually 1 to 2 cm in diameter. In addition, assess patients for concomitant disorders-such as low back pain or chronic neck or shoulder pain-that could become debilitating if left untreated.
Although trigger point injections are minimally invasive and normally well tolerated by patients, several contraindications exist:
Septicemia or localized infection at the needle insertion site.
Concomitant use of an anticoagulant.
Allergy to local anesthetics (if considering injection with lidocaine(Drug information on lidocaine)).
Significant psychiatric disturbance.
Most of these can be identified by reviewing the patient's medical history.
Injections are not appropriate for patients with diffuse, multiple trigger points who have any underlying endocrinopathy, such as hyperthyroidism, estrogen deficiency, hypoparathyroidism, hyperthyroidism, pituitary disorders, or Cushing disease.
Trigger point injections are associated with several potential adverse effects and a risk of various complications (Table 1); weigh these against the expected therapeutic benefit. Finally, never perform trigger point injections unless resuscitation equipment is available.
Thoroughly discuss the procedure with the patient. Make sure he or she understands that pain at the area of pain reference may have been caused by irritation of an area somewhat distant from this site. Point out that a period of immediate relief resulting from the procedure may be followed by pain that is greater than the original pain-often a sign that follow-up injections are needed. Explain the potential complications (see Table 1), and ask the patient to sign a form acknowledging informed consent. Finally, if the patient is susceptible to vasovagal events (eg, during blood drawing), or if he is to be given a short-acting antianxiety medication or opioid before or after the procedure, make sure he will be accompanied home by a relative or friend.
Minimal, readily available resources are required to perform trigger point injections (Table 2). The procedure generally takes less than 15 minutes (Box).
Immediately following the procedure, observe the patient for such signs and symptoms as light-headedness, tinnitus, peripheral numbness, slurring of speech, drowsiness, and evidence of seizure activity; any of these might indicate a toxic reaction to the local anesthetic. Also look for bleeding into the skin or muscle compartment.
Either during or shortly after the procedure, the patient should experience a decrease in pain as well as relaxation of the muscle band-if it was originally tight. Patients should be able to resume day-to-day activities after the procedure and return to work. To maintain pain relief and improve strength and range of motion of the affected muscle, recommend stretching exercises, physical or massage therapy, or rest, as indicated.
As noted, pain may recur and actually worsen for 1 to 3 days-either because additional injections are needed or because the trigger point was not completely injected. Thus, it is important to see the patient again in 3 or 4 days, both to assess compliance with stretching exercises (or other recommended therapy) and to evaluate the need for further injections. Instruct the patient to return immediately to your office if unusual swelling or redness develops at the injection site.
If pain has recurred or increased because of an incomplete initial injection, reinjection followed by moist heat or ice therapy together with NSAIDs or another analgesic may be appropriate.
In some patients, 4 or 5 injections per site may be necessary over a fairly short period to break the cycle of pain. If the pain persists, corticosteroids can be added to the injection solution or given in a separate injection following one with local anesthetic. More permanent pain relief can be achieved by injecting the trigger point with phenol(Drug information on phenol) or botulinum toxin. If such injections are indicated, consider referral to an anesthesiologist or a pain management specialist. Referral may also be indicated for patients who have more generalized pain related to irritation of a thoracic or intercostal nerve root.
COMPLEMENTARY AND ALTERNATIVE PROCEDURES
Optimally, trigger point injection should be used in combination with a supervised therapeutic stretching program; repetitive, gentle exercise to strengthen weak muscles; massage; and/or heat or ice treatments.
In some patients, dry needling or injection with saline or glucose may relieve pain, although the procedure is more painful than trigger point injection with local anesthetic and is generally not as well tolerated. One study of 58 patients compared the effects of injection with a local anesthetic agent to dry needling into a myofascial trigger point of the upper trapezium muscle. Most reported significant improvement in subjective pain intensity immediately after injection-with or without lidocaine. However, the intensity and duration of postinjection soreness was less with lidocaine than with dry needling.8
Table 3 lists additional alternative procedures that have been used with varying degrees of success to alleviate pain associated with trigger points.