Trigger Point Injections

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13 Trigger Point Injections

Trigger point injections (TIs) are helpful treatment options in patients with acute and chronic muscle pain often associated with underlying bone or nerve pathology. This chapter will discuss the differences in trigger points (TrPs) and tender spots (TSs), describe the three common types of trigger point injections, and discuss the specific techniques of these types of injections.

Trigger Points versus Tender Spots

Trigger points (TrPs) are small, exquisitely tender areas in various soft tissues, including muscles, ligaments, periosteum, tendons, and pericapsular areas.1–1d These points may radiate pain into a specific distant area called a “reference pain zone.”^1d–9 The referred pain may be present at rest. The pain may occur only on activation of the trigger point by local pressure, piercing by an injection needle, or activity of the involved muscle (particularly its overuse). TrPs located in muscles are called myofascial because they also may involve the fascia. In addition to the focal tenderness, they are characterized by the presence of a taut band^6,^8,⁹ that is sensitive to pressure, which indicates sensitization of the nerve endings within. The hard resistance to palpation and needle penetration is interpreted as evidence that a group of the affected muscle fibers is constantly contracted. Later, approximately 6 to 8 weeks after an injury, the resistance to the needle usually becomes very hard. This is characteristic of fibrotic (scar) tissues that fail to respond to conservative therapy. Because there are no definitive histologic studies of TrPs at different stages, it may be assumed that the damaged tissue has healed by a scar.

Trigger point injections represent specific techniques used for alleviation of pain caused by the trigger area. Optimally, TIs are aimed at mechanically breaking up the entire abnormal tissue that causes pain. The most frequent findings related to pain are tender spots, a term reserved for point tenderness without radiating pain. TSs are frequently located within taut bands that have identical characteristics as TrPs. TIs have the same effect, indications, and limitations in both TSs and TrPs. Therefore, the rest of this chapter uses the expression “TrPs” for both tender spots and TrPs, because the technique of injection in both cases is identical: directed at the point of maximum tenderness and taut bands.

Commonly, tender spots and some TrPs represent local tissue damage that causes inflammation and irritation that can be diagnosed by increased sensitivity to pressure. Figures 13-1 and 13-2 illustrate a possible concept of pathologic changes following local tissue damage. This hypothesis may explain clinical findings in acute and chronic injury and the effect of needling. Conceptually, the TSs or TrP at the chronic stage can be thought of as a pocket of fibrotic tissue that contains sensitizing agents that are the products of tissue damage. These substances cause sensitization of the entrapped nerve fibers. This sensitization increases the nerve’s reactivity so that a lower pressure produces pain.

Figure 13-1 Conceptual illustration of pathologic changes in acute tissue injury (A) that causes focal tenderness with pain.

Conceptual illustration of pathologic changes in chronic tissue injury (B) that causes focal tenderness with pain.

The effect of needling that breaks up the abnormal tissue is also shown (C).

Figure 13-2 Physical findings over a trigger point and taut band before, during, and after trigger point injection with needling.

Even without infiltration by anesthetic, the needling instantaneously abolishes the pain, tenderness, and fibrotic type of resistance. Such effect of dry needling can be best explained by breaking up a fibrotic pocket that has entrapped the nerve endings along with sensitizing substances. This allows the entering blood flow to wash away the sensitizing substances. This concept may explain the effect of TIs but has not been substantiated by histologic studies. Needling also may interrupt neuromuscular mechanisms involved in TrP activity.

Figure 13-2 and Table 13-1 illustrate physical findings over TrPs and taut bands before, during, and after injection combined with needling. TrPs and TSs are the immediate cause of pain in a variety of conditions. These include sports or work-related injuries, sprains, strains, or muscle tension related to nonphysiologic posture or stress. Headaches also are frequently caused by TrPs. Certain hormonal disorders such as thyroid or estrogen deficiencies are frequent causes and perpetuators of widespread TrPs.

Table 13-1 Physical Findings Before, During, and After Trigger Point Injections

Before Injection	During Injection	After Injection
Normal Muscle Tissue
Elastic soft resistance; nontender	Minimal resistance to needle progression; no pain	Normal tissue findings
Taut Band
Hard and tender. Local twitch response can be elicited on snapping.	Penetration of the needle causes pain and encounters hard resistance as in fibrotic tissue (particularly in chronic TrP). Local twitch response occurs when the needle enters the hyperirritable fibers.	The hard and tender areas on palpation become nontender. Pressure pain sensitivity becomes normal immediately. Soreness from injection resolves in 3-5 days. Local twitch response can no longer be elicited. Hyperirritability resolves.
Trigger Point
Maximum tender point within the taut band.	Maximum pain on needle penetration with hard resistance as in the taut band.	Trigger point sensitivity to pressure disappears. Hard consistency becomes normal, similar to improvement in taut bands.

TrP, Trigger point.

Trigger Point Injections

Needling represents the most effective treatment of trigger points and TSs.9a–9f Injecting a local anesthetic (usually lidocaine) is combined with a special needling technique to break up the abnormal tissue that causes the pain. The critical factor in TIs is not the injected substance but rather the mechanical disruption of the abnormal tissue and interruption of the TrP mechanism if one has developed.^2,^10,¹¹ Intensive stimulation also may contribute to the prolonged relief of pain by TrP injections.¹² The fact that the symptoms originated in the treated TrP is confirmed by observing whether the pain is reproduced by pressure on the trigger area and relieved after the TrP injection.¹³ The injections are followed by a specific program of stretching and exercises. After fibrotic tissue (scar) has formed in the damaged tissue, the most effective way to break it up is through needling: the repetitive insertion and withdrawal of the injection needle in the affected area.

Local anesthetics, such as 1% lidocaine or 0.5% procaine, provide temporary relief, lasting about 45 minutes. Long-term relief from pain is achieved by the needling, which mechanically breaks up the abnormal tissue.^13a The number of injections needed depends on the number of TrPs present.

One or two areas are usually injected during each treatment visit. Injections may be given 2 or 3 times a week for acute pain; once per week or once every 2 weeks is usually adequate as pain relief is being achieved. Each trigger point requires at least one injection. However, in large TrPs, injection may be limited to one segment per visit, depending on the patient’s tolerance. Sufficient tissue must be left around the needled areas for proper healing. Without proper treatment, TrPs tend to spread to additional muscles, causing flare-up of pain.

The injection technique used for TrPs (combination of needling with infiltration) is effective in alleviating pain and restoring function in focal tenderness. The procedure is effective regardless of the underlying pathology and whether or not the pain is referred or limited to the tender area. Sprains and strains of muscles, ligaments, soft tissue injuries, inflammation, injuries of pericapsular tissues, and bursitis are the most common conditions that improve dramatically after needling combined with injection of local anesthetic. TrPs caused by endocrine dysfunction (especially thyroid or estrogen deficiency), fibromyalgia, psychological tension, or ischemia caused by muscle spasm also may be treated effectively by TIs. Often psychological tension and muscle spasm may not be alleviated without eliminating TrPs, which prevent relaxation of the muscle. Inability to relax tight muscles produces more TrPs, and a vicious cycle ensues.

The main contraindications for TIs include bleeding disorders, local infection, anticoagulant therapy, certain psychiatric conditions (anxiety, paranoia, schizophrenia), and inability to rest the injured body part following the procedure. Unless the conditions that caused the TrPs and perpetuating factors are diagnosed and treated, the TrPs will recur.

Common Trigger Point Injection Techniques

Three commonly employed trigger point techniques include needling combined with infiltration of the entire taut band, technique of Travell and Simons, and injection of corticosteroids. There are some clinicians who have proposed ultrasound guidance in the cervicothoracic regions to prevent complications.¹³

1. Needling combined with infiltration of the entire taut band appears to be the most effective technique of TIs. Infiltration with a local anesthetic such as 1% lidocaine or 0.5% procaine is combined with needling. After withdrawal of the needle to the subcutaneous level, repetitive insertion and redirection of the needle is required to cover the entire abnormal (painful) area with as few skin penetrations as possible. The needling and infiltration is extended over the entire taut band, which harbors the TrP/TSs, including its attachment to the bones (enthesopathy).

2. Technique of J. Travell and D.G. Simons.¹⁴^–¹⁷ A small amount of 0.5% procaine is injected into the TrP to desensitize the most tender spot. This approach limits the needling and injection of 0.5% procaine to the most tender focus. The goal is to inactivate the neuromuscular TrP mechanism. The needling progresses in millimeters rather than centimeters, as described later.

3. Steroid injection. A 1.5-inch needle, usually 25-gauge, is used. Corticosteroids are combined with a small amount (1 to 3 mL) of local anesthetic, usually lidocaine. Corticosteroids are not necessary for myofascial TrP treatment. Precise needling, which breaks up the abnormal tissue, is more effective. In fact, corticosteroids may induce local myopathy. However, corticosteroids may be useful in the treatment of conditions involving passive tissues such as bursitis, tendinitis, epicondylitis, or ligament sprain. The disadvantages of corticosteroid injections into ligaments and tendons include loosening and incomplete healing. This may make the injected structures more susceptible to reinjury. Also, the number of corticosteroid injections is limited to 3 to 5, leaving numerous TrPs untreated.

Trigger Point Injection Techniques

The purpose of the injection is to mechanically break up the abnormal and sensitized, tender tissue by needling. Injection of any fluid adds to the mechanical effect of the procedure. Usually 1% lidocaine is optimal. However, in case of allergy to the “-caine” group, saline is satisfactory. The anesthetic also blocks pain and the irritation resulting from tissue damaged by the needle.

The needle should be sufficiently long to be able to reach deeper than the trigger point. The diameter of the needle should be large enough to facilitate mechanical disruption of the abnormal tissue areas.¹⁸ A 22- to 25-gauge needle is usually sufficient. The total amount of 1% lidocaine injected ranges from 1 to 12 mL. Commonly, an extensive area must be infiltrated that ranges from 3 to 25 cm in length and 2 to 10 cm in width. The size of the infiltration depends on the extent of the trigger point and on the length of the affected muscle fibers. At each stop of the needle’s penetration, no more than 0.1 or 0.2 mL should be injected. Larger volumes can damage the muscle, negating any benefit.

Injection Procedure

1. Ask the patient to point out with one finger the area of most intense pain. If this pain is diffuse and corresponds to a trigger point’s reference zone(s), locate the TrP causing the symptoms.^2,^6,^8,⁹ Palpate the muscle or ligament² that has a corresponding reference zone. Position the patient so that you have proper access to the painful area.

2. Palpate the point of maximum tenderness. Mark it by impression of a fingernail. Palpate around to find the entire taut and tender band, which may reach from the origin to the insertion of the muscle, and mark it by fingernail impressions.

3. Explain the procedure to the patient.

4. Clean the skin with povidone-iodine or alcohol. Use surgical gloves.

5. Spray with ethyl chloride to frost. If patient does not like the vapo-coolant, pinch the skin in the area of injection and immediately insert the needle. Because the pinching distracts and occupies the sensory pathways, the patient does not feel the needle.

6. Needle the entire area where an increased fibrotic type of resistance is present, including the entire taut band. Explore with the needle beyond the border of the trigger point and the taut band. Inject only a small amount (0.1 to 0.3 mL) each time you stop the needle penetration. It is of great importance to always aspirate at each needle stop before the injection, especially when the neck or upper body is treated. Terminate the injection if blood is aspirated.

7. Proceed with the needle insertions through the taut band. Stop in 1 to 2 cm increments and again deposit only a small amount of anesthetic (0.1 to 0.2 mL) at each stop. When you reach the normal muscle below the taut band, the pain and hard resistance to the needle cease. Inject a smaller amount in the normal tissue and then withdraw the needle to the subcutaneous level. Make sure that the needle is out of the muscle when you change the direction of the needle; otherwise, you will cut the tissue. Redirect the needle tip within the subcutaneous tissue along the plane of the taut band. Enter the band in distances 1 to 3 cm from the previous infiltration. The distance to the next insertion depends on the size of the muscle and the taut band. Proceed similarly until you needle and infiltrate the entire taut band. Depending on the patient’s tolerance, about 10 local infiltrations can be performed in one session, covering one large TrP and its taut band. If the patient becomes annoyed or the planned amount of anesthetic has been reached, the injection is terminated. If necessary, the remaining parts of the taut band can be injected in the following session, usually 1 week later.

Immediately following an effective injection, the tenderness of the TrP and taut band, as well as the associated harder consistency of the surrounding tissue, disappears or diminishes substantially.

Special attention should be directed to injecting the myotendon junction as well as the origin and the insertion of the involved muscle(s). Injection is usually particularly painful at these sites. Technique of injection to specific muscles has been described,^4,^8,⁹ and it is highly recommended that these textbooks are consulted before a novice starts TIs.

8. Compress the injected site for about 2 minutes to prevent bleeding. Cover area with an adhesive bandage.

Postinjection Care

Postinjection care includes the following steps:

1. Promote hemostasis by pressure.

2. Encourage active slow movement of the injected muscle to its full range; repeat three times.

3. Apply heat locally.

4. Use physiotherapy consisting of hot packs and electric stimulation using sinusoid surging current (adjust volume to induce strong contractions that are not too painful). Use vapo-coolant spray to inactivate remaining painful areas. This is followed by limbering and stretching exercises.

5. If soreness is excessive, give acetaminophen or an NSAID.

6. Limbering exercises and/or passive stretching should be performed by the patient every 2 hours. Limbering exercises have been proven effective in preventing the recurrence of low back pain.¹⁹ Experience shows that this applies to all types of muscle pain.

7. Advise the patient to avoid heavy use of the injected muscle such as walking or driving long distances after lower body injections and to avoid sports after upper body injections.

Other Injections

Currently, trigger point injections may be combined with other injection techniques such as preinjection blocks and paraspinous blocks.

1. Paraspinous block, which desensitizes the irritated spinal segment, is the first in sequence if spinal segmental sensitization is present. This is usually part of a cycle consisting of discopathy, radiculopathy, and paraspinal muscle spasm.¹⁰ The paraspinous block consists of two steps: (1) the spreading of the anesthetic (1% lidocaine) along the sprained (tender) supra/interspinous ligaments to achieve long-term healing and relief of spinal segmental sensitization; and (2) needling and infiltration of the sprained supra/interspinous ligaments.¹³

2. Preinjection block spreads anesthetic to prevent nociceptive impulses from the tender area to be injected.^3,^5,⁷ Preinjection block is administered before the injection of the tender area. The purpose is to block the pain sensation from the sensitive structure about to be injected. Preinjection block prevents central sensitization caused by injecting the irritative focus (a tender area) and also relaxes the neurogenic component of the taut band associated with the trigger point or tender spot.⁵ This makes the trigger point injection easier to perform and renders needling and infiltration more effective.^5,⁷

References

1. Fischer A.A. Pressure threshold measurement for diagnosis of myofascial pain and evaluation of treatment results. Clin J Pain. 1987;2:207-214.

1a. Fischer A.A. Documentation of myofascial trigger points. Arch Phys Med Rehabil. 1988;69:286-291.

1b. Kraus H. Diagnosis and Treatment of Muscle Pain. Chicago: Quintessence; 1988.

1c. Kraus H., Fischer A.A. Diagnosis and treatment of myofascial pain. Mt Sinai J Med. 1991;58:235-239.

1d. Affaitati G., Fabrizio A., Savini A., et al. A randomized, controlled study comparing a lidocaine patch, a placebo patch, and anesthetic injection for treatment of trigger points in patients with myofascial pain syndrome: Evaluation of pain and somatic pain thresholds. Clin Ther. 2009;31(4):705-720.

2. Fischer A.A. Quantitative and objective compliance recording. In: Nordhoff L.S., editor. Motor Vehicle Collision Injuries. Gaithersburg, Md: Aspen; 1996:142-148.

3. Fischer A.A. New approaches in treatment of myofascial pain. Phys Med Rehabil Clin North Am. 1997;8:153-169.

4. Fischer A.A. New developments in diagnosis of myofascial pain and fibromyalgia. Phys Med Rehabil Clin North Am. 1997;8:1-21.

5. Fischer A.A. Algometry in diagnosis of musculoskeletal pain and evaluation of treatment outcome: An update. In: Fischer A.A., editor. Muscle Pain Syndromes and Fibromyalgia. New York: Haworth Medical Press; 1998:5-32.

6. Fischer A.A. Treatment of myofascial pain. J Musculoskeletal Pain. 1999;7:131-142.

7. Fischer A.A., Imamura S.T., Imamura M. Myofascial trigger points are most frequently a manifestation of segmental spinal sensitization. J Musculoskeletal Pain. 1998;6(Suppl 2):20.