Trigger point injections: An important discussion and review
Trigger point injections are an effective treatment modality for inactivating trigger points and providing prompt relief of symptoms from myofascial pain syndrome.  Myofascial pain syndrome is a common painful muscle disorder characterized by myofascial trigger points. This syndrome is distinct from fibromyalgia syndrome, which involves multiple tender points, though the two pain syndromes may be concurrent.
Myofascial trigger points are a major cause of pain and dysfunction.  They produce pain focally and in a referred pattern and often occur in conjunction with chronic musculoskeletal pain disorders. Various modalities for the treatment of trigger points include spray and stretch, ultrasound, manipulative therapy, and trigger point injections.
Not all trigger points require injection or needling. Many active trigger points will respond to physical therapy, especially in the early stages of trigger point formation. However, for chronic trigger points, trigger point injection and needling is an effective treatment. 
Trigger point injections are indicated for patients who have symptoms and examination findings consistent with active trigger points. Latent trigger points are clinically asymptomatic and do not require treatment. Trigger points should be limited in number and should be appropriate for injection.
Conditions involving widespread pain complaints, such as fibromyalgia or endocrine disorder, are not suitable for injections. Treatment is indicated for endocrine diagnoses or fibromyalgia before trigger point injections are considered. In addition, the finding of tenderness alone is not an indication for trigger point injection, because patients with fibromyalgia may also have myofascial pain trigger points.
When indications for injections are being considered, it is not always necessary to have the classical clinical examination findings of a taut band with local twitch response and referred pain pattern. Within the total clinical context, the finding of tender points in typical trigger point locations that coincide with the patient’s pain and a “jump sign” is sufficient to justify trigger point injections.
Trigger points should not be injected in the presence of systemic or local infection. Injection of patients with bleeding disorders or patients on anticoagulation must be done with proper medical evaluation and control.
Avoid injections in the pregnant patient or patients who feel or appear to be ill. Use precautions in patients who are at high risk for infection, including debilitated patients, patients with diabetes mellitus, or patients on steroids.
Other contraindications include allergy to anesthetic agents, acute muscle trauma, and extreme fear of needles. 
Pain from myofascial trigger points is often treated by needling, with or without injection, though the evidence is inconclusive on whether this is effective. A literature review examined seven studies that assessed the effects of dry needling. One study concluded that direct dry needling was superior to no intervention; two studies comparing direct dry needling to needling elsewhere in the muscle produced contradictory results; and four studies used a placebo control and were included in a meta-analysis.
Upon analysis of these studies, needling was not found to be signiﬁcantly superior to placebo; however, marked statistical heterogeneity was present.  Thus, this review found limited evidence deriving from only a single study that deep needling directly into myofascial trigger points has an overall treatment effect when compared with standardized care.
In a 2013 systematic review and meta-analysis of 12 randomized, controlled trials designed to assess the effectiveness of dry needling for upper-quarter myofascial pain (MPS), Kietrys et al reported the following findings  :
Evidence from three studies of dry needling vs placebo suggested that dry needling could immediately decrease pain in patients with upper-quarter MPS; there was an overall effect in favor of dry needling
Evidence from two studies of dry needling vs placebo suggested that dry needling could decrease pain after 4 weeks in patients with upper-quarter MPS; the impact of this decrease was limited by the wide confidence interval for the overall effect
Studies of dry needling vs other treatments yielded highly heterogeneous results; evidence from two studies suggested that lidocaine injection may be more effective in reducing pain than dry needling at 4 weeks
On the basis of these findings, the authors of the meta-analysis recommended dry needling, as compared with sham or placebo, for decreasing pain immediately after treatment and at 4 weeks in patients with upper-quarter MPS. 
Several mechanisms have been suggested as possible explanations for the inactivation of trigger points by injection, including disruption of abnormal muscle fibers or nerve endings that make up the sensory and motor aspects of the feedback loop, which may be responsible for trigger point activity. Needling may cause a local release of intracellular potassium, which may depolarize and thus disrupt nerve conduction.
Injected fluid may dilute any nerve-sensitizing substances to reduce irritability and inactivate any neural feedback mechanisms. Procaine has a local vasodilatation effect that increases circulation at the trigger point,increasing the local removal of metabolites and increasing local energy supply. Further, a local anesthetic may interrupt feedback mechanisms between the trigger point and the central nervous system, limiting high frequency discharges transmitted by the nerve. Depending on the anesthetic, focal necrosis may destroy the trigger point.
Patients should rest the affected areas for 1-2 days after the injections. Strenuous activities should be avoided for at least the period of postinjection muscle soreness. However, the patient is encouraged to use the muscle with full range of motion rather than hold the muscle in a fixed, shortened position. 
The patient must learn to recognize the pain-provoking activities and movements that overstress the muscles. Such activities should be avoided or modified to achieve lasting relief from myofascial pain. Patients must learn the limitations of their own muscles and use proper body alignment and body mechanics. Common problems with exercise include overenthusiasm, performing activities despite exhaustion or pain, and using an incorrect technique.
The needle size is important for precise injection. A 22-gauge, 3.8-cm (1.5 in.) needle is used for superficial muscles. When capillary fragility with bleeding is a concern, a thinner 25-gauge needle may be preferred. In thick subcutaneous muscles, at least a 21-gauge, 5-cm (2-in.) needle is needed.
The needle should never be inserted to its full length, because of the risk of breaking off. A 21-gauge, 7.6-cm (3-in.) needle is generally long enough to reach trigger points in the deepest muscles, but occasionally a 8.9-cm (3.5-in.) 22-gauge spinal needle is needed. Because of the excessive flexibility of the spinal needle, it is important to keep the needle straight.
The basic equipment for trigger point injections includes, but is not limited to, the following  :
Needles and syringes of various sizes
Povidone-iodine solution or alcohol
Sterile gauze pads
Gloves (sterile or unsterile)
The following needles may be used:
Withdrawal of anesthetic solution – 16-gauge, 1.5-in. needle
Scalenus, sternocleidomastoid, and interossei: 22- to 25-gauge, 1.5-in. needle
Temporomandibular joint muscles – 25-gauge, 1.5-in. needle
Cervical and suboccipital areas, upper extremities, and ankle and foot – 22-gauge, 1.5-in. needle
Extremities – 21-gauge, 2.0-in. needle
Lumbar and gluteal areas – 20- to 21-gauge, 3-in. needle
Gastrocnemius – 25-gauge, 2.0-in. needle
Solutions for injections include 0.5% procaine, 1% lidocaine, and isotonic saline. Do not use epinephrine. Isotonic saline or dry needling may be used in patients allergic to local anesthetics. Steroids may be used for ligamentous trigger points. Long-acting anesthetics (eg, bupivacaine) have also been used. 
Several other substances, including diclofenac, botulinum toxin type A, and corticosteroids, have been used in trigger point injections. However, these substances are associated with significant myotoxicity. Procaine is the least myotoxic of all local injectable anesthetics.
Have the patient lie down (prone or supine) if possible. Injections may be done in a seated position as well. The patient may be placed in a recumbent position to avoid psychological syncope and to facilitate relaxation for easier localization of the trigger points.
Location of trigger points
Palpation of muscles for trigger points may exhibit a palpable taut band or cord of tense muscle fibers approximately 1-4 mm in diameter. The examiner should palpate along this band to locate the point of maximum tenderness, which is the area identified as the trigger point. Pressure is held firmly to elicit the referred pain pattern.
Palpation of an active trigger point often elicits a “jump sign” or local twitch response. A jump sign is a jump or involuntary reflex – like movement of the patient that is disproportionate to the amount of pressure exerted, is reproducible, and may correspond to the degree of irritability of the trigger point. 
Localized twitch response refers to a localized twitch of part of the muscle when the trigger point is rolled under the fingers or a needle is inserted into the trigger area. This twitch may be intense enough to cause a notable jerk or contraction of the muscle fibers in the taut band, lasting up to 1 second. 
Once a trigger point has been located and the overlying skin has been cleansed with alcohol, the clinician should isolate the trigger point with a pinch between the thumb and index finger or between the index and middle finger with stabilizing pressure to prevent the trigger point from rolling away from the advancing needle.
The needle is inserted 1-2 cm away from the trigger point and then advanced into the trigger point at an acute angle of 30 º to the skin. (See the image below.) Before advancing the needle into the trigger point, the physician should warn the patient of the possibility of sharp pain or muscle twitching as the needle contacts the trigger point. Aspirate before injection to avoid intravascular injection.
Once the needle is inside the trigger point, a small amount (0.2 mL) of anesthetic is injected. The needle is withdrawn to the level of the subcutaneous tissue, then redirected superiorly, inferiorly, laterally, and medially. The needling and injection process is repeated in each direction without withdrawal of the needle until the local twitch response is extinguished or until the muscle relaxes.  Pressure should be applied over injection sites.
Stretching after trigger point injection is an integral part of treatment. The physician should stretch involved muscles to try to obtain full length.
Before stretching, it may be helpful to apply a few sweeps of vapocoolant spray in a parallel direction over the muscle and its referred pain pattern to relax remaining tense fibers.  This should be followed by the application of a hot pack over all injected trigger points.
After heat has been applied topically for several minutes, the patient should perform full active range of motion of the muscle several times to relieve residual stiffness, evaluate the effectiveness of the procedure, and reestablish awareness of normal muscle function.
Strenuous activities should be avoided for at least the period of postinjection muscle soreness. However, the patient is encouraged to use the muscle with full range of motion rather than hold it in a fixed, shortened position. 
Active exercise is a critical part of the treatment program and will determine whether trigger point injection treatment is effective. Exercises can be designed to target stretching, strengthening, or conditioning of muscles.
Exercise designed for stretching the involved muscles is the key to the relief of myofascial pain. Improved conditioning and increased strength reduces the likelihood of developing trigger points. As the trigger points are inactivated and any rest pain resolves, a carefully graded exercise program begins to increase endurance.
Once tolerance of stretch I achieved , the patient may progress to strengthening exercises. They may be either isotonic or isometric, though isotonic exercises are usually better tolerated. Strengthening exercises should be prescribed with a certain number of repetitions. They should be executed smoothly and slowly, with pauses between each repetition.
When tolerated, conditioning exercises should be added and done at least twice weekly. These exercises include swimming, bicycling, tennis, jogging, and jumping rope. 
Complications may include vasovagal syncope, skin infection, pneumothorax, needle breakage, and hematoma formation. 
Infection can usually be avoided by employing sterile technique. Avoid pneumothorax complications by never aiming a needle at an intercostal space. Needle breakage is avoided by never inserting the needle all the way to its hub. Hematoma formation can be avoided by applying direct pressure for at least 2 minutes after injection.