Trigger Point Injection

Myofascial trigger point is defined as a hyperirritable spot, usually within a taut band of skeletal muscle or in the muscle fascia, which is painful on compression and can give rise to characteristic referred pain, motor dysfunction, and autonomic phenomena. Myofascial trigger points may cause autonomic, sensory, and motor dysfunction. The pain complex includes dysesthesias, hyperalgesia, and referred pain. Autonomic dysfunction produces skin temperature and proprioceptive changes, sweating, piloerection, salivation, lacrimation, and erythema. Pressing on the trigger points generates pain at the contact site and can radiate to another site.

Biochemical analysis of the fluid surrounding the trapezius muscle with active myofascial trigger point has shown an increased concentration of bradykinin, substance P, calcitonin, tumor necrosis factor alpha, interleukin, serotonin, and norepinephrine compared with a control muscle.

Differentiation between myofascial pain syndrome and tendonitis, bursitis, fasciitis, and other causes of musculoskeletal pain may prove challenging as they share similar characteristics. Ultrasonographic examination may distinguish among these conditions as they have unique sonographic characteristics, whereas that of trigger point is nonspecific.

Trigger point injections are generally very safe. However, as with any interventional procedures complications can occur including bruising, bleeding, hematoma formation, infection and nerve injury. Pneumothorax can occur depending on the site of injection, but the risk can be minimized by use of ultrasound guidance.

Contraindications include infection at the site of injection, allergy to local anaesthetics and use of anticoagulant drugs.

The technique of ultrasound guided trigger point injections has been recently described. Ultrasound allows identification of soft tissue structures like nerve, blood vessels and pleura, thus minimizing the risk of complications. The pleura is visible as a bright echoic sliding line, especially with respiration (sliding lung sign). Ultrasound also allows real time visualization of the needle tip in the appropriate muscle layer.

US imaging and guidance may reduce the risks of trigger point injections, especially pneumothorax, and accurately guide the needle to its target. A “scout” sonographic examination before injection over the area of myofascial pain may demonstrate vital structures and abnormalities that warrant precaution and additional evaluation.