Chapter 54: Myofascial Injections (Trigger Point, Piriformis, Iliopsoas, and Scalene Injections)

OVERVIEW OF MYOFASCIAL INJECTIONS

Myofascial pain is a common source of pain in the neck, low back, and other areas of the body. The term “myofascial pain” encompasses muscle strain, myofascial trigger points, and specific muscle pain syndromes. These syndromes include piriformis syndrome, iliopsoas related pain, and pain associated with the scalene muscles (trigger points, neurogenic thoracic outlet syndrome).

RELEVANT ANATOMY

Skeletal muscle consists of muscle fibers under somatic nervous control. Each nerve root innervates a muscle or group of muscles known as a myotome. The muscle belly of skeletal muscles is connected by tendons to bone. Trigger points occur in the muscle body, most often located in the center of the muscle.

TRIGGER POINT INJECTIONS

• Trigger points are hyperirritable localized taut bands of skeletal muscle that produce characteristic referral patterns.

• A trigger point (TP) may occur in isolation or concomitantly with myofascial pain syndrome or other pain generating syndromes.

• Trigger points are diagnosed by history and physical examination.

• A patient will complain of a localized pain or regional pain located in or around any skeletal muscle.

• The neck, shoulder girdle, and low back are the most common areas involved. Commonly involved muscles are the trapezius, splenii, cervical and lumbar paraspinal muscles, and the quadratus lumborum.

• On examination, localized taut bands of muscle are noted and palpation produces characteristic nondermatomal referral patterns.¹

• Trigger points may be active or latent. Active trigger points produce spontaneous pain, while latent trigger points produce pain only when palpated.

• Active trigger points may result from trauma, overload or overuse injury, or due to a muscle being in a prolonged contracted or shortened position.

• Treatments for active trigger points include physical therapy (stretching and strengthening, conditioning, therapeutic modalities); trigger point injections; acupuncture; biofeedback; transcutaneous nerve stimulation (TENS); and some medications.^{2, 3, and 4}

• Trigger point injections are intramuscular injections of local anesthetic with or without corticosteroids thought to work by local anesthetic effect, interruption of pain transmission, mechanical effects on the muscle itself, and disruption of ephaptic transmission.

Basic Concerns for Injection

• Immunocompromised patients, patients at high risk for infection.

• Patients with metastatic cancer pain may have local masses in the region.

• Patients may have thrombocytopenia secondary to chemotherapy.

• Patients with allodynia in the area of injection.

Contraindications

• Infection, systemic or localized

• Coagulopathy

• Distorted or complicated anatomy

• Patient refusal

Preoperative Considerations

• Refer to ASRA guidelines, consider the risks and benefits.

• Anticoagulation—this is less of a concern than for an epidural.

• Physical examination of the area for infection, skin ulceration or necrosis, and extent of disease.

• The ability of a patient to tolerate a supine, prone, lateral decubitus, or seated position for the injection.

Equipments

• Isopropyl alcohol ...