Chapter 138: Trigger Point Injections

INTRODUCTION

Musculoskeletal pain is a significant health problem for the North American population.^1-9 Such pain affects between 10% and 20% of the population and is a major cause of morbidity.¹ It is estimated that approximately half of chronic pain complaints result from a musculoskeletal origin.² Myofascial trigger point (MTrP) injections may alleviate much of this pain.^10-13 It is imperative that the Emergency Physician perform a thorough history and physical examination with an emphasis on the neurologic and orthopedic examination to exclude other causes of musculoskeletal pain.³ The performance of MTrP injections by Emergency Physicians is underused.^14,15

ANATOMY AND PATHOPHYSIOLOGY

The etiology and pathogenesis of MTrPs have yet to be elucidated. The precise mechanism by which MTrP injections inactivate the trigger point is unknown. Researchers agree that acute trauma or repetitive microtrauma appears to lead to the development of a MTrP.⁶ The risk for a MTrP is increased when other factors are present (e.g., poor physical conditioning, poor posture, and prolonged bending).⁷ MTrPs mostly affect the muscle groups used to maintain posture (i.e., muscles of the neck, shoulders, and back). The patient may present with a tension headache or temporomandibular joint pain when the head and neck regions are affected.⁶

MTrPs are hyperirritable points located within a taut band of skeletal muscle or fascia.² When compressed, these points may cause autonomic pain and local tenderness.² Pain may be diffuse if not localized to the MTrP. The pain can be described as burning, dull, sharp, or some combination of these. Autonomic changes associated with a MTrP include dizziness, edema at the site, lacrimation, piloerection, salivation, and tinnitus. The compression of a MTrP can further lead to muscle spasm, stiffness, shortening, and fatigue.¹ This may progress to impaired muscle coordination, reduced muscle strength, and decreased range of motion.¹

DIAGNOSIS OF MTrPs

The diagnosis of a MTrP relies on the criteria of a tender spot with an underlying taught band, pain on palpation of the tender spot, and a local twitch response (i.e., a transient local contraction of skeletal muscle fibers in response to palpation or needling).^3,10 The data on clinical outcomes provide no definitive answer. The best outcomes appear to occur in patients who exhibit a local twitch response with palpation.⁴ The current literature provides no pathophysiologic explanation for this result. There are no laboratory, pathology, or radiology studies to identify or verify a MTrP.

Identifying the palpable, taut band is critical in locating the MTrP (Figure 138-1). The MTrP can be identified by flat palpation, snapping palpation, pincer palpation, and/or deep palpation. Flat palpation uses a fingertip to slide across the skin over the affected muscle to find the MTrP (Figure 138-2). The taut band may be felt under ...