Trigger Point Injection
Trigger point
injection is a procedure used to treat painful areas of
muscle that contain trigger points, or knots of muscle
that form when muscles do not relax. Many times, such
knots can be felt under the skin. Trigger points may
irritate the nerves around them and cause referred pain,
or pain that is felt in another part of the body.
Introduction
Trigger points (see Figure 1) are classified as being
active or latent, depending on their clinical
characteristics. An active trigger point causes pain at
rest. It is tender to palpation with a referred pain
pattern that is similar to the patient’s pain complaint.
This referred pain is felt not at the site of the trigger
point origin, but remote from it. The pain is often
described as spreading or radiating. Referred pain is an
important characteristic of a trigger point. A latent
trigger point does not cause spontaneous pain, but may
restrict movement or cause muscle weakness. The patient
presenting with muscle restriction or weakness may become
aware of pain originating from a latent trigger point
only when pressure is applied directly over the point.
Pathogenesis
Many
researchers agree that acute trauma or repetitive
microtrauma may lead to the development of a trigger
point. Lack of exercise, prolonged poor posture, vitamin
deficiencies, sleep disturbances, and joint problems may
all predispose to the development of microtrauma.
Occupational or recreational activities that produce
repetitive stress on a specific muscle or muscle group
commonly cause chronic stress in muscle fibers, leading
to trigger points. Examples of predisposing activities
include holding a telephone receiver between the ear and
shoulder to free arms; prolonged bending over a table;
sitting in chairs with poor back support, improper height
of arm rests or none at all; and moving boxes using
improper body mechanics. Acute sports injuries caused by
acute sprain or repetitive stress (e.g., pitcher’s or
tennis elbow, golf shoulder), surgical scars, and tissues
under tension frequently found after spinal surgery and
hip replacement may also predispose a patient to the
development of trigger points.
Clinical
Presentation
Patients often report regional persistent pain resulting
in decreased range of movement of the muscle in question,
which are often muscles involved in maintaining posture.
In the head and neck region, trigger point pain may
manifest as tension headache, tinnitus, temporomandibular
joint pain, eye symptoms or torticollis. In the arm, the
pain may mimic bursitis or tendonitis, and in the legs
the pain can be a cause of limited range of movement of
the knee or ankle.
Evaluation
Palpation of a hypersensitive bundle or nodule of muscle
fiber of harder than normal consistency is the physical
finding most often associated with a trigger point.
Localization of a trigger point is based on the
physician's sense of feel, assisted by patient
expressions of pain and by visual and palpable
observations of local twitch response. This palpation
will elicit pain over the palpated muscle and/or cause
radiation of pain toward the zone of reference in
addition to a twitch response. The commonly encountered
locations of trigger points and their pain reference
zones are consistent (see Figure 2).
Management
Trigger point injection can effectively inactivate trigger points and provide prompt, symptomatic relief. Injections are given in the physician’s office and takes approximately 30 minutes. A small needle is inserted into the trigger point and a local anesthetic (e.g., lidocaine, procaine) with or without vitamin B12 is injected. Injection of medication inactivates the trigger point and thus alleviates pain. Sustained relief usually is achieved with a brief course of treatment. The injection may cause a twitch or pain that last a few seconds to a few minutes.