A trigger point injection consists of a saline, local anesthetic  and occasionally an anti-inflammatory. While a variety of mixtures is possible and dependent upon the healthcare provider and patient, the most common is a mixture of lidocaine and Marcaine. 
The mixed solution is administered directly into the trigger point of the skeletal muscle via a small needle. The anesthetic blocks pain receptors in the muscles and nerves so the brain does not receive the pain signal. If an anti-inflammatory is used, swelling and inflammation in the area is reduced which helps reduce pain.
Myofascial “trigger points” are areas in the muscle that are easily irritated. Trigger points usually feel like a taut band or palpable “knot,”  and can be a source of local pain, regional pain or decreased range of motion.  Trigger points form from an acute injury or can originate from a muscle that is constantly stressed (i.e., poor posture or repetitive motion)  .
In the 1950s, Dr. Janet Travell and Seymour Rinzler coined the term “trigger point”  to describe their findings:
Pain related to a localized tender point within a nodule found in a taut band of muscle fibers. 
The point of pain elicits a local twitch response with snapping palpation. 
Palpation of the point reproduces the complaint and causes a referred pain pattern. 
Contraction of the muscle is painful and has limited range of motion. 
Muscles containing trigger points fatigue faster and cause weakness. The degree of weakness will vary with each muscle and with each subject. 
What do trigger point injections do?
These myofascial trigger point “knots” are a common a source of musculoskeletal pain. In the current trigger point model, pressure on these points will cause a localized twitch response, pain, and pain that radiates to broader areas. Trigger points also produce specific referral patterns. 
Patients commonly seek trigger point injections for:
Myofascial pain syndromes
Tension headaches and Migraines
Risks and Complications of Trigger injections
Risks associated with trigger point injections are low but include:
If you experience any side effects that do not resolve within a few weeks, follow up with your doctor.
How you prepare
Trigger point injections are an outpatient procedure; so, you won’t need to stay overnight.
Patients should shower the morning of and come dressed in loose/comfortable clothes.
4 hours before getting trigger point injections, avoid solid foods (liquids are allowed up to 2 hours before).
Be sure to let your physician know any prescription or over-the-counter medications you are currently taking. Blood thinners may need to be stopped but make sure to consult with your physician first. Small adjustments made need to be made with Diabetic medications.
Let your physician know if you are having any symptoms of such as fever, chills or if you are pregnant.
How trigger point injections are administered
The physician will locate trigger points through examination and by feeling different areas of the muscle to locate the area of pain.
While the patient is either sitting or lying down, the healthcare provider inserts a small needle into the affected area and the mixed solution is injected.
Patients often ask, “how bad do trigger point injections hurt?” and while every patient is different, most patients report minimal or no discomfort from the injection itself.
Since the procedure only takes a few minutes, multiple points can be injected during one visit.
After receiving trigger injections
Patients are monitored in office for up to 20 minutes after the procedure in order to make sure there are no reactions to the medicine or the injection.
Patients can resume normal activities after getting trigger point injections; however, if the patient feels faint or confused, they should not drive home.
Trigger point injection success rates
For many patients, trigger point injections provide significant benefits  such as: immediate relief and increased range of motion; however, not everyone responds the same. Results can last for several days or months.
Research shows trigger point injections can relieve muscle pain in the low back. 
For optimal results, trigger point injections can be combined with heat, ice, stretching, and massage. 
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