Treating Myofascial Pain With Trigger Point Injections

SAN ANTONIO—Myofascial pain accounts for 75 to 90% of musculoskeletal pain, and is one of the top 10 clinical diagnoses.

During the American Academy of Pain Management’s Annual Meeting, Ben Daitz, MD, Professor of family and community medicine at the University of New Mexico, School of Medicine, presented a number of patients presenting with musculoskeletal pain, which he successfully treated with trigger point injections (TPIs).¹

All of the body’s 400 skeletal muscles can potentially develop trigger points (TPs), which are defined as “hyperirritable loci within a taut band of skeletal muscle,” located in the belly of the muscle itself, within the contractile bands, close to the endplate zone, or in associated fascia.

Two types of TPs have been identified: active TPs, which can cause pain, and latent TPs, which can reduce motion and lead to muscle weakness. Latent TPs are usually found incidentally upon examination.

Referred pain from myofascial TPs is often described by patients as “dull, aching, deep,” distinct from the “sharp and burning” neuropathic pain, and occurs in the same dermatome, sclerotome and myotome as the originating TP.

Myofascial pain syndrome can be simple or complex; it is “pain or autonomic phenomena referred from active myofascial TPs with associated dysfunction.” The muscle involved is usually weaker and with a restricted range of motion. In addition, muscles can refer pain to distant sites. “In order to make an appropriate diagnosis, one needs to know what muscle one is dealing with, and how pain can be referred from that particular muscle,” noted Dr Daitz.

Trigger points causing myofascial pain develop at the neuromuscular junction. There, a release of acetylcholine depolarizes the muscle and triggers calcium release and contraction of the sarcomeres. At the site of TPs, “sensitizing substances,” (eg, bradykinins, interleukin-6, substance P and norepinephrine) are released.² 

The sympathetic nervous system has also been implicated in the development of TPs, as evidenced by vasodilation occurring following dry needling of sciatic pain-causing TPs.³ Trigger points can easily be located using ultrasound imaging, which also facilitates identification of injection site.⁴

Dr Daitz then presented case studies of patients he successfully treated by TPI, including a case of ear pain caused by TP in the masseter muscle and referred to the ear, a case of frozen shoulder caused by TPs in the subscapularis muscle, a case if torticollis with neck pain caused by levator scapulae TP, and a case of sciatica caused by gluteus minimus TP.

None of the thousands of TPIs Dr Daitz performed over the years led to major complications, including pneumothorax, persistent nerve block, or bleeding. Dr Daitz uses 0.5 cc or less 0.5 to 1% lidocaine around the TP zone to both reduce post-injection soreness and determine whether the injection alleviates the pain, but never injects steroids. Depending on the location of the muscle, the size of needles he uses vary from 30 gauge/0.5 inch to inject the temporalis muscle, to 25 gauge/1.5 inch for most upper body injections.

Dr Daitz recommended those in the audience interested in applying TPIs to their patients take a course on myofascial pain offered yearly at the University of New Mexico. This course introduces basic concepts and teaches how to perform TPIs or the equally effective dry needling.

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References

1. Ben Daitz, MD. Myofascial Pain: A Brief History of the Present Illness and Trigger Point How-To. Presented at: AAPM 2016. San Antonio, TX; September 21-25, 2016.
2. Shah JP, Phillips TM, Danoff JV, Gerber LH. An in vivo microanalytical technique for measuring the local biochemical milieu of human skeletal muscle. J Appl Physiol. 2005;99(5):1977-1984.
3. Skorupska E, Rychlik M, Samborski W. Intensive vasodilatation in the sciatic pain area after dry needling. BMC Complement Altern Med. 2015;15:72.
4. Niraj G, Collett BJ, Bone M. Ultrasound-guided trigger point injection: first description of changes visible on ultrasound scanning in the muscle containing the trigger point. Br J Anaesth. 2011;107(3):474-175.