Trigger points (TrPs) are sensitive nodules in taut bands of skeletal muscle that are characteristic of myofascial pain syndrome (MPS).1 TrP pathogenesis has been attributed to muscle overload and direct trauma to the muscle, which cause local ischemia, insufficient ATP synthesis, and the excessive release of intracellular calcium, all of which result in muscle contraction.2 Classified as either active (causing spontaneous pain) or latent (only painful when pressure is applied), TrPs can be treated with a trigger-point injection (TPI), a local anesthetic that numbs and relaxes the hypersensitive bundle of muscle fibers. In the outpatient procedure, a physician, having palpated the TrP to determine its precise location and severity, inserts the needle into the TrP and injects the anesthetic, repeating as necessary at different angles until the muscle loosens.3
TPIs usually consist of 0.5% or 1% lidocaine solution, though other injectates and methods for treating TrPs have proven effective. Botulinum toxin type A (BTX-A) has been shown in some studies to reduce pain to the degree achieved by lidocaine,4 but mixed results from other analyses prevent most researchers from recommending BTX-A as the treatment of choice for TrPs.5 Dry needling, which relives pain by stimulating a local twitch response (LTR)6 or by triggering vasodilation,7 is less costly than “wet” injections and does not pose a risk of anaphylaxis but is less frequently administered due to increased disturbance during injection.4 Noninvasive procedures for TrPs include the spray and stretch technique, which involves spraying a vapocoolant on the target muscle and stretching it toward normal length,3 and high-power pain threshold ultrasound (HPPTUS), during which an ultrasound probe placed directly on the TrP emits high-intensity sound waves; Unalan et al. report that HPPTUS is just as effective as a TPI in eliminating TrPs.8
The conventional wisdom that TrPs cause MPS, formalized by Travell and Simons in The Trigger Point Manual,9 has come under scrutiny in the recent past, which may have ramifications for the future use of TPIs. Pointing to several studies that fail to prove the TrP/MPS link, Quintner et al. argue that both TrPs and MPS are actually caused by inflammation of peripheral nerves.10 The authors attribute the success of TPIs to the counterirritation caused by the needle at the TrP, which blocks the detection of painful stimuli,11 and to the therapy, exercise, and stretching prescribed in conjunction with them. Shah et al. highlight inflammation of the fascia surrounding the TrP as a contributor to MPS, which would also suggest that a TrP-targeted injection is insufficient to treat MPS.12
TPIs, for the time being, are still widely prescribed for MPS, and novel applications of imaging technology have made them safer and more accurate. Doppler ultrasound can precisely reveal levels of blood flow to the TrP and measure TrP stiffness, both of which are objective criteria more useful to a physician considering a TPI than palpation alone.13 Computational modeling using ultrasound data has been used to quantitatively analyze the vascular environment of TrPs and might make the pathophysiological distinction between active and latent TrPs clearer.14 More research, however, is needed to determine the precise etiologies of MPS and TrPs and the role TPIs should play in treating them.
1. “Myofascial Trigger Point Therapy – What Is It?” National Association of Myofascial Trigger Point Therapists, namtpt.wildapricot.org/MTPT_What_is_it.
2. Bron, C. and Dommerholt, J. D. “Etiology of Myofascial Trigger Points.” Current Pain and Headache Reports, vol. 16, no. 5, 2012, pp. 439–444., doi:10.1007/s11916-012-0289-4.
3. Alvarez, D. J. and Rockwell, P. G. “Trigger Points: Diagnosis and Management.” American Family Physician, 2002 Feb. 15; 65(4): 653-661., www.aafp.org/afp/2002/0215/p653.html#afp20020215p653-b10.
4. Kamanli, A., et al. “Comparison of Lidocaine Injection, Botulinum Toxin Injection, and Dry Needling to Trigger Points in Myofascial Pain Syndrome.” Rheumatology International, vol. 25, no. 8, 2004, pp. 604–611., doi:10.1007/s00296-004-0485-6.
5. Climent, J. M. et al. “Botulinum Toxin for the Treatment of Myofascial Pain Syndromes Involving the Neck and Back: A Review from a Clinical Perspective.” Evidence-Based Complementary and Alternative Medicine, vol. 2013, 2013, pp. 1–10., doi:10.1155/2013/381459.
6. Hong, C.-Z. “Lidocaine Injection Versus Dry Needling To Myofascial Trigger Point.” American Journal of Physical Medicine & Rehabilitation, vol. 73, no. 4, 1994, pp. 256–263., doi:10.1097/00002060-199407000-00006.
7. Perreault, T. et al. “The Local Twitch Response during Trigger Point Dry Needling: Is It Necessary for Successful Outcomes?” Journal of Bodywork and Movement Therapies, vol. 21, no. 4, 2017, pp. 940–947., doi:10.1016/j.jbmt.2017.03.008.
8. Unalan, H. et al. “Comparison of High-Power Pain Threshold Ultrasound Therapy With Local Injection in the Treatment of Active Myofascial Trigger Points of the Upper Trapezius Muscle.” Archives of Physical Medicine and Rehabilitation, vol. 92, no. 4, 2011, pp. 657–662., doi:10.1016/j.apmr.2010.11.030.
9. Travell, J. G. and Simons, D. G. Myofascial Pain and Dysfunction: Trigger Point Manual. Lippincott Williams & Wilkins, 1993.
10. Quintner, J. L. et al. “A Critical Evaluation of the Trigger Point Phenomenon.” Rheumatology, vol. 54, no. 3, 2014, pp. 392–399., doi:10.1093/rheumatology/keu471.
11. Sprenger, C. et al. “Treating Pain with Pain: Supraspinal Mechanisms of Endogenous Analgesia Elicited by Heterotopic Noxious Conditioning Stimulation.” Pain, vol. 152, no. 2, 2011, pp. 428–439., doi:10.1016/j.pain.2010.11.018.
12. Shah, J. P. et al. “Myofascial Trigger Points Then and Now: A Historical and Scientific Perspective.” Pm&R, vol. 7, no. 7, 2015, pp. 746–761., doi:10.1016/j.pmrj.2015.01.024.
13. Sikdar, S. et al. “Novel Applications of Ultrasound Technology to Visualize and Characterize Myofascial Trigger Points and Surrounding Soft Tissue.” Archives of Physical Medicine and Rehabilitation, vol. 90, no. 11, 2009, pp. 1829–1838., doi:10.1016/j.apmr.2009.04.015.
14. Sikdar, S. et al. “Understanding the Vascular Environment of Myofascial Trigger Points Using Ultrasonic Imaging and Computational Modeling.” 2010 Annual International Conference of the IEEE Engineering in Medicine and Biology, 2010, doi:10.1109/iembs.2010.5626326.