The Effectiveness of Radial Shockwave Therapy on Myofascial Pain Syndrome: a Mixed Method Study That Combines a Randomised Control Trial and Semi-Structured Interview.

INTRODUCTION Myofascial pain syndrome (MPS) is a common, costly and often persistent musculoskeletal problem that affects 85% of the general population at some point in their lifetime (Fleckenstein et al, 2010; Simon, 1996). Reported overall rates vary between male and female population and with different patient populations. MPS has been reported as the leading cause of chronic and persistent musculoskeletal regional pain such as neck pain, shoulder pain, chronic back pain and facial pain (Li et al, 2017). In the United States, the estimated economic cost for the management of chronic pain is $560-$635 billion per annum for medical care and disability programs, with the potential to increase year on year (Gaskin & Richard, 2012). Therefore, it is important that chronic musculoskeletal pain such as MPS in the neck and upper back is treated efficiently and effectively to improve patient's clinical outcomes and experience.

The clinical manifestation of MPS varies widely because it is not a distinct pathology. It is characterised by localized pain, muscle tenderness, palpable intramuscular taut band, local twitch response, referred pain, muscle spasm and sleep disturbance (Fernández-de-las-Peñas et al, 2012; Sciotti et al, 2001; Alvarez & Rockwell, 2001; Travell & Simmons, 1999). Myofascial trigger points can produce symptoms of pain upon palpation and pressure. A nail bed palpation by pressing manually with a thumb or using a digital algometer probe can trigger a local twitch response (LTR), which can reproduce symptoms of pain. This study will use a digital algometer to measure pressure pain threshold, which have been used by previous authors (Luan et al, 2019).

Most patients with MPS are treated by physiotherapists, physicians, chiropractors and osteopaths using trigger point injection, dry needling, acupuncture, ultrasound, stretches, deep frictional massages and taping (Galasso et al, 2020; Tough et al, 2009; Müller-Ehrenberg, 2005; Fernández-de-las-Peñas, et al, 2012). However, the most effective treatment for MPS is not known.

Radial shockwave is one of the most common and non-invasive treatments method with very few negative side effects, for musculoskeletal tissues such as MPS that normally are very difficult to treat (Watson, 2014). They are low to medium-energy pulses and their penetration depths are normally 0-6 cm ("0-2.3") (Watson, 2014). The therapeutic doses of radial shockwave ranges from low (up to 0.08mJ/mm2) to high (up to 0.63mJ/mm2) energy levels, and the number of treatment session repetitions is between 3 - 7 sessions (Watson, 2014). The number of shocks per session is usually between 1000 to 2500.

Some of the most strongly established therapeutic and biological effects of radial shockwave include mechanical stimulation, increased local blood flow that leads to tissue repair and regeneration by causing micro-functional and micro-structural changes, increase in cellular activity - release of substance P, prostaglandin E2 and tumour growth factor (TGF β), transient analgesic effect on afferent nerves and break down of calcific deposits (Watson, 2014; Wang, 2012). No evidence of serious tissue destruction at therapy level doses has been reported.