Does Site-specific Trigger Point Dry Needling Evoke Segmental Neuromodulation in the Lower Extremity and if so, do These Changes Make an Impact on the Subject's Disability?

Background Dry Needling (DN) is a skilled intervention that uses acupuncture filiform needles that are inserted into myofascial trigger points or other tissues underneath the skin [Dunning]. Trigger points are spots in taut muscle fibers that can produce local and radiating pain when irritated, for example when pressed upon. Several theories on the etiology of trigger points exist, such as a local energy crisis and increased acetylcholine release due to mechanical muscle overuse [Bron]. The existence of trigger points is widely accepted [Hong], although there are also some vocal opponents [Quintner 2015, Quintner 1994].

The aim of DN is to treat myofascial or neuromusculoskeletal pain and improve movement impairments. The mechanism which with DN purportedly works has been the subject of debate for many years. It is generally accepted that the needle has to be inserted into a trigger point, where it will produce a local muscle twitch response and consequently 'inactivate' the trigger point [Dunning]. Some propose that the quick muscle contraction induces normalization of tissue pH and reduction of biochemical and neurotransmitters that stimulate pain receptors - a local response [Shah]. Others suggest that DN interrupts the trigger point's ongoing nociceptive input into the dorsal horn - a segmental response [Fernandez-de-las-Penas]. Others again submit that, because some trigger points affect limbic and dorsal hippocampus activity, DN might have a central response [Niddam].

The efficacy of DN is also not completely clear, but shows a trend. One early literature review and meta-analysis concluded that DN was not significantly superior to placebo control in regards to pain decrease [Tough]. However, since then several systematic reviews with meta-analyses [Tekin, Kietrys, Boyles] determined that the evidence suggested that DN for trigger point-derived pain was likely to be the most effective approach, was superior in decreasing pain compared to stretching and percutaneous electric nerve stimulation and at least as effective as manual trigger point release and other needling treatments. One literature analysis supports the use of DN not only for its immediate, but also short-term effectiveness in reducing pain in patients with upper quarter myofascial pain syndrome [Kietrys].

Controlled trials that assess DN efficacy either use 1) sham or control (such as no or an inactive treatment) or 2) other treatments (such as lidocaine injections, non-local DN, or "usual care", such as stretching and exercise) for the comparison group. A blunted needle that does not penetrate the skin is a good sham treatment [Streitberger] and has been recommended as adequate control. As discussed elsewhere [Streitberger], every needle penetration, be it at a trigger point or not, will induce physiological responses and are as such not appropriate to use as control.

Srbely et al. found that one intervention of trigger point stimulation with DN evoked palliative effects in other areas innervated by the same spinal segment. They dry needled trigger points in the supraspinatus and assessed pressure sensitivity changes in the infraspinatus (same segment, C5) and gluteus maximus (different segment, L4/5, S1). Their results suggest that pain pressure threshold was increased after 3 and 5 minutes of DN in the areas supplied by the C5 segment, but not in the area supplied by L4/5, S1.