The role of a dry needling technique in pain reduction

Introduction: Dry needling is a therapeutic procedure using the insertion of thin needles through the skin into myofascial trigger points (MTrPs), muscular or connective tissue with the aim to reduce pain intensity. The objective of this systematic review is to analyze the literature for the efficacy of the dry needle technique in pain reduction in conditions of musculoskeletal pain caused by MTrPs.


INTRODUCTION
The myofascial trigger point (MTrPs) is the very irritable place in the narrow belt of skeletal muscle or myofascial, which is painful at touch or pressure poor body standing, and scoliosis. Trigger points are classified as active and latent. The active trigger points induce local and referred pain or paraesthesia while latent trigger points induce symptoms only at prior mechanical stimulation of the point (3).
The first stage in the development of a trigger point is the establishment of a narrow belt in the muscle as a result of an abnormal potential motoric plate due to excessive release of acetylcholine neuromuscular connections on the motor plate. EMG interpretation of such condition is a "spontaneous electrical activity" (SEA) so that the trigger point irritation can be objectively evaluated with the differences of the amplitudes change of SEA. Constant stimulation of the motor points can lead to a continuous contraction of sarcomere leading to ischemia and hypoxia. Accordingly, they release vasoactive and allogenic substances (noradrenaline, histamine, serotonin, and bradykinin), which stimulate the peripheral nociceptors (peripheral sensitization). Continual stimulation of peripheral nociceptors may stimulate neurons of spinal cord rear roots and supraspinal structures, leading to the clinical forms of hyperalgesia, allodynia, and referred pain (central sensitization) (4,5).
Myofascial pain origin was brought in focus in the middle of the past century by Dr. Janet Travell, who discovered that injection of the hypertonic solution in a MTrP causes referral pattern of pain, while injection of analgesic drugs leads to a reduction of pain intensity and the sensitivity of muscles to touch. Further studies have shown that insertion of a needle without the analgesic drugs leads to a reduction of pain intensity, after which began the development of the techniques of dry needling (3). The dry needling, also known as intramuscular stimulation, is a relatively new technique in the arsenal of methods of pain intensity reduction (6).
The dry needling is the therapeutic procedure which involves insertion of a fine needle through the skin into MTrPs or connective muscle tissue to reduce the pain intensity. The technique is used for the treatment of skeletal muscles dysfunction, of fascia and connective tissue in the end to minimize the continuous peripheral nociceptive stimulation and for the restoration of damaged structure and function of the body (7). Dry needling is applied by superficial (Baldry model) or deep technique (Travell model). Deep technique acts by deactivation of the trigger point for local twitch response (LTR). A LTR is a reflex of the spinal cord, which is characterized by involuntary contraction of a contracted thin band of muscles induced by a briefly sudden blow to the muscle or by inserting a thin needle. The deep dry needling technique is associated with a reduction of the local intensity and referral pain, improving the range of motion, decrease in trigger point irritation, stabilizing chemical and pH environment, and restoring the local circulation. The superficial dry needling technique is considered that activates Aβ fibers which lead to an inhibition in the spinal cord by obstruction of synaptic transmission between the Aδ and C fibers and cells of the spinal cord dorsal horn due to their slower transfer of impulses. It also activates the endogenous opioid system, i.e., the three main groups of opioids β-endorphin, enkephalins, and dynorphins, whose analgesic effects are reflected to inhibit directly the transmission of afferent nociceptive information from the rear horns of the spinal cord (1,4,8).
The aim of this systematic review of the literature is to determine, on the basis of the available studies, the efficacy of the dry needling technique in pain intensity reduction of aching musculoskeletal painful conditions induced by MTrPs.

Search strategy
We performed a search of Web of Science, Scopus and EBSCOhost databases for e-books and articles published from January 2010 to December 2018. We included randomized controlled studies, randomized clinical studies, prospective studies, longitudinal studies, and case reports with with various forms of musculoskeletal pain conditions treated by dry needling technique compared to physical therapy or sham dry needle technique. We also included studies which compared the efficacy of different handling techniques with needles for dry needling as well as the treatment of both active and latent trigger points. We searched for the following terms: "Dry needling," "electro needling," "MTrPs," "MPS," "musculoskeletal conditions," and "trigger point stimulation."

Criteria for inclusion and exclusion
In the systematic literature review we included studies consistent with the above strategy of literature survey, including patients diagnosed with painful musculoskeletal condition, one or more control measurement after the treatment, instrument of pain intensity evaluation, comparison of dry needling techniques before and after the treatment, the other treated and placebo dry needle techniques or various techniques of dry needling treatment of painful musculoskeletal conditions.

Study selection and data extraction
Articles that met the criteria for inclusion in the systematic review of the literature underwent a detailed evaluation. The data extracted were: name of the first author, study design, the country and city of study, the number of patients in the study and control groups of research, gender, and age structure of the patients, the year of the research publication, the main objectives, methods and instruments of research, and research results and conclusion.

Selection of studies
A total of 13 studies with 540 patients were selected out of 496 articles found in Web of Science, Scopus, and EBSCOhost.

Study characteristics
The reviews, which research met the above criteria for inclusion, had been accomplished in Cyprus, Iran, India, Australia, Spain, USA, and Canada. Our systematic searching of the literature was focused on the efficacy of the dry needle technique in painful musculoskeletal conditions and included 13 studies: Two reviews on painful lumbar syndrome (LBS) (one review on acute LBS and one review on radicular LBS), three reviews on pain in the upper part of Trapezius muscle, and one review on pain in the cervical spine, one review on plantar pain of heel, one review on effects of dry needle stimulation of quadriceps femoris muscle and pain intensity of patients after operative reconstruction of front cruciate ligaments of the knee, one review on effects of dry needle stimulation of infraspinatus muscle on pain intensity at patients with painful shoulder, one review on effects of dry needle technique on pain reduction, one review on occipital neuralgia, and one review on effects of two different techniques of dry needle stimulation of trigger points. The survey and characteristics of the studies included in the systematic review of the literature are presented in Table 1.

Comparison of dry needling effects and other forms of pain intensity reduction treatments
We included two studies in which were compared effects of dry needling and standard physical treatment for pain intensity reduction in patients with the painful LBS.
Tüzün et al. investigated the effects of dry needle technique (study group) and the standard physical treatment (control group) in the reduction of the pain intensity in patients with chronic LBS. A significant decrease in pain intensity was achieved of pain in the study group (visual analog scale [VAS] 2.5 before the treatment, VAS 0.6 after the treatment) compared to the control group (VAS 2.4 before the treatment, VAS 3.3 after the treatment) (9).
The influence of the standard physical treatment, with the addition of dry needling technique, in reduction of the pain intensity in patients with two radicular discogenic LBS (study group) was investigated by Mahmoudzadeh et al. The condition evaluation of the study group was performed before treatment, and directly 2 months after the treatment and was compared to the standard physical treatment (control group). It was found a more significant reduction of pain intensity in patients of the study groups (study group 78.96/37.24/25.17 and control group 74.13/45.51/42.41) (10).
In the literature review was also analyzed three reviews on the effects of dry needle techniques on trigger points of the upper/descending part of trapezius muscle.
Abbaszadeh-Amirdehi et al. have investigated the effects of dry needling in patients with trigger point of upper/descending part of trapezius muscle compared to healthy volunteers. The pain intensity was significantly reduced in patients of the study group (VAS 5 before treatment 5/after treatment 2) in healthy volunteers was decreased the pressure pain threshold (11).

DISCUSSION
The investigation results showed that dry needle treatment alone, or as an addition to standard physical treatment, was effective in reducing pain intensity in patients with LBS.
Liu et al. conducted a systematic review and meta-analysis on the effects of dry needling in the treatment of MTrP associated with LBS. The results showed that dry needling, especially in combination with other treatments, may be effective in reducing pain in patients with LBS-om (22).
By the literature survey was found that dry needling is effective in reducing pain intensity of neck and shoulders in patients with MTrPs of the upper trapezius muscle, infraspinatus muscle of paraspinal muscles or cervical part of the spine.
Liu et al. investigated the effects of dry needle technique in the treatment of MTrP associated with pain in the neck and shoulder. They conducted a systematic review and meta-analysis, by which was determined that the dry needling is recommended for reduction of pain intensity of MTrP localized in neck and shoulder, but without long-term effects (23).
In analysis of the systematic survey results was found that dry needling treatment is effective for reduction of the pain intensity in patients with non-specific pain in the thoracic portion of spine, occipital neuralgia, after reconstruction of the anterior cruciate ligament of the knee, and to be more effective in reducing pain intensity compared to the sham dry needling treatment. It was also found that different techniques of dry needling are effective in the treatment of MPS.
Gattie et al. found by the systematic review of the literature and meta-analysis found that the dry needling treatment conducted directly by a physical therapist is more efficient than not carrying out the treatment, the sham dry needling, and other forms of treatment in instantaneous reduction of musculoskeletal pain intensity as well as 12 weeks after the treatment (24).

CONCLUSION
The systematic survey of the literature has provided the evidence on the basis of which the dry needling alone or as an addition to other treatments' interventions is recommended in the treatment of painful musculoskeletal conditions caused by MTrPs. We found its superiority compared to sham dry needling or not carrying out the treatment. Various techniques of dry needling treatments were almost equally effective in reducing myofascial pain intensity.