1. Background
Musculoskeletal pain is a major cause of morbidity in today’s societies (1-3). About one-third of the patients with musculoskeletal pain meet the diagnostic criteria for myofascial pain syndrome (1). A myofascial trigger point (MTP) has been explained as a hyperirritability spot located in a taut band of muscle; described as resembling a small pea or as a rope-like nodular or crepitant (crackling, grating) area within the muscle which is painful in palpation or compression and refers pain, tenderness, or an autonomic response to a remote area. Some investigators stated that when pressure is applied to a MTP, a “jump sign” or “jump response” is elicited whereby the patient reacts with facial grimacing or by jumping away from the examiner (4).
Previous studies have indicated that MTPs are the primary source of musculoskeletal pain in 21-85% of patients (5, 6). The prevalence of MTP varies from 21% of patients seen in a general orthopedic clinic, to 30% of general medical clinic patients with regional pain, to as high as 85% to 93% of patients presenting to specialty pain management centers (7, 8). It has detrimental effects on people’s social and work-related activities and has a significant impact on the quality of life and causes pain and functional disability in neck and shoulder area (2, 3, 9).
It is thought that MTP may result from or be irritated by trauma, overuse, mechanical overload, postural faults, or psychological stress (4). Considering the sedentary lifestyle in today’s societies, as one spends much time in static postures, phasic muscles will become progressively inhibited and lax while postural muscles are gradually tightened. A muscle imbalance between the dynamic and postural muscles may lead to MTP in lumbo-pelvic or cervical region (3).
Some chemical changes such as increased level of bradykinin, substance P, and calcitonin gene-related peptide (CGRP), and lowered pH has been shown in MTP (10, 11). Investigators established that the local oxygen saturation at a MTP site is less than 5% of normal. Hypoxia leads to the release of local release of several nociceptive chemicals, including bradykinin, CGRP, and substance P (10). Local tenderness and referred pain following MTP ensues as muscle nociceptors are stimulated in response to reduced oxygen levels and increased inflammatory chemicals (6, 10, 12, 13).
Histological studies have confirmed the presence of extreme sacromere contractions, resulting in localized tissue hypoxia (10). The combination of increased levels of CGRP and lowered pH suggest that the MTP site is too acidic for ACh to work efficiently. It has been hypothesized that the injured muscle fibers shorten (making taut bands) either in response to excessive amounts of calcium ions being released from within the damaged fibers, or in response to the corresponding motor end plate releasing excessive amounts of ACh (6, 10, 13).
The upper trapezius (UT) muscle was found by investigators to be the muscle most often affected by MTP (14-16). The common symptoms and pain pattern in subjects with MTP in UT muscle is taut and painful muscle, tension headache, neck pain, dizziness or vertigo, limited neck and shoulder ROM (4, 17-19).
Considering the attachment of the UT muscle to cervical spine and suboccipital region and with regard to the role of UT in controlling range of motion (ROM) of the cervical lateral flexion, it is thought that MTP in UT muscle can result in limited cervical ROM (20). Local twitch response (LTR); an spontaneous spinal cord reflex contraction of the taut band muscle fibers in response to palpation or needling, is one of the most important characteristics of MTP (5, 10, 21).
Physical therapy programs play a significant role in treatment and improvement of symptoms in patients with MTP. The ischemic compression (IC) is currently used for the subjects with MTP attending physical therapy clinics (1, 13, 22). Dry needling (DN) has been recently used by therapists to treat MTP. The objectives of DN are achieved by inactivating the MTP, normalizing the chemical environment of active MTP, releasing muscle shortening, removing the source of muscle irritation, normalizing peripheral nerve sensitization, promoting self-healing of the injured tissue and decreasing spontaneous muscle activity (10).
Investigators have attributed the therapeutic effects of DN to various mechanisms, such as mechanical, neurophysiologic and chemical effects (10). It is thought that DN mechanically provides a localized stretch to the shortened sarcomeres and contracted cytoskeletal structures within the MTP. This would allow the sarcomere to resume its resting length by reducing the degree of overlap between actin and myosin filaments (5, 10, 21).
In favor of neurophysiological explanations of the DN effects, it has been suggested that DN stimulates the A-delta nerve fibers (group III), which in turn, may activate the enkephalinergic inhibitory dorsal horn interneurons, resulting in opioid mediated pain suppression (Pain relief) (10, 21). For chemical effect of DN, some studies have demonstrated that the increased levels of bradykinin, CGRP, substance P, and other chemicals at MTP are directly corrected by eliciting LTR following DN (10).
It has been suggested that DN may influence the microcirculation. Several investigators have demonstrated that needle insertion in the muscles increased both skin and muscle blood flow in the stimulated region (23). A change in inflammatory mediators has been demonstrated after DN of the UT, which suggested increasing local blood flow to the MTP region (23, 24). Although some previous studies have assessed the effect of DN on MTP in UT, review of the literature showed that a few RCT (randomized clinical trials) have been conducted to determine the effectiveness of DN in the treatment of MTP in UT muscle (25, 26).
However, with the use of different designs, samples and testing procedures, controversial results have been reported regarding the effect of DN on MTP in UT. Some previous studies assessed the immediate effect of DN, some others investigated the efficacy of DN combined with other modalities and some others investigated the remote effect of DN on UT muscle. Review of the literature showed that a few RCT (randomized clinical trials) have been conducted to determine the effectiveness of DN alone in the treatment of MTP in UT muscle (23, 25-29).
2. Objectives
The purpose of this study was to investigate the effect of DN on active cervical lateral flexion range of motion compared with IC in individuals with MTP in UT muscle.
4. Results
Demographic data (Mean ± SD) for the subjects in both groups is presented in Table 1. Pre- and post-measurement scores for active ILF and CLF of the cervical ROM in the control and intervention group and the results of paired t- test are provided in Table 2. The mean ILF ROM score increased from 39.33 and 41.26 pre-test to 47.5 and 44.46 post-test respectively for DN and IC group. The mean CLF ROM scores increased from 38.5 and 39.33 before treatment to 46.66 and 43.4 after treatment respectively in DN and IC group.
The result of paired t-test revealed a significant change in CLF after treatment in DN and IC group compared with before treatment (P < 0.05) but a significant change in ILF after treatment only in DN group compared with before treatment (P < 0.05). The result of ANCOVA revealed no significant difference was found between the two groups on the post-measurement score of ILF (P = 0.06), and CLF (P = 0.15).
| Variables | Before Treatment | After Treatment | P Value |
|---|---|---|---|
| ILF | |||
| DN | 39.33 ± 6.63 | 47.5 ± 5.83 | 0.001 |
| IC | 41.26 ± 9.66 | 44.46 ± 7.55 | 0.08 |
| CLF | |||
| DN | 38.5 ± 8.35 | 46.66 ± 6.51 | 0.005 |
| IC | 39.33 ± 8.85 | 43.4 ± 8.6 | 0.04 |
a Abbreviations: CLF, contera lateral flex; DN, Dry needling; IC, ischemic compression; ILF, ipsi lateral flex.
b Data are presented as mean ± SD.
Table 3. The Results of ANCOVA in Control and Experimental Groups a
| Variable | Sum square | DF | Mean square | F | P Value |
|---|---|---|---|---|---|
| ILF | 106.5 | 1 | 106.5 | 3.64 | 0.06 |
| CLF | 90.94 | 1 | 90.94 | 2.17 | 0.15 |
a Abbreviations: CLF, contera lateral flex; ILF, ipsi lateral flex.
5. Discussion
The result of this study is in agreement with the study conducted by Dominic et al who showed the increase in cervical ROM after needling (27). Limitation in ROM is one of the most important strategies in the human body to decrease the muscular injury. This ROM limitation is accompanied by muscle stiffness especially in chronic musculoskeletal syndromes (20). In today’s sedentary lifestyle, peoples are in static position for long time duration. Postural muscles like UT tend to be tightened. Muscle imbalance between postural and phasic muscles results in myofascial pain syndromes. Tightness in postural muscles can induce limited ROM. Thus, myofascial pain syndromes may present in the forms of pain, decreased joint motion, and muscle tightness or spasm (4).
Pain signal transferred to the spinal cord induces a nociceptive reflex. Continuous nociceptive reflex results in sustained muscle spasm (pain/spasm cycle). Continuous spinal stimulation and sustained muscle contraction results in muscle shortening and trigger point formation. Tissue hyper-sensitivity and reflexive shortening in MTP can increase mechanical pressure on the nerve endings. Released substance P from the nerve endings increases tissue sensitivity and excitability. Increased tissue excitability causes sustained muscle contraction in response to normal mechanical stimulants. Continuous muscle contraction leads to muscle spasm and pain. Prolonged local spasm results in muscle fiber shortening and tightness. Shortened muscle fibers will limit the joint ROM (10). DN may mechanically disrupt the integrity of the hyper tone muscle fibers – trigger points. Inserted needle can provide a localized stretch to the muscle fibers and can induce LTR which can cause muscle relaxation through reflex inhibition. Muscle relaxation can improve the ROM (10, 21).
The result of this study showed a significant change in CLF after treatment sessions compared with pre-treatment score in control and experimental group and a significant change in ILF after treatment sessions compared with pre-treatment score only in experimental group. Our data showed no significant difference in increasing ILF and increasing CLF score between two groups after treatment. The fact that the experimental group showed a significantly greater improvement in ILF and CLF after treatment, may suggest that the application of DN could be considered as a therapy of choice for subjects with MTP in UT muscle.
This finding is in accordance with other studies showing effects of DN in patients with MTP in UT muscle. However, with the use of different designs and testing procedures, controversial results have been reported regarding the effect of DN on MTP. Most of the previous studies assessed the immediate effect of DN in MTP. Some others investigated the efficacy of DN combined with other modalities and some others investigated the remote effect of DN on UT muscle (25-29). Review of the literature showed that a few RCT (randomized clinical trials) have been conducted to assess the efficacy of DN in the treatment of MTP in UT muscle (25-29). To our knowledge, this is the first study that directly investigated the effect of DN on MTP after one week. Investigators have attributed the therapeutic effects of DN to mechanical, neurophysiologic and chemical effects (10). Some chemical and mechanical changes such as increased level of bradykinin, substance P, and CGRP, and lowered pH, hypoxia, local tenderness and decrease in PPT has been shown in MTP (10, 11). Local tenderness and referred pain following MTP ensues as muscle nociceptors are stimulated in response to reduced oxygen levels and increased inflammatory chemicals (6, 10, 12, 13).
The results’ following the application of DN is reflected in the work of some other researchers who studied the mechanical, neurophysiologic and chemical effects of the tissue in response to the DN (10). DN mechanically provides a localized stretch to the shortened sarcomeres which allow the sarcomere to resume its resting length by reducing the degree of overlap between actin and myosin filaments (5, 10, 21). It has been also suggested that DN stimulates the A-delta nerve fibers which in turn may activate the enkephalinergic inhibitory dorsal horn interneurons (10, 21). Some studies have demonstrated an increased levels of bradykinin, CGRP, substance P, and other chemicals at MTP combined with eliciting LTR following DN (10).
Our data, however, showed no significant difference in increasing ILF and CLF between two groups after treatment. The reason we found no statistical differences between groups can be explained by the relatively small between group differences observed. As shown, the maximum between group change scores for ILF scores was 4.97 and the maximum between group change scores for CLF scores was 4.09 which was not statistically different. However, this difference could be considered clinically important and it is possible that if the sample size had been larger. The application of DN produces an improvement in ILF and CLF can be prescribed for subjects with MTP in UT muscles.
