Comparison of pressure release,phonophoresis and dry needling in treatment of latent myofascial trigger point of upper trapezius muscle

2.1 Participants

This experiment included a study of 60 men (mean ± SD age, 23.6 ± 2.1 y) with at least one LMTP in the upper trapezius muscle. The LMTP was recognized based on the presence of a tender spot within the taut band in the upper trapezius muscle, which became painful in response to 25 Newton pressures [16, 22]. Exclusion criteria were diagnosis of fibromyalgia syndrome, history of whiplash, history of neck surgery, myofascial trigger point treatment during the past month, presence of cervical radiculopathy determined by a physician, presence of severe postural deviation (e.g. scoliosis or hyperkyphosis), presence of active myofascial trigger point sign (including jump sign), local hemorrhage, use of any anticoagulant drug, use of alcohol or any material that disturbs the person’s consciousness [4, 18]. All participants were given a clear explanation of the tests and signed informed consent forms before taking part in this research. Approval of the study was granted by the Institutional Ethics Committee (RCT no. IRCT2015103024729N1).

2.2 Identifying LMTP

To find LMTP regions in each session, a predesigned transparency sheet (10 × 1 cm) containing one central and four lateral hollow parts was used after LMTP identification. During the first evaluation session, the sheet was positioned on the LMTP, and its four lateral parts were filled with skin markers. This method facilitated LMTP differentiation during subsequent sessions.

2.3 Outcome measurement

For each group, pain intensity, pain pressure threshold (PPT) and active ROM were examined by an expert physiotherapist in all sessions.

2.4 Interventions

Randomization was achieved through use of a computer-generated random number table (Research Randomizer, version 4; www.randomizer.org). Total treatment duration was two weeks. Considering that DN repetition may disturb its effectiveness [4], the PB and PR groups had three, and the DN group had two treatment sessions per week. To have a better statistical curve, all variables were evaluated in each session and 24 hours after last treatment session.

4.1 Pain intensity

The ANOVA revealed that significant differences are present for the time factor ( F = 863.65, 0.001) with large effect size ( η p 2 = 0.938) and significant group × time interaction ( F = 10.81, 0.001) with effect size ( η p 2 = 0.3) regarding pain intensity. The LSD test showed the DN and PB groups had better results compared to the two PR groups ( 0.001). There was no significant difference between the DN and PB groups on decrement of pain ( p = 0.96) (Fig. 1).

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The ANOVA revealed significant differences are present for the time factor ( F = 1738.8, 0.001) with a large effect size ( η p 2 = 0.98) and significant group × time interaction ( F = 30.9, 0.001) with effect size ( η p 2 = 0.66) regarding pain intensity. LSD test showed the DN and PB groups had better results compared to the PR group( 0.001). There was no significant difference between the DN and PB groups on increment of PPT ( p = 0.18) (Fig. 2).

4.3 Range of motion

In this study, cervical ROM included ILF, CLF, IR and CR. The ANOVA test revealed that a significant time factor difference is present for ILF ( F = 1124.26, 0.001, η p 2 = 0.97), CLF ( F = 1554.49, 0.001, η p 2 = 0.98), IR ( F = 1187.5, 0.001, η p 2 = 0.97), CR ( F = 774.59, 0.001, η p 2 = 0.96). There is also a significant group × time interaction for ILF ( F = 36.27, 0.001, η p 2 = 0.68), CLF ( F = 19.21, 0.001, η p 2 = 0.65), IR ( F = 35.93, 0.001, η p 2 = 0.71), CR ( F = 16.8, 0.001, η p 2 = 0.51). The east significant difference (LSD) test showed the DN and PB groups had better results when compared with PR group ( 0.001). There was no significant difference between DN and PB groups on increment of cervical ROM in ILF ( p = 0.13), CLF ( p = 0.21), IR ( p = 0.16), CR ( p = 0.28) (Fig. 3).

5.1 LMTP and relevant symptoms

Although LMTPs are found in skeletal muscle fibers, they contribute to several musculoskeletal and nervous system disorders such as ROM restriction, muscle contraction inefficiency, accelerated muscle fatigability, motor control and autonomous system disturbance (Fig. 4) [2, 5, 14, 26, 27, 28]. Research has shown that LMTP could lead to tension increment and length restriction in skeletal muscles. Grieve et al. reported five-degree ankle dorsiflexion improvement secondary to treatment of active and passive myofascial soleus trigger points [2]. Zhang et al. recorded surface and intramuscular electrical activity before, during and after glutamate injection into different muscle points. Further, they reported significant muscle cramp and tension increment trigger points in comparison with healthy muscle points [28]. Interestingly, another study found a relationship between fatigue and LMTP in skeletal muscles [5]. Furthermore, an incorrect actin and myosin relationship in LMTP was reported as a cause of muscle physiological inefficiency leading to weakness without atrophy in skeletal muscles [5, 9]. Some studies have reported that motor control disorders such as early or delayed muscle activation before movement initiation, alteration in recruitment pattern and movement pattern disturbance correlated with the presence of LMTP [7, 26]. Other researchers have suggested a relationship between MTP and psychological and behavioral disorders [29].

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Energy crisis, motor end plate and radiculopathy are three hypothesized reasons for myofascial trigger point formation. Based on the energy crisis hypothesis, any muscular overload, including gradual microtrauma through changes in cellular membrane permeability, leads to a permanent sarcomere shortening, hypoxia and, finally, myofascial trigger point formation [1, 8, 9]. The motor end plate hypothesis was proposed to find the primary causes of the energy crisis hypothesis. In motor end plate hypothesis, excessive acetylcholine release from motor end plate on muscle and accumulation of pain-producing substance are major factors for myofascial trigger point formation. Gunn et al. developed the radiculopathy hypothesis, in which any nerve damage, including denervation and pressure on the nerve or nerve root, contributes to abnormal muscle tension and, finally, myofascial trigger point formation [1].

In this study, all PR, PB and DN groups had clinically significant improvements. Since patients with radiculopathy were excluded, the radiculopathy hypothesis would not apply in explaining the improvements in the present study. The finding of this study could be processed based on the energy crisis and motor end plate hypotheses Simons integrated in 2004. Simons showed several factors, such as correction of sarcomeres length, pain-producing substance reduction, ceasing energy crisis cycle and decreasing local hypoxia, should be attended in the treatment of LMTP [2, 18, 28].

The findings of the current randomized clinical trial suggest thatall three groups improved in pain score and PPT following treatment. Different mechanisms are proposed in pain alleviation [8, 18, 28]. The suggested mechanism in the PR technique is initial hypoxia followed by sudden blood supply increment. The final result would be pain-producing substance, local blood circulation correction and increased ROM [2, 17, 30].

Generally, mechanical and neurological aspects are considered as the dominant components to explain the changes found in the current study. Based on Simons’ findings and travelling theory, the mechanical effect of the needle will stimulate two healing processes, local muscle regeneration process and abnormal acetylcholine release cease about seven to ten days after treatment [1, 4]. Simultaneously, needle exertion itself could facilitate local stretching in the shortened sarcomere. Needle movement in muscle to optimize the effect might activate A-delta and C fibers. Such effect will remain as long as 72 hours after needle insertion [4, 8]. Also, prolonged stimulation of A-delta fiber might activate enkephalinergic, serotonergic and noradrenergic inhibitory system, implying that DN in LMTP could cause an opioid-mediated pain suppression mechanism. Intra-tissue mechanical disturbances of the needle cause pulling of collagen fibers toward the needle and initiate specific change in fibroblasts around the needle. The transduction of a mechanical signal into fibroblasts could lead to various intra- and extracellular events, leading to both sarcomere position and cellular function modification [4]. More research is needed to determine various aspects of DN mechanisms

Two significant effects of phonophoresis on LMTP contribute to ultrasonic waves and pharmacological aspects. The impact of ultrasonic waves on cells would result in a change of the outside cellular ion concentration. In other words, perhaps a transition increase in ions such as calcium might correct the sarcomere shortening in LMTP [18]. Betamethasone lotion is a safer steroid, anti-inflammatory agent and has the least side effects. Sarrafzadeh et al. revealed that phonophoresis of hydrocortisone, as an anti-inflammatory solution, was effective in the treatment of LMTP [18]. On the one hand, Ay et al. reported active myofascial trigger point phonophoresis with diclofenac had a significant improvement related to control group [10]. On the other hand, Shah et al. reported that while the level of inflammatory substance was evaluated in active myofascial trigger points, they found no significant difference between a patient with LMTP and healthy subjects [27]. Although the PB method was effective in LMTP treatment, probable ultrasonic wave side effects such as tissue destruction, blood cell stenosis and risk of tumor growth should be considered [18].

5.3 Cervical ROM

The findings of this study suggest that LMTP treatment increased cervical ROM. Some studies have shown that LMTP in a skeletal muscle could limit both inner and outer range of joint movement [2, 6, 7]. In this study, the upper trapezius muscle was shortened in ILF and CR (inner range) but lengthened in CLF and IR (outer range). Lucas et al. reported that LMTP could restrict inner active ROM of the muscle via decreasing contractile efficiency [7]. Additionally, some researchers proposed that LMTP could restrict outer active ROM of the involved muscles by increasing antagonist muscle activity and shortening the sarcomeres [2, 5, 6]. In the present study, both ipsilateral and contralateral movements (ILF, CLF, IR and CR) were significantly increased after the treatments in all groups.

5.4 Differentiation among the outcome of the three therapeutic methods

The present study’s findings suggest that DN and PB group subjects show greater improvement in pain, PPT and cervical ROM relative to the PR group after two week treatment. This difference may have its origin in a variety of therapeutic techniques. The direct access of ultrasonic waves and needle to LMTP may be considered as a rational reason to show a better result of PB and DN group relative to the PR group. In other words, tissue layers between LMTP and the location of manual pressure in the PR group may decrease the efficiency of this method. Generally, more research is needed to investigate the physiological effect of the DN and PB methods for treatment of LMTP.

5.5 Limitations

This study has a few limitations, including treatment of one muscle LMTP, lack of a control group, use of an objective device (e.g. diagnosis ultrasound) for outcome measurement and lack of including both sexes. These limitations should be considered in future studies. The comparison between DN, PB and PR was investigated for the first time in this study. Cervical rotation was also investigated for the first time.