RETRACTED: Immediate effect of muscle energy technique on latent trigger point of upper trapezius muscle

Clinical Chiropractic (2012) 15, 112—120

www.elsevier.com/locate/clch

ORIGINAL ARTICLE

Immediate effect of muscle energy technique on latent trigger point of upper trapezius muscle Royah Mehdikhani a,*, Farshad Okhovatian b a b

Rehabilitation Faculty, Shahid Beheshti University of Medical Sciences, Tehran, Iran Physiotherapy Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Received 5 June 2012; accepted 21 October 2012

KEYWORDS Myofascial trigger points; Upper trapezius muscle; Muscle energy technique; Pressure pain threshold; Visual analog scale

Summary Objective: The aim of this study was to investigate the immediate effect of muscle energy technique (MET) on latent myofascial trigger point (MTrPs) of the upper trapezius muscle. Methods: Thirty-six female volunteers participated in this study. Subjects were divided randomly into 2 groups: MET and control groups. Outcomes measures were pressure pain thresholds (PPTs), and pain intensity (visual analog scale, VAS) and cervical contralateral flexion (CLF). Within-group effect sizes were large (d > 1) in the intervention group; but small to medium for the control group in all outcomes. Results: The results showed an immediate decrease in pain sensitivity in the upper trapezius muscle and increase in cervical contralateral flexion. There were significant changes between groups, MET group was effectiveness than control group. Conclusions: Our results suggest that muscle energy technique induced changes in pressure pain sensitivity in latent MTrPs in the upper trapezius muscle. # 2012 The College of Chiropractors. Published by Elsevier Ltd. All rights reserved.

It has been suggested that mechanical neck pain has a lifetime prevalence of 45—54% in the general population,1—3 and up to 30% of men and 50% of women experience neck pain in the course of a lifetime.4 Saringovallis and Hollins5 estimated that the occurrence of neck pain at any given point of time is between 13.4% and 22.2%. It has further been reported that 14% of neck pain patients are at risk of

* Corresponding author. Tel.: +98 912 742 72 33; fax: +98 241 218 68 12. E-mail address: [email protected] (R. Mehdikhani).

their pain becoming chronic which, makes neck pain very expensive in terms of absenteeism from work and in terms of healthcare costs.6 Simons et al. (1999) have defined MTrPs as discrete foci (Fig. 1), often palpable as a nodule, within taut bands of skeletal muscle that are tender on palpation and produce characteristic referred pain and autonomic phenomena (dysautonomia or autonomic dysfunction is a broad term that describes any disease or malfunction of the autonomic nervous system (ANS). The autonomic nervous system controls a number of functions in the body, such as heart rate, blood pressure, digestive tract peristalsis,

1479-2354/$36.00 # 2012 The College of Chiropractors. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.clch.2012.10.040

[(Figure_1)TD$IG]Immediate effect of muscle energy technique

Figure 1

The trigger point in the muscle fiber.

sweating, amongst others. Dysfunction of the ANS can involve any of these functions). Active MTrPs are a cause of symptoms (pain, autonomic phenomena, restricted motion), whereas latent MTrPs may not be an immediate source of pain, but produce characteristic referred pain when manual pressure is applied. Latent MTrPs are believed to be prevalent in symptomatic and asymptomatic individuals alike, are claimed to be easily rendered ‘active’ by minor muscle overload or fatigue7 and there is evidence that they may disturb normal patterns of motor recruitment and movement efficiency.8 Tender points and myofascial trigger points are usually associated in the literature. There are claims, however, from experts in clinical practice that myofascial trigger points (MTrPs), described as a ‘tender points located in taut bands of skeletal muscle, which on palpation reproduce the patient’s pain’,7—9 although the two disorders have different features that is shown in Table 1. The multitude of differences speak against a common etiology and pathophysiology.10 Muscle energy technique is a manual procedure that uses controlled, voluntary isometric contractions of a targeted muscle group and is widely advocated by authors in the field of osteopathy. MET is claimed to be useful for lengthening a

113 shortened muscle, improving range of motion at a joint and increasing drainage of fluid from peripheral regions.11 Muscle energy procedures, and related post-isometric procedures such as proprioceptive neuromuscular facilitation (PNF), have been demonstrated to be more effective than static stretching for improving the extensibility of shortened muscles.12—14 MET is safe, effective, easy to use, and easy to teach to patients for self-use.15 Like many manual therapeutic approaches, the efficacy and effectiveness of MET is underresearched, and there is little evidence to guide practitioners in the choice of the most useful technique variations (such as number of repetitions, strength of contraction, duration of stretch phase), causing frustration for those endeavoring to integrate relevant evidence into practice. A limited but growing number of studies show positive change following MET intervention. Studies that demonstrate an increase in the extensibility of muscles16—21 and spinal range of motion22—26 support the rationale for not of treating patients with reduced mobility, although research involving clinical outcomes is scarce. One case study series27 and one randomized singular-trial28 for the treatment of acute low back pain (LBP) are the only English language studies that examined MET as the sole treatment using clinical outcomes. Both reported decreased pain following treatment. The lack of clinically relevant research is not surprising given that MET is typically used in conjunction with other techniques. Several clinical trials investigating osteopathic management of spinal pain have included MET as a treatment component, and given that treatment significantly reduced the reported pain and disability in these trials, they provide further support for the effectiveness of MET, as part of a package.29—31 While there is need for further investigation of MET, available evidence supports the use of this approach to treat restricted mobility and spinal pain. Although limited evidence exists for the efficacy of muscle energy, the current research

Table 1 Different features between trigger and tender point. Features

Trigger point

Tender point

Palpable nodule Site of nodule Allodynia and hyperalgesia Referral of the MTrP pain Local twitch response Local contracture Mechanism probable

Yes Often located close to muscle belly At the MTrP Yes Yes Yes Peripheral

No Often close to the muscle attachments Outside the tender points No No No Central

114 literature indicates a need to reconsider the clinical diagnostic methods and the physiological mechanisms causing therapeutic effect. The mechanisms underlying the possible therapeutic effects are largely speculative, but evidence supports the plausibility of several modes of action. An understanding of the likely mode of action may inform and influence the application of muscle energy technique. The authors have not found any studies relating to changes in sensitivity and range of motion of upper trapezius muscle trigger point following a single application of muscle energy technique. The aim of this study was to investigate the immediate effects of MET intervention on an upper trapezius latent trigger point. It was hypothesized that the MET intervention would elicit reductions in trigger point sensitivity and increasing in cervical contralateral flexion.

Methods This study was a randomized, single-blind, sham controlled clinical trial. The study was conducted at the Physical Therapy Research Center (PTRC) of Shahid Beheshti University of Medical Sciences in the Iran and approval for the study was obtained from the PTRS Research Ethics Sub-Committee. Data collection occurred between December 2010 and March 2012. The sample size and power calculations were performed with a local software (Taman ˜o de la Muestra, 1.1, Madrid, Spain). The calculations were based on detecting a 20% difference in pressure pain threshold at post intervention data, assuming SD of 10%, an a level of .05, and a desired power of 80%. These assumptions generated a sample size of at least 20 subjects per group.

The participants Through local newspaper advertisements, 36 female students from PTRC, between the ages of 18—35 years, suffering from neck/shoulder pain corresponding with the area covered by the upper trapezius muscle were recruited. The volunteers were female, because the gender differences may have influenced the results.32 They were healthy individuals, diagnosed with latent MTrPs in the trapezius muscle. Subjects were randomly divided into 2 groups for treating MTrPs: G1 receiving MET; and G2, control group, who received sham ultrasound. To locate trapezius MTrPs, we followed the exploration diagnostic criteria established by Simons et al. (1999)33:

R. Mehdikhani, F. Okhovatian 1. Presence of palpable taut band in a skeletal muscle. 2. Presence of a hypersensitive tender spot in the taut band. 3. Local twitch response provoked by the snapping palpation of the taut band. 4. Reproduction of the typical referred pain pattern of the MTrPs in response to compression. 5. Spontaneous presence of the typical referred pain pattern and/or patient recognition of the referred pain as familiar.34 If only the four first criteria were satisfied, the MTrP was considered to be latent. If all of the aforementioned criteria were present the MTrP, was considered to be active.33,34 None of the participants demonstrated criteria 5. Range of active CLF of the cervical spine was measured by using a dual inclinometer consisting of master and slave parts that records the greatest range of motion for each movement. The master part was placed parallel to the shoulders horizontally, and the slave part was placed on the lateral border of the head. The reliability of this method was investigated in 30 healthy subjects before the study and an interclass correlation coefficient model 2, 1 of 97% and standard error of measurement of 0.998 were obtained.35,36 The assessor applied continuous pressure with the algometer at approximately a rate of 1 kg/ cm2/s, until it recorded a pressure of 2.5 kg/cm2. If the referred pain evoked by the MTrP was obtained before 2.5 kg/cm2, criteria 4 was seen to be fulfilled. Subjects were excluded if they showed any of the following: 1. 2. 3. 4.

Diagnosis of fibromyalgia syndrome. History of a whiplash injury. History of cervical spine surgery. Diagnosis of cervical radiculopathy or myelopathy determined by their primary care physician. 5. Having undergone myofascial pain therapy within the past month before the study. Each subject read a Study Information Sheet and signed an Informed Consent Form before enrolment the study. The randomization scheme was generated by using the web site Randomization.com (http:// www.randomization.com). To ensure equal numbers in the groups, subjects were randomized in blocks of two. Sealed opaque envelopes were prepared containing the assigned treatment and numbered consecutively. Subjects were allocated to the next available envelope number.

Immediate effect of muscle energy technique

Interventions Muscle energy technique

115 disconnected, allowing them to be used as a control group. This same method has been used in earlier studies.37

For MET technique as advocated by Chaitow: the sitting subject’s neck was passively side flexed and opposite side rotated until tension was sensed by the researcher and the subject reported a moderate stretching sensation. The participant provided a moderate (approximately 40% of maximal contraction) neck opposite side flexion and rotation isometric contraction, against the researcher’s hand for 7—10 s. This was followed by 2—3 s of relaxation, and then the neck was passively stretched to the palpated barrier and/or tolerance to stretch and held for 30 s. The neck was then relaxed on neutral position for a short resting period (approximately 10 s). Subjects lay supine on a treatment table, with the practitioner present at the head of the table. If the direction of restriction was labeled as right the therapist passively flexed the subjects head and neck to approximately 458 until a sense of resistance was palpated (to relatively lock the mid and lower cervical segments), and then rotated the head to the right until a restrictive barrier was palpated. The subject was then instructed to gently push into the practitioner’s hand (rotate to the left) approximately 40% of maximal contraction for 7—10 s, followed by 2—3 s of relaxation, and then the neck was passively stretched to the palpated barrier and/or tolerance to stretch and held for 30 s. The neck was then relaxed on neutral position for a short resting period (approximately 10 s). This procedure was performed three times. On the final relaxation phase, the subject was instructed to breath in and out assist relaxation.

Pressure pain threshold

Sham ultrasound

Analysis of data

A Novin ultrasound (512X model) machine was used. The subject was informed that pulsed ultrasound was going to be used; she should not feel any sensation of heat or pain. If this was felt, to let the clinician know and the machine would be turned down. Since this was a sham procedure, such adjustment made no actual difference. Ultrasound lotion was applied over the MTrPs and the ultrasound head was moved slowly over the upper trapezius muscle in the region of the MTrPs, to reduce the effect of massage with less pushing (for the lowest possible effect on the blood circulation, lymph, muscular tone and nervous system), for 2 min. Ultrasound was chosen because subjects are not aware of the apparatus being connected or

Data was analyzed with the SPSS (Statistical Package for the Social Sciences) package (version 16). Mean and standard deviations of the values were calculated for each variable. A normal distribution of quantitative data was assessed by means of the kolmogorov—Smirnov test (P > 0.05). Baseline features were compared between groups using the one way ANOVA (ANalysis Of VAriance between groups). Within-group differences were assessed with the dependent t-test. Within-group effect sizes were calculated using Cohen’s d coefficient. Inter-group comparisons between both studies groups were also achieved with the independent t-test. The statistical analysis was conducted at a 95% confidence

Pressure pain threshold (PPT) is defined as the minimal amount of pressure where a sense of pressure first changes to pain. An algometer (Taivan, model 5020 F) was used in this study. This device consists of a round rubber disk (area, 1 cm) attached to a force gauge. A pressure of 2.5 kg/cm2 was applied on MTrPs. The VAS was used to evaluate a possible change in pain intensity. Each participant was instructed to indicate the intensity of pain by marking a 10-cm horizontal line with 2 extremes: no pain and worst imaginable pain. Subjects were advised to not utilize drugs such as: opioid and non-opioid analgesics, anti-inflammatory drugs and anti-depressants. Subjects received the treatments, as described for each group, after which the same measurements were performed. Examiner 1 (neurologist) performed the outcome measures, having been blinded to the treatment techniques, while examiner 2 (physical therapist) performed the treatment techniques. In our study, all measurements were made by a 4th year chiropractic student, who had been trained by a chiropractor with 7 years of clinical experience. Intra Class Correlation (ICC) was used for assessing intra-examiner repeatability of PPT readings taken from the four pre-intervention trials. The intra-rater reliability of pressure algometry has been found to be high on the same day i.e., ICC = 0.87, P < 0.0001. It should be mentioned that a 30 s resting period time was allowed between each trial.

116

R. Mehdikhani, F. Okhovatian

Table 2 Baseline data for the groups. Variable

Muscle energy technique

Control

P-value

Mean Mean Mean Mean

23.61 1.96 4.89 40.44

24.06 1.83 5.22 39.77

0.50 0.27 0.21 0.53

age (SD) PPT before VAS before CLF before

(2.06) (0.39) (0.47) (3.05)

(1.92) (0.31) (0.54) (3.38)

Age in years; height in m; weight in kg; BMI in kg/m2; VAS in cm; pressure pain threshold (PPT) in kg/cm2; CLF in degree; ANOVA used for outcome measures.

Table 3 Pre—post values of each group. PPT (SD) VAS (SD) LCF (SD)

Muscle energy technique

Control

P-value

1.96  0.39; 2.67  0.41 4.89  0.47; 3.56  0.70 40.44  3.05; 46.17  3.23

1.83  0.31; 1.89  0.30 5.22  0.54; 5.0  0.59 39.77  3.38; 40.35  3.41

<0.001 <0.001 <0.001

Values are expressed as mean  S.D.

Table 4 Paired sample test. Group

PPT (kg/cm2) Mean (SD) t

VAS Mean (SD) t

CLF (8) Mean (SD) t

G1 G2

0.70 (0.10) 28.54 0.06 (0.01) 14.38

1.33 (0.48) 11.66 0.22 (0.42) 2.20

5.73 (0.10) 24.31 0.57 (0.23) 10.25

level. The P-values less than 0.05 were considered as statistically significant.

Results Both study groups were comparable at the start of the study. Table 2 shows clinical pre intervention data for each group at the beginning of the study. The mean changes between experimental and control groups was compared using an independent t-test, and was found to be significantly different. Tables 3 and 4 show pre—post value and paired sample test of each group. Effect sizes were calculated using Cohen’s d,38 and can be interpreted as being large (d = 0.8), medium (d = 0.5) and small (d = 0.2) (Cohen, 1988). The within-group effect sizes for the intervention group were found to be very large (d > 1), whereas the effect size was small to medium for the control group. Table 5 shows effect sizes of each group.

Table 5 Effect sizes of each group. Muscle energy technique Control

PPT

VAS

CLF

1.85 0.19

2.25 0.38

1.85 0.16

Discussion Applications of MET to stretch and increase myofascial tissue extensibility seem to affect viscoelastic and plastic tissue properties,39,40 autonomicmediated change in extracellular fluid dynamics,41 and fibroblast mechanotransduction,41,42 but few lasting changes in human muscle properties have been found.43 Studies measuring pre and post-force (torque) show little viscoelastic change after passive or isometric stretching and indicate that muscle extensibility is due to increased tolerance to an increased stretching force.16,18,44 Although short and medium term application of stretching and MET may alter the perception of pain, it does not appear to affect the biomechanics of healthy muscle, but studies are required for injured and healing muscle tissue. MET may influence pain mechanisms and promote hypoalgesia. Studies suggest that MET and related post-isometric techniques reduce pain and discomfort when applied to the spine28 or muscles.16,18 The mechanisms are not known, but may involve central and peripheral modulatory mechanisms, such as activation of muscle and joint mechanoreceptors that involve centrally mediated pathways, like the periaqueductal gray (PAG) in the midbrain, or nonopioid serotonergic and noradrenergic descending inhibitory pathways. Animal and human studies have shown sympathoexcitation and localized activation of the lateral and

Immediate effect of muscle energy technique dorsolateral PAG from induced or voluntary muscle contraction,45,46 and activation of non-opioid descending inhibitory pathways from peripheral joint mobilization.47,48 Additionally, MET may increase fluid drainage and augment hypoalgesia. Rhythmic muscle contraction increases muscle blood and lymph flow rates,49 and mechanical forces acting on fibroblasts in connective tissues change interstitial pressure and increase transcapillary blood flow.50 MET application may reduce pro-inflammatory cytokines and desensitize peripheral nociceptors. MET may also produce changes in proprioception, motor programming, and control. Spinal pain disturbs proprioception and motor control, causing decreased awareness of spinal motion and position51,52 and cutaneous touch perception.53,54 Spinal pain affects motor programming, inhibiting the stabilizing paraspinal musculature, while causing superficial spinal muscles to overreact to stimuli.55,56 No study (to the authors knowledge) has investigated the effect of MET on proprioception or motor control, but limited evidence suggests benefit from other manipulative treatments.57—61 Since MET produces joint motion while actively recruiting muscles, it may affect proprioceptive feedback, motor control, and motor learning; this should be investigated in the future. Authors of MET texts have proposed that the technique improves lymphatic flow and reduces edema,62 and evidence from muscle contraction and physical activity studies support this.63—65 Muscle contraction increases interstitial tissue fluid collection and lymphatic flow,49,66 and physical activity increases lymph flow peripherally in the collecting ducts, centrally in the thoracic duct, and within the muscle during concentric and isometric muscle contraction.63 MET may assist lymphatic flow and clearance of excess tissue fluid to augment hypoalgesia, changing intramuscular pressure and the passive tone of the tissue. The mechanisms outlined above may explain some of the therapeutic action of MET technique, but are not likely to be specific to this technique and will possibly be activated by any physical activity that produces muscle contraction. It is argued by authors that METapplied specifically to a painful and dysfunctional region may produce local changes in circulation, inflammation and proprioception, and although these proposed mechanisms appear plausible they are still largely speculative. The relative efficacy of specifically applied MET compared to general physical activity has not been explored and would help to determine the usefulness of MET for regional pain and dysfunction. Evidence suggests MET (or similar isometric stretching techniques) is more effective than passive stretching for increasing muscle extensibility.

117 Due to lack of studies or conflicting evidence, little information exists about the optimal number of isometric contractions, the duration and intensity of contraction, or the force of the stretch.43 Evidence for the most effective direction of contraction to increase flexibility in healthy muscle does exist. To gain maximum ROM and muscle extensibility, the use of isometric variations that include recruitment of the agonist muscle is suggested.7 Agonist contract (AC) and contract—relax agonist—contract (CRAC) are variants of proprioceptive neuromuscular facilitation, where the patient actively pushes further into the barrier (AC) or where isometric contractions away from and into the barrier are alternated. These techniques have been consistently effective for increasing flexibility43 but are appropriate where muscles are not painful. It is not recommended for muscles or joints that are painful because pushing into the painful barrier would likely produce protective muscle guarding and apprehension. The duration of the stretch phase for maximum gains in flexibility should be considered. Many recommend only a few seconds of relaxation before re-engaging the new barrier,63—69 but Chaitow recommends a duration of up to 60 s for chronically shortened muscles. Studies reporting that duration of stretch influences the amount and longevity of ROM gains support this recommendation.70—73 Further, longer stretching durations are more effective than short durations, with 15 s more effective than 573 and 30 s more effective than 15 but no different than 60.72,73 Feland et al.,73 reported a 60s stretch produced greater gains in ROM that lasted longer than lesser durations for elderly people with tight hamstrings, and their subjects may be representative of those with chronically shortened fibrotic muscles. Although no studies suggest the best application for stretching painful muscles, healing muscles, or active trigger points, gentle contraction and stretching forces with shorter durations should be used to recruit sensitized fibers (as suggested for myofascial trigger points), avoid further tissue damage, and promote repair and healing. An evidence-informed approach for painless, chronic, fibrotic muscles indicates moderate contraction and stretching forces, maintain the stretch phase up to 60 s, and use AC or CRAC where appropriate. The exact mechanism by which increased PPTand decreased VAS occurs by MET is still unclear, and probably involves both neurophysiological and mechanical factors (such as viscoelastic and plastic changes in the connective tissue elements of the muscle.73,74 Dearing et al., found that both ischemic compression and muscle energy techniques produce

118 a significant reduction in pain sensitivity at MTrPs in the upper trapezius muscle. A small number of studies have demonstrated that MET can produce increased ROM in the cervical, thoracic and lumbar spine.22—25 All the studies examined the effect of MET on active ROM where no measure of ‘‘passive torque’’ could be made, and so little can be concluded regarding the possible mechanism behind the increased range of motion. Changes to the viscoelasticity of segmental muscles of particular tissue are unlikely given the evidence relating to stretching and hamstring extensibility. The lighter loads applied to spinal tissues (most authors of MET recommend positioning the spinal segment at the first or featheredge restrictive barrier) would mean there is little loading on tissues to produce viscoelastic or plastic change. The theory of reflex muscle relaxation following MET applied to muscles is not supported by evidence (discussed above), and no study has examined changes to paraspinal muscle EMG activity or reflex relaxation following spinal MET. Given that only active spinal ROM has been reported to increase, it seems likely that a change in stretch tolerance (as appears to be the case when stretching muscles) may be responsible for spinal ROM gains. The few studies that have examined the effect of MET and effort, support for the hypoalgesic effects of the technique. According these researches, MET reduces the pain sensitivity (stretch tolerance) of treated muscles. The exact mechanism of pain relief from manual techniques is unclear, but it has been suggested that pain is modulated at either the spinal cord or in the higher centers of the central nervous system.75—79 It is quite plausible that MET may exert a strong affect on pain perception.

Study limitations This study merely examined the immediate effect of MET technique and used females only. A follow-up session in order to measure long-term effectiveness of treatment would possibly have altered the results.

Conclusions According to the present study, MET technique is a suitable method for upper trapezius latent MTPs. MET was not used in previous studies for the treatment of upper trapezius muscle latent MTPs, and now is being introduced as an effective and suitable treatment for latent MTPs.

R. Mehdikhani, F. Okhovatian

Conflict of interest statement There is no conflict of interest.

Acknowledgments This research was a part of an MSc thesis (Royah Mehdikhani, Shahid Beheshti University of Medical Sciences, February 2011). We would like to thank Dr Isa Ahmadi, assistance professor of mechanical engineering, Zanjan University, Iran, for his kind encouragement and support.

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