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The role of myofascial trigger points in shoulder pain: a literature review.

INTRODUCTION

Myofascial Trigger Points are described by Travell and Simons1 as hyperirritable loci within a taut band of skeletal muscle or the fascia that surrounds it. A trigger point is by definition painful to palpate and when palpated refers pain in a specific pattern known as a referral pattern. Trigger points can be classified as being either active or latent. An active trigger point will refer pain during both rest and activity whereas a latent trigger point will refer pain only when palpated. (1) The intensity of the pain and the extent of the referral depend on how irritable the trigger point is. Muscle size has little to do with the pain referral and it is not uncommon for small muscles to harbor trigger points that give rise to very intense pain. (2)

The exact cause of trigger points is unknown but recent studies have attempted to explain the underlying pathophysiology. One suggestion is abnormal electrical activity, called endplate noise.3 Simons and Travell1 contend that trigger points are perpetuated by mechanical stresses such as asymmetry, poor posture, prolonged immobility at one end and overuse of muscles at the other. Nutritional deficits and systemic disease are also considered perpetuating factors, along with sudden changes in climate or acute trauma. Shoulder pain is a very common type of pain and it is one of the major reasons why people present for treatment. Aside from acute injuries like rotator cuff tears and shoulder dislocations, the most common cause of shoulder pain is thought to be subacromial impingement syndrome. (3) Subacromial impingement can develop secondary to incorrect activation of the rotator cuff muscles, allowing the superior translation of the humeral head under the acromion. This mechanical pressure on the subacromial soft tissues can lead to inflammation of the supraspinatus tendon and the subacromial bursa. (4) It is not uncommon for this type of non-traumatic shoulder pain to recur and eventually become chronic. The challenge when assessing and treating shoulder pain is working out which structure(s) within the shoulder complex is responsible for the pain. If the shoulder pain involves inflammation of tissues, then treatment including non-steroidal anti-inflammatory medication (NSAIDs) may be useful, but this is not always the case. It has become evident that there are other sources within the shoulder complex that can contribute to the pain experienced by people with non-traumatic shoulder pain, and that myofascial trigger points may be one such source. (3,5)

This literature review aims to present some of the most recent studies of the connection between myofascial trigger points and non-traumatic shoulder pain.

It will look at how the presence of trigger points in shoulder musculature can be accurately diagnosed, whether there is an obvious difference in the number of trigger points between painful and pain-free shoulders, how trigger points affect the shoulder musculature and whether specific treatment of trigger points will lead to a decrease in the pain experienced by the patient.

MYOFASCIAL TRIGGER POINTS

Shoulder pain is difficult to diagnose because of the lack of reliable tests and the poor understanding of the pathophysiological mechanisms that underlie it.3 The only way to diagnose myofascial trigger points is by palpation.6 Questions have been raised as to how accurate diagnosis by palpation can be and whether there is sufficient inter-rater reliability when palpating trigger points. A study by Bron et al. (6) looked at this by testing three very experienced raters who were blinded

to the condition of the subject. The raters received pre-study training in the palpation protocol and a consensus was reached on the palpation of the following muscles: infraspinatus, anterior deltoid and biceps brachii. (6)

Four essential criteria were used to diagnose myofascial trigger points:

1. Presence of a hyper-irritable point in a taut band

2. Pain when applying pressure to the trigger point that refers distant to the point

3. A local twitch response in the muscle

4. A jump sign (i.e. when the client flinches away from the palpation) (1)

The researchers looked at the pair-wise inter-rater agreement (PA) between the raters as to the presence or absence of myofascial trigger points. The subjects were not allowed to mention whether they felt any pain in the area being palpated at the time of palpation, but they were later asked if pain and referred pain were felt when certain areas were palpated. The results were quite convincing and the inter-rater agreement for the presence of trigger points in the infraspinatus was over 70%. The jump sign had a PA of 93% for the infraspinatus and 63% for biceps. Referred pain was the most reliable criterion even without immediate patient feedback. The researchers acknowledged that the pre-study training and standardizing of the palpation could affect the results in a positive way, but contended that based on results trigger point palpation is a reliable tool in the diagnosis of myofascial pain in patients with non-traumatic shoulder pain. (6)

More experienced clinicians had a higher agreement rate on the presence of myofascial trigger points in the muscles assessed, so it seems that with an experienced clinician and a predetermined protocol for palpation, the presence of myofascial trigger points can be successfully established. (7)

The pathophysiological mechanism underlying trigger points is still not clearly understood. Shah et al. (8) found that subjects with active trigger points in the trapezius muscle had higher concentrations of inflammatory mediators, neuropeptides. cytokines and catecholamines in the tissue than subjects with latent or no trigger points. Interestingly they also had higher levels of these biochemicals in their gastrocnemius muscles, which were used as a control. (8)

Perhaps it is the biochemical change that promotes trigger point formation, or perhaps the trigger point induces an increase in certain biochemical concentrations, or perhaps it is as simple that people with shoulder pain have more trigger points than those with no pain.

Bron et al. (3) examined 72 subjects with unilateral shoulder pain and assessed the number of muscles with trigger points. Seventeen muscles that act on the shoulder were assessed. Both active and latent trigger points were counted and patients were asked to fill out Disabilities of Arm, Shoulder and Hand--Dutch language version (DASH-DLV) and Visual Analog Scale for Pain (VAS-P) questionnaires relating to their shoulder pain. The results showed that all subjects had a number of muscles containing trigger points but by far the most frequent presentation was in infraspinatus 56 and upper trapezius 42. There was moderate correlation between both the DASH-DLV outcome and VAS-P, which would indicate that trigger points in shoulder muscles contribute to common shoulder pain problems. (3)

One has to consider that if trigger points are the cause of shoulder pain then the standard treatment involving anti-inflammatory medication and exercises may not be suitable. Deactivation of the trigger points using manual compression and/or dry needling followed by heat and dynamic stretching exercises could be a better choice of treatment. (3)

Hidalgo-Lozano et al. (9) argued that the presence of trigger points in muscles might have something to do with muscle recruitment and activation. This seemed to be the case especially in the trapezius muscle and if trigger points can alter the activation of a muscle perhaps that can lead to shoulder pain. In fact, this was exactly what Lucas, Rich & Polus (4,10) found when they looked at the effects of latent trigger points in scapular positioning muscles. In 2008 Lucas et al. (4) published a study in which 137 healthy and pain-free subjects were examined bilaterally for the presence of latent trigger points in trapezius, serratus anterior, levator scapulae, rhomboids and pectoralis minor. Palpation and diagnosis was in accordance with the guidelines set by Simons et al. (1) and in their first study the researchers wanted to establish how commonly latent trigger points appear in scapular positioning muscles. Results showed that there was no significant difference caused by gender, age or occupation. Of the 137 subjects tested 89.8% had at least one latent trigger point. Of these 62% had more latent trigger points on the dominant side and 25% had more on the non-dominant side; 78.8% had a least one latent trigger point in the upper trapezius muscle, 77.3% in the serratus anterior and 68.9% in the levator scapulae. The researchers acknowledge that their subjects were employed in desk-bound jobs which may predispose them to trigger points, involving as they do long hours at a desk in usually very static postures.

Lucas et al. (4) also examined how latent trigger points affect muscle activation patterns in the same scapular positioning muscles during unloaded and loaded scapular plane elevation. They found that muscle activation patterns were significantly altered in the unloaded movements and that deactivation of the trigger points normalized the muscle activation patterns. No further change was noticed when the muscles were tested under load.

Hidalgo-Lozano et al. (9) investigated the involvement of trigger points and the changes in pressure pain hyperalgesia in patients with unilateral shoulder impingement. In the study the investigator was blinded to the subjects' conditions at the time of assessment. The muscles they assessed were levator scapulae, supraspinatus and infraspinatus, subscapularis, pectoralis major and biceps brachii. They used Simons et al's.1 criteria for diagnosis of a myofascial trigger point. The trigger points were then classified as active if the patient indicated that palpation of the trigger points reproduced the pain symptoms in the location they recognized as familiar. (9) Once the trigger point assessment was completed the researchers tested the pressure pain threshold, which is described by Vanderweeen et al. (11) as 'minimal amount of pressure where the sensation of pressure first changes to pain'.

Patients with shoulder impingement had significantly lower pressure pain threshold levels in all muscles than those in the control group. Trigger point activity was also significantly different between the two groups. The control group had only latent trigger points whereas the subjects with shoulder impingement had both latent and active trigger points in their shoulder muscles. When these trigger points were palpated both local and referred pain were present in all patients. This pain corresponded to their familiar shoulder pain. (9)

The researchers also found that an increased number of trigger points in a muscle led to lower pressure point threshold for that muscle and an increase in pain intensity, suggesting that active trigger points are involved in the pathophysiology of shoulder impingement and that referred pain can contribute directly to shoulder pain. They also state that the presence of latent trigger points may contribute to the altered activation pattern described by Lucas et al. (12) which in turn can bring about increased mechanical pressure on the subacromial structures leading to shoulder impingement. (9)

The infraspinatus muscle commonly has trigger points, and the referral pattern from these can extend as far down the arm as the wrist and even into the hand. (2) Ge et al. (13) divided the infraspinatus muscle into ten 1cm x 1cm squares. They placed a pressure algometer on each square and measured it. After the pressure point thresholds were taken they also looked for the presence of trigger points by inserting a needle into each sub-area. The needle was inserted swiftly and moved in five different directions to elicit a local twitch response and referred pain. They assessed both sides and found a significantly higher number of trigger points on the painful side, and that the non-painful side had latent trigger points only in the infraspinatus.

This exposition is interesting as it may indicate a phenomenon called segmental sensitization of mechanical hyperalgesia. This means that a pain pattern is mirrored on the opposite side to the injury mediated by the central nervous system pathways. The pressure point threshold was significantly

lower on the painful side and pressure point threshold levels were lower where there was an active trigger point than where the trigger point was latent. The most common sub-areas for active myofascial trigger points were along the lateral border of the muscle, which were also the sites where pressure point thresholds were the lowest on the painful side. (13)

DOES TRIGGER POINT THERAPY WORK?

Physiotherapists, chiropractors, osteopaths and massage therapists use trigger point therapy as part of their treatment of myofascial pain, but often without scientifically-based evidential support. Recent studies are encouraging as they give validity to the work many clinicians already do. Hains, Descarreaux and Hains (14) used digital ischaemic pressure to treat trigger points in 41 patients with chronic non-traumatic shoulder pain. They specifically treated supraspinatus, infraspinatus, deltoid and the biceps tendon to establish whether eliminating myofascial trigger points would normalize the area and eliminate pain. In this study the subjects, who were blinded to the treatment, were given three treatments a week for five weeks. Eighteen controls received treatment to trigger points in muscles deemed to be outside the referral area for shoulder pain (sham treatment). The outcome was measured using the Shoulder Pain and Disability Index (SPADI) and the results were significant after 15 treatments with a decrease in SPADI of 44 points, a measure that was still present at 6 months after the conclusion of the treatments.

Bron et al.5 studied the effects of trigger point treatment on non-traumatic shoulder pain, especially the type of shoulder pain in the category of subacromial impingement syndrome. Treatment consisted of inactivation of active trigger points using digital ischemic pressure, deep stroking, cross-fibre friction, ice and stretching. Detailed history, DASH and VAS-P and GPE scores were among the pre-study requirements and these tests were also administered at 6 and 12 weeks during the study. A 'stop rule' was in place so that treatment was stopped when patients were free of symptoms or if the therapist-judged that no further benefits were possible. The control group continued with the normal management routine for their pain and were told that their treatments would start at the end of12 weeks.

The results showed that at 6 weeks there was little difference between the groups, but at 12 weeks some of the more noticeable changes were that 50% of the intervention group improved more than 10 points on the DASH, and their VAS-P scores were significantly lower. The number of muscles with latent trigger points did not change a lot but the number of muscles with active trigger points was significantly lower after 12 weeks, indicating that trigger point therapy may be a promising new approach for people with chronic unilateral non-traumatic shoulder pain. (5)

In May 2011 Hidalgo-Lozano et al. (15) published a study of shoulder pain among elite swimmers. Swimmers frequently experience shoulder pain and dysfunction, with prevalence slightly higher than in the general population at 43%-72%, compared to 20%-50%. Swimmers' shoulder pain can be related to repetitive overhead shoulder movements that may increase joint laxity and supraspinatus tendinopathy.16 Seventeen elite swimmers with shoulder pain, 18 elite swimmers without pain and a control froup of 15 elite athletes made up the study. Criteria for inclusion in the study were that the duration of shoulder pain was of greater than three months' duration, and a positive Neer and Hawkins test. Trigger points and pressure point thresholds were explored in the levator scapulae, sternocleidomastoid, upper trapezius, infraspinatus, subscapularis and scalenes. Tibialis anterior was used as a distant site.

A blinded trigger point examination took place in which questions related to the patient's pain were asked only after palpation was completed. Pressure point thresholds were assessed in all muscles in a randomized order. The results were similar to those of other studies, showing a significant increase in the number of active trigger points among elite swimmers with shoulder pain over both elite swimmers with no pain and the control group. The number of latent trigger points was higher among elite swimmers without pain than among swimmers with pain and the control group. The number of trigger points in upper trapezius, levator scapulae and infraspinatus was significantly higher for the elite swimmers with pain than for the control group of elite athletes. Pressure point thresholds was lower in both elite swimmer groups than in the elite athlete control group. (15)

The higher number of latent trigger points in elite swimmers without pain is interesting when considered along with the study by Lucas et al. (12) showing altered muscle activation when latent trigger points are present in shoulder stabilizing muscles. It may be possible that shoulder pain develops secondary to the changes in activation caused by latent trigger points, or that the pain comes from the presence of latent trigger points that over time become active ones. The current findings the researchers suggest trigger point evaluation and treatment be included when working with elite swimmers with shoulder pain. They also suggest that longitudinal studies be undertaken with larger sample groups to look at the role of mechanical sensitization and active trigger points in the development of shoulder pain in elite swimmers. (15)

CONCLUSION

The aim of this literature review has been to present some of the most recent studies investigating the connection between myofascial trigger points and non-traumatic shoulder pain. Sixteen studies undertaken since 2004 by researchers from across the globe have produced quite positive results pointing to a definite and perhaps multi-modal connection.

The majority of studies showed that active trigger points were present in subjects with shoulder pain and that these were found in the musculature acting on the painful shoulder. The trigger points were most frequent in the infraspinatus and upper trapezius. (3) Hidalgo-Lozano (9) demonstrated similar results, where all patients reported feeling their usual trigger point pain when the examiner pressed on the location corresponding to the trigger point. This study also concluded that pressure pain thresholds are much lower in muscles containing trigger points, especially if they are active.

Lucas et al (12) found that latent trigger points, even in pain-free shoulders, will alter the muscle activation pattern, which in turn can lead to imbalances. This altered pattern was normalized if the latent trigger points were deactivated using specific treatment. Treatment options include digital ischaemic pressure, dry needling, ice and deep longitudinal gliding and injection. There was strong agreement among the researchers that assessment and treatment of trigger points should be standard practice for patients with shoulder pain. It is certainly less invasive than surgery and obviates the need for anti- inflammatory medication. There was also agreement that further research is needed that includes larger samples and has a longitudinal study design.

REFERENCES

(1.) Travell JG, Simons DG. Myofascial pain and dysfunction the trigger point manual, Vol 1. Baltimore: Lippincott, Williams and Wilkins; 1983.

(2.) Simons DG, Travell JG, Simons, LS. Myofascial pain and dysfunction the trigger point manual, upper half of body. Baltimore: Lippincott, Williams and Wilkins; 1999.

(3.) Bron C, Dommerholt J, S tegenga B, Wensing, M, Oostendorp RAB. High prevalence of shoulder girdle muscles with myofascial trigger points in patients with shoulder pain. BMC Musculoskeletal Disorders. 2011;12(139).

(4.) Lucas K, Rich PA, Polus BI. Muscle activation patterns in the scapular positioning muscles during loaded scapular plane elevation: the effects of latent myofascial trigger points. Clin Biomech. 2010;25:765-70.

(5.) Bron C, de Gast A, Dommerholt J, Stegenga B, Wensing M, Oostendorp RAB. Treatment of myofascial trigger points in patients with chronic shoulder pain: a randomized, controlled trial. BMC Medicine. 2011;9(8).

(6.) Bron C, Franssen J, Wensing M, Oostendorp RA. Interrater reliability of palpation of myofascial trigger points in three shoulder muscles. J Man Manip Ther. 2007;15(4):203-15.

(7.) Myburgh C, Lauridsen HH, Larsen AH, Hartvigsen J. Standardized manual palpation of myofascial trigger points in relation to neck/shoulder pain; the influence of clinical experience on inter-examiner reproducibility. Man Ther. 2011;16:136-40

(8.) Shah J, Danoff JV, Desai MJ, Parikh S, Nakamura LY, Phillips TM, Gerber LH. Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points. Arch Phys Med Rehabil. 2008;89(1):16-23.

(9.) Hidalgo-Lozano A, Fernandez-de-las-Penas C, Alonso-Blanco C, Ge H-Y, Arendt-Nielsen L, Arroyo-Morales M. Muscle trigger points and pressure pain hyperalgesia in the shoulder muscles in patients with unilateral shoulder impingement: a blinded, controlled study. Exp Brain Res. 2010;(202):915-25. doi: 10.1007/s00221-010-2196-4

(10.) Lucas K, Rich PA, Polus BI. How common are latent myofascial trigger points in the scapular positioning muscles? J Musculoskeletal Pain. 2008; 16(4):279-86. doi: 10.1080/10582450802479800

(11.) Vanderweeen L, Oostendorp RAB, Vaes P, Duquet W. Pressure algometry in manual therapy. Man Ther. 1996;1(5):258-65.

(12.) Lucas K, Rich PA, Polus BI. Latent myofascial trigger points: their effects on muscle activation and movement efficiency. Jbmt. 2004;8{3):160-66.

(13.) Ge H, Fernandez-de-las-Penas C, Madeleine P, Arendt-Nielsen L. Topographical mapping and mechanical pain sensitivity of myofascial trigger points in the infraspinatus muscle. Eur J Pain. 2008;12:859-65.

(14.) Hains G, Descarreaux M, Hains F. Chronic shoulder pain of myofascial origin: A randomized clinical trial using ischemic compression therapy. J Manipulative Physiol Ther. 2010;33(5):362-69.

(15.) Hidalgo-Lozano A, Fernandez-de-las-Penas C, Calderon-Soto C, Domingo-Camara A, Madeleine P, Arroyo-Morales M. Elite swimmers with and without unilateral shoulder pain: mechanical hyperalgesia and active/latent muscle trigger points in neck-shoulder muscles. Scan J Med Sci Sports. 2011 May 12. doi: 10.1111/j.1600-0838.2011.01331.

(16.) Sein M, Walton J, Linklater J, Appleyard R, Kirkbride B, Kuah D, Murrell GAC. Shoulder pain in elite swimmers: primarily due to swim-volume-induced supraspinatus tendinopathy. Br J Sports Med. 2010;44:105-13.

Catrin Jonsson BHlthSc, MEx&SpSc

Catrin Jonsson is a sports and remedial massage therapist with more than 10 years experience. She is currently in private practice at Macquarie University Sports Centre in Sydney. She holds a Masters degree in Exercise and Sport Science and has worked with NSWIS, Soccer NSW and the Australian Olympic Committee. She has a particular passion for trigger points and their involvement in chronic pain.
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Author:Jonsson, Catrin
Publication:Journal of the Australian Traditional-Medicine Society
Article Type:Report
Geographic Code:8AUST
Date:Sep 1, 2012
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