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Myofascial Trigger Points in Early Life
251
ORIGINAL ARTICLE
Myofascial Trigger Points in Early Life Mu-Jung Kao, MD, Ting-I Han, MD, Ta-Shen Kuan, MD, MS, Yueh-Ling Hsieh, PhD, PT, Bai-Horng Su, MD, Chang-Zern Hong, MD or ABSTRACT. Kao M-J, Han T-I, Kuan T-S, Hsieh Y-L, Su B-H, Hong C-Z. Myofascial trigger points in early life. Arch Phys Med Rehabil 2007;88:251-4. Objective: To determine whether latent myofascial trigger points (MTPs) can be identified in healthy infants and in healthy adult subjects. Design: Blind comparison. Setting: Ambulatory. Participants: A convenience sample of 60 healthy adults and 60 infants (age range, 0⫺12mo). Interventions: Not applicable. Main Outcome Measures: An algometer was used to measure the pressure pain threshold (PPT) on 3 different sites, including a midpoint (assumed to be the MTP site) in the brachioradialis muscle. Results: The mean PPT values at the MTP site were significantly lower than the other sites in the adult muscles. However, no significant differences in PPT values among these 3 sites were found in the infants. Taut bands were found in all the adult muscles but none in the infants. Conclusions: In the adult subjects, the midpoint of brachioradialis muscle was significantly more irritable than other sites and the midpoint was probably a latent MTP. However, in the infants younger than 1 year old, such a phenomenon could not be observed in this study. It is very likely that the latent MTPs might not exist in early life, but develop in later life. Key Words: Infant; Muscle; Pain; Rehabilitation; Trigger points, myofascial. © 2007 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation CCORDING TO THE classical definition, a myofascial trigger point (MTP) is a hypersensitive spot in a taut band A of skeletal muscle fibers. Latent MTPs are tender to palpation
MTPs may become active in response to a stimulation from a lesion in a site other than the MTP itself, reflexively via the spinal cord, as a consequence of central sensitization.1-4 In other words, an active MTP is probably an acquired phenomenon, although it is still unknown whether a latent MTP is acquired or congenital. The pathophysiology of the MTP has now become better understood, based on recent electrophysiologic studies on both human and animal subjects.2-15 It has been hypothesized that there are multiple sensitive MTP loci in an MTP region.5 Histologic study suggested that these sensitive loci might be sensitized nociceptors.16 An MTP is usually identified in the endplate zone (usually, the middle portion of the muscle fibers).14,15 Based on electrophysiologic studies, in an MTP region, a sensitive locus is usually found in the vicinity of an endplate.14,15 The endplate near the sensitive locus of an MTP has been considered as a dysfunctional endplate with excessive acetylcholine leakage, based on the electrophysiologic studies.12,14,15 The endplate noise, instead of miniature endplate potentials, can be recorded frequently in an MTP region, because MTPs are usually found in the endplate zone containing some dysfunctional endplates. The result of excessive secretion of acetylcholine, the “contracture knot,” has been demonstrated in a histological study in dog.1,17 It appears that the pathogenesis of MTP may involve both sensory and motor components, the nociceptor and the motor unit. However, the pathogenesis of the formation of an MTP is still unclear. Based on clinical observation and informal studies, Hong3,4,18 has claimed that newborn babies and infants may have no MTPs, and, as they grow up, latent MTPs may develop gradually. However, because we have found no support for this view in the literature, we have designed this study to investigate the occurrence of latent MTP in early life. The hypothesis is that latent MTPs cannot be found in early life, but may develop gradually when the newborns grow up.
1
but do not cause spontaneous clinical pain. Active MTPs typically cause spontaneous painful symptoms referred to a site distant from the MTP and are painful to palpation. Normal adults usually have latent MTPs in the clinically “normal” (nonpainful) muscles. It has been hypothesized that latent
From the Department of Physical Medicine & Rehabilitation, Taipei City Hospital, Taipei, Taiwan (Kao); Department of Rehabilitation Medicine, College of Medicine, China Medical University, Taichung, Taiwan (Kao); Departments of Rehabilitation Medicine (Han) and Pediatrics (Su), China Medical University Hospital, Taichung, Taiwan; Department of Physical Medicine & Rehabilitation, College of Medicine, National Cheng-Kung University, Tainan, Taiwan (Kuan, Hong); and Department of Physical Therapy, Hungkuang University, Taichung, Taiwan (Hsieh, Hong). Supported by the National Science Council (Taiwan) (grant no. NSC93-2314-B241-002). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s)is/are associated. Reprint requests to Chang-Zern Hong, MD, Dept of Physical Therapy, HungKuang University, 34, Chung-Chie Rd, Sha-Lu, Taichung 433, Taiwan, e-mail: [email protected]. 0003-9993/07/8802-11107$32.00/0 doi:10.1016/j.apmr.2006.11.004
METHODS General Design For each infant or adult subject, we measured the pressure pain threshold (PPT) with a pressure algometer at 3 different sites (the midpoint was assumed to be the site of latent MTP) of the brachioradialis muscle to see if the MTP site was more irritable (with lower PPT) than the other sites. Our institutional review board has reviewed and approved this study. Participants We recruited 60 adults and 60 infants aged less than 1 year for this study. The subjects or their legal guardians signed the informed consent forms that were approved by the institutional review board of a university hospital. The mean age of the subjects and the age distribution of the infants are shown in table 1 and figure 1, respectively. The exclusion criteria included any acute or serious illness, any trauma to the upper limb, any deformity in the upper limb, or any signs of emotional instability or evidence of poor cooperation. Arch Phys Med Rehabil Vol 88, February 2007
252
MYOFASCIAL TRIGGER POINTS IN EARLY LIFE, Kao Table 1: Mean Ages of Subjects Subjects
Infants
All subjects Mean age ⫾ SD Range N Men Mean age ⫾ SD Range N Women Mean age ⫾ SD Range N
Adult
98.0⫾85.6d 2–360d 60
45.7⫾15.9y 20–75y 60
100.2⫾91.6d 2–360d 39
43.5⫾15.7y 20–74y 34
94.0⫾75.2d 10–293d 21
48.5⫾16.1y 20–75y 26
Fig 2. Sites for measurement of PPT: A, site just above the lateral epicondyle; B, assumed MTP site; C, junction of muscle and tendon.
Abbreviation: SD, standard deviation.
Identification of the Sites for the Measurement of PPT in the Brachioradialis Muscle Brachioradialis muscle is a typical fusiform muscle with an endplate zone in the middle portion of the muscle. It attaches proximally to the lateral supracondylar ridge of the humerus and to the lateral intermuscular septum, distal to where the radial nerve penetrates the septum at mid-arm level. Distally the brachioradialis tendon expands laterally as it approaches the styloid process of the radius and connects with the neighboring ligaments. It is then anchored by a tendinous attachment to the styloid process. When the subject attempts to flex the elbow against resistance with elbow at 90° of flexion, this muscle can be identified easily. When the infant’s hand is held tightly, the withdrawal reflex of the elbow can be induced and the brachioradialis muscle can be identified.1 In this study, we identified the brachioradialis muscle by palpation based on the anatomic landmarks and maneuver as described above. The distance between the lateral epicondyle and the styloid process was measured. The midpoint of this distance was considered as the junction of muscle and tendon. The MTP was approximately one third of the way from the lateral epicondyle to this junction site.1 Three spots on the skin over the brachioradialis muscle in each side were marked with a surface marker for the measurement of PPT: point A was the site just above the lateral epicondyle (because the exact origin site of the brachioradialis is difficult to identify), point B was the assumed MTP site, one third of the way from the lateral epicondyle to the junction of muscle and tendon, and point C was at the junction of muscle and tendon (fig 2). In adults, point B had been confirmed as the MTP. In all, 6 sites, 3 in each side, were marked for the measurement of PPT.
Age (d)
Male Female
200
100
Palpation of Taut Bands After completion of the PPT measurements, we examined the MTP site for the existence of taut bands by the same examiners who did PPT measurements. They had also been well trained in the examination of MTPs. Training for palpation of taut band is essential to avoid intrarater or interrater variation because this maneuver is a relatively subjective measurement.23 Data Analysis We analyzed the differences of PPT among the 3 sites by analysis of variance. The sex differences and the differences between 2 sides were analyzed with the t test. A P value less than .05 was considered as statistically significant.
400
300
Measurement of the PPT We used a pressure algometer described by Fischer19 for the measurement of the pressure pain threshold. This algometer has been confirmed as a reliable and valid measure of MTP sensitivity.20-22 To measure the PPT, we placed a pressure algometer on the site to be measured, perpendicular to the surface of the skin. Then, the pressure of compression was increased gradually at a speed of approximately 1kg/s, while asking if the subject felt any pain or discomfort. The compression was stopped as soon as the subject said “yes.” The subject was asked to remember this level of pain discomfort and to apply the same criterion for the subsequent measurements. In the measurement of the infant, the pressure of compression was increased gradually until the infant began to withdraw or cry or make an unpleasant facial expression, whichever occurred first. At this point, the examiner stopped the compression and read the scale in the algometer (in kg/cm2) to find the PPT at that site. Three measurements were performed on each site, and a total of 9 measurements were performed for each muscle. At least 1 minute elapsed between the 2 consecutive measurements, as suggested by Fischer.19 The sequence of measurement on the 6 sites in 2 sides was randomly assigned using a randomization table. Two different well-trained examiners did the measurements; one performed this task with the infants and the other on the adult subjects.
RESULTS
n=39
n=21
Fig 1. Age distribution of the infants.
Arch Phys Med Rehabil Vol 88, February 2007
Differences Among the 3 Measured Sites In the adult subjects, the mean PPT value was significantly lower (P⬍.01) over the MTP site than at other sites on either right or left side (table 2). However, in the infants, there were no significant differences (P⬎0.1) in the mean values of PPT
MYOFASCIAL TRIGGER POINTS IN EARLY LIFE, Kao Table 2: Mean PPT at Different Sites Infants (n⫽60)
Adults (n⫽60)
Site
Right
Left
Right
Left
Proximal Middle (MTP) Distal Middle vs proximal P Middle vs distal P Distal vs proximal P
2.06⫾0.80 2.12⫾1.11 2.07⫾1.03
2.09⫾0.78 2.17⫾1.12 2.14⫾0.81
3.81⫾0.65 2.54⫾0.47 4.00⫾0.63
4.03⫾0.66 2.87⫾0.52 4.24⫾0.67
⬎0.1
⬎0.1
⬍.05
⬍.05
⬎0.1
⬎0.1
⬍.05
⬍.05
⬎0.1
⬎0.1
⬎0.1
⬎0.1
NOTE. Values are mean kg/cm ⫾ SD or P value. 2
among the 3 sites on either side. In most infants, we were unable to see remarkable differences in PPT values among the 3 measured spots as usually found in the adult subjects. For each adult subject, the MTP site was always the most painful site, with the lowest PPT value as compared with the other 2 sites. However, for each infant, the responses to the pressure stimuli were frequently similar at 3 different stimulating sites. Differences Between the 2 Sides For each measured site, there was no significant difference (P⬎0.1) in PPT values between male and female subjects or between right and left sides. Existence of Taut Band On palpation of the MTP site, 1 or more taut bands could be identified in all of the adult subjects. On the other hand, no taut band could be identified in any infant. DISCUSSION Existence of Latent MTP In this study, we found that every adult subject had a hyperirritable spot in the middle portion of taut band(s) in the brachioradialis muscle, which could be a latent MTP or in the vicinity of the latent MTP. In an earlier study,24 it was found that a site in the taut band, but not the latent MTP, also had reduced PPT as compared with the normal muscle site. Therefore, the assumed MTP site in our study might not be exactly the real MTP site. At least we know that some spots may be more irritable than others in this muscle of the adult subjects. However, we were unable to validate this phenomenon in the infants. No taut band could be identified in any infant. Therefore, we could not confirm the existence of latent MTPs in the infants less than 1 year of age, because all 3 measured sites had the same irritability. This finding supports the hypothesis that latent MTPs do not exist in early life and probably develop later, because we were unable to distinguish a relatively hyperirritable spot in any infant in this study. As soon as a latent MTP developed in the center of the muscle fibers (endplate zone), it would be the most sensitive spot (most tender site) in muscle fibers. The findings in the adult subjects in this study have strongly supported that. Formation of Latent MTPs (Hypothesis) The exact mechanism of MTP formation is still uncertain. At least we know that the latent MTP is not inherent, based on the
253
findings in our study. In early life, an infant may have many chances to suffer from either gross or minor neuromuscular injuries. A minor injury is usually ignored in most cases. Although the tissue damage may be mild, the subsequent chronic inflammation may create certain influences in the later life. For example, a stretch or direct trauma to the spine may cause mild radiculopathy with no obvious clinical symptoms or signs, but may be sufficient enough to induce excessive secretion of acetylcholine. Similarly, a stretch of the shoulder or hip joint may cause mild traction to the cervical or lumbosacral plexus with no clinical manifestations but may still cause excessive acetylcholine secretion. Other possible injuries include minor damage to the peripheral nerves or skeletal muscle fibers which may cause similar reactions. Gunn25 has suggested that neuropathic lesions are the primary mechanism of MTP formation. Simons et al1 proposed that excessive acetylcholine secretion may induce electrotonic potentials (endplate noise observed in the MTP region) and cause focal contraction of sarcomeres (contraction knot1) near the endplate zone, and these may subsequently develop an energy crisis (excessive energy consumption due to persistent muscle contraction). The sensitizing substances released during an energy crisis may cause peripheral sensitization of the nociceptors near the endplate. An MTP may be formed in this way. Hong26 agrees with this hypothesis for a latent MTP formation, but not for the process of the activation of a latent MTP to become an active one. There is evidence that a latent MTP can be activated to become an active MTP via central sensitization.4,27-29 However, it is very likely that the formation of a latent MTP is due to minor neuromuscular damage, as mentioned above, when the baby is growing up. CONCLUSIONS In this study on the brachioradialis muscle, we found that the assumed MTP site was more irritable than other sites in the adult subjects, but not in infants (⬍1y). It appears that infants do not have trigger points identified by this study. Latent MTPs probably do not exist in the newborn or young infant, but develop in later life. References 1. Simons DG, Travell JG, Simons LS. Travell & Simons’s myofascial pain and dysfunction: the trigger point manual. Vol 1, 2nd ed. Baltimore: Williams & Wilkins; 1999. 2. Hong CZ, Simons DG. Pathophysiologic and electrophysiologic mechanism of myofascial trigger points. Arch Phys Med Rehabil 1998;79:863-72. 3. Hong CZ. Current research on myofascial trigger points: pathophysiological studies. J Musculoskeletal Pain 1999;7:121-9. 4. Hong CZ. Myofascial trigger points: pathophysiology and correlation with acupuncture points. Acupunct Med 2000;18:41-7. 5. Hong CZ. Lidocaine injection versus dry needling to myofascial trigger point: the importance of the local twitch response. Am J Phys Med Rehabil 1994;73:256-63. 6. Hong CZ. Persistence of local twitch response with loss of conduction to and from the spinal cord. Arch Phys Med Rehabil 1994;75:12-6. 7. Hong CZ. Pathophysiology of myofascial trigger point. J Formos Med Assoc 1996;95:93-104. 8. Hong CZ, Torigoe Y. Electrophysiologic characteristics of localized twitch responses in responsive bands of rabbit skeletal muscle fibers. J Musculoskeletal Pain 1994;2:17-43. 9. Hong CZ, Yu J. Spontaneous electrical activity of rabbit trigger spot after transection of spinal cord and peripheral nerve. J Musculoskeletal Pain 1998;6:45-58. Arch Phys Med Rehabil Vol 88, February 2007
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10. Hong CZ, Torigoe Y, Yu J. The localized twitch responses in responsive bands of rabbit skeletal muscle fibers are related to the reflexes at spinal cord level. J Musculoskeletal Pain 1995;3:15-33. 11. Hubbard DR, Berkoff GM. Myofascial trigger points show spontaneous needle EMG activity. Spine 1993;18:1803-7. 12. Simons DG. Clinical and etiological update of myofascial pain from trigger points. J Musculoskeletal Pain 1996;4:93-121. 13. Simons DG. Diagnostic criteria of myofascial pain caused by trigger points. J Musculoskeletal Pain 1999;7:111-20. 14. Simons DG, Hong CZ, Simons LS. Prevalence of spontaneous electrical activity at trigger spots and at control sites in rabbit skeletal muscle. J Musculoskeletal Pain 1995;3:35-48. 15. Simons DG, Hong CZ, Simons LS. Endplate potentials are common to midfiber myofascial trigger points. Am J Phys Med Rehabil 2002;81:212-22. 16. Hong CZ, Chen JT, Chen SM, Yan JJ, Su YJ. Histological findings of responsive loci in a myofascial trigger spot of rabbit skeletal muscle from where localized twitch responses could be elicited [abstract]. Arch Phys Med Rehabil 1996;77:962. 17. Simons DG, Stolov WC. Microscopic features and transient contraction of palpable bands in canine muscle. Am J Phys Med 1976;55:65-88. 18. Hong CZ. New trends in myofascial pain syndrome. Zhonghua Yi Xue Za Zhi (Taipei) 2002;65:501-12. 19. Fischer AA. Pressure threshold meter: its use for quantification of tender spots. Arch Phys Med Rehabil 1986;67:836-8.
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20. Ohrbach R, Gale EN. Pressure pain thresholds, clinical assessment, and differential diagnosis: reliability and validity in patients with myogenic pain. Pain 1989;39:157-69. 21. Ohrbach R, Gale EN. Pressure pain thresholds in normal muscles: reliability, measurement effects and topographic differences. Pain 1989;37:257-63. 22. Reeves JL, Jaeger B, Graff-Radford SB. Reliability of the pressure algometer as a measure of myofascial trigger point sensitivity. Pain 1986;24:313-21. 23. Gerwin RD, Shannon S, Hong CZ, Hubbard D, Gevirtz R. Identification of myofascial trigger points: interrater agreement and effect of training. Pain 1997;69:65-73. 24. Hong CZ, Chen YN, Twehous D, Hong DH. Pressure threshold for referred pain by compression on the trigger point and adjacent areas. J Musculoskeletal Pain 1996;4:61-79. 25. Gunn CC. Radiculopathic pain: diagnosis and treatment of segmental irritation or sensitization. J Musculoskeletal Pain 1997;5: 119-34. 26. Hong CZ. Comment on Gunn’s “radiculopathy model of myofascial trigger points.” J Musculoskeletal Pain 2000;8:133-5. 27. Mense S. Nociception from skeletal muscle in relation to clinical muscle pain. Pain 1993;54:241-89. 28. Mense S. Referral of muscle pain: new aspects. Am Pain Soc J 1994;3:1-9. 29. Mense S. Biochemical pathogenesis of myofascial pain. J Musculoskeletal Pain 1996;4:145-62.
ORIGINAL ARTICLE
Myofascial Trigger Points in Early Life Mu-Jung Kao, MD, Ting-I Han, MD, Ta-Shen Kuan, MD, MS, Yueh-Ling Hsieh, PhD, PT, Bai-Horng Su, MD, Chang-Zern Hong, MD or ABSTRACT. Kao M-J, Han T-I, Kuan T-S, Hsieh Y-L, Su B-H, Hong C-Z. Myofascial trigger points in early life. Arch Phys Med Rehabil 2007;88:251-4. Objective: To determine whether latent myofascial trigger points (MTPs) can be identified in healthy infants and in healthy adult subjects. Design: Blind comparison. Setting: Ambulatory. Participants: A convenience sample of 60 healthy adults and 60 infants (age range, 0⫺12mo). Interventions: Not applicable. Main Outcome Measures: An algometer was used to measure the pressure pain threshold (PPT) on 3 different sites, including a midpoint (assumed to be the MTP site) in the brachioradialis muscle. Results: The mean PPT values at the MTP site were significantly lower than the other sites in the adult muscles. However, no significant differences in PPT values among these 3 sites were found in the infants. Taut bands were found in all the adult muscles but none in the infants. Conclusions: In the adult subjects, the midpoint of brachioradialis muscle was significantly more irritable than other sites and the midpoint was probably a latent MTP. However, in the infants younger than 1 year old, such a phenomenon could not be observed in this study. It is very likely that the latent MTPs might not exist in early life, but develop in later life. Key Words: Infant; Muscle; Pain; Rehabilitation; Trigger points, myofascial. © 2007 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation CCORDING TO THE classical definition, a myofascial trigger point (MTP) is a hypersensitive spot in a taut band A of skeletal muscle fibers. Latent MTPs are tender to palpation
MTPs may become active in response to a stimulation from a lesion in a site other than the MTP itself, reflexively via the spinal cord, as a consequence of central sensitization.1-4 In other words, an active MTP is probably an acquired phenomenon, although it is still unknown whether a latent MTP is acquired or congenital. The pathophysiology of the MTP has now become better understood, based on recent electrophysiologic studies on both human and animal subjects.2-15 It has been hypothesized that there are multiple sensitive MTP loci in an MTP region.5 Histologic study suggested that these sensitive loci might be sensitized nociceptors.16 An MTP is usually identified in the endplate zone (usually, the middle portion of the muscle fibers).14,15 Based on electrophysiologic studies, in an MTP region, a sensitive locus is usually found in the vicinity of an endplate.14,15 The endplate near the sensitive locus of an MTP has been considered as a dysfunctional endplate with excessive acetylcholine leakage, based on the electrophysiologic studies.12,14,15 The endplate noise, instead of miniature endplate potentials, can be recorded frequently in an MTP region, because MTPs are usually found in the endplate zone containing some dysfunctional endplates. The result of excessive secretion of acetylcholine, the “contracture knot,” has been demonstrated in a histological study in dog.1,17 It appears that the pathogenesis of MTP may involve both sensory and motor components, the nociceptor and the motor unit. However, the pathogenesis of the formation of an MTP is still unclear. Based on clinical observation and informal studies, Hong3,4,18 has claimed that newborn babies and infants may have no MTPs, and, as they grow up, latent MTPs may develop gradually. However, because we have found no support for this view in the literature, we have designed this study to investigate the occurrence of latent MTP in early life. The hypothesis is that latent MTPs cannot be found in early life, but may develop gradually when the newborns grow up.
1
but do not cause spontaneous clinical pain. Active MTPs typically cause spontaneous painful symptoms referred to a site distant from the MTP and are painful to palpation. Normal adults usually have latent MTPs in the clinically “normal” (nonpainful) muscles. It has been hypothesized that latent
From the Department of Physical Medicine & Rehabilitation, Taipei City Hospital, Taipei, Taiwan (Kao); Department of Rehabilitation Medicine, College of Medicine, China Medical University, Taichung, Taiwan (Kao); Departments of Rehabilitation Medicine (Han) and Pediatrics (Su), China Medical University Hospital, Taichung, Taiwan; Department of Physical Medicine & Rehabilitation, College of Medicine, National Cheng-Kung University, Tainan, Taiwan (Kuan, Hong); and Department of Physical Therapy, Hungkuang University, Taichung, Taiwan (Hsieh, Hong). Supported by the National Science Council (Taiwan) (grant no. NSC93-2314-B241-002). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s)is/are associated. Reprint requests to Chang-Zern Hong, MD, Dept of Physical Therapy, HungKuang University, 34, Chung-Chie Rd, Sha-Lu, Taichung 433, Taiwan, e-mail: [email protected]. 0003-9993/07/8802-11107$32.00/0 doi:10.1016/j.apmr.2006.11.004
METHODS General Design For each infant or adult subject, we measured the pressure pain threshold (PPT) with a pressure algometer at 3 different sites (the midpoint was assumed to be the site of latent MTP) of the brachioradialis muscle to see if the MTP site was more irritable (with lower PPT) than the other sites. Our institutional review board has reviewed and approved this study. Participants We recruited 60 adults and 60 infants aged less than 1 year for this study. The subjects or their legal guardians signed the informed consent forms that were approved by the institutional review board of a university hospital. The mean age of the subjects and the age distribution of the infants are shown in table 1 and figure 1, respectively. The exclusion criteria included any acute or serious illness, any trauma to the upper limb, any deformity in the upper limb, or any signs of emotional instability or evidence of poor cooperation. Arch Phys Med Rehabil Vol 88, February 2007
252
MYOFASCIAL TRIGGER POINTS IN EARLY LIFE, Kao Table 1: Mean Ages of Subjects Subjects
Infants
All subjects Mean age ⫾ SD Range N Men Mean age ⫾ SD Range N Women Mean age ⫾ SD Range N
Adult
98.0⫾85.6d 2–360d 60
45.7⫾15.9y 20–75y 60
100.2⫾91.6d 2–360d 39
43.5⫾15.7y 20–74y 34
94.0⫾75.2d 10–293d 21
48.5⫾16.1y 20–75y 26
Fig 2. Sites for measurement of PPT: A, site just above the lateral epicondyle; B, assumed MTP site; C, junction of muscle and tendon.
Abbreviation: SD, standard deviation.
Identification of the Sites for the Measurement of PPT in the Brachioradialis Muscle Brachioradialis muscle is a typical fusiform muscle with an endplate zone in the middle portion of the muscle. It attaches proximally to the lateral supracondylar ridge of the humerus and to the lateral intermuscular septum, distal to where the radial nerve penetrates the septum at mid-arm level. Distally the brachioradialis tendon expands laterally as it approaches the styloid process of the radius and connects with the neighboring ligaments. It is then anchored by a tendinous attachment to the styloid process. When the subject attempts to flex the elbow against resistance with elbow at 90° of flexion, this muscle can be identified easily. When the infant’s hand is held tightly, the withdrawal reflex of the elbow can be induced and the brachioradialis muscle can be identified.1 In this study, we identified the brachioradialis muscle by palpation based on the anatomic landmarks and maneuver as described above. The distance between the lateral epicondyle and the styloid process was measured. The midpoint of this distance was considered as the junction of muscle and tendon. The MTP was approximately one third of the way from the lateral epicondyle to this junction site.1 Three spots on the skin over the brachioradialis muscle in each side were marked with a surface marker for the measurement of PPT: point A was the site just above the lateral epicondyle (because the exact origin site of the brachioradialis is difficult to identify), point B was the assumed MTP site, one third of the way from the lateral epicondyle to the junction of muscle and tendon, and point C was at the junction of muscle and tendon (fig 2). In adults, point B had been confirmed as the MTP. In all, 6 sites, 3 in each side, were marked for the measurement of PPT.
Age (d)
Male Female
200
100
Palpation of Taut Bands After completion of the PPT measurements, we examined the MTP site for the existence of taut bands by the same examiners who did PPT measurements. They had also been well trained in the examination of MTPs. Training for palpation of taut band is essential to avoid intrarater or interrater variation because this maneuver is a relatively subjective measurement.23 Data Analysis We analyzed the differences of PPT among the 3 sites by analysis of variance. The sex differences and the differences between 2 sides were analyzed with the t test. A P value less than .05 was considered as statistically significant.
400
300
Measurement of the PPT We used a pressure algometer described by Fischer19 for the measurement of the pressure pain threshold. This algometer has been confirmed as a reliable and valid measure of MTP sensitivity.20-22 To measure the PPT, we placed a pressure algometer on the site to be measured, perpendicular to the surface of the skin. Then, the pressure of compression was increased gradually at a speed of approximately 1kg/s, while asking if the subject felt any pain or discomfort. The compression was stopped as soon as the subject said “yes.” The subject was asked to remember this level of pain discomfort and to apply the same criterion for the subsequent measurements. In the measurement of the infant, the pressure of compression was increased gradually until the infant began to withdraw or cry or make an unpleasant facial expression, whichever occurred first. At this point, the examiner stopped the compression and read the scale in the algometer (in kg/cm2) to find the PPT at that site. Three measurements were performed on each site, and a total of 9 measurements were performed for each muscle. At least 1 minute elapsed between the 2 consecutive measurements, as suggested by Fischer.19 The sequence of measurement on the 6 sites in 2 sides was randomly assigned using a randomization table. Two different well-trained examiners did the measurements; one performed this task with the infants and the other on the adult subjects.
RESULTS
n=39
n=21
Fig 1. Age distribution of the infants.
Arch Phys Med Rehabil Vol 88, February 2007
Differences Among the 3 Measured Sites In the adult subjects, the mean PPT value was significantly lower (P⬍.01) over the MTP site than at other sites on either right or left side (table 2). However, in the infants, there were no significant differences (P⬎0.1) in the mean values of PPT
MYOFASCIAL TRIGGER POINTS IN EARLY LIFE, Kao Table 2: Mean PPT at Different Sites Infants (n⫽60)
Adults (n⫽60)
Site
Right
Left
Right
Left
Proximal Middle (MTP) Distal Middle vs proximal P Middle vs distal P Distal vs proximal P
2.06⫾0.80 2.12⫾1.11 2.07⫾1.03
2.09⫾0.78 2.17⫾1.12 2.14⫾0.81
3.81⫾0.65 2.54⫾0.47 4.00⫾0.63
4.03⫾0.66 2.87⫾0.52 4.24⫾0.67
⬎0.1
⬎0.1
⬍.05
⬍.05
⬎0.1
⬎0.1
⬍.05
⬍.05
⬎0.1
⬎0.1
⬎0.1
⬎0.1
NOTE. Values are mean kg/cm ⫾ SD or P value. 2
among the 3 sites on either side. In most infants, we were unable to see remarkable differences in PPT values among the 3 measured spots as usually found in the adult subjects. For each adult subject, the MTP site was always the most painful site, with the lowest PPT value as compared with the other 2 sites. However, for each infant, the responses to the pressure stimuli were frequently similar at 3 different stimulating sites. Differences Between the 2 Sides For each measured site, there was no significant difference (P⬎0.1) in PPT values between male and female subjects or between right and left sides. Existence of Taut Band On palpation of the MTP site, 1 or more taut bands could be identified in all of the adult subjects. On the other hand, no taut band could be identified in any infant. DISCUSSION Existence of Latent MTP In this study, we found that every adult subject had a hyperirritable spot in the middle portion of taut band(s) in the brachioradialis muscle, which could be a latent MTP or in the vicinity of the latent MTP. In an earlier study,24 it was found that a site in the taut band, but not the latent MTP, also had reduced PPT as compared with the normal muscle site. Therefore, the assumed MTP site in our study might not be exactly the real MTP site. At least we know that some spots may be more irritable than others in this muscle of the adult subjects. However, we were unable to validate this phenomenon in the infants. No taut band could be identified in any infant. Therefore, we could not confirm the existence of latent MTPs in the infants less than 1 year of age, because all 3 measured sites had the same irritability. This finding supports the hypothesis that latent MTPs do not exist in early life and probably develop later, because we were unable to distinguish a relatively hyperirritable spot in any infant in this study. As soon as a latent MTP developed in the center of the muscle fibers (endplate zone), it would be the most sensitive spot (most tender site) in muscle fibers. The findings in the adult subjects in this study have strongly supported that. Formation of Latent MTPs (Hypothesis) The exact mechanism of MTP formation is still uncertain. At least we know that the latent MTP is not inherent, based on the
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findings in our study. In early life, an infant may have many chances to suffer from either gross or minor neuromuscular injuries. A minor injury is usually ignored in most cases. Although the tissue damage may be mild, the subsequent chronic inflammation may create certain influences in the later life. For example, a stretch or direct trauma to the spine may cause mild radiculopathy with no obvious clinical symptoms or signs, but may be sufficient enough to induce excessive secretion of acetylcholine. Similarly, a stretch of the shoulder or hip joint may cause mild traction to the cervical or lumbosacral plexus with no clinical manifestations but may still cause excessive acetylcholine secretion. Other possible injuries include minor damage to the peripheral nerves or skeletal muscle fibers which may cause similar reactions. Gunn25 has suggested that neuropathic lesions are the primary mechanism of MTP formation. Simons et al1 proposed that excessive acetylcholine secretion may induce electrotonic potentials (endplate noise observed in the MTP region) and cause focal contraction of sarcomeres (contraction knot1) near the endplate zone, and these may subsequently develop an energy crisis (excessive energy consumption due to persistent muscle contraction). The sensitizing substances released during an energy crisis may cause peripheral sensitization of the nociceptors near the endplate. An MTP may be formed in this way. Hong26 agrees with this hypothesis for a latent MTP formation, but not for the process of the activation of a latent MTP to become an active one. There is evidence that a latent MTP can be activated to become an active MTP via central sensitization.4,27-29 However, it is very likely that the formation of a latent MTP is due to minor neuromuscular damage, as mentioned above, when the baby is growing up. CONCLUSIONS In this study on the brachioradialis muscle, we found that the assumed MTP site was more irritable than other sites in the adult subjects, but not in infants (⬍1y). It appears that infants do not have trigger points identified by this study. Latent MTPs probably do not exist in the newborn or young infant, but develop in later life. References 1. Simons DG, Travell JG, Simons LS. Travell & Simons’s myofascial pain and dysfunction: the trigger point manual. Vol 1, 2nd ed. Baltimore: Williams & Wilkins; 1999. 2. Hong CZ, Simons DG. Pathophysiologic and electrophysiologic mechanism of myofascial trigger points. Arch Phys Med Rehabil 1998;79:863-72. 3. Hong CZ. Current research on myofascial trigger points: pathophysiological studies. J Musculoskeletal Pain 1999;7:121-9. 4. Hong CZ. Myofascial trigger points: pathophysiology and correlation with acupuncture points. Acupunct Med 2000;18:41-7. 5. Hong CZ. Lidocaine injection versus dry needling to myofascial trigger point: the importance of the local twitch response. Am J Phys Med Rehabil 1994;73:256-63. 6. Hong CZ. Persistence of local twitch response with loss of conduction to and from the spinal cord. Arch Phys Med Rehabil 1994;75:12-6. 7. Hong CZ. Pathophysiology of myofascial trigger point. J Formos Med Assoc 1996;95:93-104. 8. Hong CZ, Torigoe Y. Electrophysiologic characteristics of localized twitch responses in responsive bands of rabbit skeletal muscle fibers. J Musculoskeletal Pain 1994;2:17-43. 9. Hong CZ, Yu J. Spontaneous electrical activity of rabbit trigger spot after transection of spinal cord and peripheral nerve. J Musculoskeletal Pain 1998;6:45-58. Arch Phys Med Rehabil Vol 88, February 2007
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10. Hong CZ, Torigoe Y, Yu J. The localized twitch responses in responsive bands of rabbit skeletal muscle fibers are related to the reflexes at spinal cord level. J Musculoskeletal Pain 1995;3:15-33. 11. Hubbard DR, Berkoff GM. Myofascial trigger points show spontaneous needle EMG activity. Spine 1993;18:1803-7. 12. Simons DG. Clinical and etiological update of myofascial pain from trigger points. J Musculoskeletal Pain 1996;4:93-121. 13. Simons DG. Diagnostic criteria of myofascial pain caused by trigger points. J Musculoskeletal Pain 1999;7:111-20. 14. Simons DG, Hong CZ, Simons LS. Prevalence of spontaneous electrical activity at trigger spots and at control sites in rabbit skeletal muscle. J Musculoskeletal Pain 1995;3:35-48. 15. Simons DG, Hong CZ, Simons LS. Endplate potentials are common to midfiber myofascial trigger points. Am J Phys Med Rehabil 2002;81:212-22. 16. Hong CZ, Chen JT, Chen SM, Yan JJ, Su YJ. Histological findings of responsive loci in a myofascial trigger spot of rabbit skeletal muscle from where localized twitch responses could be elicited [abstract]. Arch Phys Med Rehabil 1996;77:962. 17. Simons DG, Stolov WC. Microscopic features and transient contraction of palpable bands in canine muscle. Am J Phys Med 1976;55:65-88. 18. Hong CZ. New trends in myofascial pain syndrome. Zhonghua Yi Xue Za Zhi (Taipei) 2002;65:501-12. 19. Fischer AA. Pressure threshold meter: its use for quantification of tender spots. Arch Phys Med Rehabil 1986;67:836-8.
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20. Ohrbach R, Gale EN. Pressure pain thresholds, clinical assessment, and differential diagnosis: reliability and validity in patients with myogenic pain. Pain 1989;39:157-69. 21. Ohrbach R, Gale EN. Pressure pain thresholds in normal muscles: reliability, measurement effects and topographic differences. Pain 1989;37:257-63. 22. Reeves JL, Jaeger B, Graff-Radford SB. Reliability of the pressure algometer as a measure of myofascial trigger point sensitivity. Pain 1986;24:313-21. 23. Gerwin RD, Shannon S, Hong CZ, Hubbard D, Gevirtz R. Identification of myofascial trigger points: interrater agreement and effect of training. Pain 1997;69:65-73. 24. Hong CZ, Chen YN, Twehous D, Hong DH. Pressure threshold for referred pain by compression on the trigger point and adjacent areas. J Musculoskeletal Pain 1996;4:61-79. 25. Gunn CC. Radiculopathic pain: diagnosis and treatment of segmental irritation or sensitization. J Musculoskeletal Pain 1997;5: 119-34. 26. Hong CZ. Comment on Gunn’s “radiculopathy model of myofascial trigger points.” J Musculoskeletal Pain 2000;8:133-5. 27. Mense S. Nociception from skeletal muscle in relation to clinical muscle pain. Pain 1993;54:241-89. 28. Mense S. Referral of muscle pain: new aspects. Am Pain Soc J 1994;3:1-9. 29. Mense S. Biochemical pathogenesis of myofascial pain. J Musculoskeletal Pain 1996;4:145-62.