Shu Min Chen

Dry needling to a key Myofascial trigger point may reduce the irritability of satellite MTrPs

Hsieh Y-L, Kao M-J, Kuan T-S, Chen S-M, Chen J-T, Hong C-Z: Dry needling to a key myofascial trigger point may reduce the irritability of satellite myofascial trigger points. Am J Phys Med Rehabil 2007;86:397–403. Objective:To investigate the changes in pressure pain threshold of the secondary (satellite) myofascial trigger points (MTrPs) after dry needling of a primary (key) active MTrP. Design:Single blinded within-subject design, with the same subjects serving as their own controls (randomized). Fourteen patients with bilateral shoulder pain and active MTrPs in bilateral infraspinatus muscles were involved. An MTrP in the infraspinatus muscle on a randomly selected side was dry needled, and the MTrP on the contralateral side was not (control). Shoulder pain intensity, range of motion (ROM) of shoulder internal rotation, and pressure pain threshold of the MTrPs in the infraspinatus, anterior deltoid, and extensor carpi radialis longus muscles were measured in both sides before and immediately after dry needling. Results:Both active and passive ROM of shoulder internal rotation, and the pressure pain threshold of MTrPs on the treated side, were significantly increased (P < 0.01), and the pain intensity of the treated shoulder was significantly reduced (P < 0.001) after dry needling. However, there were no significant changes in all parameters in the control (untreated) side. Percent changes in the data after needling were also analyzed. For every parameter, the percent change was significantly higher in the treated side than in the control side. Conclusions:This study provides evidence that dry needle–evoked inactivation of a primary (key) MTrP inhibits the activity in satellite MTrPs situated in its zone of pain referral. This supports the concept that activity in a primary MTrP leads to the development of activity in satellite MTrPs and the suggested spinal cord mechanism responsible for this phenomenon.

Phentolamine effect on the spontaneous electrical activity of active loci in a myofascial trigger spot of rabbit skeletal muscle

OBJECTIVE To investigate the effect of phentolamine, a sympathetic blocking agent, on the spontaneous electrical activity (SEA) recorded from a locus of a myofascial trigger spot (MTrS), equivalent to a human trigger point, in rabbit skeletal muscle. DESIGN Randomized control trial. SETTING A university medical laboratory. PATIENTS OR OTHER PARTICIPANTS Nine adult New Zealand rabbits. INTERVENTION In the experimental group phentolamine mesylate (1mg/kg) was injected into the external iliac artery, followed by flushing with normal saline. The control group was treated with normal saline instead of phentolamine using the same procedure. MAIN OUTCOME MEASURES SEA was recorded from multiple active loci of MTrSs in the biceps femoris muscle: initially SEA in the same locus was recorded before and immediately after phentolamine (or normal saline) injection; then SEA was recorded from 25 different active loci. The mean of the average integrated signal (AIS) of SEA was analyzed, comparing the effects of phentolamine and normal saline on SEA. RESULTS In the same active locus, the AIS of SEA showed statistically a linear decay with time after phentolamine injection, with a correlation coefficient of .56 at p < .05. However, no statistical relationship could be derived for the control group data with time by using regression analysis, probably because of large variations among the rabbits and movement artifacts during the experiment. In 25 different loci in the phentolamine group, the mean of the AIS of SEA (7.92 microV) was significantly lower than that of the control group (9.89 microV) at p < .05. CONCLUSIONS The results support the hypothesis that the autonomic nervous system is involved in the pathogenesis of myofascial trigger points. The application of the AIS as an evaluation index seems to be feasible in the quantitative measurement of SEA.

The myofascial trigger point region: correlation between the degree of irritability and the prevalence of endplate noise.

Kuan T-S, Hsieh Y-L, Chen S-M, Chen J-T, Yen W-C, Hong C-Z: The myofascial trigger point region: correlation between the degree of irritability and the prevalence of endplate noise. Am J Phys Med Rehabil 2007;86:183–189. Objective: This study was designed to investigate the correlation between the irritability of the myofascial trigger point (MTrP) and the prevalence of endplate noise (EPN) in the MTrP region of human skeletal muscle. Design: Twenty normal subjects with latent MTrPs and 12 patients with active MTrPs in the upper trapezius muscles were recruited for this study. The patients reported the subjective pain intensity of the active MTrP (0–10). The MTrP and an adjacent non-MTrP site were confirmed and marked for the measurement of pressure pain threshold (with a pressure algometer) and the prevalence of EPN (with electromyographic recordings). Results: The prevalence of EPN in the MTrP regions was significantly higher (P < 0.01) in the active MTrPs than in the latent ones. However, no EPN could be found in the non-MTrP region near either the active or the latent MTrPs. The pain intensity and the pressure pain threshold were highly correlated with the prevalence of EPN in the MTrP region (r = 0.742 and −0.716, respectively). Conclusions: The irritability of an MTrP is highly correlated with the prevalence of EPN in the MTrP region of the upper trapezius muscle. The assessment of EPN prevalence in an MTrP region may be applied to evaluate the irritability of that MTrP.

Referred pain elicited by palpation and by needling of myofascial trigger points: A comparison

OBJECTIVE To investigate the occurrence of referred pain (ReP) elicited by palpation (Pal-ReP) or by needle injection (Inj-ReP) of myofascial trigger point (MTrP), and to assess the correlated factors, including the pain intensity of an active MTrP and the occurrence of local twitch response (LTR). DESIGN Correlational study. PATIENTS Ninety-five patients who were treated with MTrP injections. INTERVENTION MTrP injections. MAIN OUTCOME MEASURE Pain intensity of MTrP and occurrence of Pal-ReP, Inj-ReP, and LTR. RESULTS Both Pal-ReP and Inj-ReP were elicited in 53.9% of MTrPs, Inj-ReP, but not Pal-ReP, was elicited in 33.7% of MTrPs. Both Pal-ReP and Inj-ReP were unobtainable in 12.3% of MTrPs. The occurrence of ReP was significantly correlated to the pain intensity of active MTrP and the occurrence of LTR. CONCLUSION ReP could be elicited more frequently by needling than by palpation. The frequency of occurrence in ReP mainly depends on pain intensity of an active MTrP.

The spinal cord connections of the myofascial trigger spots

Background: Recent electrophysiological studies revealed that endplate noise (EPN) could be specifically recorded from a myofascial trigger point (MTrP) region. EPN has been considered as the focal graded potentials due to excessive acetylcholine release in neuromuscular junction. A recent histological study has demonstrated a free nerve ending at the vicinity of the site, from where EPN could be recorded in an MTrP region. However, the sensory (afferent) and the motor (efferent) connections between an MTrP and the spinal cord still has never been fully studied.

Myofascial trigger points in intercostal muscles secondary to herpes zoster infection of the intercostal nerve

Chronic pain in the chest wall is a major complication after herpes zoster infection of intercostal nerves. It is usually difficult to control pain of such origin. Two cases are reported of postherpetic neuralgia after herpes zoster infection involving the intercostal nerves. Both patients had shooting, burning, aching, and localized pain in the muscle supplied by the involved intercostal nerves 1 to 3 months after onset. Compression palpation of a tender spot in one of these muscles induced a referred pain that followed the corresponding interspace, usually in the distal anterior direction. Local twitch responses could be elicited during injection of 0.5% or 1% lidocaine into one of these tender spots; the pain in the interspace was consistently eliminated immediately after injection. One patient had complete pain relief after three series of injections. The effect of pain relief for the other patient lasted for 1 to 2 weeks after the initial injection and lasted progressively longer (up to 2 months) after repeated injections. It appears that many of the tender spots formed in intercostal muscles after herpes zoster are myofascial trigger points that respond to injection with referred pain, local twitch responses, and immediate pain relief.

Decrease in pressure pain thresholds of latent myofascial trigger points in the middle finger extensors immediately after continuous piano practice

Objectives: This study is designed to investigate the change of the pressure pain threshold [PPT] of latent myofascial trigger points [MTrPs], immediately after rapid repetitive contraction of the involved muscle. Methods: Forty 8–19 year-old students who had taken piano lessons for longer than one year. Three consecutive measurements of PPT were obtained on the latent MTrPs of bilateral extensor digitorium communis muscles 20 minutes before, immediately before, immediately after, and 20 minutes after continuous piano practice of fast music pieces for 20 minutes. Results: Mean pain threshold was significantly [P < 0.01] reduced immediately after piano practice, and returned to original value 20 minutes after practice. There was no statistically significant difference between the mean value of 20 minutes before practice and immediately before practice [control values]. There was no significant difference between the right and the left hands. Age and experience were not significantly correlated with the changes of pain threshold. Conclusion: A latent MTrP in a muscle may increase the irritability after rapid repetitive use [over loading of that muscle]. Usually, this change is a temporary phenomenon after an adequate rest period. Therefore, adequate rest may be important to reduce the probability in the development of an active MTrP.

Precision Pinch Performance in Patients with Sensory Deficits of the Median Nerve at the Carpal Tunnel

To investigate how sensory symptoms impact the motor control of hands, in this study we examined the differences in conventional sensibility assessments and pinch force control in the pinch-holding-up activity (PHUA) test between carpal tunnel syndrome (CTS) patients and healthy controls. CTS patients (n = 82) with 122 affected hands and an equal number of control subjects were recruited to participate in the threshold, discrimination, and PHUA tests. The patients showed significantly poorer hand sensibility and lower efficiency of force adjustment in the PHUA test as compared with the control subjects. Baseline pinch strength and the percentage of maximal pinch strength for the PHUA were significantly higher for the subgroup of sensory nerve action potential (SNAP) of <16 μV than for the subgroup of SNAP of 16 μV. Using a PHUA perspective to analyze the efficiency of force-adjustment could assist the clinical detection of sensory nerve dysfunction.

Myofascial Pain Syndrome: Correlation between the Irritability of Trigger Points and the Prevalence of Local Twitch Responses during Trigger Point Injection

Objective To assess the correlation between the trigger point [TrP] irritability in the myofascial pain syndrome [MPS] and the prevalence of one or more local twitch responses [LTRs] during TrP injection. Methods Patients with MPS, active TrPs in the trapezius muscle, and a pain intensity greater than 5 [numerical pain scale, 0 = no pain; 10 = worst pain in life] were recruited for this study. Pain intensity and pressure pain threshold [PPT] were measured before and immediately after TrP injection. Results A total of 72 MPS patients [30 males, 42 females] participated in this study. It was found that the pain intensity was significantly reduced [P < 0.05] and the PPT was significantly increased [P < 0.05] immediately after TrP injection. Conclusions This study supports the hypothesis that in MPS there are multiple sensitized loci nociceptors in TrP regions and that the Local Twitch Response is related to the irritability of the TrP.

No Increased Neuromuscular Jitter at Rabbit Skeletal Muscle Trigger Spot Spontaneous Electrical Activity Sites

Objective: One of the important characteristics of myofascial trigger point [MTrP] is spontaneous electrical activity [SEA]. Spontaneous electrical activity is recorded from an active locus [a basic unit] of MTrP and has been considered as an abnormal endplate potential, which might be due to excessive acetylcholine release in neuromuscular junction. This study is designed to test the hypothesis that active loci in MTrPs are related to neuromuscular transmission disorder. Methods: Twenty-one adult New Zealand rabbits were anesthetized and their biceps femoris were exposed to localize myofascial trigger spot [MTrS, equivalent to MTrP in human]. A monopolar needle electrode was first used for searching SEA in an MTrS region. Then, a single fiber electromyography [SFEMG] electrode was used to collect the neuromuscular jitter at the site where SEA was recorded. The same procedure was performed at the normal muscle site [no SEA recorded] in contralateral limb to collect the neuromuscular jitter as a control. Mean value of consecutive differences [MCD] of 100 successive inter-potential intervals was calculated to express the neuromuscular jitter. Results: There was no statistically significant difference [P > 0.05] in MCD of MTrS between the active loci and control sites. Conclusion: It appears that the neuromuscular transmission of end-plate in MTrS in rabbits is not impaired based on this SFEMG study using jitter as the sole criteria. Spontaneous electrical activity is not related to neuromuscular transmission abnormality. Further studies are required to clarify the mechanism of dysfunctional endplates in relation to MTrP.