A New Unified Theory of Trigger Point Formation: Failure of Pre- and Post-Synaptic Feedback Control Mechanisms

Blood Flow of the Infraspinatus Muscle in Individuals With and Without Shoulder Pain and Myofascial Trigger Points: A Color Doppler Ultrasound and Reliability Study

OBJECTIVES

Myofascial trigger points (MTrPs) are potential contributors to shoulder pain and can lead to local ischemia and hypoxia, thus causing pain. Color Doppler ultrasound (US) has been used to examine the vascular environment around MTrPs, but has not been used to examine blood flow impairments in patients with shoulder pain and MTrPs. The reliability of color Doppler US for measuring infraspinatus muscle blood flow also has not been established. This study aimed to investigate differences in blood flow between individuals with and without shoulder pain and the reliability of Doppler US for measuring infraspinatus muscle blood flow.

METHODS

Forty participants were enrolled, 20 with shoulder pain and MTrPs and 20 without. Color Doppler US examination was performed twice on each participant to measure peak systolic velocity (PSV), end-diastolic velocity (EDV), resistive index (RI), and pulsatile index (PI) of the infraspinatus muscle.

RESULTS

The symptomatic participants had significantly higher PSV (ie, impaired blood flow) than the asymptomatic participants. There were no significant between-group differences in EDV, RI, and PI. The results also demonstrated good-to-excellent intra-rater reliability for color Doppler US measurements of PSV, EDV, RI, and PI for both groups.

CONCLUSION

This study demonstrated differences in blood flow near MTrPs in the infraspinatus muscle between individuals with and without shoulder pain. It also established good-to-excellent reliability of color Doppler US in measuring infraspinatus muscle blood flow. These findings suggest color Doppler US is a useful tool to identify vascular impairments for shoulder pain associated with MTrPs.

Effects of platelet-rich plasma injection on electrical activity and biomechanics of the erector spinae muscles in lumbar myofascial pain syndrome

Low back pain (LBP) is a highly prevalent disease. Among the various causes of LBP, one of the most frequent is myofascial pain syndrome (MPS) which affects the spinal stabilizer muscles. The aims of this study were to compare the differences in muscular electrical activity and biomechanical properties between the painful and non-painful sides in patients with unilateral MPS and to verify the feasibility of surface electromyography (sEMG) and MyotonPRO for assisting in MPS assessment. Forty patients with unilateral lumbar MPS were recruited via the Department of Rehabilitation Medicine Center of West China Hospital Sichuan University from October 2022 to October 2023. The electrical properties of the bilateral erector spinae muscles were characterized by sEMG signals during a trunk extension task. The following four time-domain features of sEMG were extracted: root mean square (RMS), mean absolute value (MAV), integrated EMG (iEMG), and waveform length (WL). And two frequency domain features were extracted: the median frequency (MDF) and mean power frequency (MPF). The mechanical properties of the muscles were assessed by MyotonPRO at rest. The following biomechanical parameters were acquired: oscillation frequency [Hz], dynamic stiffness [N/m], logarithmic decrement, relaxation time [ms], and Creep. The visual analog scale (VAS) was used to evaluate the pain severity, and the Oswestry Disability Index (ODI) was used to evaluate the severity of disability and disruption to lifestyle activities caused by LBP pain. The outcome measures were obtained prior to the Platelet-rich plasma (PRP) treatment and repeated two weeks after treatment. (1) Prior to the PRP treatment, all sEMG time-domain features on the painful side were significantly higher than those on the non-painful side (RMS, p < 0.001; MAV, p < 0.001; iEMG, p < 0.001; WL, p = 0.001). However, there was no significant difference in the sEMG frequency-domain features (MPF, p = 0.478; MDF, p = 0.758). On the mechanical side, there were significant differences in oscillation frequency (p = 0.041) and logarithmic decrement (p = 0.022) between the painful side and non-painful side, but no significant differences in dynamic stiffness, relaxation time, and creep (both p > 0.05). (2) Two weeks after the PRP treatment, statistically significant decreases were observed in both post-treatment VAS (p < 0.001) and ODI scales (p < 0.001), indicating the PRP treatment clinically significantly reduced the level of. MPS. This change coincided with all sEMG time-domain features, in which the values at the painful side decreased significantly (RMS, p = 0.001; MAV, p = 0.001; iEMG, p = 0.001; WL, p = 0.001). However, no significant difference in the sEMG frequency-domain features (MPF, p = 0.620; MDF, p = 0.850) was found. On the mechanical side, only logarithmic decrement on the painful side increased significantly (p < 0.001). Our combined MyotonPRO and sEMG results indicated that MPS likely leads to increased muscle tone and decreased muscle elasticity, manifested by abnormal time-domain features of sEMG and biomechanical properties. The changes in these objective measurements were agreed with the changes in subjective outcome measures of pain and function currently assessed in the patients with MPS. A single PRP treatment may alleviate muscle dysfunction caused by MPS. These preliminary results demonstrated the potential feasibility of using sEMG and MyotonPRO as tools for assessing the neuromuscular function of MPS.

Prevalence of Myofascial Trigger Points in Isolated Idiopathic Cervical Dystonia: A Possible Contributor to Pain, Movement and Disability

BACKGROUND

Myofascial trigger points (TrPs) are hypersensitive points located in a tight band of muscle that, when palpated, produce not only local pain but also referred (distant) pain. The role of TrPs in patients with cervical dystonia (CD) has not been investigated.

OBJECTIVE

To identify the presence of TrPs in patients with isolated idiopathic CD and their association with pain.

METHODS

Thirty-one patients (74.2% women; age: 61.2 years, SD: 10.1 years) participated. TrPs were explored in the sternocleidomastoid, upper trapezius, splenius capitis, levator scapulae, anterior scalene, suboccipital, and infraspinatus muscles. Clinical features of CD were documented as well as the presence of pain. The severity of dystonia and its consequences were assessed using the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS).

RESULTS

The mean number of TrPs for each patient was 12 (SD:3), with no differences between patients with pain (n = 20) and those without pain (n = 11). Active TrPs were only found in patients with pain (mean: 7.5, SD:4). Latent TrPs were found in both groups but were more prevalent (P < 0.001) in patients without pain (mean: 11, SD:3.5) than in those with pain (mean: 5, SD:3.5). The number of active TrPs or latent TrPs was positively associated with the TWSTRS disability subscale and the TWSTRS total score. The number of active, but not latent, TrPs was associated with worse scores on the TWSTRS pain subscale.

CONCLUSION

Active TrPs were present in patients with CD reporting pain, while latent TrPs were present in all CD patients, irrespective of their pain status. The numbers of active/latent TrPs were associated with disability. TrPs could act as pain generators in CD and also contribute to the involuntary muscle contractions characteristic of dystonia.

Advancing musculoskeletal diagnosis and therapy: a comprehensive review of trigger point theory and muscle pain patterns

Musculoskeletal disorders, especially chronic muscle pain, have a significant impact on public health, affecting millions worldwide. This review examines recent advancements in the diagnosis and management of myofascial pain, with a focus on the refined application of trigger point theory. This theory now incorporates an intricate model that blends biomechanical and neurophysiological mechanisms, essential for understanding the initiation and persistence of pain, and necessitating targeted therapeutic interventions. Utilizing a methodical approach, this paper categorizes muscle pain into three types: Muscle Belly Pain, Origin-Insertion Pain, and Referred Pain, as delineated in the most recent edition of "Myofascial Pain and Dysfunction-The Trigger Point Manual." Such classification enhances diagnostic precision and therapeutic effectiveness by establishing a specific treatment protocol for each type of pain. The paper discusses the implications of various treatments, such as dry needling and manual therapy, which are informed by empirically derived trigger point charts. These charts are instrumental in pinpointing the exact locations of pain sources and customizing treatment plans. Moreover, this review critically assesses the evolving nature of trigger point charts and champions a holistic approach to pain management. It underscores the necessity of integrating biomechanics, kinesiology, and compensatory mechanisms to provide a comprehensive understanding that allows practitioners to address not only symptomatic pain but also the root causes of musculoskeletal disorders, thereby enhancing long-term patient care outcomes in clinical environments.

Effect of transcutaneous neuromodulation on normalization of dermal body temperature and pain in a tender scar in the presence of low back pain: An update and case report

Low back pain affects over 20% of individuals during their lifetime, and in some patients, it may be associated with scar tissue formation after surgery. Small-fiber neuropathy and scar tissue dysfunction can lead to localized pain by affecting signals to the thalamus. Transcutaneous neuromodulation using Tape with Magnetic Particles shows promise in relieving perceived pain, modulating vascularization and the autonomic nervous system, and reducing dermal temperature. In the present case, a 24-year-old woman with L5-S1 disk herniation experienced low back pain and leg pressure. The surgical intervention provided temporary relief, but scar restrictions caused pain recurrence. Tape with Magnetic Particles application initially induced scar hypothermia and pressure tolerance during posteroanterior tests on lumbar spinous processes increased, reducing pain perception for at least 12 h. Transcutaneous neuromodulation with Tape with Magnetic Particles modulated dermal temperature immediately and for 12 h, reducing perceived pain and sustaining improvement thereafter. This highlights the potential of Tape with Magnetic Particles in managing chronic low back pain associated with scar tissue.

Research Progress on the Experimental Model and Underlying Mechanistic Studies of Tension-Type Headaches

PURPOSE OF REVIEW

Tension-type headaches (TTH) significantly diminish patients' quality of life and increase absenteeism, thereby imposing a substantial economic burden. Animal models are essential tools for studying disease mechanisms and drug development. However, until now, little focus has been placed on summarizing the animal models of TTH and associated mechanistic studies. This narrative review discusses the current animal models of TTH and related mechanistic studies to provide insights into the pathophysiological mechanisms of and treatments for TTH.

RECENT FINDINGS

The primary method for constructing an animal model of TTH involves injecting a solution of pain relievers, such as adenosine triphosphate, nerve growth factor, or a high concentration of salt solution, into the neck to initiate harmful cervical muscle responses. This model enables the examination of the interaction between peripheral muscles and central sensitization, which is crucial for understanding the pathophysiology of TTH. Mechanistic studies based on this model have investigated the effect of the P2X receptor antagonist, P2X7 receptor blockade, the P2Y1 receptor agonist 2-MESADP, P2Y1 receptor antagonist MRS2179, nitric oxide synthase inhibitors, and acetylsalicylic acid. Despite notable advancements, the current model of TTH has limitations, including surgical complexity and the inability to replicate chronic tension-type headache (CTTH). To gain a more comprehensive understanding and develop more effective treatment methods, future studies should focus on simplifying surgical procedures, examining other predisposing factors, and establishing a model for chronic TTH. This will offer a deeper insight into the pathophysiological mechanism of TTH and pave the way for improved treatment approaches.

Modeling of the Effect of Subperiosteal Hydrostatic Pressure Conductivity between Joints on Decreasing Contact Loads on Cartilage and of the Effect of Myofascial Relief in Treating Trigger Points: The Floating Skeleton Theory

Chronic overloading of the cartilage can lead to its irreversible destruction, as observed in people with osteoarthritis. The floating skeleton model previously introduced postulates that overloading begins and progresses when a joint is isolated from the hydrostatical connection with other joints. Such a connection occurs via the interstitial fluid in subperiosteal space and allows for pressure transmission between synovial capsules modulating intra-articular pressure. In the current study, a simple experiment was performed to model an obstruction in the subperiosteal hydrostatic pressure conductivity between joints to illustrate the effect of that obstruction on loads borne by the joint. When the obstruction was removed, the load experienced by the joint was reduced as it was redistributed throughout the model structure. The experiment demonstrated that contact pressures can be redistributed when the conditions of Pascal's Law are met.

Myofascial trigger point (MTrP) size and elasticity properties can be used to differentiate characteristics of MTrPs in lower back skeletal muscle

Myofascial trigger points (MTrPs) are localized contraction knots that develop after muscle overuse or an acute trauma. Significant work has been done to understand, diagnose, and treat MTrPs in order to improve patients suffering from their effects. However, effective non-invasive diagnostic tools are still a missing gap in both understanding and treating MTrPs. Effective treatments for patients suffering from MTrP mediated pain require a means to measure MTrP properties quantitatively and diagnostically both prior to and during intervention. Further, quantitative measurements of MTrPs are often limited by the availability of equipment and training. Here we develop ultrasound (US) based diagnostic metrics that can be used to distinguish the biophysical properties of MTrPs, and show how those metrics can be used by clinicians during patient diagnosis and treatment. We highlight the advantages and limitations of previous US-based approaches that utilize elasticity theory. To overcome these previous limitations, we use a hierarchical approach to distinguish MTrP properties by patients' reported pain and clinician measured palpation. We show how US-based measurements can characterize MTrPs with this approach. We demonstrate that MTrPs tend to be smaller, stiffer, and deeper in the muscle tissue for patients with pain compared to patients without pain. We provide evidence that more than one MTrP within a single US-image field increases the stiffness of neighboring MTrPs. Finally, we highlight a combination of metrics (depth, thickness, and stiffness) that can be used by clinicians to evaluate individual MTrPs in combination with standard clinical assessments.

Stress increases the spontaneous release of ACh and may be involved in the generation and maintenance of myofascial trigger points in mouse

An increase in spontaneous neurotransmission may be related to myofascial pain. Sympathetic neurons innervate most of the neuromuscular junction sand are involved in the modulation of synaptic transmission. Therefore, a direct action of stress on acetylcholine release is expected. For this reason, this study aims to evaluate the relationship between stress and spontaneous neurotransmission. Five acute stressors (immobilization, forced swimming, food and water deprivation, social isolation and ultrasound) were tested in 6 weeks adult Swiss male mice. Subsequently, these types of stress were combined to generate a model of chronic stress. The study of ACh release was evaluated before and after the application of stress by intracellular recording of spontaneous neurotransmission (mEPPs). In each one of the stressors, an increase in the frequency of mEPPs was obtained immediately after treatment, which remained elevated for 5 days and thereafter returned to control values after a week. With chronic stress, a much higher increase in the frequency of mEPPs was obtained and it was maintained for 15 days. In summary, stress, both in its acute and chronic forms, increased spontaneous neurotransmission significantly. There is a possibility that chronic stress is related with the genesis or maintenance of myofascial pain.

Sensory and emotional responses to deep pressure stimulation at myofascial trigger points: a pilot study

Objective

Although manual pressure, such as that used during a massage, is often associated with pain, it can simultaneously be perceived as pleasant when applied to certain body areas. We hypothesized that stimulation of myofascial trigger points (TPs) leads to simultaneous pain and pleasure. TPs are hyperirritable points located in the taut band of the skeletal muscle.

Method

In this study, we measured the muscle tone, muscle stiffness, and pressure pain threshold of TPs and control points in the left brachioradialis muscle of 48 healthy participants. We also applied deep compression to the two points and collected subjective data on pain, pleasantness, unpleasantness, and relief.

Result

Greater muscle stiffness was observed in the TPs versus control points (t = 6.55, p < 0.001), and the pain threshold was significantly lower in the TPs (t = -6.21, p < 0.001). Unpleasantness ratings after deep compression were significantly lower in the TPs compared with control points (t = -2.68, p < 0.05). Participants experienced greater relief at the TPs compared with control points (t = 2.01, p < 0.05), although the perceived pain did not differ between the two types of points.

Conclusion

We compared the properties of TPs and control points, and found that deep compression at TPs was associated with higher muscle tone and stiffness, lower unpleasantness ratings, and higher relief ratings compared with the control points. These findings suggest that, at least for some TPs, pain and pleasantness are simultaneously elicited by deep pressure stimulation.