Epimuscular myofascial force transmission occurs in the rat between the deep flexor muscles and their antagonistic muscles

A clinical study on the incidence of internal derangement of the temporomandibular joint following harvesting of temporalis fascia

OBJECTIVE

The aim of the current clinical study was to reveal whether harvesting of a temporalis fascia graft would be associated with a higher incidence of temporomandibular joint (TMJ) internal derangement.

METHODS

The study group involved 104 patients who had middle-ear operations, 67 of which involved harvesting of temporalis fascia and 37 that did not. The TMJs were clinically examined in each group.

RESULTS

The total incidence of internal derangement of the TMJ was significantly higher in the group that had temporalis fascia harvesting (79.1%), compared to the group that did not have temporalis fascia harvesting (29.7%), (p= 0.001).

CONCLUSION

Harvesting of temporalis fascia probably alters mandibular kinematics and predisposes to internal derangement of the TMJs.

Densification: Hyaluronan Aggregation in Different Human Organs

Hyaluronan (HA) has complex biological roles that have catalyzed clinical interest in several fields of medicine. In this narrative review, we provide an overview of HA aggregation, also called densification, in human organs. The literature suggests that HA aggregation can occur in the liver, eye, lung, kidney, blood vessel, muscle, fascia, skin, pancreatic cancer and malignant melanoma. In all these organs, aggregation of HA leads to an increase in extracellular matrix viscosity, causing stiffness and organ dysfunction. Fibrosis, in some of these organs, may also occur as a direct consequence of densification in the long term. Specific imaging evaluation, such dynamic ultrasonography, elasto-sonography, elasto-MRI and T1ρ MRI can permit early diagnosis to enable the clinician to organize the treatment plan and avoid further progression of the pathology and dysfunction.

Fascial or Muscle Stretching? A Narrative Review

Stretching exercises are integral part of the rehabilitation and sport. Despite this, the mechanism behind its proposed effect remains ambiguous. It is assumed that flexibility increases, e.g., action on muscle and tendon, respectively, but this is not always present in the stretching protocol of the exercises used. Recently, the fasciae have increased popularity and seems that they can have a role to define the flexibility and the perception of the limitation of the maximal range of motion (ROM). Deep fascia is also considered a key element to transmit load in parallel bypassing the joints, transmitting around 30% of the force generated during a muscular contraction. So, it seems impossible dividing the action of the muscles from the fasciae, but they have to be considered as a “myofascial unit”. The purpose of this manuscript is to evaluate the mechanical behavior of muscles, tendons, and fasciae to better understand how they can interact during passive stretching. Stress-strain values of muscle, tendon and fascia demonstrate that during passive stretching, the fascia is the first tissue that limit the elongation, suggesting that fascial tissue is probably the major target of static stretching. A better understanding of myofascial force transmission, and the study of the biomechanical behavior of fasciae, with also the thixotropic effect, can help to design a correct plan of stretching.

Not merely a protective packing organ? A review of fascia and its force transmission capacity

Recent research indicates that fascia is capable of changing its biomechanical properties. Moreover, as it links the skeletal muscles, forming a body-wide network of multidirectional myofascial continuity, the classical conception of muscles as independent actuators has been challenged. Hence, the present synthesis review aims to characterize the mechanical relevance of the connective tissue for the locomotor system. Results of cadaveric and animal studies suggest a clinically relevant myofascial force transmission to neighboring structures within one limb (e.g., between synergists) and in the course of muscle-fascia chains (e.g., between leg and trunk). Initial in vivo trials appear to underpin these findings, demonstrating the existence of nonlocal exercise effects. However, the factors influencing the amount of transmitted force (e.g., age and physical activity) remain controversial, as well as the role of the central nervous system within the context of the observed remote exercise effects.

In vivo relationship between pelvis motion and deep fascia displacement of the medial gastrocnemius: anatomical and functional implications

Different authors have modelled myofascial tissue connectivity over a distance using cadaveric models, but in vivo models are scarce. The aim of this study was to evaluate the relationship between pelvic motion and deep fascia displacement in the medial gastrocnemius (MG). Deep fascia displacement of the MG was evaluated through automatic tracking with an ultrasound. Angular variation of the pelvis was determined by 2D kinematic analysis. The average maximum fascia displacement and pelvic motion were 1.501 ± 0.78 mm and 6.55 ± 2.47 °, respectively. The result of a simple linear regression between fascia displacement and pelvic motion for three task executions by 17 individuals was r = 0.791 (P < 0.001). Moreover, hamstring flexibility was related to a lower anterior tilt of the pelvis (r = 0.544, P < 0.024) and a lower deep fascia displacement of the MG (r = 0.449, P < 0.042). These results support the concept of myofascial tissue connectivity over a distance in an in vivo model, reinforce the functional concept of force transmission through synergistic muscle groups, and grant new perspectives for the role of fasciae in restricting movement in remote zones.

Significant mechanical interactions at physiological lengths and relative positions of rat plantar flexors

In situ studies involving supraphysiological muscle lengths and relative positions have shown that connective tissue linkages connecting adjacent muscles can transmit substantial forces, but the physiological significance is still subject to debate. The present study investigates effects of such epimuscular myofascial force transmission in the rat calf muscles. Unlike previous approaches, we quantified the mechanical interaction between the soleus (SO) and the lateral gastrocnemius and plantaris complex (LG+PL) applying a set of muscle lengths and relative positions corresponding to the range of knee and ankle angles occurring during normal movements. In nine deeply anesthetized Wistar rats, the superficial posterior crural compartment was exposed, and distal and proximal tendons of LG+PL and the distal SO tendon were severed and connected to force transducers. The target muscles were excited simultaneously. We found that SO active and passive tendon force was substantially affected by proximally lengthening of LG+PL mimicking knee extension (10% and 0.8% of maximal active SO force, respectively; P < 0.05). Moreover, SO relative position significantly changed the LG+PL length-force relationship, resulting in nonunique values for passive slack-length and optimum-length estimates. We conclude that also, for physiological muscle conditions, isometric force of rat triceps surae muscles is determined by its muscle-tendon unit length as well as by the length and relative position of its synergists. This has implications for understanding the neuromechanics of skeletal muscle in normal and pathological conditions, as well as for studies relying on the assumption that muscles act as independent force actuators.

Muscle-specific changes in length-force characteristics of the calf muscles in the spastic Han-Wistar rat

The purpose of the present study was to investigate muscle mechanical properties and mechanical interaction between muscles in the lower hindlimb of the spastic mutant rat. Length-force characteristics of gastrocnemius (GA), soleus (SO), and plantaris (PL) were assessed in anesthetized spastic and normally developed Han-Wistar rats. In addition, the extent of epimuscular myofascial force transmission between synergistic GA, SO, and PL, as well as between the calf muscles and antagonistic tibialis anterior (TA), was investigated. Active length-force curves of spastic GA and PL were narrower with a reduced maximal active force. In contrast, active length-force characteristics of spastic SO were similar to those of controls. In reference position (90° ankle and knee angle), higher resistance to ankle dorsiflexion and increased passive stiffness was found for the spastic calf muscle group. At optimum length, passive stiffness and passive force of spastic GA were decreased, whereas those of spastic SO were increased. No mechanical interaction between the calf muscles and TA was found. As GA was lengthened, force from SO and PL declined despite a constant muscle-tendon unit length of SO and PL. However, the extent of this interaction was not different in spastic rats. In conclusion, the effects of spasticity on length-force characteristics were muscle specific. The changes observed for GA and PL muscles are consistent with the changes in limb mechanics reported for human patients. Our results indicate that altered mechanics in spastic rats cannot be attributed to differences in mechanical interaction, but originate from individual muscular structures.

Intraoperative experiments show relevance of inter-antagonistic mechanical interaction for spastic muscle's contribution to joint movement disorder

BACKGROUND

Recent intra-operative knee angle-muscle force data showed no abnormal muscular mechanics (i.e., a narrow joint range of muscle force exertion and peak muscle force availability at flexed joint positions), if the spastic gracilis muscle was stimulated alone. This can limit inter-muscular mechanical interactions, which have been shown to affect muscular mechanics substantially. We aimed at testing the hypothesis that the knee angle-muscle force curves of the spastic gracilis muscle activated simultaneously with a knee extensor are representative of joint movement disorder.

METHODS

Experiments were performed during remedial surgery of spastic cerebral palsy patients (n=6, 10 limbs tested). Condition-I: muscle forces were measured in flexed knee positions (120° and 90°) after activating the gracilis exclusively. Condition-II: knee angle-muscle force data were measured from 120° to full extension after activating the vastus medialis, simultaneously.

FINDINGS

Condition-II vs. I: Inter-antagonistic interaction did not consistently cause a gracilis force increase. Condition-II: Peak muscle force=mean 47.92 N (SD 22.08 N). Seven limbs showed availability of high muscle force in flexed knee positions (with minimally 84.8% of peak force at 120°). Knee angle-muscle force curves of four of them showed a local minimum followed by an increasing force (explained by an increasing passive force, indicating muscle lengths unfavorable for active force exertion). High active gracilis forces measured at flexed knee positions and narrow operational joint range of force exertion do indicate abnormality. The remainder of the limbs showed no such abnormality.

INTERPRETATION

Our hypothesis is confirmed for most, but not all limbs tested. Therefore, tested inter-antagonistic mechanical interaction can certainly, but not exclusively be a factor for abnormal mechanics of the spastic muscle.

Magnetic resonance imaging assessment of mechanical interactions between human lower leg muscles in vivo

Evidence on epimuscular myofascial force transmission (EMFT) was shown for undissected muscle in situ. We hypothesize that global length changes of gastrocnemius muscle-tendon complex in vivo will cause sizable and heterogeneous local strains within all muscles of the human lower leg. Our goal is to test this hypothesis. A method was developed and validated using high-resolution 3D magnetic resonance image sets and Demons nonrigid registration algorithm for performing large deformation analyses. Calculation of strain tensors per voxel in human muscles in vivo allowed quantifying local heterogeneous tissue deformations and volume changes. After hip and knee movement (Δ knee angle ≈ 25 deg) but without any ankle movement, local lengthening within m. gastrocnemius was shown to occur simultaneously with local shortening (maximally by +34.2% and -32.6%, respectively) at different locations. Moreover, similar local strains occur also within other muscles, despite being kept at constant muscle-tendon complex length. This is shown for synergistic m. soleus and deep flexors, as well as for antagonistic anterior crural and peroneal muscle groups: minimum peak lengthening and shortening equaled 23.3% and 25.54%, respectively despite global isometric conditions. These findings confirm our hypothesis and show that in vivo, muscles are in principle not independent mechanically.

Human spastic Gracilis muscle isometric forces measured intraoperatively as a function of knee angle show no abnormal muscular mechanics

BACKGROUND

To show whether mechanics of activated spastic muscle are representative of the functional deficiencies clearly apparent in the joints, our goal was to test the following hypotheses: (1) The muscle's joint range of force exertion is narrow, and (2) high muscle forces are available at low muscle length.

METHODS

During remedial surgery, we measured the forces of the Gracilis muscle of spastic cerebral palsy patients (n=7, 10 limbs tested) as a function of knee joint angle from flexion (120°) to full extension (0°).

FINDINGS

The spastic Gracilis exerted non-zero forces for the entire knee angles studied. For four limbs, the peak force was exerted at the highest length. For the remainder limbs, the closest knee angle of peak force exertion to 120° was 66°. Maximally 79.1%, and for most limbs only a much lower percentage (minimally 22.4%) of peak Gracilis force (mean 41.59N (SD 41.76N)) was available at 120° knee flexion. Moreover, a clinical metric was obtained showing that the occurrence of a contracture was not correlated significantly with key determinants of knee angle-Gracilis force characteristics.

INTERPRETATION

Our hypotheses are rejected: the spastic Gracilis has no narrow operational joint range of force exertion and no supreme active resistance capacity to stretch at low length. We conclude that if activated alone, spastic muscle shows no abnormal mechanics representative of joint movement disorder. Simultaneous stimulation of other muscles as in daily activities may change this situation.

BTX-A Administration to the Target Muscle Affects Forces of All Muscles Within an Intact Compartment and Epimuscular Myofascial Force Transmission

Measurement of forces of mono- and bi-articular muscles of an entire intact muscle compartment can allow for a comprehensive assessment of the effects of Botulinum toxin type A (BTX-A) both at and beyond the injection site, and in conditions close to those in vivo. The goal was to test the hypotheses that BTX-A affects (1) the forces of not only the injected but also the noninjected muscles of the compartment, and (2) epimuscular myofascial force transmission (EMFT). Two groups of Wistar rats were tested: Control (no BTX-A injected) and BTX (0.1 units of BTX-A were injected exclusively to the mid-belly of TA). Isometric forces were measured simultaneously at the distal tendons of the tibialis anterior (TA) at different lengths, the restrained extensor digitorum longus (EDL) and the extensor hallucis longus (EHL) muscles and at the proximal tendon of EDL. Five days post-injection, BTX-A did affect the total forces of all muscles significantly: (1) The TA force decreased differentially (by 46.6%–55.9%) for most lengths such that a significant negative correlation was found between force reductions and increased muscle length. The maximum TA force decreased by 47.3%. However, the muscle’s length range of force production did not change significantly. (2) Distal and proximal EDL forces decreased (on average by 67.8% and 62.9%, respectively). (3) The EHL force also decreased (on average by 9.2%). The passive forces of only the TA showed a significant increase at higher lengths. EMFT effects were shown for the control group: (1) at the shortest TA lengths, the EDL proximo-distal force differences were in favor of the distal force, which was reversed at higher lengths. (2) the EHL force measured at the shortest TA length decreased (by 34%) as a function of TA lengthening. After BTX-A exposure, such EMFT effects disappeared for the EDL, whereas they remained as profound for the EHL. Exposure to BTX-A does affect forces of all muscles operating in an intact compartment. For the BTX-A injected muscle, the reduction in muscle force becomes less pronounced at higher muscle lengths. BTX-A also has effects on EMFT, however, these effects are not uniform within the anterior crural compartment. Decreased forces of the noninjected synergistic muscles suggest the presence of unintended additional effects of BTX-A both for the targeted distal joint and for the nontargeted proximal joint.