The effect of immobilization on myotendinous junction: an ultrastructural, histochemical and immunohistochemical study

Mechanical loading is required for initiation of extracellular matrix deposition at the developing murine myotendinous junction

The myotendinous junction (MTJ) contributes to the generation of motion by connecting muscle to tendon. At the adult MTJ, a specialized extracellular matrix (ECM) is thought to contribute to the mechanical integrity of the muscle-tendon interface, but the factors that influence MTJ formation during mammalian development are unclear. Here, we combined 3D imaging and proteomics with murine models in which muscle contractility and patterning are disrupted to resolve morphological and compositional changes in the ECM during MTJ development. We found that MTJ-specific ECM deposition can be initiated via static loading due to growth; however, it required cyclic loading to develop a mature morphology. Furthermore, the MTJ can mature without the tendon terminating into cartilage. Based on these results, we describe a model wherein MTJ development depends on mechanical loading but not insertion into an enthesis.

Larger interface area at the human myotendinous junction in type 1 compared with type 2 muscle fibers

The myotendinous junction (MTJ) is structurally specialized to transmit force. The highly folded muscle membrane at the MTJ increases the contact area between muscle and tendon and potentially the load tolerance of the MTJ. Muscles with a high content of type II fibers are more often subject to strain injury compared with muscles with type I fibers. It is hypothesized that this is explained by a smaller interface area of MTJ in type II compared with type I muscle fibers. The aim was to investigate by confocal microscopy whether there is difference in the surface area at the MTJ between type I and II muscle fibers. Individual muscle fibers with an intact MTJ were isolated by microscopic dissection in samples from human semitendinosus, and they were labeled with antibodies against collagen XXII (indicating MTJ) and type I myosin (MHCI). Using a spinning disc confocal microscope, the MTJ from each fiber was scanned and subsequently reconstructed to a 3D-model. The interface area between muscle and tendon was calculated in type I and II fibers from these reconstructions. The MTJ was analyzed in 314 muscle fibers. Type I muscle fibers had a 22% larger MTJ interface area compared with type II fibers (p < 0.05), also when the area was normalized to fiber diameter. By the new method, it was possible to analyze the structure of the MTJ from a large number of human muscle fibers. The finding that the interface area between muscle and tendon is higher in type I compared with type II fibers suggests that type II fibers are less resistant to strain and therefore more susceptible to injury.

Aquatic Training after Joint Immobilization in Rats Promotes Adaptations in Myotendinous Junctions

The myotendinous junction (MTJ) is the muscle-tendon interface and constitutes an integrated mechanical unit to force transmission. Joint immobilization promotes muscle atrophy via disuse, while physical exercise can be used as an adaptative stimulus. In this study, we aimed to investigate the components of the MTJ and their adaptations and the associated elements triggered with aquatic training after joint immobilization. Forty-four male Wistar rats were divided into sedentary (SD), aquatic training (AT), immobilization (IM), and immobilization/aquatic training (IMAT) groups. The samples were processed to measure fiber area, nuclear fractal dimension, MTJ nuclear density, identification of telocytes, sarcomeres, and MTJ perimeter length. In the AT group, the maintenance of ultrastructure and elements in the MTJ region were observed; the IM group presented muscle atrophy effects with reduced MTJ perimeter; the IMAT group demonstrated that aquatic training after joint immobilization promotes benefits in the muscle fiber area and fractal dimension, in the MTJ region shows longer sarcomeres and MTJ perimeter. We identified the presence of telocytes in the MTJ region in all experimental groups. We concluded that aquatic training is an effective rehabilitation method after joint immobilization due to reduced muscle atrophy and regeneration effects on MTJ in rats.

Negative impact of disuse and unloading on tendon enthesis structure and function

Exposure to chronic skeletal muscle disuse and unloading that astronauts experience results in muscle deconditioning and bone remodeling. Tendons involved in the transmission of force from muscles to skeleton are also affected. Understanding the changes that occur in muscle, tendon, and bone is an essential step toward limiting or preventing the deleterious effects of chronic reduction in mechanical load. Numerous reviews have reported the effects of this reduction on both muscle and bone, and to a lesser extent on the tendon. However, none focused on the tendon enthesis, the tendon-to-bone attachment site. While the enthesis structure appears to be determined by mechanical stress, little is known about enthesis plasticity. Our review first looks at the relationship between entheses and mechanical stress, exploring how tensile and compressive loads determine and influence enthesis structure and composition. The second part of this review addresses the deleterious effects of skeletal muscle disuse and unloading on enthesis structure, composition, and function. We discuss the possibility that spaceflight-induced enthesis remodeling could impact both the capacity of the enthesis to withstand compressive stress and its potential weakness. Finally, we point out how altered compressive strength at entheses could expose astronauts to the risk of developing enthesopathies.

The Myotendinous Junction-A Vulnerable Companion in Sports. A Narrative Review

The incidence of strain injuries continues to be high in many popular sports, especially hamstring strain injuries in football, despite a documented important effect of eccentric exercise to prevent strains. Studies investigating the anatomical properties of these injuries in humans are sparse. The majority of strains are seen at the interface between muscle fibers and tendon: the myotendinous junction (MTJ). It has a unique morphology with a highly folded muscle membrane filled with invaginations of collagen fibrils from the tendon, establishing an increased area of force transmission between muscle and tendon. There is a very high rate of remodeling of the muscle cells approaching the MTJ, but little is known about how the tissue adapts to exercise and which structural changes heavy eccentric exercise may introduce. This review summarizes the current knowledge about the anatomy, composition and adaptability of the MTJ, and discusses reasons why strain injuries can be prevented by eccentric exercise.

In the human, true myocutaneous junctions of skeletal muscle fibers are limited to the face

Within the panniculus carnosus‐associated skeletal muscles in the human, the palmaris brevis and the platysma showed myotendinous/myofascial junctions with clear distance to the corium and the specific connection collagen type XXII. The orbicularis oris muscle, in contrast, contained bundles of striated muscle fibers reaching the corium at two distinct levels: the predominant inner ending was connected to the elastic network of the inner corium and the outer ending was within the more superficial collagen network. At both locations, the striated muscle fibers showed brush‐like cytoplasmic protrusions connecting a network which was not oriented toward the muscle fibers. Collagen type XXII was not present.

Effects of 12 Weeks of Progressive Early Active Exercise Therapy After Surgical Rotator Cuff Repair: 12 Weeks and 1-Year Results From the CUT-N-MOVE Randomized Controlled Trial

BACKGROUND

Traumatic full-thickness rotator cuff tears are typically managed surgically, followed by rehabilitation, but the load progression to reach an optimal clinical outcome during postoperative rehabilitation is unknown.

PURPOSE

To evaluate whether there was a superior effect of 12 weeks of progressive active exercise therapy on shoulder function, pain, and quality of life compared with usual care.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

Patients with surgically repaired traumatic full-thickness rotator cuff tears were recruited from 2 orthopaedic departments and randomized to progressive active exercise therapy (PR) or limited passive exercise therapy (UC [usual care]). The primary outcome was the change in the Western Ontario Rotator Cuff Index (WORC) score between groups from before surgery to 12 weeks after surgery. Secondary outcomes included changes in the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire score, pain, range of motion, and strength. Adverse events were registered during the intervention period.

RESULTS

A total of 82 patients were randomized to the PR (n = 41) or UC (n = 41) group. All 82 patients (100%) participated in the 12-week assessment and 79 in the 1-year follow-up. At 12 weeks, there was no significant difference between the groups in the change in the WORC score from baseline adjusted for age, sex, and center (physical symptoms: P = .834; sports and recreation: P = .723; work: P = .541; lifestyle: P = .508; emotions: P = .568). Additionally, there was no between-group difference for the secondary outcomes including the WORC score at 1 year and the DASH score, pain, range of motion, and strength at 12 weeks and 1 year. Both groups showed significant improvements over time in all outcomes. In total, there were 13 retears (16%) at 1-year follow-up: 6 in the PR group and 7 in the UC group.

CONCLUSION

PR did not result in superior patient-reported and objective outcomes compared with UC at either short- or long-term follow-up (12 weeks and 1 year).

REGISTRATION

NCT02969135 (ClinicalTrials.gov identifier).

Shear Wave Elastographic Study of the Myotendinous Junction of the Medial Gastrocnemius: Normal Patterns and Dynamic Evaluation

OBJECTIVES

The myotendinous junction (MTJ) represents a specialized anatomic region through which the contractile strength is transmitted from the muscle to the tendon. The integrity of this region is essential to permit force transmission and to optimize energy expenditure during walking, running, and globally for human movement. We evaluated the MTJ with shear wave elastography to assess its elasticity variation during a functional test.

METHODS

Forty professional soccer players were enrolled in the study. Shear wave elastography was performed at the level of the medial gastrocnemius MTJ both in a resting position and during a standing calf rise position to assess functional contraction.

RESULTS

All 40 participants were male, aged between 18 and 38 years (mean age, 25 years). The results of the elastographic study showed mean stiffness values ± SD of 4.19 ± 0.86 m/s for the right medial gastrocnemius and 4.20 ± 0.87 m/s for the left medial gastrocnemius with the muscle relaxed. During contraction, the stiffness values were 8.33 ± 0.5 m/s for the right medial gastrocnemius and 8.30 ± 0.48 m/s for the left medial gastrocnemius.

CONCLUSIONS

Our study showed an increase of stiffness at the level of the MTJ during muscle contraction. This result is in line with the physiologic stiffening of the MTJ to resist the high level of force applied during muscle contraction. Shear wave elastography could be a useful method to assess the characteristics of the MTJ under both physiologic and pathologic conditions.

Rectus femoris myotendinous lesion treated with PRP: a case report

BACKGROUND AND AIM OF WORK

Musculoskeletal injuries are the most common cause of severe, chronic pain and physical disability for the majority of all sport-related injuries. Platelet-rich plasma is being used more frequently to promote healing of muscle injuries. We report a case of 39 years old non professional soccer player who came to our attention for a quadriceps muscle pain onset after kicking the ball during a match.

METHODS

Clinical and instrumental evaluation revealed a myotendinous junction rupture of the rectus femoris with retraction of 1.5 cm from the anterior inferior iliac spine. We decided to treat the patient with PRP ultrasound guided injections and a specific rehabilitation protocol.

RESULTS

Clinical evaluation 45 days following the end of the treatment showed the resolution of the pain and the full recovery of strength and range of motion. Muscle healing was documented by magnetic resonance imaging.

CONCLUSIONS

Even if the role of PRP in muscle injury is not still clear, the result observed confirms that it could be used in the treatment of muscle lesions.

Progressive early passive and active exercise therapy after surgical rotator cuff repair - study protocol for a randomized controlled trial (the CUT-N-MOVE trial)

Background

Rotator cuff tear is a common cause of shoulder disability and results in patients predominantly complaining of pain and loss of motion and strength. Traumatic rotator cuff tears are typically managed surgically followed by ~ 20 weeks of rehabilitation. However, the timing and intensity of the postoperative rehabilitation strategy required to reach an optimal clinical outcome is unknown. Early controlled and gradually increased tendon loading has been suggested to positively influence tendon healing and recovery. The aim of this trial is therefore to examine the effect of a progressive rehabilitation strategy on pain, physical function and quality of life compared to usual care (that limits tendon loading in the early postoperative phase) in patients who have a rotator cuff repair of a traumatic tear.

Methods

The current study is a randomized, controlled, outcome-assessor blinded, multicenter, superiority trial with a two-group paralleled design. A total of 100 patients with surgically repaired traumatic rotator cuff tears will be recruited from up to three orthopedic departments in Denmark, and randomized to either a progressive early passive and active movement program or a limited early passive movement program (usual care). The primary outcome measure will be the change from pre-surgery to 12 weeks post-surgery in the Western Ontario Rotator Cuff Index questionnaire. Secondary outcomes include the Disabilities Arm, Shoulder and Hand questionnaire (DASH), range of motion, strength and tendon healing characteristics from ultrasound measurements at 12 months follow up.

Discussion

We hypothesized that patients who receive the progressive rehabilitation strategy will benefit more with respect to pain reduction, physical function and quality of life than those who receive care as usual. If this is confirmed our study can be used clinically to enhance the recovery of patients with traumatic rotator cuff tear.

Trial registration

ClinicalTrials.gov, NCT02969135. Registered on 15 November 2016.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-2839-5) contains supplementary material, which is available to authorized users.

Myotendinous junction plasticity in aged ovariectomized rats submitted to aquatic training

The study aims to describe the tissue plasticity of MTJ through the morphological analysis of MTJ soleus in ovariectomized aged female Wistar rats submitted to aquatic training. Forty aged Wistar rats, 1 year and 2 months of age, were divided into four groups: sedentary (S), trained (T), ovariectomized (O), and trained/ovariectomized (OT). Employing the transmission electron microscopy, the ultrastructural and morphometric elements were revealed. In the S group, changes in morphological characteristics as a consequence of the aging process were seen, demonstrated by the conical shape of the muscle cell extremity, a large area with collagen deposit, and misalignment of sarcomeres in series. The T group presented ample adjustments when revealed the organization of MTJ, through the increase of the contact area and greater lengths of sarcoplasmatic invaginations and evaginations. The O group revealed extensive tissue disorganization with muscle atrophy, reduction of MTJ contact area, and consequently, changes in sarcoplasmatic invaginations and evaginations. The OT group demonstrated extensive remodeling with restructuring MTJ through the increase of tissue contact area, extensive organization, parallel arrangement, and increased length of sarcoplasmatic invaginations and evaginations. The distal sarcomeres presented higher lengths compared to the proximal sarcomeres in both the groups. We conclude that aquatic training was effective in the organization and structural remodeling of the myotendinous interface of ovariectomized aged rats. There was a greater area of contact, and consequently, greater resistance in the myotendinous interface promoting a lower predisposition to injuries.

Achilles Tendon Vascularization of Proximal, Medial, and Distal Portion Before and After Partial Lesion in Rats Treated with Phototherapy

BACKGROUND

The Achilles tendon is one of the tendons most commonly injured by microtraumas and overuse during sports practice. This tendon is especially fragile because of the low blood supply in its central part. Nevertheless, the literature does not offer enough scientific support to explain the composition and vascular dynamic of animal tendons, despite the relevance of being able to observe if the animal tendon undergoes the same processes of vascularization in different regions, as occurs in humans.

METHODS

We used 28 rats weighing 280 ± 20 g, which were divided into four groups with seven animals each (control, sham, 830 nm, 660 nm). The laser parameters were: power output 60 mW for both lasers, 40 J/cm(2) of energy density, total energy 1.1 J, power density 2.14 W/cm(2), and application time 18.6 sec. This study evaluated the vascular constitution of healthy and injured calcaneous tendons. The tendons of each animal were processed to be embedded in Paraplast and, after that, they were divided into three parts: proximal, medial, and distal. Afterwards, they were cut in slices of 6 μm were made, then they were stained with hematoxylin and eosin. Using an ocular lens reticulated with magnification × 400, we analyzed the number and the area density of the blood vessels using morphometric methods. Data were analyzed with the Shapiro-Wilk test, followed by Tukey, considering p as <0.05.

RESULTS

The area density and the number of blood vessels in the proximal part were 36% and 42%, respectively, of the values found in the medial part. The distal part had 64% more vessels and 52.8% more area density (p < 0.05) than the medial part.

CONCLUSIONS

Low-level laser therapy (LLLT) had no effect on the studied parameters. The vascularization of rat tendon is similar to that of humans, which contributes to the studies of therapies that have been applied in humans.

Effects of detraining on motor unit potential area, muscle function and physical performance based on CNTF gene polymorphism

[Purpose]

The purpose of this study was to identify the effect of detraining on motor unit potential area (SMUP), muscular function and physical performance, according to CNTF gene polymorphism.

[Methods]

For this study, GG (normal homozygote, n = 8) group and GA + AA (mutation heterozygote and homozygote, n = 10) group were divided by CNTF gene polymorphism and both groups were performed detraining for 4 weeks. The data was analyzed by two-way repeated measures ANOVA for verifying the differences between two groups and interaction using SPSS (ver. 20.0) statistical program.

[Results]

The results were as follows. First, changes in body composition were measured but there was no significant interaction effect between time and group. Seconds, changes in SMUP were measured by SEMG. Interaction effect between time and group was found lateral vastus during isokinetic exercise of 180°/sec (p < .05). Third, changes in isokinetic muscle strength of 60°/sec and 180°/sec were measured but there was no significant interaction effect. Fourth, significant statistical differences were not showed changes of sports performance after detraining.

[Conclusion]

In conclusion, there were no significantly differences between GG and GA + AA group after detraining, therefore, further study will be considered a matter in various its interventions such as serum levels of CNTF and changes in receptors and muscle fiber types.

Quantitative analysis of muscle histologic method in rodent facial nerve injury

OBJECTIVE

To describe denervation features of facial musculature following facial nerve injury in a rodent model.

METHODS

Six Wistar-Hannover rats underwent unilateral transection and immediate repair of the facial nerve. After 8 weeks, muscular bundles consisting of dilator naris and levator labii superioris from both sides were analyzed for mean muscle cell diameter and the percentage of muscle cell cross-sectional area using image processing software. The atrophic features of facial muscles were quantified and compared with the contralateral, healthy side of the face.

RESULTS

Weekly postoperative whisking assessment demonstrated the anticipated course of recovery. We observed significant differences between the normal side and the manipulated side, respectively, in the percentage of muscle specimen cross-sectional area attributable to muscle cell profiles (57% vs 29%; P = .006) and total fiber counts (1346 vs 794; P = .02). The mean cross-sectional area of individual muscle fibers was higher on the normal side (1129 vs 928 μm2; P = .39); however, this difference was statistically nonsignificant.

CONCLUSION

The objective, quantitative measures of muscle microstructure used in this report provide a valuable point of comparison for whisking function and electrophysiologic measures and can be used in future studies to assess muscle atrophic features associated with facial nerve injury and repair techniques.

Ultrastructural features of the myotendinous junction of the sternomastoid muscle in Wistar rats: from newborn to aging

The myotendinous junction (MTJ) is a major area for transmitting force from the skeletal muscle system and acts in joint position and stabilization. This study aimed to use transmission electron microscopy to describe the ultrastructural features of the MTJ of the sternomastoid muscle in Wistar rats from newborn to formation during adulthood and possible changes with aging. Ultrastructural features of the MTJ from the newborn group revealed pattern during development with interactions between muscle cells and extracellular matrix elements with thin folds in the sarcolemma and high cellular activity evidenced through numerous oval mitochondria groupings. The adult group had classical morphological features of the MTJ, with folds in the sarcolemma forming long projections called "finger-like processes" and sarcoplasmic invaginations. Sarcomeres were aligned in series, showing mitochondria near the Z line in groupings between collagen fiber bundles. The old group had altered "finger-like processes," thickened in both levels of sarcoplasmic invaginations and in central connections with the lateral junctions. We conclude that the MTJ undergoes intense activity from newborn to its formation during adulthood. With increasing age, changes to the MTJ were observed in the shapes of the invaginations and "finger-like processes" due to hypoactivity, potentially compromising force transmission and joint stability.

How physical exercise changes rat myotendinous junctions: an ultrastructural study

Myotendinous junctions can be easily injured by overloading or trauma, and exercise training may be a way of increasing their resistance to mechanical stress. To this end, we examined herein the morphological changes induced by moderate exercise training in the myotendinous junctions of extensor digitorum longus and gastrocnemius muscles in rats. Twelve Sprague-Dawley rats were used in this investigation. Six of them were trained to run on a treadmill for 1 h/day, 3 days/week over 10 weeks in order for them to achieve a running rate of 25 m/min at the end of the training period. Six age-matched sedentary rats were used as controls. The rats were sacrificed 24 h after the final training session, and the extensor digitorum longum (EDL) and the gastrocnemium were excised; the myotendinous junctions (MTJ) were then prepared and observed with electron microscopy. Digitation branching was evaluated by counting the bifurcations in the MTJ protrusions. Our observations indicate that exercise does indeed induce changes in MTJ morphology. In both muscles the number of bifurcated interdigitations increased significantly, as well as, in gastrocnemius, the branching of the finger-like processes. It was demonstrated that the MTJ is able to adapt to an increase in tensile force by enlarging the muscle-tendon contact area and, consequently, mechanical resistance.

Myofeedback training and intensive muscular strength training to decrease pain and improve work ability among female workers on long-term sick leave with neck pain: a randomized controlled trial

Abstract

The theoretical framework is that muscle tension in the neck is related to insufficient muscular rest and is a risk factor for chronic pain and reduced work ability. Promoting muscle strength and muscle rest may increase work ability and reduce neck pain.

Objectives

To test whether myofeedback training or intensive strength training leads to decreased pain and increased work ability in women on long-term sick leave.

Methods

This is a randomized controlled trial of two 1-month interventions with myofeedback or muscular strength training in the home environment. Female human service organization workers (n = 60) on long-term (>60 days) sick leave and with chronic neck pain were followed with self-reported and laboratory-observed data of health, pain, muscular activation, and work ability, at baseline, immediately after the intervention and 3 months after baseline.

Results

For both intervention groups, pain was lowered over time compared with the control group. Decreased pain and muscular activity was associated with increased self-rated work ability and with laboratory-observed work ability at 3-month follow-up. Decreased pain was also associated with increased self-rated work ability at 1-month follow-up. Muscular strength training was associated with increased self-rated work ability and mental health. Myofeedback was associated with increased observed work ability and self- rated vitality.

Conclusions

The two interventions showed positive results, suggesting that they could be developed for use in health care practice to address pain and work ability. The intensive muscular strength training program, which is both easy to conduct at home and easy to coach, was associated with increased work ability.

Ultrastructure of the myotendinous junction of the medial pterygoid muscle of adult and aged Wistar rats

The myotendon junction (MTJ) is a specialised area into the muscle fibers where the sarcoplasmic membranes connect to the collagen fibers bundles. There are few data about plasticity of the MTJ in aging processes. The aim of this study is to analyse the ultrastructure characteristics of MTJ of medial pterygoid muscle of adult and aged rats. Employing the transmission electron microscopy method, twenty male rats Wistar (Rattus norvegicus) were divided into two groups: A (n=10) with 12 months of age; B (n=10) 24 months of age. The animals were anaesthetised with overdose the urethane (3g/kg, i.p.) and sacrified during the perfusion with modified Karnovsky solution. The specimens were post-fixed in a 1% osmium tetroxide solution, dehydrated in ascending concentration of ethanol and embedded in Spurr resin. The thin sections, of 90 nm thick, were counterstained with uranyl acetate and lead citrate solution, and examined in a Jeol 1010 transmission electron microscope. The fine structure of the MTJ of group A revealed the defined interdigitations and disposed in several levels of deep formations containing the collagen fibers. In the group B, such structures did not observed, detecting the projections irregular in shape, and large of extra matrix with in aspect of remodelling. In conclusion it was possible to identify the plasticity of MTJ in the group B which presented several morphological alterations comparing to the adult animals. These data of group B suggested the occurrence of aging processes in the MTJ in rats.

Bioreactors for guiding muscle tissue growth and development

Muscle tissue bioreactors are devices which are employed to guide and monitor the development of engineered muscle tissue. These devices have a modern history that can be traced back more than a century, because the key elements of muscle tissue bioreactors have been studied for a very long time. These include barrier isolation and culture of cells, tissues and organs after isolation from a host organism; the provision of various stimuli intended to promote growth and maintain the muscle, such as electrical and mechanical stimulation; and the provision of a perfusate such as culture media or blood derived substances. An accurate appraisal of our current progress in the development of muscle bioreactors can only be made in the context of the history of this endeavor. Modern efforts tend to focus more upon the use of computer control and the application of mechanical strain as a stimulus, as well as substrate surface modifications to induce cellular organization at the early stages of culture of isolated muscle cells.

Ultrastructural changes at the myotendinous junction induced by exercise

BACKGROUND

Although exercise is believed to reduce the risk of rupture of the myotendinous junction, exercise-induced structural changes in this region have not been studied. We examined exercise-induced ultrastructural changes in the myotendinous junction of the lower legs in rats.

METHODS

Ten adult male LETO rats were used. Five rats were randomly placed in the Exercise group; the remaining five were used as controls and placed in the non-Exercise group. Running exercise was performed every day for 4 weeks. The tibialis anterior and gastrocnemius muscles were then removed from both legs from each animal in the two groups. The specimens were subsequently examined by transmission electron microscopy (TEM). Numerous finger-like processes were observed at the myotendinous junction. The changes in frequency of branching of the finger-like process (the number of times one finger-like process branched) and the direction of the processes (the angle of the major axis of a finger-like process to the longitudinal direction of the muscle fiber) were studied. To evaluate the two indicators above, each 10 fingerlike process was randomly and separately selected from the tibialis anterior and gastrocnemius muscles of rats, providing 50 finger-like processes of both muscles for evaluation per group.

RESULTS

In terms of the frequency of branching of the fingerlike processes, the mean values obtained in the non-Exercise group were 0.04 and 0.18 times, respectively, in the tibialis anterior and gastrocnemius muscles and were 0.38 and 1.16 times, respectively, in these two muscles in the Exercise group. Regarding the direction of the finger-like processes, the values were 4.1 degrees and 3.6 degrees, respectively in the non-Exercise group and 10.4 degrees and 14.5 degrees , respectively in the Exercise group. The differences between the two animal groups were significant.

CONCLUSIONS

Morphological changes in the myotendinous junction occurred as an adaptation to tension increased by exercise.

Structural and biochemical analysis of the effect of immobilization followed by stretching on the calcaneal tendon of rats

Little is known about the stretching effects on the biochemical and morphological features of tendons submitted to a long period of immobilization. Our purpose was to evaluate the response of rat tendons to stretching procedures after immobilization. The animals were separated into five experimental groups: GI--control of immobilized and euthanized animals; GII--immobilized and euthanized animals; GIII--control of immobilized animals and afterward stretched or allowed free cage activity; GIV--immobilized and stretched animals; and GV--immobilized and allowed free cage activity. Analysis in SDS-PAGE showed no remarkable differences among the groups, but a prominent collagen band was observed in GV, as compared to GIV and the control group, both in the compression and tension regions. Hydroxyproline content was highest in the compression region of GII. No differences among the groups were observed in the tension region. In regard to the concentration of noncollagenous proteins, differences were detected only in the tension region, where larger concentrations were found in the GII. When GII and GIV were compared, highest values were found in the GII. A more abundant presence of sulfated glycosaminoglycans, especially chondroitin sulfate, was detected in GIV, at the compression region of tendons. The presence of dermatan sulfate was outstanding in the compression and tension regions of the GII and GV groups. In the Ponceau SS stained sections, analyzed under polarization microscopy, GII exhibited the highest disorganization of the collagen bundles, partially recovered after stretching or with only remobilization. Our results indicate that a revision in the stretching procedures, in terms of duration and periodicity of the sessions, could benefit the efficiency of the stretching in cases of previous immobilization of tendons.

Structural remodeling of unweighted soleus myotendinous junction in monkey

This study describes the morphology of the soleus myotendinous junction (MTJ) in the Rhesus monkey. Ultrastructural observations revealed a structural complexity that probably reflects functional adaptations. We also studied ultrastructural modifications of the MTJ in response to 14 days of hypokinesia and microgravity (Bion 11 mission). The reduced limb mobility of the animals, placed in a safety seat aboard the satellite, induced a sarcolemmal remodeling that was enhanced by the microgravity conditions. Signs of MTJ remodeling such as alterations of contractile apparatus and myofilament-anchoring structures, T-tubule dilation, and autophagic vacuoles could be ascribed to the microgravity.

Pullout forces of sutures in muscle lacerations

The purpose of this study was to determine if complex suture techniques had higher pullout forces from muscle tissue than conventional stitching. Using transected cadaver muscle bellies, we performed repairs with various suture techniques and measured pullout forces. Epimyseal repair with conventional stitches (Kessler, figure eight, horizontal mattress) was inferior to complex stitches (modified Mason-Allen, perimeter). The combined complex stitches (perimeter and Mason-Allen) were strongest. Conventional stitches failed longitudinally through the muscle, whereas complex stitches failed transversely across the muscle. The complex combination of perimeter and Mason-Allen stitches had superior pullout resistance compared to conventional stitches.

Pathophysiology of spastic paresis. I: Paresis and soft tissue changes

Spastic paresis follows chronic disruption of the central execution of volitional command. Motor function in patients with spastic paresis is subjected over time to three fundamental insults, of which the last two are avoidable: (1) the neural insult itself, which causes paresis, i.e., reduced voluntary motor unit recruitment; (2) the relative immobilization of the paretic body part, commonly imposed by the current care environment, which causes adaptive shortening of the muscles left in a shortened position and joint contracture; and (3) the chronic disuse of the paretic body part, which is typically self-imposed in most patients. Chronic disuse causes plastic rearrangements in the higher centers that further reduce the ability to voluntarily recruit motor units, i.e., that aggravate baseline paresis. Part I of this review focuses on the pathophysiology of the first two factors causing motor impairment in spastic paresis: the vicious cycle of paresis-disuse-paresis and the contracture in soft tissues.

The role of epimysium in suturing skeletal muscle lacerations

BACKGROUND

Direct muscle trauma is a common and disabling clinical problem. Surgical muscle repair is difficult to evaluate because reliable repair techniques have not been established scientifically. The purpose of this study was to assess the biomechanical properties of epimysium, the collagenous tissue sheath that surrounds muscles in the body.

STUDY DESIGN

We surgically repaired transected porcine muscle bellies with and without epimysium. For both groups, 25 figure-eight stitches in lacerated quadriceps bellies from a euthanatized pig were loaded under tension on a biomechanical machine (model 8521S, Instron Company). Maximum loads and strains were measured and mechanisms of failure recorded.

RESULTS

The mean load for repairs with epimysium (25.1 N) was significantly higher (p = 0.034) than that for repairs without epimysium (21.2 N). The mean strain for repairs with epimysium (10.4%) was significantly higher (p < 0.001) than that for repairs without epimysium (7.3%). The mechanisms of failure were also different. Among epimysium repairs, 15 stitches avulsed muscle transversely, and 10 stitches tore out longitudinally from the muscle. In the nonepimysium group, 1 suture avulsed muscle and 24 sutures tore out. Muscle was the weakest element in each test.

CONCLUSIONS

These data showed that epimysium incorporation into suturing improves the capacity of repairs to bear force. These findings fill a knowledge gap and may improve outcomes of muscle suturing. By focusing the experiment on biomechanical properties of muscle stitching, this study showed the key role epimysium plays in muscle suturing.

A home-based two-year strength training period in early rheumatoid arthritis led to good long-term compliance: a five-year followup

OBJECTIVE

To evaluate the impact of a 2-year home-based strength-training program on physical function in patients with early rheumatoid arthritis (RA) after a subsequent 3-year followup.

METHODS

Seventy patients with early RA were randomized to perform either strength training (experimental group [EG]) or range-of-motion exercises (control group [CG]). Maximal strength values were recorded by dynamometers. The Modified Disease Activity Score (DAS28), pain, Health Assessment Questionnaire (HAQ), walking speed, and stair-climbing speed were also measured.

RESULTS

The maximum strength of assessed muscle groups increased by 19-59% in the EG during the training period and remained at the reached level throughout the subsequent 3 years. Muscle strength improved in the CG by 1-31%, but less compared with the EG. During the 2-year training period, DAS28 decreased by 50% and 45% and pain by 67% and 39% in the EG and CG, respectively. The differences in muscle strength, DAS28, and HAQ were significantly in favor of the EG both at the 2-year and 5-year followup assessments.

CONCLUSIONS

The improvements achieved during the 2-year strength-training period were sustained for 3 years in patients with early RA.

Organization and distribution of intramuscular connective tissue in normal and immobilized skeletal muscles. An immunohistochemical, polarization and scanning electron microscopic study

Collagen fiber network is a major contributor to the coherence and tensile strength of normal skeletal muscle. Despite the well-recognized importance of the intramuscular connective tissue to the normal integrity and function of the skeletal muscle, the specific architecture including the location and three-dimensional orientation of the intramuscular connective tissue within the muscle tissue is poorly described. The structure of the intramuscular connective tissue was studied by immunohistochemistry, polarization microscopy (the crimp length and angle of the collagen fibers) and scanning electron microscope (SEM) in rat skeletal muscles (gastrocnemius, soleus and tibialis anterior) in normal situation and after 3 weeks of disuse (immobilization). Three separate networks of collagen fibers were distinguished by SEM in the normal endomysium; fibers running longitudinally on the surface of the muscle fibers (the main collagen orientation), fibers running perpendicularly to the long axis of the muscle fibers and having contacts with adjacent muscle fibers, and fibers attached to the intramuscular nerves and arteries. Similarly, the SEM analysis also disclosed three distinct collagen fiber networks running in different directions in the perimysium, but, contrary to the endomysium, the main fiber orientation could not be established. Immobilization resulted in a marked increase in the endo- and perimysial connective tissue, the majority of the increased endomysial collagen being deposited directly on the sarcolemma of the muscle cells. Immobilization also resulted in substantial increase in the number of perpendicularly oriented collagen fibers with contacts to two adjacent muscle fibers in the endomysium. Further, immobilization clearly disturbed the normal structure of the endomysium making it impossible to distinguish the various networks of fibers from each other. In the perimysium, immobilization-induced changes were similar, the number of longitudinally oriented collagen fibers was increased, the connective tissue was very dense, the number of irregularly oriented collagen fibers was markedly increased, and consequently, the different networks of collagen fibers could not be distinguished from each other. Of the three studied intact muscles, the crimp angle of the collagen fibers was lowest in the soleus and highest in the gastrocnemius muscle, and the crimp angle decreased over 10% in all muscles after the immobilization-period. Altogether, the above described quantitative and qualitative changes in the intramuscular connective tissue are likely to contribute to the deteriorated function and biomechanical properties of the immobilized skeletal muscle.

Application of passive stretch and its implications for muscle fibers

To increase range of motion, physical therapists frequently use passive stretch as a means of gaining increased excursion around a joint. In addition to clinical studies showing effectiveness, thereby supporting evidence-based practice, the basic sciences can provide an explanation how a technique might work once a technique is known to be effective. The goal of this article is to review the potential cellular events that may occur when muscle fibers are stretched passively. A biomechanical example of passive stretch applied to the ankle is used to provide a means to discuss passive stretch at the cellular and molecular levels. The implications of passive stretch on muscle fibers and the related connective tissue are discussed with respect to tissue biomechanics. Emphasis is placed on structures that are potentially involved in the sensing and signal transduction of stretch, and the mechanisms that may result in myofibrillogenesis are explored.

Tenology: a new frontier

Tendons were long given little recognition by rheumatologists. Yet, their complex structure and distinctive functional characteristics have been demonstrated by an abundance of histological, biochemical, and biomechanical studies: clearly, tendons are not inert cords linking muscles to bones. The current wave of popularity of sporting activities has brought with it an epidemic of disorders of the tendons, thus focusing attention on these structures. At the same time, modern imaging techniques (particularly magnetic resonance imaging) have allowed clinicians to improve their knowledge of and classification schemes fortendon disorders. Several risk factors, including technical factors, have been identified, so that preventive treatment is now as important as curative treatment. Culture systems for tenocytes (the specialized fibroblasts found in tendons) are now available and have been used to develop experimental models, paving the way for significant advances in tendon repair techniques.

Increase in rat soleus myotendinous interface after a 14-d spaceflight

Myotendinous junctions (MTJs) transmit contractile force from skeletal muscles to tendons. The effects of a 14-d spaceflight on MTJ were studied in the soleus muscle of male adult Sprague Dawley rats by transmission electron microscopy and histomorphometric techniques. We showed that the length of the junctional membrane relative to the muscle fiber diameter increased by 58% after 14 d of spaceflight. This increase accompanies morphological changes at MTJs. The flight MTJs appeared more shredded. The ends of the muscle fibers exhibited T tubule dilatation, swollen mitochondria, Z-disk streaming, loss of myofilaments, a thinning down of subplasmalemmal densitites, multivesicular bodies and signs of junctional membrane and basal lamina remodelling. The ultrastructural observations suggest that the increase in myotendinous interface could result from the extracellular matrix spreading into remodelling muscle fiber, whereas the constraints related to unloading were reduced by spaceflight conditions.

Biochemistry and biomechanics of healing tendon: Part I. Effects of rigid plaster casts and functional casts

PURPOSE

Traditional treatment of surgically repaired Achilles tendons includes complete immobilization of the joint in rigid casts for 6 to 8 wk. We tested the use of functional polyurethane casts as an alternative to rigid plaster casts after experimental tenotomy and repair of the rabbit Achilles tendon.

METHODS

After repair the limbs of 15 experimental rabbits were immobilized in a functional polyurethane cast for 15 d, while those of 14 controls were immobilized in traditional rigid plaster casts for the same period.

RESULTS

Functional casting resulted in a 60% increase in total collagen in the neotendon compared with that in rigid casting (P < 0.05). Mature collagen cross-links declined 8% in the tendons with functional casts. The biomechanical parameters of the tendons changed with functional casting, showing a 20% increase in maximum load and 21% increase in maximum stress.

CONCLUSIONS

These changes were noted without any cases of tendon re-rupture in either type of cast. Thus, functional casting following surgery of Achilles tendons appears to improve healing without significant risks of re-rupture.

Effects of immobilization and subsequent low- and high-intensity exercise on morphology of rat calf muscles

After a cast immobilization of 3 weeks, the effects of 4-week remobilization by free cage activity or treadmill running on the morphology of the rat soleus and gastrocnemius muscles were studied. The studied morphometric parameters were: percentage volume of intramuscular connective tissue, capillary density, muscle fiber size, number of fibers with a pathological structural alteration, and fiber type distribution. In both muscles, immobilization of 3 weeks produced a significant increase in the connective tissue volume and number of fibers with pathological alterations, with a similar decrease in the capillary number and fiber size. At the same time, the relative amount of type I fibers decreased and type IIA fibers increased. Free remobilization and especially intensified remobilization by treadmill running significantly restored these values towards controls. These findings indicate that in rat soleus and gastrocnemius muscles immobilization-induced accumulation of intramuscular connective tissue, capillary loss, reduction in fiber size, accumulation of fibers with pathological structural alterations, and changes in fiber type distribution are to a great extent reversible phenomena, especially if remobilization is intensified by physical training. In clinical practice, this suggests that in patients with musculoskeletal injuries the postimmobilization rehabilitation should be early and effective.

Respective effects of hindlimb suspension, confinement and spaceflight on myotendinous junction ultrastructure

This study compares the effects of 14-day confinement and spaceflight with the respective effects of 8, 18 and 29-day hindlimb suspension on rat soleus and plantaris MTJ ultrastructure. Independently of the experimental situation, greater morphological changes were observed in the soleus as compared to the plantaris MTJ. 18 days of suspension and 14 days of confinement resulted in ultrastructural modifications of the digit-like processes in the soleus MTJ. Additional changes were observed in the myofibrils, microtendon and tendon after 29 days of suspension and 4 days of spaceflight. These results emphasize the influence of the intensity and duration of the muscle loading on the MTJ ultrastructure.

Vascular density at the myotendinous junction of the rat gastrocnemius muscle after immobilization and remobilization

Muscle injuries often occur at or near the myotendinous junction. Immobilization decreases the tensile strength of the myotendinous junction and predisposes it to strain injury. However, there are no data available on whether physical training or remobilization can lower the susceptibility of the myotendinous junction to strain injuries. We investigated the effects of three different remobilization programs (8 weeks) after immobilization (3 weeks) by evaluating the vascular density at the myotendinous junction of the rat gastrocnemius muscle. The myotendinous junctions had a portal system vascularity, or capillary-arteriole-capillary system, which probably protects the blood supply against pathologic conditions. The vascular density at the myotendinous junction decreased about 30% after immobilization (P < 0.001). After free cage remobilization for 8 weeks, the mean vascular density returned to the level of the controls. After progressively increasing running programs the vascular density was slightly higher in the immobilized myotendinous junction and about 50% higher than controls in the contralateral myotendinous junction (P < 0.001). The capacity of the vascular bed of the rat myotendinous junction to recover from immobilization atrophy seems to be good. Progressively increasing physical training improves the process of revascularization and probably protects an injured and immobilized muscle from reinjury.

Changes in geometry of actively shortening unipennate rat gastrocnemius muscle

Muscle geometry of the unipennate medial gastrocnemius (GM) muscle of the rat was examined with photographic techniques during isometric contractions at different muscle lengths. It was found that the length of fibers in different regions of GM differs significantly, and proximal aponeurosis length varies significantly from distal aponeurosis length; the angle of the aponeurosis with the muscular action differs significantly among regions at short muscle lengths (full contraction). These data support the idea that the unipennate GM cannot be represented by a parallelogram in a two-dimensional analysis. As the muscle shortens, the area of the mid-longitudinal plane of the GM decreases by 24%, a decrease that may be explained by assuming fiber diameter to increase in all directions. The angle between fiber and aponeurosis is determined by more than fiber length. Hence, such important assumptions as a parallelogram with constant area and fiber angle gamma changes determined by fiber length changes, frequently used in the theoretical analysis of the morphological mechanism of unipennate muscle contraction, do not hold for the unipennate GM of the rat. Length of the sarcomere within the mid-longitudinal plane of GM varies from 1.92 to 2.14 microns among the different muscle regions at muscle optimum length (length at which force production is highest), whereas shortening to 6 mm less than optimum length produces a range of sarcomere lengths from 0.89 to 1.52 microns. These data suggest that fibers located in different regions of the GM reach their optimum and slack lengths at various muscle lengths.