Injuries in Muscle-Tendon-Bone Units: A Systematic Review Considering the Role of Passive Tissue Fatigue

The challenge of thigh tendon reinjuries: an expert opinion

This review critically examines the issue of thigh tendon reinjury in athletes, drawing on recent advancements and diverse perspectives in sports medicine. The findings underscore the paramount importance of an early and accurate diagnosis, which significantly influences treatment efficacy and rehabilitation outcomes. We explore the intricacies of tendon anatomy and the mechanisms underlying injuries, highlighting how these factors interplay with athlete-specific risk profiles to affect reinjury rates. A major finding from the review is the necessity for individualized rehabilitation approaches that integrate both traditional methods and emerging technologies. These technologies show promise in enhancing monitoring and facilitating precise adjustments to rehabilitation protocols, thus improving recovery trajectories. Additionally, the review identifies a common shortfall in current practices - premature to play (RTP) - which often results from inadequate adherence to tailored rehabilitation strategies or underestimation of the injury's severity. Such premature RTP significantly heightens the risk of further injury. Through this synthesis of contemporary research and expert opinion, the review advocates for a multidisciplinary approach in managing thigh tendon injuries, emphasizing the need for ongoing research to refine RTP criteria and optimize rehabilitation techniques. The ultimate goal is to support athletes in achieving safer and more effective recoveries, thereby reducing the likelihood of tendon reinjury.

Facile and rapid fabrication of a novel 3D-printable, visible light-crosslinkable and bioactive polythiourethane for large-to-massive rotator cuff tendon repair

Facile and rapid 3D fabrication of strong, bioactive materials can address challenges that impede repair of large-to-massive rotator cuff tears including personalized grafts, limited mechanical support, and inadequate tissue regeneration. Herein, we developed a facile and rapid methodology that generates visible light-crosslinkable polythiourethane (PHT) pre-polymer resin (∼30 min at room temperature), yielding 3D-printable scaffolds with tendon-like mechanical attributes capable of delivering tenogenic bioactive factors. Ex vivo characterization confirmed successful fabrication, robust human supraspinatus tendon (SST)-like tensile properties (strength: 23 MPa, modulus: 459 MPa, at least 10,000 physiological loading cycles without failure), excellent suture retention (8.62-fold lower than acellular dermal matrix (ADM)-based clinical graft), slow degradation, and controlled release of fibroblast growth factor-2 (FGF-2) and transforming growth factor-β3 (TGF-β3). In vitro studies showed cytocompatibility and growth factor-mediated tenogenic-like differentiation of mesenchymal stem cells. In vivo studies demonstrated biocompatibility (3-week mouse subcutaneous implantation) and ability of growth factor-containing scaffolds to notably regenerate at least 1-cm of tendon with native-like biomechanical attributes as uninjured shoulder (8-week, large-to-massive 1-cm gap rabbit rotator cuff injury). This study demonstrates use of a 3D-printable, strong, and bioactive material to provide mechanical support and pro-regenerative cues for challenging injuries such as large-to-massive rotator cuff tears.

In vitro development of a muscle-tendon junction construct using decellularised extracellular matrix: Effect of cyclic tensile loading

The muscle tendon junction (MTJ) plays a crucial role in transmitting the force generated by muscles to the tendon and then to the bone. Injuries such as tears and strains frequently happen at the MTJ, where the regenerative process is limited due to poor vascularization and the complex structure of the tissue. Current solutions for a complete tear at the MTJ have not been successful and therefore, the development of a tissue-engineered MTJ may provide a more effective treatment. In this study, decellularised extracellular matrix (DECM) derived from sheep MTJ was used to provide a scaffold for the MTJ with the relevant mechanical properties and differentiation cues such as the relase of growth factors. Human mesenchymal stem cells (MSCs) were seeded on DECM and 10 % cyclic strain was applied using a bioreactor. MSCs cultured on DECM showed significantly higher gene and protein expression of MTJ markers such as collagen 22, paxillin and talin, than MSCs in 2D culture. Although collagen 22 protein expression was higher in the cells with strain than without strain, reduced gene expression of other MTJ markers was observed when the strain was applied. DECM combined with 10 % strain enhanced myogenic differentiation, while tenogenic differentiation was reduced when compared to static cultures of MSCs on DECM. For the first time, these results showed that DECM derived from the MTJ can induce MTJ marker gene and protein expression by MSCs, however, the effect of strain on the MTJ development in DECM culture needs further investigation.

Engineering interfacial tissues: The myotendinous junction

The myotendinous junction (MTJ) is the interface connecting skeletal muscle and tendon tissues. This specialized region represents the bridge that facilitates the transmission of contractile forces from muscle to tendon, and ultimately the skeletal system for the creation of movement. MTJs are, therefore, subject to high stress concentrations, rendering them susceptible to severe, life-altering injuries. Despite the scarcity of knowledge obtained from MTJ formation during embryogenesis, several attempts have been made to engineer this complex interfacial tissue. These attempts, however, fail to achieve the level of maturity and mechanical complexity required for in vivo transplantation. This review summarizes the strategies taken to engineer the MTJ, with an emphasis on how transitioning from static to mechanically inducive dynamic cultures may assist in achieving myotendinous maturity.

Associations Between Hip Pathology, Hip and Groin Pain, and Injuries in Hockey Athletes: A Clinical Commentary

Femoroacetabular impingement (FAI), particularly cam morphology, is highly prevalent among elite hockey athletes. Moreover, hip and groin pain has become a common issue in hockey, with approximately 50% of European professional athletes reported to experience a hip or groin problem during a season. While most athletes will not miss training or competition due to this, restricted competitive performance and increased risk of reduced physical and psychological well-being are likely. Recent research suggests that the development of cam morphology is related to the repetitive shear stresses experienced at the hip joint during adolescence from skating. This condition likely increases the potential for intra-articular and extra-articular injuries in these athletes later in their careers. Research also indicates that the hip joint mechanics during forward skating substantially increase the possibility of sustaining a labral tear compared to other sports. Such an injury can increase femoral head movement within the joint, potentially causing secondary damage to the iliofemoral ligament, ligamentum teres and joint capsule. These injuries and the high density of nociceptors in the affected structures may explain the high prevalence of hip and groin pain in hockey athletes. Compensatory adaptations, such as reduced hip strength, stability, and range-of-motion (ROM) likely increase the opportunity for core muscle injuries and hip flexor and adductor injuries. Specifically, the limited hip ROM associated with cam morphology appears to exacerbate the risk of these injuries as there will be an increase in pubic symphysis stress and transverse strain during rotational movements. It is hoped that this article will assist practitioners currently working with hockey athletes to develop evidence-informed monitoring strategies and training interventions, aimed at reducing the incidence and severity of hip and groin problems, ultimately enhancing athlete performance and well-being. Therefore, the purpose of this clinical commentary was to examine current evidence on common hip pathologies in hockey athletes, exploring potential associations between hip and groin pain and the biomechanics of hockey activities.

Level of Evidence

5.

Bioactive fiber-reinforced hydrogel to tailor cell microenvironment for structural and functional regeneration of myotendinous junction

Myotendinous junction (MTJ) injuries are prevalent in clinical practice, yet the treatment approaches are limited to surgical suturing and conservative therapy, exhibiting a high recurrence rate. Current research on MTJ tissue engineering is scarce and lacks in vivo evaluation of repair efficacy. Here, we developed a three-dimensional-printed bioactive fiber-reinforced hydrogel containing mesenchymal stem cells (MSCs) and Klotho for structural and functional MTJ regeneration. In a rat MTJ defect model, the bioactive fiber-reinforced hydrogel promoted the structural restoration of muscle, tendon, and muscle-tendon interface and enhanced the functional recovery of injured MTJ. In vivo proteomics and in vitro cell cultures elucidated the regenerative mechanisms of the bioactive fiber-reinforced hydrogel by modulating oxidative stress and inflammation, thus engineering an optimized microenvironment to support the survival and differentiation of transplanted MSCs and maintain the functional phenotype of resident cells within MTJ tissues, including tendon/muscle cells and macrophages. This strategy provides a promising treatment for MTJ injuries.

Enthesopathies - Mechanical, inflammatory or both?

Entheses have the challenging task of transferring biomechanical forces between tendon and bone, two tissues that differ greatly in composition and mechanical properties. Consequently, entheses are adapted to withstand these forces through continuous repair mechanisms. Locally specialized cells (mechanosensitive tenocytes) are crucial in the repair, physiologically triggering biochemical processes to maintain hemostasis. When repetitive forces cause "material fatigue," or trauma exceeds the entheses' repair capacity, structural changes occur, and patients become symptomatic. Clinical assessment of enthesopathies mainly depends on subjective reports by the patient and lacks specificity, especially in patients with central sensitization syndromes. Ultrasonography has been increasingly used to improve the diagnosis of enthesopathies. In this article, the literature on how biomechanical forces lead to entheseal inflammation, including factors contributing to differentiation into a "clinical enthesitis" state and the value of ultrasound to diagnose enthesopathies will be reviewed, as well as providing clues to overcome the pitfalls of imaging.

Clinical applications of stem cell-derived exosomes

Although stem cell-based therapy has demonstrated considerable potential to manage certain diseases more successfully than conventional surgery, it nevertheless comes with inescapable drawbacks that might limit its clinical translation. Compared to stem cells, stem cell-derived exosomes possess numerous advantages, such as non-immunogenicity, non-infusion toxicity, easy access, effortless preservation, and freedom from tumorigenic potential and ethical issues. Exosomes can inherit similar therapeutic effects from their parental cells such as embryonic stem cells and adult stem cells through vertical delivery of their pluripotency or multipotency. After a thorough search and meticulous dissection of relevant literature from the last five years, we present this comprehensive, up-to-date, specialty-specific and disease-oriented review to highlight the surgical application and potential of stem cell-derived exosomes. Exosomes derived from stem cells (e.g., embryonic, induced pluripotent, hematopoietic, mesenchymal, neural, and endothelial stem cells) are capable of treating numerous diseases encountered in orthopedic surgery, neurosurgery, plastic surgery, general surgery, cardiothoracic surgery, urology, head and neck surgery, ophthalmology, and obstetrics and gynecology. The diverse therapeutic effects of stem cells-derived exosomes are a hierarchical translation through tissue-specific responses, and cell-specific molecular signaling pathways. In this review, we highlight stem cell-derived exosomes as a viable and potent alternative to stem cell-based therapy in managing various surgical conditions. We recommend that future research combines wisdoms from surgeons, nanomedicine practitioners, and stem cell researchers in this relevant and intriguing research area.

Mild to moderate damage in knee extensor muscles accumulates after two bouts of maximal eccentric contractions

PURPOSE

This study aimed to determine whether mild to moderate muscle damage accumulates on the knee extensors after two bouts of maximal eccentric contractions performed over two consecutive days.

METHODS

Thirty participants performed an initial bout of maximal eccentric contractions of knee extensors during the first day of the protocol (ECC1). Then, they were separated in two groups. The Experimental (EXP) group repeated the eccentric bout 24 h later (ECC2) while the Control (CON) group did not. Indirect markers of muscle damage (i.e., strength loss, muscle soreness, and shear modulus) were measured to quantify the amount of muscle damage and its time course.

RESULTS

Two days after the initial eccentric session, participants from EXP had a higher strength deficit (- 14.5 ± 10.6%) than CON (- 6.6 ± 8.7%) (P = 0.017, d = 0.9). Although both groups exhibited an increase in knee extensors shear modulus after ECC1, we found a significant increase in muscle shear modulus (+ 13.3 ± 22.7%; P < 0.01; d = 0.5) after ECC2 for the EXP group, despite the presence of mild to moderate muscle damage (i.e., strength deficit about 16%).

CONCLUSION

Although the markers of muscle damage used in the current study were indirect, they suggest that the repetition of two bouts of maximal eccentric contractions with 24 h apart induces additional muscle damage in the knee extensors in presence of mild to moderate muscle damage.

Semimembranosus Tendon Findings in Acute Anterior Cruciate Ligament Tears: MRI Evaluation and Associated Lesions

BACKGROUND

The semimembranosus (SM) tendon acts as a secondary dynamic stabilizer of the knee. It restrains external rotation and anterior translation of the medial compartment. Its role in the mechanism of injury during anterior cruciate ligament (ACL) rupture is unknown.

HYPOTHESIS

The bone bruise (BB) often detected at the posteromedial tibia in association with acute ACL tear may be related to the traction force from the SM tendon insertion. Magnetic resonance imaging (MRI) alterations can be detectable at the direct arm of the SM tendon in association with acute ACL injury.

STUDY DESIGN

Cross-sectional study: Level of evidence, 3.

METHODS

In the first study phase, 36 noninjured patients underwent knee MRI. The anatomic appearance of the SM tendon was evaluated. An imaging score for evaluating the SM tendon was developed for the purpose of the study. The intensity (in the axial or sagittal plane), morphology, and thickness of the distal SM tendon was evaluated and scored (4 total points). In the second study phase, 52 patients undergoing acute ACL reconstruction were included. Preoperative MRI was examined and scored, with documentation of BB at the posteromedial tibial plateau. Finally, arthroscopic diagnosis of a ramp lesion was confirmed. Logistic regression analysis was carried out for correlation between an altered MRI scoring system and the presence of BB at the posteromedial tibial plateau, the presence of a ramp lesion, or both.

RESULTS

Interrater agreement of 100% was obtained in the noninjured cohort (ie, no alteration found in any patient). The score validation in the cohort of patients with acute ACL injury showed a Cohen κ of 0.78 (interrater agreement, 82.7%). The direct arm of the SM tendon was altered in 35 of 52 patients (67.3%). A ramp lesion of the medial meniscus was arthroscopically detected in 21 patients (40.4%). The presence of BB at the posteromedial tibial plateau was detected in 33 patients (63.5%) and at the posterior medial femoral condyle in 1 (1.9%). Correlation analysis showed a significant association of a pathologic SM score with the presence of BB at the posteromedial tibial plateau (odds ratio = 2.7; P = .001). Conversely, no correlation was observed between the pathologic score and the presence of a ramp lesion (odds ratio = 0.88; P = .578).

CONCLUSION

The prevalence of pathologic findings in the direct arm of the SM tendon insertion was high in the acutely injured cohort with ACL rupture and is correlated with the presence of BB at the posteromedial tibial plateau. The main hypothesis formulated for the study was confirmed.

A passive ankle dorsiflexion testing system to assess mechanobiological and structural response to cyclic loading in rat Achilles tendon

Tendinopathy is thought to be caused by repeated overload of the tendon with insufficient recovery time, leading to an inadequate healing response and incomplete recovery of preinjury material strength and function. The etiology of tendinopathy induced by mechanical load is being explored with a variety of mechanical load scenarios in small animals. This study establishes a testing system that applies passive ankle dorsiflexion to a rat hindlimb, estimates the force applied to the tendon during cyclic loading and enables the assessment of subsequent structural and biological changes. We demonstrated that the system had no drift in the applied angle, and the registered maximum angle and torque inputs and outputs were consistent between tests. We showed that cyclic loading decreased hysteresis and loading and unloading moduli with increasing cycles applied to the tendon. Histology showed gross changes to tendon structure. This work establishes a system for passively loading the rat Achilles tendon in-vivo in a physiological manner, facilitating future studies that will explore how mechanics, structure, and biology are altered by mechanical repetitive loading.

Characteristics of external loads of Hockey5s associated with the new version of U16 youth field hockey competition

External workloads associated Hockey 5 s, the new version of youth field hockey, were evaluated in 31 elite U16 male field players (15.4 ± 0.7 years) from three national teams. Mixed-longitudinal observations for the 31 players provided complete data for 33 forwards and 43 defenders. Activities of the players during games were monitored with the GPSports SPI Elite System with a sampling frequency of 10 Hz and were analysed with GPSports Team AMS (version R1 2015.14, Australia). Observed variables did not differ between forwards and defenders, and the three periods of play were differentiated only by maximal speed in the second and third periods. The greatest distances covered were in speed zone 3 (10.0-15.9 km h^-1; 35.5-38.2%) and the smallest in speed zones 4 (16.0-22.9 km h^-1; 14.8-15.6%) and 5 (> 23 km h^-1; 0.4-1.4%). The trends indicated high intensity levels for the entire match and by position and periods. Active time of forwards and defenders accounted for about one-half of a game's duration (~ 15.7 of 30 min). Overall, the Hockey 5s format was highly demanding of players and included relatively short intervals for recovery. The results emphasize the need for preparation that includes specific mixed anaerobic and aerobic training and also the importance of recovery during breaks.

A discrete shear lag model of the mechanics of hitchhiker plants, and its prospective application to tendon-to-bone repair

Tendon-to-bone repairs often fail when sutures pull through tendon, like a wire through cheese. Repair strength is maximized when loads are balanced equally among all sutures, relative to the pullout resistance of the tendon and the strength of the sutures. This problem of balancing loads across multiple, discrete attachment sites has been solved in nature by hitchhiker plants that proliferate by adhering relatively stiff fruit to relatively soft fur and fabrics through arrays of hooks. We, therefore, studied the fruits of such a plant, Harpagonella palmeri , and developed a discrete shear lag analysis of the force distributions in H. palmeri 's linear arrays of long, slender hooks of varied lengths and spacing. Results suggested that strategies were used by the plant to distribute loads, including variations in the spacing and stiffnesses of hooks that serve to equalize forces over attachment sites. When applying these models to suturing schemes for surgical reattachment of tendon to bone, results suggested that strategies exhibited by H. palmeri show promise for balancing forces over sutures, potentially doubling repair strength relative to what could be achieved with a uniform suture distribution. Results suggest a potential pathway for strengthening surgical repairs, and more broadly for optimizing fasteners for bi-material attachment.

On the management of maternal pushing during the second stage of labor: a biomechanical study considering passive tissue fatigue damage accumulation

BACKGROUND

During the second stage of labor, the maternal pelvic floor muscles undergo repetitive stretch loading as uterine contractions and strenuous maternal pushes combined to expel the fetus, and it is not uncommon that these muscles sustain a partial or complete rupture. It has recently been demonstrated that soft tissues, including the anterior cruciate ligament and connective tissue in sheep pelvic floor muscle, can accumulate damage under repetitive physiological (submaximal) loads. It is well known to material scientists that this damage accumulation can not only decrease tissue resistance to stretch but also result in a partial or complete structural failure. Thus, we wondered whether certain maternal pushing patterns (in terms of frequency and duration of each push) could increase the risk of excessive damage accumulation in the pelvic floor tissue, thereby inadvertently contributing to the development of pelvic floor muscle injury.

OBJECTIVE

This study aimed to determine which labor management practices (spontaneous vs directed pushing) are less prone to accumulate damage in the pelvic floor muscles during the second stage of labor and find the optimum approach in terms of minimizing the risk of pelvic floor muscle injury.

STUDY DESIGN

We developed a biomechanical model for the expulsive phase of the second stage of labor that includes the ability to measure the damage accumulation because of repetitive physiological submaximal loads. We performed 4 simulations of the second stage of labor, reflecting a directed pushing technique and 3 alternatives for spontaneous pushing.

RESULTS

The finite element model predicted that the origin of the pubovisceral muscle accumulates the most damage and so it is the most likely place for a tear to develop. This result was independent of the pushing pattern. Performing 3 maternal pushes per contraction, with each push lasting 5 seconds, caused less damage and seemed the best approach. The directed pushing technique (3 pushes per contraction, with each push lasting 10 seconds) did not reduce the duration of the second stage of labor and caused higher damage accumulation.

CONCLUSION

The frequency and duration of the maternal pushes influenced the damage accumulation in the passive tissues of the pelvic floor muscles, indicating that it can influence the prevalence of pelvic floor muscle injuries. Our results suggested that the maternal pushes should not last longer than 5 seconds and that the duration of active pushing is a better measurement than the total duration of the second stage of labor. Hopefully, this research will help to shed new light on the best practices needed to improve the experience of labor for women.

Pelvic floor muscle injury during a difficult labor. Can tissue fatigue damage play a role?

Pubovisceral muscle (PVM) injury during a difficult vaginal delivery leads to pelvic organ prolapse later in life. If one could address how and why the muscle injury originates, one might be able to better prevent these injuries in the future. In a recent review we concluded that many atraumatic injuries of the muscle-tendon unit are consistent with it being weakened by an accumulation of passive tissue damage during repetitive loading. While the PVM can tear due to a single overstretch at the end of the second stage of labor we hypothesize that it can also be weakened by an accumulation of microdamage and then tear after a series of submaximal loading cycles. We conclude that there is strong indirect evidence that low cycle fatigue of PVM passive tissue is a possible mechanism of its proximal failure. This has implications for finding new ways to better prevent PVM injury in the future.