Mechanical properties and collagen cross-linking of the patellar tendon in old and young men

Structure and function of Achilles and patellar tendons following moderate slow resistance training in young and old men

The aim of this study was to investigate the effect of aging and resistance training with a moderate load on the size and mechanical properties of the patellar (PT) and Achilles tendon (AT) and their associated aponeuroses; medial gastrocnemius (MG) and vastus lateralis (VL). Young (Y55; 24.8 ± 3.8 yrs, n = 11) and old men (O55; 70.0 ± 4.6 yrs, n = 13) were assigned to undergo a training program (12 weeks; 3 times/week) of moderate slow resistance training [55% of one repetition maximum (RM)] of the triceps surae and quadriceps muscles. Tendon dimensions were assessed using 1.5 T magnetic resonance imaging before and after 12 weeks. AT and PT cross sectional area (CSA) were determined every 10% of tendon length. Mechanical properties of the free AT, MG aponeurosis, PT, and VL aponeurosis were assessed using ultrasonography (deformation) and tendon force measurements. CSA of the AT but not PT was greater in O55 compared with Y55. At baseline, mechanical properties were generally lower in O55 than Y55 for AT, MG aponeurosis and VL aponeurosis (Young's modulus) but not for PT. CSA of the AT and PT increased equally in both groups following training. Further, for a given force, stiffness and Young's modulus also increased equally for VL aponeurosis and AT, for boths groups. The present study highlights that except for the PT, older men have lower tendon (AT, MG aponeurosis, and VL aponeurosis) mechanical properties than young men and 12-weeks of moderate slow resistance training appears sufficient to improve tendon size and mechanical adaptations in both young and older men. New and Noteworthy: These novel findings suggest that short-term moderate slow resistance training induces equal improvements in tendon size and mechanics regardless of age.

Greater Protein Intake Emphasizing Lean Beef Does Not Affect Resistance Training-Induced Adaptations in Skeletal Muscle and Tendon of Older Women: A Randomized Controlled Feeding Trial

BACKGROUND

Although experimental research supports that resistance training (RT), especially with greater dietary protein intake, improves muscle mass and strength in older adults, comparable research on tendons is needed.

OBJECTIVES

We assessed the effects of a protein-rich diet emphasizing lean beef, compared with 2 control diets, on RT-induced changes in skeletal muscle and tendon size and strength in older women.

METHODS

We randomly assigned women [age: 66 ± 1 y, body mass index (BMI): 28 ± 1] to groups that consumed 1) 0.8 g total protein/kg body weight/day from mixed food sources (normal protein control, n = 16); 2) 1.4 g/kg/d protein from mixed food sources (high protein control, n = 17); or 3) 1.4 g/kg/d protein emphasizing unprocessed lean beef (high protein experimental group, n = 16). Participants were provided with all foods and performed RT 3 times/wk, 70% of 1-repetition maximum for 12 wk. We measured quadriceps muscle volume via magnetic resonance imaging (MRI). We estimated patellar tendon biomechanical properties and cross-sectional area (CSA) using ultrasound and MRI.

RESULTS

Dietary intake did not influence RT-induced increases in quadriceps strength (P < 0.0001) or muscle volume (P < 0.05). We noted a trend for an RT effect on mean tendon CSA (P = 0.07), with no differences among diets (P > 0.05). Proximal tendon CSA increased with RT (P < 0.05) with no difference between dietary groups (P > 0.05). Among all participants, midtendon CSA increased with RT (P ≤ 0.05). We found a decrease in distal CSA in the 0.8 g group (P < 0.05) but no change in the 1.4 g group (P > 0.05). Patellar tendon MRI signal or biomechanical properties were unchanged.

CONCLUSIONS

Our findings indicated that greater daily protein intake, emphasizing beef, did not influence RT-induced changes in quadriceps muscle strength or muscle volume of older women. Although we noted trends in tendon CSA, we did not find a statistically significant impact of greater daily protein intake from beef on tendon outcomes. This trial was registered at clinicaltrials.gov as NCT04347447.

Open-system force-elongation relationship of collagen in chemo-mechanical equilibrium with water

A significant deformation mechanism of collagen at low loads is molecular uncoiling and rearrangement. Although the effect of hydration and cross-linking has been investigated at larger loads when collagen undergoes molecular sliding, their effects on collagen molecular reorganization remain unclear. Here we develop two thermodynamic models that use the notion of open-system elasticity to elucidate the effect of swelling due to water uptake during deformation of collagen networks under low and high cross-linking conditions. With low crosslinking, entropic contributions dominate resulting in rejection of solvent from the polymer network leading to reduced collagen stiffness with increased loads. Contrarily, high cross-linking inhibits initial coiling and structural kinking and the mechanical behavior is dominated by elastic energy. In this configuration, the solvent content depends on the sign of the applied load resulting in a non-linear open-system stress-strain relationship. The models provide insight on the parameters that impact the stress-strain relationships of hydrated collagen and can inform the way collagenous matrices are treated both in medical and laboratory settings.

Effects of aging and diabetes on the deformation mechanisms and molecular structural characteristics of collagen fibrils under daily activity

Crosslinking plays an important role in collagen-based tissues since it affects mechanical behavior and tissue metabolism. Aging and diabetes affect the type and density of crosslinking, effectively altering tissue properties. However, most studies focus on these effects under large stress rather than daily activities. We focus on the deformation mechanisms and structural change at the binding sites for integrins, proteoglycans, and collagenase in collagen fibrils using a fully atomistic model. We show that high-connectivity enzymatic crosslinking (our "HC" model, representing normal tissues) and advanced-glycation end-products (our "Glucosepane" model, which increase in diabetes) result in uniform deformation under daily activity, but low-connectivity enzymatic crosslinking (our "LC" model, representing aging tissues) does not. In particular, the HC model displays more sliding, which may explain the ability of healthy tissues to absorb more strain energy. In contrast, AGEs induce instability in the structures near the binding sites, which would affect the tissue metabolism of the collagen molecule. Our results provide important insights into the molecular mechanisms of collagen and a possible explanation for the role of crosslinking in tissues undergoing daily activity.

Sirtuin 6 Overexpression Improves Rotator Cuff Tendon-to-Bone Healing in the Aged

Aging is an independent risk factor for recurrent tearing after surgical repair of rotator cuff ruptures around the tendon-to-bone area. However, aging signature factors and related mechanisms involved in the healing of the rotator cuff are still unknown. We hypothesized that differences in proteins involved in the rotator cuff according to age may affect tendon-to-bone healing. The proteome analysis performed to identify the signature aging proteins of the rotator cuff confirmed the sirtuin signal as an age-specific protein. In particular, the expression of SIRT6 was markedly down-regulated with age. Ingenuity pathway analysis of omics data from age-dependent rat rotator cuffs and linear regression from human rotator cuffs showed SIRT6 to be closely related to the Wnt/β-catenin signal. We confirmed that overexpression of SIRT6 in the rotator cuff and primary tenocyte regulated canonical Wnt signaling by inhibiting the transcriptional expression of sclerostin, a Wnt antagonist. Finally, SIRT6 overexpression promoted tendon-to-bone healing after tenotomy with reconstruction in elderly rats. This approach is considered an effective treatment method for recovery from recurrent rotator cuff tears, which frequently occur in the elderly.

Effect of Physical Parameters and Training Load on Patellar Tendon Stiffness in Professional Athletes

BACKGROUND

Injuries of the patellar tendon commonly occur as a result of mechanical loading of the tendon during physical activity. Shear wave elastography (SWE) is an established technique for assessing tendon stiffness, and has good interindividual reliability. The aim of this study was to investigate the impacts of physical parameters and different sports on patellar tendon stiffness in professional athletes using SWE.

METHODS

Standardized patellar tendon SWE was performed in a relaxed supine position with a small roll under the knee (20° flexion) in 60 healthy professional athletes (30 female, 30 male). Multiple linear regression was performed for patellar tendon stiffness including gender, age, body mass index (BMI), and type of sport.

RESULTS

Patellar tendon stiffness showed no significant difference between female (3.320 m/s) and male (3.416 m/s) professional athletes. Mean age (female: 20.53 years; male: 19.80 years) and BMI (female: 23.24 kg/m2; male: 23.52 kg/m2) were comparable. Female professional athletes with oral contraceptive (OC) intake showed higher patellar tendon stiffness than athletes without OC intake (3.723 versus 3.017; p = 0.053), but not significantly.

CONCLUSION

In professional athletes, there are no significant differences in patellar tendon stiffness according to gender, age, BMI and type of sport (handball, volleyball, soccer, sprint, hammer throw). Oral contraceptives may not have an impact on patellar tendon stiffness in female athletes. Further studies are necessary.

Single collagen fibrils isolated from high stress and low stress tendons show differing susceptibility to enzymatic degradation by the interstitial collagenase matrix metalloproteinase-1 (MMP-1)

Bovine forelimb flexor and extensor tendons serve as a model for examining high stress, energy storing and low stress, positional tendons, respectively. Previous research has shown structural differences between the collagen fibrils of these tissues. The nanoscale collagen fibrils of flexor tendons are smaller in size, more heavily crosslinked, and respond differently to mechanical loading. Meanwhile, energy storing tendons undergo less collagen turnover compared to positional tendons and are more commonly injured. These observations raise the question of whether collagen fibril structure influences the collagen degradation processes necessary for remodelling. Atomic force microscopy was used to image dry collagen fibrils before and after 5-hour exposure to matrix metalloproteinase-1 (MMP-1) to detect changes in fibril size. Collagen fibrils from three tissue types were studied: bovine superficial digital flexor tendons, matched-pair bovine lateral digital extensor tendons, and rat tail tendons. Compared to control fibrils exposed only to buffer, a significant decrease in fibril cross-sectional area (CSA) following MMP-1 exposure was observed for bovine extensor and rat tail fibrils, with larger fibrils experiencing a greater magnitude of CSA decrease in both fibril types. Fibrils from bovine flexor tendons, on the other hand, showed no decrease in CSA when exposed to MMP-1. The result did not appear to be linked to the small size of flexor fibrils, as equivalently sized extensor fibrils were readily degraded by the enzyme. Increased proteolytic resistance of collagen fibrils from high stress tendons may help to explain the longevity of collagen within these tissues in vivo.

Impact of essential amino acid intake, resistance exercise, and aging on the concentration of Achilles peritendinous amino acids and procollagen Iα1 in humans

Recent studies have shown that consuming amino acid-rich compounds improves tendon collagen content and biomechanical properties. Yet, it is unclear if the consumption of amino acids alters local (peritendinous) amino acid concentrations. If aging or exercise influence local amino acid concentrations in conjunction with an amino acid bolus is also not known. We conducted two studies. In Study 1, young women (n = 7, 25 ± 2 years) completed two identical resistance training sessions with either essential amino acid (EAA) or placebo consumption. In Study 2, an EAA bolus identical to Study 1 was given to younger (n = 7; 27 ± 1 year) and older adults (n = 6; 68 ± 2 years). Microdialysis was used to determine Achilles peritendinous amino acid and pro-collagen Iα1 (a marker of collagen synthesis) concentrations. In Study 1, amino acid consumption increased peritendinous concentrations of all EAA except histidine (p < 0.05). In Study 2, the peritendinous concentration of EAAs except for methionine, histidine, and lysine (p > 0.05) increased with time (p < 0.05). Further, the concentrations of most measured amino acids were greater in older adults (p < 0.05). Pro-collagen Iα1 concentration (p > 0.05) was unaffected by exercise, EAA, or aging (p > 0.05). Our findings demonstrate the following: (1) when not combined with exercise, an oral EAA bolus leads to only modest increases in Achilles peritendinous amino acid concentrations; (2) when combined with resistance exercise, EAA consumption resulted in greater peritendinous amino acid concentrations compared to no exercise; (3) the basal concentrations of most amino acids were greater in older adults, and (4) neither the EAA bolus nor exercise altered peritendinous pro-collagen concentrations.

Effect of Anthropometric Parameters on Achilles Tendon Stiffness of Professional Athletes Measured by Shear Wave Elastography

BACKGROUND

Shear wave elastography (SWE) is currently used to detect tissue pathologies and, in the setting of preventive medicine, may have the potential to reveal structural changes before they lead to functional impairment. Hence, it would be desirable to determine the sensitivity of SWE and to investigate how Achilles tendon stiffness is affected by anthropometric variables and sport-specific locomotion.

METHODS

To investigate the influence of anthropometric parameters on Achilles tendon stiffness using SWE and examine different types of sports to develop approaches in preventive medicine for professional athletes, standardized SWE of Achilles tendon stiffness was performed in 65 healthy professional athletes (33 female, 32 male) in the longitudinal plane and relaxed tendon position. Descriptive analysis and linear regression were performed. Furthermore, subgroup analysis was performed for different sports (soccer, handball, sprint, volleyball, hammer throw).

RESULTS

In the total study population (n = 65), Achilles tendon stiffness was significantly higher in male professional athletes (p < 0.001) than in female professional athletes (10.98 m/s (10.15-11.65) vs. 12.19 m/s (11.25-14.74)). Multiple linear regression for AT stiffness did not reveal a significant impact of age or body mass index (BMI) (p > 0.05). Subgroup analysis for type of sport showed the highest AT stiffness values in sprinters (14.02 m/s (13.50-14.63)).

CONCLUSION

There are significant gender differences in AT stiffness across different types of professional athletes. The highest AT stiffness values were found in sprinters, which needs to be considered when diagnosing tendon pathologies. Future studies are needed to investigate the benefit of pre- and post-season musculoskeletal SWE examinations of professional athletes and a possible benefit of rehabilitation or preventive medicine.

Impact of aging on tendon homeostasis, tendinopathy development, and impaired healing

Aging is a complex and progressive process where the tissues of the body demonstrate a decreased ability to maintain homeostasis. During aging, there are substantial cellular and molecular changes, with a subsequent increase in susceptibility to pathological degeneration of normal tissue function. In tendon, aging results in well characterized alterations in extracellular matrix (ECM) structure and composition. In addition, the cellular environment of aged tendons is altered, including a marked decrease in cell density and metabolic activity, as well as an increase in cellular senescence. Collectively, these degenerative changes make aging a key risk factor for the development of tendinopathies and can increase the frequency of tendon injuries. However, inconsistencies in the extent of age-related degenerative impairments in tendons have been reported, likely due to differences in how "old" and "young" age-groups have been defined, differences between anatomically distinct tendons, and differences between animal models that have been utilized to study the impact of aging on tendon homeostasis. In this review, we address these issues by summarizing data by well-defined age categories (young adults, middle-aged, and aged) and from anatomically distinct tendon types. We then summarize in detail how aging affects tendon mechanics, structure, composition, and the cellular environment based on current data and underscore what is currently not known. Finally, we discuss gaps in the current understanding of tendon aging and propose key avenues for future research that can shed light on the specific mechanisms of tendon pathogenesis due to aging.

Tendon Aging

Tendons are mechanosensitive connective tissues responsible for the connection between muscles and bones by transmitting forces that allow the movement of the body, yet, with advancing age, tendons become more prone to degeneration followed by injuries. Tendon diseases are one of the main causes of incapacity worldwide, leading to changes in tendon composition, structure, and biomechanical properties, as well as a decline in regenerative potential. There is still a great lack of knowledge regarding tendon cellular and molecular biology, interplay between biochemistry and biomechanics, and the complex pathomechanisms involved in tendon diseases. Consequently, this reflects a huge need for basic and clinical research to better elucidate the nature of healthy tendon tissue and also tendon aging process and associated diseases. This chapter concisely describes the effects that the aging process has on tendons at the tissue, cellular, and molecular levels and briefly reviews potential biological predictors of tendon aging. Recent research findings that are herein reviewed and discussed might contribute to the development of precision tendon therapies targeting the elderly population.

Chemical Markers of Human Tendon Health Identified Using Raman Spectroscopy: Potential for In Vivo Assessment

The purpose of this study is to determine whether age-related changes to tendon matrix molecules can be detected using Raman spectroscopy. Raman spectra were collected from human Achilles (n = 8) and tibialis anterior (n = 8) tendon tissue excised from young (17 ± 3 years) and old (72 ± 7 years) age groups. Normalised Raman spectra underwent principal component analysis (PCA), to objectively identify differences between age groups and tendon types. Certain Raman band intensities were correlated with levels of advanced glycation end-product (AGE) collagen crosslinks, quantified using conventional destructive biochemistry techniques. Achilles and tibialis anterior tendons in the old age group demonstrated significantly higher overall Raman intensities and fluorescence levels compared to young tendons. PCA was able to distinguish young and old age groups and different tendon types. Raman intensities differed significantly for several bands, including those previously associated with AGE crosslinks, where a significant positive correlation with biochemical measures was demonstrated. Differences in Raman spectra between old and young tendon tissue and correlation with AGE crosslinks provides the basis for quantifying age-related chemical modifications to tendon matrix molecules in intact tissue. Our results suggest that Raman spectroscopy may provide a powerful tool to assess tendon health and vitality in the future.

Aşil tendonu gerinim oranı ile mitral anulus kalsifikasyonu varlığı arasındaki ilişki

Amaç: Aşil tendonu (AT)- ultrasonografisi (US) ve gerinim elastografisi (SE) ile elde edilen AT- kalınlığı (T) ve AT- gerinim oranının (SR) mitral kapak kalsifikasyonlu (MAC) hastaları belirlemedeki önemini araştırmayı amaçladık. Gereç ve Yöntem: Çalışmaya ekokardiyografi sonrası MAC tanısı alan 100 hasta (65 kadın, 35 erkek ve ortalama yaş 64.7 ± 12.1) ve kardiyovasküler risk faktörü benzer olan 50 kontrol (32 kadın, 18 erkek ve ortalama yaş 63.2 ± 12.8) alındı. Laboratuvar incelemeler ve AT US yapıldı. AT-T ve AT-SR hesaplandı. Bulgular: MAC olan hastalarda AT-T ve AT-SR belirgin olarak yüksek olduğu bulundu. Logistic regresyon analizinde, AT-T ve AT-SR değerlerinin MAC olma riskini bağımsız olarak belirlediği bulundu. Bu analize göre AT-T (her 1 mm) ve AT-SR (her 0.1)’nin MAC olma riskini sırası ile %69.9 ve %12.7 oranlarında artırdığı saptandı. AT-T ve AT-SR değerlerinin MAC olan hastaları belirlemesi açısından ROC analizi yapıldığında, ROC eğri altında kalan alanın sırası ile 0.684 ve 0.819 belirlendi. Aynı analizde, AT-SR için sınır değer 1.25 olarak alındığında %94.1 sensitivite ve %76.2 spesivite ile MAC varlığını belirlediği tespit edildi. Sonuç: AT SE incelemesinde saptanan AT-SR, MAC olan hastaları önceden belirlemede kullanılabilecek basit, ucuz, tekrarlanabilir ve non-invaziv bir parametredir. Bu durum MAC ve AT-SR artışının benzer fizyopatolojik mekanizma ile meydana gelebilmesinin bir sonucu olabilir.

Role of Knee and Ankle Extensors' Muscle-Tendon Properties in Dynamic Balance Recovery from a Simulated Slip

Participants exposed to a simulated slip with forward loss of balance (FLB) develop large lower limb joint moments which may be a limiting factor for those whose muscle-tendon units’ (MTUs) properties are deteriorated. Whether the age-related decline in these properties limits participants’ capacity to recover their balance following a slip with FLB remains unclear. We combined isokinetic dynamometry, ultrasound and EMG to understand how knee extensor and ankle plantarflexor muscle strength and power, rate of moment development, electromechanical delay, and tendon stiffness affected the balance of young (25.3 ± 3.9 years) and older adults (62.8 ± 7.1 years) when recovering from a single slip with FLB triggered whilst walking on a split-belt instrumented treadmill. Except for the patellar tendon’s stiffness, knee extensor and ankle plantarflexor electromechanical delays, older adults’ MTUs properties were deteriorated compared to those of young participants (p < 0.05). We found no significant relationship between age or the MTUs properties of participants and balance recovery. These findings provide additional support that neither maximal nor explosive strength training are likely to be successful in preventing a fall for healthy older adults, and that other type of interventions, such as task-specific training that has already proved efficacious in reducing the risk of falling, should be developed.

Multiscale Characterization of Type I Collagen Fibril Stress–Strain Behavior under Tensile Load: Analytical vs. MD Approaches

Type I collagen is one of the most important proteins in the human body because of its role in providing structural support to the extracellular matrix of the connective tissues. Understanding its mechanical properties was widely investigated using experimental testing as well as molecular and finite element simulations. In this work, we present a new approach for defining the properties of the type I collagen fibrils by analytically formulating its response when subjected to a tensile load and investigating the effects of enzymatic crosslinks on the behavioral response. We reveal some of the shortcomings of the molecular dynamics (MD) method and how they affect the obtained stress–strain behavior of the fibril, and we prove that not only does MD underestimate the Young’s modulus and the ultimate tensile strength of the collagen fibrils, but also fails to detect the mechanics of some stretching phases of the fibril. We prove that non-crosslinked fibrils have three tension phases: (i) an initial elastic deformation corresponding to the collagen molecule uncoiling, (ii) a linear regime related to the stretching of the backbone of the tropocollagen molecules, and (iii) a plastic regime dominated by molecular sliding. We also show that for crosslinked fibrils, the second regime can be subdivided into three sub-regimes, and we define the properties of each regime. We also prove, analytically, the alleged MD quadratic relation between the ultimate tensile strength of the fibril and the concentration of enzymatic crosslinks (β).

Muscle fiber type-dependence effect of exercise on genomic networks in aged mice models

Skeletal muscles are made up of various muscle fiber type including slow and fast-twitch fibers. Because each muscle fiber has its own physiological characteristics, the effects of aging and exercise vary depending on the type of muscle fiber. We used bioinformatics screening techniques such as differentially expressed gene analysis, gene ontology analysis and gene set enrichment analysis, to try to understand the genetic differences between muscle fiber types. The experiment and gene expression profiling in this study used the soleus (SOL, slow-twitch muscle) and gastrocnemius (GAS, fast-twitch muscle). According to our findings, fatty acid metabolism is significantly up-regulated in SOL compared to GAS, whereas the glucose metabolism pathway is significantly down-regulated in SOL compared to GAS.

Furthermore, apoptosis and myogenesis patterns differ between SOL and GAS. SOL did not show differences in apoptosis due to the aging effect, but apoptosis in GAS was significantly up-regulated with age. Apoptosis in GAS of old groups is significantly reduced after 4 weeks of aerobic exercise, but no such finding was found in SOL. In terms of myogenesis, exercise intervention up-regulated this process in GAS of old groups but not in SOL. Taken together, muscle fiber type significantly interacts with aging and exercise. Despite the importance of the interaction between these factors, large-scale gene expression data has rarely been studied. We hope to contribute to a better understanding of the relationship between muscle fiber type, aging and exercise at the molecular level.

Conservative treatment of iliotibial band syndrome in runners: Are we targeting the right goals?

OBJECTIVE

Iliotibial band syndrome (ITBS) is presumably caused by excessive tension in the iliotibial band (ITB) leading to compression and inflammation of tissues lying beneath it. Usually managed conservatively, there is a lack of scientific evidence supporting the treatment recommendations, and high symptom recurrence rates cast doubt on their causal effectiveness. This review discusses the influence of common physiotherapeutic measures on risk factors contributing to tissue compression beneath the ITB.

METHODS

The potential pathogenic factors are presented on the basis of a simple biomechanical model showing the forces acting on the lateral aspect of the knee. Existent literature on the most commonly prescribed physiotherapeutic interventions is critically discussed against the background of this model. Practical recommendations for the optimization of physiotherapy are derived.

RESULTS

According to biomechanical considerations, ITBS may be promoted by anatomical predisposition, joint malalignments, aberrant activation of inserting muscles as well as excessive ITB stiffness. Hip abductor strengthening may correct excessive hip adduction but also increase ITB strain. Intermittent stretching interventions are unlikely to change the ITB's length or mechanical properties. Running retraining is a promising yet understudied intervention.

CONCLUSIONS

High-quality research directly testing different physiotherapeutic treatment approaches in randomized controlled trials is needed.

Circular RNA PVT1 inhibits tendon stem/progenitor cell senescence by sponging microRNA-199a-5p

Tendon stem/progenitor cell (TSPC) senescence can lead to age-dependent tendon maladies and undermines both tendon repair and replacement capacity in humans. The mechanisms underlying TSPC senescence and sensitivity to adverse factors are complicated. In this study, we analyzed involvement of the circular RNA (circRNA) PVT1 (circPVT1) in TSPC senescence. circPVT1 expression was found to be significantly diminished in human TSPCs under prolonged in vitro culture. Accordingly, circPVT1 knockdown promoted senescence progression and suppressed self renewal, migration, and tenogenic differentiation of TSPCs. Furthermore, we found that circPVT1 directly targets microRNA (miR)-199a-5p thereby attenuating its negative regulation of SIRT1 expression. Either miR-199a-5p inhibition or SIRT1 overexpression attenuated the senescence-boosting effect of circPVT1 knockdown, implying that circPVT1 suppresses TSPC senescence in part by upregulating the miR-199a-5p-SIRT1 signaling axis. Our findings conclusively explain the major roles of circPVT1 in TSPC senescence regulation; circPVT1 is a novel potential therapeutic target for reducing tendon senescence.

Increased Collagen Crosslinking in Stiff Clubfoot Tissue: Implications for the Improvement of Therapeutic Strategies

Congenital clubfoot is a complex musculoskeletal deformity, in which a stiff, contracted tissue forms in the medial part of the foot. Fibrotic changes are associated with increased collagen deposition and lysyl oxidase (LOX)-mediated crosslinking, which impair collagen degradation and increase the tissue stiffness. First, we studied collagen deposition, as well as the expression of collagen and the amount of pyridinoline and deoxypyridinoline crosslinks in the tissue of relapsed clubfoot by immunohistochemistry, real-time PCR, and enzyme-linked immunosorbent assay (ELISA). We then isolated fibroblast-like cells from the contracted tissue to study the potential inhibition of these processes in vitro. We assessed the effects of a LOX inhibitor, β-aminopropionitrile (BAPN), on the cells by a hydroxyproline assay, ELISA, and Second Harmonic Generation imaging. We also evaluated the cell-mediated contraction of extracellular matrix in 3D cell-populated collagen gels. For the first time, we have confirmed significantly increased crosslinking and excessive collagen type I deposition in the clubfoot-contracted tissue. We successfully reduced these processes in vitro in a dose-dependent manner with 10–40 µg/mL of BAPN, and we observed an increasing trend in the inhibition of the cell-mediated contraction of collagen gels. The in vitro inhibitory effects indicate that BAPN has good potential for the treatment of relapsed and resistant clubfeet.

Mechanical properties of human patellar tendon collagen fibrils. An exploratory study of aging and sex

Tendons are connective tissues that transmit mechanical forces from muscle to bone and consist mainly of nano-scale fibrils of type I collagen. Aging has been associated with reduced mechanical function of tendons at the whole-tendon level and also with increased glycation of tendon collagen fibrils. Yet, the mechanical effects of aging at the fibril level remain unknown. In vitro glycation has previously been reported to substantially increase fibril strength and stiffness in young rats, suggesting a potentially large effect of aging through the glycation mechanism. We therefore expected that aging would have a similar major impact on fibril mechanical properties. In addition, differences in fibril mechanical properties between men and women have never been studied. This study investigated human patellar tendon biopsies from young (26 ± 4 years) and elderly (66 ± 1 years), men and women by measuring the mechanical properties of individual collagen fibrils using a custom nano-mechanical device. There were no major mechanical differences with either age or sex, but there were modestly greater failure stress (22%) and tensile modulus at both low and high strain (16% and 26% respectively) in the elderly group. No significant differences in mechanical properties were observed between men and women. The slightly greater strength and stiffness in the elderly group are in contrasts to the age-related deficits observed for whole-tendons in vivo, although the study was not designed to investigate these minor differences.

The Effect of Enzymatic Crosslink Degradation on the Mechanics of the Anterior Cruciate Ligament: A Hybrid Multi-Domain Model

The anterior cruciate ligament’s (ACL) mechanics is an important factor governing the ligament’s integrity and, hence, the knee joint’s response. Despite many investigations in this area, the cause and effect of injuries remain unclear or unknown. This may be due to the complexity of the direct link between macro- and micro-scale damage mechanisms. In the first part of this investigation, a three-dimensional coarse-grained model of collagen fibril (type I) was developed using a bottom-up approach to investigate deformation mechanisms under tensile testing. The output of this molecular level was used later to calibrate the parameters of a hierarchical multi-scale fibril-reinforced hyper-elastoplastic model of the ACL. Our model enabled us to determine the mechanical behavior of the ACL as a function of the basic response of the collagen molecules. Modeled elastic response and damage distribution were in good agreement with the reported measurements and computational investigations. Our results suggest that degradation of crosslink content dictates the loss of the stiffness of the fibrils and, hence, damage to the ACL. Therefore, the proposed computational frame is a promising tool that will allow new insights into the biomechanics of the ACL.

Habitual side-specific loading leads to structural, mechanical and compositional changes in the patellar tendon of young and senior life-long male athletes

Effects of life-long physical activity on tendon function have been investigated in cross-sectional studies, but these are at risk of "survivorship" bias. Here, we investigate if life-long side-specific loading is associated with greater cross-sectional area (CSA), mechanical properties, cell density (DNA content) and collagen cross-link composition of the male human patellar tendon (PT), in vivo. Nine seniors and six young male life-long elite badminton players and fencers were included. CSA of the PT obtained by 3-tesla MRI, and ultrasonography-based bilateral PT mechanics were assessed. Collagen fibril characteristics, enzymatic cross-links, non-enzymatic glycation (autofluorescence), collagen and DNA content were measured biochemically in PT biopsies. The elite athletes had a ≥15% side-to-side difference in maximal knee extensor strength, reflecting chronic unilateral sport-specific loading patterns. The PT CSA was greater on the lead extremity compared with the non-lead extremity (17 %, p=0.0001). Furthermore, greater tendon stiffness (18 %, p=0.0404) together with lower tendon stress (22 %, p=0.0005) and tendon strain (18 %, p=0.0433) were observed on the lead extremity. No effects were demonstrated from side-to-side for glycation, enzymatic cross-link, collagen, and DNA content (50%, p=0.1160). Moreover, tendon fibril density was 87±28 fibrils/μm² on the lead extremity and 68±26 fibrils/μm² on the non-lead extremity (28%, p=0.0544). Tendon fibril diameter was 86±14 nm on the lead extremity and 94±14 nm on the non-lead extremity (-9%, p=0.1076). These novel data suggest that life-long side-specific loading in males yields greater patellar tendon size and stiffness possibly with concomitant greater fibril density but without changes of collagen cross-link composition.

Muscle and tendon adaptations to moderate load eccentric vs. concentric resistance exercise in young and older males

Resistance exercise training (RET) is well-known to counteract negative age-related changes in both muscle and tendon tissue. Traditional RET consists of both concentric (CON) and eccentric (ECC) contractions; nevertheless, isolated ECC contractions are metabolically less demanding and, thus, may be more suitable for older populations. However, whether submaximal (60% 1RM) CON or ECC contractions differ in their effectiveness is relatively unknown. Further, whether the time course of muscle and tendon adaptations differs to the above is also unknown. Therefore, this study aimed to establish the time course of muscle and tendon adaptations to submaximal CON and ECC RET. Twenty healthy young (24.5 ± 5.1 years) and 17 older males (68.1 ± 2.4 years) were randomly allocated to either isolated CON or ECC RET which took place 3/week for 8 weeks. Tendon biomechanical properties, muscle architecture and maximal voluntary contraction were assessed every 2 weeks and quadriceps muscle volume every 4 weeks. Positive changes in tendon Young's modulus were observed after 4 weeks in all groups after which adaptations in young males plateaued but continued to increase in older males, suggesting a dampened rate of adaptation with age. However, both CON and ECC resulted in similar overall changes in tendon Young's modulus, in all groups. Muscle hypertrophy and strength increases were similar between CON and ECC in all groups. However, pennation angle increases were greater in CON, and fascicle length changes were greater in ECC. Notably, muscle and tendon adaptations appeared to occur in synergy, presumably to maintain the efficacy of the muscle-tendon unit.

Aging Decreases the Ultimate Tensile Strength of Bone-Patellar Tendon-Bone Allografts

PURPOSE

The purpose of this study was to determine whether aging imparts a clinically significant effect on the (1) mechanism of graft failure and (2) structural, material, and viscoelastic properties of patellar tendon allografts by evaluating these properties in younger donors (≤30 years of age) and older donors (>50 years of age).

METHODS

A total of 34 younger (≤30 years of age) and 34 older (>50 years of age) nonirradiated, whole bone-tendon-bone allografts were prepared for testing by isolating the central third of the patellar tendon using a double-bladed 10-mm width scalpel under a 10-N load to ensure uniformity of harvest. Bone blocks were potted in polymethylmethacrylate within custom molds. Tendon length and cross-sectional area were measured using an area micrometer. A mechanical loading system was used to precondition the grafts for 100 cycles with a load between 50 N and 250 N (1 Hz). A creep load (500 N) was then applied at a rate of 100 mm/min (10 minutes). Grafts were allowed to recover at 1 N (10 minutes), followed by pull-to-failure at a rate of 100% strain per second. Mechanisms of failure (midsubstance vs avulsion) were noted and the structural, material, and viscoelastic properties calculated and compared between groups.

RESULTS

There were 33 (97%) midsubstance tears in the younger group and 28 (82%) in the older group (P = .034). Younger grafts showed greater ultimate load to failure (1,782 N [1,533, 2,032] vs 1,319 N [1,103, 1,533]) (P = .006) and ultimate tensile stress (37.4 MPa [32.4, 42.4] vs 27.5 MPa [22.9, 32.0]) (P = .006). There were no significant differences in displacement (P = .595), stiffness (P = .950), strain (P = .783), elastic modulus (P = .114), creep displacement (P = .881), and creep strain (P = .614).

CONCLUSIONS

This in vitro study suggests that aging weakens the bone-tendon junction and decreases the ultimate tensile strength of patellar tendon allografts. However, aging did not affect the displacement, strain, stiffness, elastic modulus, creep displacement, or creep strain of patellar tendon allografts.

CLINICAL RELEVANCE

Surgeons should be aware that patellar tendon allografts from donors >50 years of age have a lower ultimate tensile stress than donors ≤30 years of age.

Updating futsal physiology, immune system, and performance

Futsal promotes stress by handling the ball, physical contact, and exhaustive muscle contractions, elevating the risks for injury, oxidative stress, and inflammation after a training session or a match. In this review, we critically evaluate the more recent advances in the performance and health of futsal players. We searched the effects of futsal on performance, physiological parameters, muscle injury, inflammation, and oxidative stress. Although the stressful factors apply to all futsal players, goalkeepers require special attention during the competition and the recovery phase. We also show that the FIFA injury prevention programme, called The 11+, is effective in improving athletic performance and avoiding injury in futsal players. Research with different training durations and intensities and a wider range of studies involving oxidative stress, inflammation, and physiological mechanisms are of interest to design a more precise map of the biochemical regulation of training load and competition season in futsal.

Explaining Variability in the Prevalence of Achilles Tendon Abnormalities: A Systematic Review With Meta-analysis of Imaging Studies in Asymptomatic Individuals

OBJECTIVE

To estimate the prevalence of, and factors associated with, Achilles tendon abnormalities observed on imaging in asymptomatic individuals.

DESIGN

Systematic review with stratified meta-analysis and meta-regression.

LITERATURE SEARCH

Embase, Scopus, MEDLINE, CINAHL, SPORTDiscus, and Web of Science were searched from 1980 to August 2020.

STUDY SELECTION CRITERIA

We included studies that reported the prevalence of Achilles tendon abnormalities, observed with any imaging modality, in an asymptomatic population. We excluded studies if participant mean age was younger than 12 years or if participants had current/previous lower-limb tendon injuries/symptoms or other systemic conditions.

DATA SYNTHESIS

Random-effects proportion meta-analysis was used to estimate prevalence. We used meta-regression for continuous variables (mean age and body mass index [BMI], sample size, proportion of female participants) and stratified categorical variables (imaging modality and participation in physical activity) to explain between-study heterogeneity.

RESULTS

We included 91 studies (10 156 limbs, 5841 participants). The prevalence of Achilles tendon abnormalities on imaging ranged from 0% to 80% per participant. Between-study heterogeneity was high (I²>90%, P<.001), precluding data pooling. Between-study heterogeneity was partly explained by participant mean BMI (slope, 2.8% per 1-unit increase in BMI; 95% confidence interval: 0.57%, 5.03%; P = .015) and participation in physical activity per limb, and mean age of 40 years old or older (P = .022) per participant.

CONCLUSION

There was substantial variability in the prevalence of Achilles tendon abnormalities on imaging in asymptomatic individuals. Higher prevalence of abnormalities was associated with older age (40 years old or older), higher BMI, and participation in physical activity. A large proportion of heterogeneity remains unaccounted for, likely due to variations in abnormality definitions and study design. J Orthop Sports Phys Ther 2021;51(5):232-252. Epub 28 Mar 2021. doi:10.2519/jospt.2021.9970.

Influence of Bias in the Assessment of Patellar Tendon Stiffness: A Systematic Review and Meta-analysis

The aim of the present study was to provide a systematic review and meta-analysis of the main biases in practical applications of the different types of elastography in assessment of the stiffness of healthy patellar tendons. A literature search on four databases (Scopus, Web of Science, Pubmed and SportDiscus) was conducted on March 25, 2020. After analysis of 1,052 resultant articles, studies were included if they met two inclusion criteria: (1) studies were observational or randomized controlled trials; (2) studies included outcomes of patellar tendon stiffness. Twenty-one studies met the inclusion criteria and were included in this meta-analysis. Four meta-analyses were performed with respect to assessment procedure and participant characteristics. This meta-analysis found a low effect of examined portion of patellar tendon (standardized mean difference [SMD] = 0.27, 95% confidence interval [CI]: 0.01-0.54, n = 379, Z = 2.01, p = 0.04) and a high effect of knee flexion angle during assessment (SMD = -2.12; 95% CI: -2.67 to -1.58, n = 97, Z = 7.68, p < 0.01) in stiffness outcomes. The risk of bias was generally low, but the heterogenicity of the results downgraded the level of evidence. There is evidence in the elastography assessment of patellar tendon suggesting that the knee position and patellar tendon portion evaluated influence stiffness outcomes for patellar tendon in healthy volunteers.

Effects of genipin crosslinking on mechanical cell-matrix interaction in 3D engineered tendon constructs

It is well known that cells can generate endogenous forces onto the extracellular matrix, but to what extent the mechanical properties of the matrix influences these endogenous cellular forces remains unclear. We therefore sought to quantify the influence of matrix rigidity on cell-matrix interactions by inducing cross-links using increasing concentrations of genipin (0.01-1 mM) or by blocking cross-link formation using beta-aminopropionitrile (BAPN) in engineered human tendon tissue constructs. The cell-matrix mechanics of the tendon constructs were evaluated as cell-generated tissue re-tensioning and stress-relaxation responses using a novel custom-made force monitor, which can apply and detect tensional forces in real-time in addition to mechanical failure testing. Genipin treatment had no influence on the biochemical profile (hydroxyproline, glycosaminoglycan and DNA content) of the constructs and cell viability was comparable between genipin-treated and control constructs, except at the highest genipin concentration. Endogenous re-tension after unloading was significantly decreased with increasing genipin concentrations compared to controls. Mechanical failure testing of tendon constructs showed increased (56%) peak stress at the highest genipin concentration but decreased (72%) with BAPN treatment when compared to controls. Tendon construct stiffness increased with high genipin concentrations (0.1 and 1 mM) and decreased by 70% in BAPN-treated constructs, relative to the controls. These data demonstrate that human tendon fibroblasts regulate their force exertion inversely proportional to increased cross-link capacity but did so independently of matrix stiffness. Overall, these findings support the notion of an interaction between cell force generation and cross-linking, and thus a role for this interplay in mechanical homeostasis of the tissue.

Translational research on Myology and Mobility Medicine: 2021 semi-virtual PDM3 from Thermae of Euganean Hills, May 26 - 29, 2021

On 19-21 November 2020, the meeting of the 30 years of the Padova Muscle Days was virtually held while the SARS-CoV-2 epidemic was hitting the world after a seemingly quiet summer. During the 2020-2021 winter, the epidemic is still active, despite the start of vaccinations. The organizers hope to hold the 2021 Padua Days on Myology and Mobility Medicine in a semi-virtual form (2021 S-V PDM3) from May 26 to May 29 at the Thermae of Euganean Hills, Padova, Italy. Here the program and the Collection of Abstracts are presented. Despite numerous world problems, the number of submitted/selected presentations (lectures and oral presentations) has increased, prompting the organizers to extend the program to four dense days.

Muscles adaptation to aging and training: architectural changes - a randomised trial

Background

To investigate how anatomical cross-sectional area and volume of quadriceps and triceps surae muscles were affected by ageing, and by resistance training in older and younger men, in vivo.

Methods

The old participants were randomly assigned to moderate (O55, n = 13) or high-load (O80, n = 14) resistance training intervention (12 weeks; 3 times/week) corresponding to 55% or 80% of one repetition maximum, respectively. Young men (Y55, n = 11) were assigned to the moderate-intensity strengthening exercise program. Each group received the exact same training volume on triceps surae and quadriceps group (Reps x Sets x Intensity). The fitting polynomial regression equations for each of anatomical cross-sectional area-muscle length curves were used to calculate muscle volume (contractile content) before and after 12 weeks using magnetic resonance imaging scans.

Results

Only Rectus femoris and medial gastrocnemius muscle showed a higher relative anatomical cross-sectional area in the young than the elderly on the proximal end. The old group displayed a higher absolute volume of non-contractile material than young men in triceps surae (+ 96%). After training, Y55, O55 and O80 showed an increase in total quadriceps (+ 4.3%; + 6.7%; 4.2% respectively) and triceps surae (+ 2.8%; + 7.5%; 4.3% respectively) volume. O55 demonstrated a greater increase on average gains compared to Y55, while no difference between O55 and O80 was observed.

Conclusions

Muscle loss with aging is region-specific for some muscles and uniform for others. Equivalent strength training volume at moderate or high intensities increased muscle volume with no differences in muscle volume gains for old men. These data suggest that physical exercise at moderate intensity (55 to 60% of one repetition maximum) can reverse the aging related loss of muscle mass.

Trial registration

NCT03079180 in ClinicalTrials.gov. Registration date: March 14, 2017.

Tendon Extracellular Matrix Assembly, Maintenance and Dysregulation Throughout Life

In his Lissner Award medal lecture in 2000, Stephen Cowin asked the question: "How is a tissue built?" It is not a new question, but it remains as relevant today as it did when it was asked 20 years ago. In fact, research on the organization and development of tissue structure has been a primary focus of tendon and ligament research for over two centuries. The tendon extracellular matrix (ECM) is critical to overall tissue function; it gives the tissue its unique mechanical properties, exhibiting complex non-linear responses, viscoelasticity and flow mechanisms, excellent energy storage and fatigue resistance. This matrix also creates a unique microenvironment for resident cells, allowing cells to maintain their phenotype and translate mechanical and chemical signals into biological responses. Importantly, this architecture is constantly remodeled by local cell populations in response to changing biochemical (systemic and local disease or injury) and mechanical (exercise, disuse, and overuse) stimuli. Here, we review the current understanding of matrix remodeling throughout life, focusing on formation and assembly during the postnatal period, maintenance and homeostasis during adulthood, and changes to homeostasis in natural aging. We also discuss advances in model systems and novel tools for studying collagen and non-collagenous matrix remodeling throughout life, and finally conclude by identifying key questions that have yet to be answered.

Ultrasound-based speckle-tracking in tendons: a critical analysis for the technician and the clinician

Ultrasound has risen to the forefront as one of the primary tools in tendon research, with benefits including its relatively low cost, ease of use, and high safety. Moreover, it has been shown that cine ultrasound can be used to evaluate tendon deformation by tracking the motion of anatomical landmarks during physical movement. Estimates from landmark tracking, however, are typically limited to global tissue properties, such that clinically relevant regional nonuniformities may be missed. Fortunately, advancements in ultrasound scanning have led to the development of speckle-tracking algorithms, which enable the noninvasive measurement of in vivo local deformation patterns. Despite the successes in other fields, the adaptation of speckle-tracking to tendon research has presented some unique challenges as a result of tissue anisotropy and microstructural changes under load. With no generally accepted standards for its use, current methodological approaches vary substantially between studies and research groups. Therefore, the goal of this paper is to provide a summative review of the technical complexities and variations of speckle-tracking approaches being used and the impact these decisions may have on measured results and their interpretation. Variations in these approaches currently being used with relevant technical aspects are discussed first (for the technician), followed by a discussion of the more clinical considerations (for the clinician). Finally, a summary table of common challenges encountered when implementing speckle-tracking is provided, with suggested recommendations for minimizing the impact of such potential sources of error.

Age Related Changes in Motor Function (II). Decline in Motor Performance Outcomes

Age-related impairments in motor performance are caused by a deterioration in mechanical and neuromuscular functions, which have been investigated from the macro-level of muscle-tendon unit to the micro-level of the single muscle fiber. When compared to the healthy young skeletal muscle, aged skeletal muscle is: (1) weaker, slower and less powerful during the performance of voluntary contractions; (2) less steady during the performance of isometric contractions, particularly at low levels of force; and (3) less susceptible to fatigue during the performance of sustained isometric contractions, but more susceptible to fatigue during the performance of high-velocity dynamic contractions. These impairments have been discussed to be mainly the result of: a) loss of muscle mass and selective atrophy of type II muscle fibers; b) altered tendon mechanical properties (decreased tendon stiffness); c) reduced number and altered function of motor units; d) slower muscle fiber shortening velocity; e) increased oscillation in common synaptic input to motor neurons; and f) altered properties and activity of sarcoplasmic reticulum. In this second part of a two-part review we have detailed the age-related impairments in motor performance with a reference to the most important mechanical and neuromuscular contributing factors.

Mass spectrometric quantitation of AGEs and enzymatic crosslinks in human cancellous bone

Advanced glycation end-products (AGEs) deteriorate bone strength. Among over 40 species identified in vivo, AGEs other than pentosidine were roughly estimated as total fluorescent AGEs (tfAGEs) due to technical difficulties. Using LC-QqTOF-MS, we established a system that enabled the quantitation of five AGEs (CML, CEL, MG-H1, CMA and pentosidine) as well as two mature and three immature enzymatic crosslinks. Human bone samples were collected from 149 patients who underwent total knee arthroplasty. Their clinical parameters were collected to investigate parameters that may be predictive of AGE accumulation. All the analytes were quantitated and showed significant linearity with high sensitivity and precision. The results showed that MG-H1 was the most abundant AGE, whereas pentosidine was 1/200–1/20-fold less abundant than the other four AGEs. The AGEs were significantly and strongly correlated with pentosidine, while showing moderate correlation with tfAGEs. Interestingly, multiple linear regression analysis revealed that gender contributed most to the accumulation of all the AGEs, followed by age, tartrate-resistant acid phosphatase-5b and HbA1c. Furthermore, the AGEs were negatively correlated with immature crosslinks. Mass spectrometric quantitation of AGEs and enzymatic crosslinks is crucial to a better understanding of ageing- and disease-related deterioration of bone strength.

A brief history of tendon and ligament bioreactors: Impact and future prospects

Bioreactors are powerful tools with the potential to model tissue development and disease in vitro. For nearly four decades, bioreactors have been used to create tendon and ligament tissue-engineered constructs in order to define basic mechanisms of cell function, extracellular matrix deposition, tissue organization, injury, and tissue remodeling. This review provides a historical perspective of tendon and ligament bioreactors and their contributions to this advancing field. First, we demonstrate the need for bioreactors to improve understanding of tendon and ligament function and dysfunction. Next, we detail the history and evolution of bioreactor development and design from simple stretching of explants to fabrication and stimulation of two- and three-dimensional constructs. Then, we demonstrate how research using tendon and ligament bioreactors has led to pivotal basic science and tissue-engineering discoveries. Finally, we provide guidance for new basic, applied, and clinical research utilizing these valuable systems, recognizing that fundamental knowledge of cell-cell and cell-matrix interactions combined with appropriate mechanical and chemical stimulation of constructs could ultimately lead to functional tendon and ligament repairs in the coming decades.

Epigenetic mechanisms in Tendon Ageing

INTRODUCTION

Tendon is a composite material with a well-ordered hierarchical structure exhibiting viscoelastic properties designed to transfer force. It is recognized that the incidence of tendon injury increases with age, suggesting a deterioration in homeostatic mechanisms or reparative processes. This review summarizes epigenetic mechanisms identified in ageing healthy tendon.

SOURCES OF DATA

We searched multiple databases to produce a systematic review on the role of epigenetic mechanisms in tendon ageing.

AREAS OF AGREEMENT

Epigenetic mechanisms are important in predisposing ageing tendon to injury.

AREAS OF CONTROVERSY

The relative importance of epigenetic mechanisms are unknown in terms of promoting healthy ageing. It is also unknown whether these changes represent protective mechanisms to function or predispose to pathology.

GROWING POINT

Epigenetic markers in ageing tendon, which are under-researched including genome-wide chromatin accessibility, should be investigated.

AREAS TIMELY FOR DEVELOPING RESEARCH

Metanalysis through integration of multiple datasets and platforms will enable a holistic understanding of the epigenome in ageing and its relevance to disease.

Strain Assessment of Deep Fascia of the Thigh During Leg Movement: An in situ Study

Fascia is a fibrous connective tissue present all over the body. At the lower limb level, the deep fascia that is overlying muscles of the outer thigh and sheathing them (fascia lata) is involved in various pathologies. However, the understanding and quantification of the mechanisms involved in these sheathing effects are still unclear. The aim of this study is to observe and quantify the strain field of the fascia lata, including the iliotibial tract (ITT), during a passive movement of the knee. Three fresh postmortem human subjects were studied. To measure hip and knee angles during knee flexion-extension, passive movements from 0° to around 120° were recorded with a motion analysis system and strain fields of the fascia were acquired using digital image correlation. Strains were computed for three areas of the fascia lata: anterior fascia, lateral fascia, and ITT. Mean principal strains showed different strain mechanisms depending on location on the fascia and knee angle. For the ITT, two strain mechanisms were observed depending on knee movement: compression is observed when the knee is extended relative to the reference position of 47°, however, tension and pure shear can be observed when the knee is flexed. For the anterior and lateral fascia, in most cases, minor strain is higher than major strain in absolute value, suggesting high tissue compression probably due to microstructural fiber rearrangements. This in situ study is the first attempt to quantify the superficial strain field of fascia lata during passive leg movement. The study presents some limitations but provides a step in understanding strain mechanism of the fascia lata during passive knee movement.

Collagen analysis with mass spectrometry

Mass spectrometry-based techniques can be applied to investigate collagen with respect to identification, quantification, supramolecular organization, and various post-translational modifications. The continuous interest in collagen research has led to a shift from techniques to analyze the physical characteristics of collagen to methods to study collagen abundance and modifications. In this review, we illustrate the potential of mass spectrometry for in-depth analyses of collagen.

Structural and Functional Changes in the Coupling of Fascial Tissue, Skeletal Muscle, and Nerves During Aging

Aging is a one-way process associated with profound structural and functional changes in the organism. Indeed, the neuromuscular system undergoes a wide remodeling, which involves muscles, fascia, and the central and peripheral nervous systems. As a result, intrinsic features of tissues, as well as their functional and structural coupling, are affected and a decline in overall physical performance occurs. Evidence from the scientific literature demonstrates that senescence is associated with increased stiffness and reduced elasticity of fascia, as well as loss of skeletal muscle mass, strength, and regenerative potential. The interaction between muscular and fascial structures is also weakened. As for the nervous system, aging leads to motor cortex atrophy, reduced motor cortical excitability, and plasticity, thus leading to accumulation of denervated muscle fibers. As a result, the magnitude of force generated by the neuromuscular apparatus, its transmission along the myofascial chain, joint mobility, and movement coordination are impaired. In this review, we summarize the evidence about the deleterious effect of aging on skeletal muscle, fascial tissue, and the nervous system. In particular, we address the structural and functional changes occurring within and between these tissues and discuss the effect of inflammation in aging. From the clinical perspective, this article outlines promising approaches for analyzing the composition and the viscoelastic properties of skeletal muscle, such as ultrasonography and elastography, which could be applied for a better understanding of musculoskeletal modifications occurring with aging. Moreover, we describe the use of tissue manipulation techniques, such as massage, traction, mobilization as well as acupuncture, dry needling, and nerve block, to enhance fascial repair.

Distalising tibial tubercle osteotomy decreases patellar tendon force - A treatment rationale for recalcitrant patellar tendinopathy

BACKGROUND

Patellar tendinopathy is an overuse condition affecting athletes, often with a high morbidity if left untreated. High-level evidence fails to support the use of surgery. A tibial tubercle osteotomy (TTO) has been suggested as a surgical option to improve patient outcomes. Our aim was to explore whether a distalising TTO will alter the patellar tendon to quadriceps tendon force ratio and the sagittal patellar tilt.

METHODS

Six cadaver limbs were placed in a custom jig with a mechanical testing machine applying cyclical loads of 200-500 N to the quadriceps tendon. The knee was fixed at 0, 15, 30, 45, 60, 75 and 90° of flexion and a buckle transducer recorded the resultant patellar tendon force. Testing was performed with the native tibial tubercle position and with the tubercle distalised by 11 mm. Testing was also performed with the tubercle anteriorised by 10 mm at both of these tubercle positions, a total of four different testing positions.

RESULTS

There was a significant decrease in the patellar tendon to quadriceps tendon force ratio from 30-60° of knee flexion. There was a significant increase in the sagittal patellar tilt at 30° of knee flexion with distalisation.

CONCLUSION

This biomechanical study shows that the patellar tendon to quadriceps tendon force ratio can be altered with a distalising tibial tubercle osteotomy. A tibial tubercle osteotomy may be a biomechanical treatment option for recalcitrant patellar tendinopathy by decreasing the load through the patellar tendon, allowing the athlete to maintain higher training volumes and loads.

Therapeutic potential of microRNA in tendon injuries

INTRODUCTION

The regulatory role of microRNA (miRNA) in several conditions has been studied, but their function in tendon healing remains elusive. This review summarizes how miRNAs are related to the pathogenesis of tendon injuries and highlights their clinical potential, focusing on the issues related to their delivery for clinical purposes.

SOURCES OF DATA

We searched multiple databases to perform a systematic review on miRNA in relation to tendon injuries. We included in the present work a total of 15 articles.

AREAS OF AGREEMENT

The mechanism of repair of tendon injuries is probably mediated by resident tenocytes. These maintain a fine equilibrium between anabolic and catabolic events of the extracellular matrix. Specific miRNAs regulate cytokine expression and orchestrate proliferation and differentiation of stromal cell lines involved in the composition of the extracellular matrix.

AREAS OF CONTROVERSY

The lack of effective delivery systems poses serious obstacles to the clinical translation of these basic science findings.

GROWING POINT

In vivo studies should be planned to better explore the relationship between miRNA and tendon injuries and evaluate the most suitable delivery system for these molecules.

AREAS TIMELY FOR DEVELOPING RESEARCH

Investigations ex vivo suggest therapeutic opportunities of miRNA for the management of tendon injuries. Given the poor pharmacokinetic properties of miRNAs, these must be delivered by an adequate adjuvant transport system.

Aged Tendon Stem/Progenitor Cells Are Less Competent to Form 3D Tendon Organoids Due to Cell Autonomous and Matrix Production Deficits

Tendons are dense connective tissues, which are critical for the integrity and function of our musculoskeletal system. During tendon aging and degeneration, tendon stem/progenitor cells (TSPCs) experience profound phenotypic changes with declined cellular functions that can be linked to the known increase in complications during tendon healing process in elderly patients. Tissue engineering is a promising approach for achieving a complete recovery of injured tendons. However, use of autologous cells from aged individuals would require restoring the cellular fitness prior to implantation. In this study, we applied an established cell sheet model for in vitro tenogenesis and compared the sheet formation of TSPC derived from young/healthy (Y-TSPCs) versus aged/degenerative (A-TSPCs) human Achilles tendon biopsies with the purpose to unravel differences in their potential to form self-assembled three-dimensional (3D) tendon organoids. Using our three-step protocol, 4 donors of Y-TSPCs and 9 donors of A-TSPCs were subjected to cell sheet formation and maturation in a period of 5 weeks. The sheets were then cross evaluated by weight and diameter measurements; quantification of cell density, proliferation, senescence and apoptosis; histomorphometry; gene expression of 48 target genes; and collagen type I protein production. The results revealed very obvious and significant phenotype in A-TSPC sheets characterized by being fragile and thin with poor tissue morphology, and significantly lower cell density and proliferation, but significantly higher levels of the senescence-related gene markers and apoptotic cells. Quantitative gene expression analyses at the mRNA and protein levels, also demonstrated abnormal molecular circuits in the A-TSPC sheets. Taken together, we report for the first time that A-TSPCs exhibit profound deficits in forming 3D tendon tissue organoids, thus making the cell sheet model suitable to investigate the molecular mechanisms involved in tendon aging and degeneration, as well as examining novel pharmacologic strategies for rejuvenation of aged cells.

Detection of Age-Related Changes in Tendon Molecular Composition by Raman Spectroscopy-Potential for Rapid, Non-Invasive Assessment of Susceptibility to Injury

The lack of clinical detection tools at the molecular level hinders our progression in preventing age-related tendon pathologies. Raman spectroscopy can rapidly and non-invasively detect tissue molecular compositions and has great potential for in vivo applications. In biological tissues, a highly fluorescent background masks the Raman spectral features and is usually removed during data processing, but including this background could help age differentiation since fluorescence level in tendons increases with age. Therefore, we conducted a stepwise analysis of fluorescence and Raman combined spectra for better understanding of the chemical differences between young and old tendons. Spectra were collected from random locations of vacuum-dried young and old equine tendon samples (superficial digital flexor tendon (SDFT) and deep digital flexor tendon (DDFT), total n = 15) under identical instrumental settings. The fluorescence-Raman spectra showed an increase in old tendons as expected. Normalising the fluorescence-Raman spectra further indicated a potential change in intra-tendinous fluorophores as tendon ages. After fluorescence removal, the pure Raman spectra demonstrated between-group differences in CH2 bending (1450 cm-1) and various ring-structure and carbohydrate-associated bands (1000-1100 cm-1), possibly relating to a decline in cellular numbers and an accumulation of advanced glycation end products in old tendons. These results demonstrated that Raman spectroscopy can successfully detect age-related tendon molecular differences.

Relationship between mechanical properties (shear modulus and viscosity), age, and sex in uninjured Achilles tendons

Tendon mechanical properties have been proposed as a biomarker of tendon health to track response to injury and treatment. Prior to utilizing these properties in an injured population, it is critical to understand how these are influenced by age and sex in an uninjured population. A retrospective analysis was conducted of 118 uninjured Achilles tendons to evaluate the relationship between tendon mechanical properties, age and sex. Mechanical properties (shear modulus and viscosity) were assessed using continuous shear wave elastography. A moderator regression analysis was completed to examine the relationship between tendon mechanical properties, age and sex, after adjusting for body mass index and physical activity level. There was an interaction between age and sex for shear modulus (p=0.049, R² change=0.034). Females had a negative relationship between age and shear modulus (p=0.030, β=-0.350) but no relationship was observed for males (p=0.78, β=0.031). A positive relationship was found between age and viscosity (p=0.034, β=0.214). Increased viscosity was related to increased age with no difference between sexes. The effect of aging on shear modulus differed between men and women and may help explain sex specific injury risks and their differing response to mechanical load.

Myotonometry for the evaluation of Achilles tendon mechanical properties: a reliability and construct validity study

Objective

This study evaluates the intra-rater and inter-rater reliability of the MyotonPRO and its construct validity for the assessment of Achilles tendon stiffness.

Design

Reliability and construct validity study.

Methods

Forty healthy participants were assessed using the MyotonPRO by two raters on two different occasions. Tendon was evaluated in three different positions (relaxed, 0° plantarflexion and standing) and during different isometric contractions (range 0–3 kg). Reliability was calculated using intraclass correlation coefficient (ICC and 95% CI) standard error of measurement and minimal detectable change. Construct validity was evaluated between the different positions and the different contraction intensities using Friedman test.

Results

Intra-rater reliability was very high ICC_2,k 0.87–0.98. The reliability of the 0.5 kg contraction was moderate with an ICC_2,k of 0.59. Inter-rater reliability ranged from high to very high with an ICC_2,k of 0.76–0.86. The reliability of the 0.5 kg, 1 kg contraction and the standing position was moderate with an ICC_2,k of 0.55, 0.54 and 0.56 respectively. Inter-session reliability ranged from high to very high with an ICC_2,k of 0.70–0.89. The reliability of the 0.5 kg contraction was moderate with an ICC_2,k of 0.54. Construct validity was demonstrated between different contraction levels and different positions.

Conclusion

MyotonPRO is a reliable tool for the evaluation of Achilles tendon stiffness during different contraction levels and in different positions. Construct validity was supported by changes of tendon stiffness during the explored conditions. MyotonPRO can be implemented, as a ready to use device, in the evaluation of tendon tissue mechanical properties.

Biology of Tendon Stem Cells and Tendon in Aging

Both tendon injuries and tendinopathies, particularly rotator cuff tears, increase with tendon aging. Tendon stem cells play important roles in promoting tendon growth, maintenance, and repair. Aged tendons show a decline in regenerative potential coupled with a loss of stem cell function. Recent studies draw attention to aging primarily a disorder of stem cells. The micro-environment (“niche”) where stem cells resided in vivo provides signals that direct them to metabolize, self-renew, differentiate, or remain quiescent. These signals include receptors and secreted soluble factors for cell-cell communication, extracellular matrix, oxidative stress, and vascularity. Both intrinsic cellular deficits and aged niche, coupled with age-associated systemic changes of hormonal and metabolic signals can inhibit or alter the functions of tendon stem cells, resulting in reduced fitness of these primitive cells and hence more frequent injuries and poor outcomes of tendon repair. This review aims to summarize the biological changes of aged tendons. The biological changes of tendon stem cells in aging are reviewed after a systematic search of the PubMed. Relevant factors of stem cell aging including cell-intrinsic factors, changes of microenvironment, and age-associated systemic changes of hormonal and metabolic signals are examined, with findings related to tendon stem cells highlighted when literature is available. Future research directions on the aging mechanisms of tendon stem cells are discussed. Better understanding of the molecular mechanisms underlying the functional decline of aged tendon stem cells would provide insight for the rational design of rejuvenating therapies.

Age-associated changes in the response of tendon explants to stress deprivation is sex-dependent

Purpose of the Study: The incidence of tendon injuries increases dramatically with age, which presents a major clinical burden. While previous studies have sought to identify age-related changes in extracellular matrix structure and function, few have been able to explain fully why aged tissues are more prone to degeneration and injury. In addition, recent studies have also demonstrated that age-related processes in humans may be sex-dependent, which could be responsible for muddled conclusions in changes with age. In this study, we investigate short-term responses through an ex vivo explant culture model of stress deprivation that specifically questions how age and sex differentially affect the ability of tendons to respond to altered mechanical stimulus.Materials and Methods: We subjected murine flexor explants from young (4 months of age) and aged (22-24 months of age) male and female mice to stress-deprived culture conditions for up to 1 week and investigated changes in viability, cell metabolism and proliferation, matrix biosynthesis and composition, gene expression, and inflammatory responses throughout the culture period.Results and Conclusions: We found that aging did have a significant influence on the response to stress deprivation, demonstrating that aged explants have a less robust response overall with reduced metabolic activity, viability, proliferation, and biosynthesis. However, age-related changes appeared to be sex-dependent. Together, this work demonstrates that the aging process and the subsequent effect of age on the ability of tendons to respond to stress-deprivation are inherently different based on sex, where male explants favor increased activity, apoptosis, and matrix remodeling while female explants favor reduced activity and tissue preservation.

Mechanical properties and collagen fiber orientation of tendon in young and elderly

BACKGROUND

The purpose of this study was to investigate differences in the mechanical properties and collagen fiber orientation of tendon structures between young and elderly groups.

METHODS

The mechanical properties of tendon structures in medial gastrocnemius muscle were measured using ultrasonography during ramp and ballistic contractions. Tendon collagen fiber orientation was estimated from coefficient of variation (CV) of echogenicity on transverse ultrasonic images of Achilles tendon.

FINDINGS

Differences in elongation between ramp and ballistic contractions of elderly were significantly smaller than those of young group at 20-80% of MVC. During ramp contraction, hysteresis of elderly was significantly higher than that of young, whereas no difference in hysteresis during ballistic contraction was found between the two groups. Difference in hysteresis between ramp and ballistic contractions of elderly tended to be lower than that of young group. Mean echogenicity of elderly was significantly higher than that of young group, whereas no difference in CV of echogenicity was found between the two groups.

INTERPRETATION

These results suggest that smaller differences in elongation and hysteresis between ramp and ballistic contractions of elderly may be related to decreased water content within tendons. Furthermore, no difference in collagen fiber orientation of tendons was noted between the two groups.