Structure-function relationships in tendons: a review

Functionally distinct tendon fascicles exhibit different creep and stress relaxation behaviour

Most overuse tendinopathies are thought to be associated with repeated microstrain below the failure threshold, analogous to the fatigue failure that affects materials placed under repetitive loading. Investigating the progression of fatigue damage within tendons is therefore of critical importance. There are obvious challenges associated with the sourcing of human tendon samples for in vitro analysis so animal models are regularly adopted. However, data indicates that fatigue life varies significantly between tendons of different species and with different stresses in life. Positional tendons such as rat tail tendon or the bovine digital extensor are commonly applied in in vitro studies of tendon overuse, but there is no evidence to suggest their behaviour is indicative of the types of human tendon particularly prone to overuse injuries. In this study, the fatigue response of the largely positional digital extensor and the more energy storing deep digital flexor tendon of the bovine hoof were compared to the semitendinosus tendon of the human hamstring. Fascicles from each tendon type were subjected to either stress or strain controlled fatigue loading (cyclic creep or cyclic stress relaxation respectively). Gross fascicle mechanics were monitored after cyclic stress relaxation and the mean number of cycles to failure investigated with creep loading. Bovine extensor fascicles demonstrated the poorest fatigue response, while the energy storing human semitendinosus was the most fatigue resistant. Despite the superior fatigue response of the energy storing tendons, confocal imaging suggested a similar degree of damage in all three tendon types; it appears the more energy storing tendons are better able to withstand damage without detriment to mechanics.

Functional tissue engineering of tendon: Establishing biological success criteria for improving tendon repair

Improving tendon repair using Functional Tissue Engineering (FTE) principles has been the focus of our laboratory over the last decade. Although our primary goals were initially focused only on mechanical outcomes, we are now carefully assessing the biological properties of our tissue-engineered tendon repairs so as to link biological influences with mechanics. However, given the complexities of tendon development and healing, it remains challenging to determine which aspects of tendon biology are the most important to focus on in the context of tissue engineering. To address this problem, we have formalized a strategy to identify, prioritize, and evaluate potential biological success criteria for tendon repair. We have defined numerous biological properties of normal tendon relative to cellular phenotype, extracellular matrix and tissue ultra-structure that we would like to reproduce in our tissue-engineered repairs and prioritized these biological criteria by examining their relative importance during both normal development and natural tendon healing. Here, we propose three specific biological criteria which we believe are essential for normal tendon function: (1) scleraxis-expressing cells; (2) well-organized and axially-aligned collagen fibrils having bimodal diameter distribution; and (3) a specialized tendon-to-bone insertion site. Moving forward, these biological success criteria will be used in conjunction with our already established mechanical success criteria to evaluate the effectiveness of our tissue-engineered tendon repairs.

Healing of subcutaneous tendons: Influence of the mechanical environment at the suture line on the healing process

Tendon ruptures remain a significant musculoskeletal injury. Despite advances in surgical techniques and procedures, traditional repair techniques maintain a high incidence of rerupture or tendon elongation. Mechanical loading and biochemical signaling both control tissue healing. This has led some researchers to consider using a technique based on tension regulation at the suture line for obtaining good healing. However, it is unknown how they interact and to what extent mechanics control biochemistry. This review will open the way for understanding the interplay between mechanical loading and the process of tendon healing.

Fatigue loading of tendon

Tendon injuries, often called tendinopathies, are debilitating and painful conditions, generally considered to develop as a result of tendon overuse. The aetiology of tendinopathy remains poorly understood, and whilst tendon biopsies have provided some information concerning tendon appearance in late-stage disease, there is still little information concerning the mechanical and cellular events associated with disease initiation and progression. Investigating this in situ is challenging, and numerous models have been developed to investigate how overuse may generate tendon fatigue damage and how this may relate to tendinopathy conditions. This article aims to review these models and our current understanding of tendon fatigue damage. We review the strengths and limitations of different methodologies for characterizing tendon fatigue, considering in vitro methods that adopt both viable and non-viable samples, as well as the range of different in vivo approaches. By comparing data across model systems, we review the current understanding of fatigue damage development. Additionally, we compare these findings with data from tendinopathic tissue biopsies to provide some insights into how these models may relate to the aetiology of tendinopathy. Fatigue-induced damage consistently highlights the same microstructural, biological and mechanical changes to the tendon across all model systems and also correlates well with the findings from tendinopathic biopsy tissue. The multiple testing routes support matrix damage as an important contributor to tendinopathic conditions, but cellular responses to fatigue appear complex and often contradictory.

Mechanical factors in embryonic tendon development: potential cues for stem cell tenogenesis

Tendons are connective tissues required for motion and are frequently injured. Poor healing and inadequate return to normal tissue structure and mechanical function make tendon a prime candidate for tissue engineering; however functional tendons have yet to be engineered. The physical environment, from substrate stiffness to dynamic mechanical loading, may regulate tenogenic stem cell differentiation. Tissue stiffness and loading parameters derived from embryonic development may enhance tenogenic stem cell differentiation and tendon tissue formation. We highlight the current understanding of the mechanical environment experienced by embryonic tendons and how progenitor cells may sense and respond to physical inputs. We further discuss how mechanical factors have only recently been used to induce tenogenic fate in stem cells.

The critical role of interleukin-23 in spondyloarthropathy

The spondyloarthropathies represent highly enigmatic conditions and although their clinical features, anatomical distribution of disease and genetic predisposing factors have been known for some time, a unified concept of the basic pathobiology underlying these illnesses has remained undefined. Recently progress has been made because numerous independent studies have converged upon IL-23 as a central cytokine in spondyloarthropathy and the mechanism and sites of action of this cytokine have now become much clearer. These findings enable the rational design of therapeutic strategies which it is hoped will profoundly modify the progression of these diseases. We will review the anatomical sites affected and the evidence for the importance of IL-23 in these conditions, before drawing these lines of investigation together to propose a model for the unified understanding of spondyloarthropathy.

Helical sub-structures in energy-storing tendons provide a possible mechanism for efficient energy storage and return

The predominant function of tendons is to position the limb during locomotion. Specific tendons also act as energy stores. Energy-storing (ES) tendons are prone to injury, the incidence of which increases with age. This is likely related to their function; ES tendons are exposed to higher strains and require a greater ability to recoil than positional tendons. The specialized properties of ES tendons are thought to be achieved through structural and compositional differences. However, little is known about structure-function relationships in tendons. This study uses fascicles from the equine superficial digital flexor (SDFT) and common digital extensor (CDET) as examples of ES and positional tendons. We hypothesized that extension and recoil behaviour at the micro-level would differ between tendon types, and would alter with age in the injury-prone SDFT. Supporting this, the results show that extension in the CDET is dominated by fibre sliding. By contrast, greater rotation was observed in the SDFT, suggesting a helical component to fascicles in this tendon. This was accompanied by greater recovery and less hysteresis loss in SDFT samples. In samples from aged SDFTs, the amount of rotation and the ability to recover decreased, while hysteresis loss increased. These findings indicate that fascicles in the ES SDFT may have a helical structure, enabling the more efficient recoil observed. Further, the helix structure appears to alter with ageing; this coincides with a reduction in the ability of SDFT fascicles to recoil. This may affect tendon fatigue resistance and predispose aged tendons to injury.

The role of hind limb tendons in gibbon locomotion: springs or strings?

Tendon properties have an important effect on the mechanical behaviour of muscles, with compliant tendons allowing near-isometric muscle contraction and facilitating elastic energy storage and recoil. Stiff tendons, in contrast, facilitate rapid force transfer and precise positional control. In humans, the long Achilles tendon contributes to the mechanical efficiency of running via elastic energy storage and recovery, and its presence has been linked to the evolution of habitual bipedalism. Gibbons also possess relatively long hind limb tendons; however, their role is as yet unknown. Based on their large dimensions, and inferring from the situation in humans, we hypothesize that the tendons in the gibbon hind limb will facilitate elastic energy storage and recoil during hind-limb-powered locomotion. To investigate this, we determined the material properties of the gibbon Achilles and patellar tendon in vitro and linked this with available kinematic and kinetic data to evaluate their role in leaping and bipedalism. Tensile tests were conducted on tendon samples using a material testing machine and the load-displacement data were used to calculate stiffness, Young's modulus and hysteresis. In addition, the average stress-in-life and energy absorption capacity of both tendons were estimated. We found a functional difference between the gibbon Achilles and patellar tendon, with the Achilles tendon being more suitable for elastic energy storage and release. The patellar tendon, in contrast, has a relatively high hysteresis, making it less suitable to act as elastic spring. This suggests that the gibbon Achilles tendon might fulfil a similar function as in humans, contributing to reducing the locomotor cost of bipedalism by acting as elastic spring, while the high stiffness of the patellar tendon might favour fast force transfer upon recoil and, possibly, enhance leaping performance.

Investigating tendon mineralisation in the avian hindlimb: a model for tendon ageing, injury and disease

Mineralisation of the tendon tissue has been described in various models of injury, ageing and disease. Often resulting in painful and debilitating conditions, the processes underlying this mechanism are poorly understood. To elucidate the progression from healthy tendon to mineralised tendon, an appropriate model is required. In this study, we describe the spontaneous and non-pathological ossification and calcification of tendons of the hindlimb of the domestic chicken (Gallus gallus domesticus). The appearance of the ossified avian tendon has been described previously, although there have been no studies investigating the developmental processes and underlying mechanisms leading to the ossified avian tendon. The tissue and cells from three tendons - the ossifying extensor and flexor digitorum longus tendons and the non-ossifying Achilles tendon - were analysed for markers of ageing and mineralisation using histology, immunohistochemistry, cytochemistry and molecular analysis. Histologically, the adult tissue showed a loss of healthy tendon crimp morphology as well as markers of calcium deposits and mineralisation. The tissue showed a lowered expression of collagens inherent to the tendon extracellular matrix and presented proteins expressed by bone. The cells from the ossified tendons showed a chondrogenic and osteogenic phenotype as well as tenogenic phenotype and expressed the same markers of ossification and calcification as the tissue. A molecular analysis of the gene expression of the cells confirmed these results. Tendon ossification within the ossified avian tendon seems to be the result of an endochondral process driven by its cells, although the roles of the different cell populations have yet to be elucidated. Understanding the role of the tenocyte within this tissue and the process behind tendon ossification may help us prevent or treat ossification that occurs in injured, ageing or diseased tendon.

Inflammatory process induced by carrageenan in adjacent tissue triggers the acute inflammation in deep digital flexor tendon of rats

Tendinopathy is a pathology found mainly in the rotator cuff, patellar, Achilles and flexor tendons. Tendinopathy is a significant impediment to performance in athletes and in workers in the labor market. Some studies have indicated that inflammation in adjacent tissues may affect the rotator cuff and Achilles tendon. In this study alterations were verified in the extracellular matrix (ECM) of the deep digital flexor tendon after two periods (12 and 24 hr) of induction inflammation in rat paw. Wistar rats were divided into three groups: those that received injection of 1% carrageenan; those that received 0.9% NaCl; and those that received no application. The tendon was divided into distal (d), proximal (p), and intermediate (i) regions. Biochemical analyses were performed and included non-collagenous proteins (NCP), glycosaminoglycans (GAGs), hydroxyproline (HoPro) and metalloproteinases 2 and 9. Tissue sections were stained with toluidine blue, hematoxylin-eosin, and Ponceau SS and observed under polarization microscopy. Remarkable results were detected that included the presence of MMP-9, degradation of NCP and GAG and the presence of cellular infiltrate closer to digits in d region. The different concentrations of HoPro, as well as alterations in the organization of the collagen fibers showed the collagenous matrix undergoing some alterations. The results indicated that the induced inflammation in rat paw exhibited characteristics similar to the typical acute inflammatory process observed in tendons.

A conceptual framework for computational models of Achilles tendon homeostasis

Computational modeling of tendon lags the development of computational models for other tissues. A major bottleneck in the development of realistic computational models for Achilles tendon is the absence of detailed conceptual and theoretical models as to how the tissue actually functions. Without the conceptual models to provide a theoretical framework to guide the development and integration of multiscale computational models, modeling of the Achilles tendon to date has tended to be piecemeal and focused on specific mechanical or biochemical issues. In this paper, we present a new conceptual model of Achilles tendon tissue homeostasis, and discuss this model in terms of existing computational models of tendon. This approach has the benefits of structuring the research on relevant computational modeling to date, while allowing us to identify new computational models requiring development. The critically important functional issue for tendon is that it is continually damaged during use and so has to be repaired. From this follows the centrally important issue of homeostasis of the load carrying collagen fibrils within the collagen fibers of the Achilles tendon. Collagen fibrils may be damaged mechanically-by loading, or damaged biochemically-by proteases. Upon reviewing existing computational models within this conceptual framework of the Achilles tendon structure and function, we demonstrate that a great deal of theoretical and experimental research remains to be done before there are reliably predictive multiscale computational model of Achilles tendon in health and disease.

Tibialis posterior tenosynovitis and associated pes plano valgus in rheumatoid arthritis: electromyography, multisegment foot kinematics, and ultrasound features

Objective

To compare electromyographic (EMG), kinematic, kinetic, and ultrasound (US) features of pes plano valgus associated with US-confirmed tibialis posterior (TP) tenosynovitis in rheumatoid arthritis (RA) and healthy control subjects.

Methods

In this cross-sectional study, patients with RA and US-confirmed tenosynovitis of TP underwent gait analysis, including 3-dimensional kinematics, kinetics, and intramuscular EMG of TP, and findings were compared with a group of healthy individuals. The RA group also underwent B mode and power Doppler US scanning of the TP tendon to assess and score levels of pathology.

Results

Ten patients with RA, median (range) disease duration of 3 years (1–18 years), and 5 control subjects were recruited. Compared to control subjects, the RA patients walked slower and presented with moderate levels of foot-related disability. The mean ± SD Disease Activity Score in 28 joints was 4.6 ± 1.6. Increased magnitude of TP activity was recorded in the RA group compared to controls in the contact period of stance (P = 0.007), in conjunction with reduced ankle joint power (P = 0.005), reduced navicular height in the medial arch (P = 0.023), and increased forefoot dorsiflexion (P = 0.027). TP tendon thickening, fluid, and power Doppler signal were observed in the majority of patients.

Conclusion

This study has demonstrated, for the first time, increased TP EMG activity in the presence of US-confirmed TP tenosynovitis in RA. Altered muscle function occurred in conjunction with suboptimal mechanics, moderate levels of tendon pathology, and active disease. Targeted therapy may be warranted to reduce inflammation and mechanically off-load diseased tendon states.

Sports and exercise-related tendinopathies: a review of selected topical issues by participants of the second International Scientific Tendinopathy Symposium (ISTS) Vancouver 2012

In September 2010, the first International Scientific Tendinopathy Symposium (ISTS) was held in Umeå, Sweden, to establish a forum for original scientific and clinical insights in this growing field of clinical research and practice. The second ISTS was organised by the same group and held in Vancouver, Canada, in September 2012. This symposium was preceded by a round-table meeting in which the participants engaged in focused discussions, resulting in the following overview of tendinopathy clinical and research issues. This paper is a narrative review and summary developed during and after the second ISTS. The document is designed to highlight some key issues raised at ISTS 2012, and to integrate them into a shared conceptual framework. It should be considered an update and a signposting document rather than a comprehensive review. The document is developed for use by physiotherapists, physicians, athletic trainers, massage therapists and other health professionals as well as team coaches and strength/conditioning managers involved in care of sportspeople or workers with tendinopathy.

The jaw adductor muscle complex in teleostean fishes: evolution, homologies and revised nomenclature (osteichthyes: actinopterygii)

The infraclass Teleostei is a highly diversified group of bony fishes that encompasses 96% of all species of living fishes and almost half of extant vertebrates. Evolution of various morphological complexes in teleosts, particularly those involving soft anatomy, remains poorly understood. Notable among these problematic complexes is the adductor mandibulae, the muscle that provides the primary force for jaw adduction and mouth closure and whose architecture varies from a simple arrangement of two segments to an intricate complex of up to ten discrete subdivisions. The present study analyzed multiple morphological attributes of the adductor mandibulae in representatives of 53 of the 55 extant teleostean orders, as well as significant information from the literature in order to elucidate the homologies of the main subdivisions of this muscle. The traditional alphanumeric terminology applied to the four main divisions of the adductor mandibulae - A1, A2, A3, and Aω - patently fails to reflect homologous components of that muscle across the expanse of the Teleostei. Some features traditionally used as landmarks for identification of some divisions of the adductor mandibulae proved highly variable across the Teleostei; notably the insertion on the maxilla and the position of muscle components relative to the path of the ramus mandibularis trigeminus nerve. The evolutionary model of gain and loss of sections of the adductor mandibulae most commonly adopted under the alphanumeric system additionally proved ontogenetically incongruent and less parsimonious than a model of subdivision and coalescence of facial muscle sections. Results of the analysis demonstrate the impossibility of adapting the alphanumeric terminology so as to reflect homologous entities across the spectrum of teleosts. A new nomenclatural scheme is proposed in order to achieve congruence between homology and nomenclature of the adductor mandibulae components across the entire Teleostei.

Decellularized tendon extracellular matrix-a valuable approach for tendon reconstruction?

Tendon healing is generally a time-consuming process and often leads to a functionally altered reparative tissue. Using degradable scaffolds for tendon reconstruction still remains a compromise in view of the required high mechanical strength of tendons. Regenerative approaches based on natural decellularized allo- or xenogenic tendon extracellular matrix (ECM) have recently started to attract interest. This ECM combines the advantages of its intrinsic mechanical competence with that of providing tenogenic stimuli for immigrating cells mediated, for example, by the growth factors and other mediators entrapped within the natural ECM. A major restriction for their therapeutic application is the mainly cell-associated immunogenicity of xenogenic or allogenic tissues and, in the case of allogenic tissues, also the risk of disease transmission. A survey of approaches for tendon reconstruction using cell-free tendon ECM is presented here, whereby the problems associated with the decellularization procedures, the success of various recellularization strategies, and the applicable cell types will be thoroughly discussed. Encouraging in vivo results using cell-free ECM, as, for instance, in rabbit models, have already been reported. However, in comparison to native tendon, cells remain mostly inhomogeneously distributed in the reseeded ECM and do not align. Hence, future work should focus on the optimization of tendon ECM decellularization and recolonization strategies to restore tendon functionality.

Tendinopathies of the elbow, wrist, and hand: histopathology and clinical considerations

This article reviews the current opinion of the histopathological findings of common elbow, wrist, and hand tendinopathies. Implications for client management including examination, diagnosis, prognosis, intervention, and outcomes are addressed. Concepts for further research regarding common therapeutic interventions are discussed.

Reliability of a consensus-based ultrasound score for tenosynovitis in rheumatoid arthritis

OBJECTIVE

To produce consensus-based scoring systems for ultrasound (US) tenosynovitis and to assess the intraobserver and interobserver reliability of these scoring systems in rheumatoid arthritis (RA).

METHODS

We undertook a Delphi process on US-defined tenosynovitis and US scoring system of tenosynovitis in RA among 35 rheumatologists, experts in musculoskeletal US (MSUS), from 16 countries. Then, we assessed the intraobserver and interobserver reliability of US in scoring tenosynovitis on B-mode and with a power Doppler (PD) technique. Ten patients with RA with symptoms in the hands or feet were recruited. Ten rheumatologists expert in MSUS blindly, independently and consecutively scored for tenosynovitis in B-mode and PD mode three wrist extensor compartments, two finger flexor tendons and two ankle tendons of each patient in two rounds in a blinded fashion. Intraobserver reliability was assessed by Cohen's κ. Interobserver reliability was assessed by Light's κ. Weighted κ coefficients with absolute weighting were computed for B-mode and PD signal.

RESULTS

Four-grade semiquantitative scoring systems were agreed upon for scoring tenosynovitis in B-mode and for scoring pathological peritendinous Doppler signal within the synovial sheath. The intraobserver reliability for tenosynovitis scoring on B-mode and PD mode was good (κ value 0.72 for B-mode; κ value 0.78 for PD mode). Interobserver reliability assessment showed good κ values for PD tenosynovitis scoring (first round, 0.64; second round, 0.65) and moderate κ values for B-mode tenosynovitis scoring (first round, 0.47; second round, 0.45).

CONCLUSIONS

US appears to be a reproducible tool for evaluating and monitoring tenosynovitis in RA.

What is 'fascia'? A review of different nomenclatures

There are many different definitions of fascia. Here the three most common nomenclatures are compared, including that of the Federative International Committee on Anatomical Terminology (1998), the definition included in the latest British edition of Gray's Anatomy (2008) and the newer and more comprehensive terminology suggested at the last international Fascia Research Congress (2012). This review covers which tissues are included and excluded in each of these nomenclatures. The advantages and disadvantages of each terminology system are suggested and related to different fields of application, ranging from histology, tissue repair, to muscular force transmission and proprioception. Interdisciplinary communication involving professionals of different fields is also discussed.

Arthroscopic suture bridge transosseus equivalent fixation of rotator cuff tendon preserves intratendinous blood flow at the time of initial fixation

BACKGROUND

Current etiologic theories concerning healing rates in rotator cuff repair have focused on the blood supply in the tendinous portion of the cuff. We currently have little information regarding the effect of our repair techniques on this critical variable. We hypothesize that intratendinous blood flow is changed during transosseus equivalent tendon fixation.

METHODS

Eighteen consecutive patients with rotator cuff tears amenable to double row fixation were included in the study. Each patient underwent a standard arthroscopic transosseous equivalent double row fixation procedure using the Arthrex SutureBridge technique (Arthrex, Naples, FL, USA). After tying down of the medial row, a first set of recordings was taken using a custom laser doppler flowmetry probe (Perimed, Inc., Ohio, USA). A second recording was made following securing of the lateral PushLock anchors. The data were compared to determine the overall effect on blood flow associated with this technique.

RESULTS

Summated averages for the 2 groups show a significant (44.67%) decline in the blood flow present after the second row of implants are placed (P < .01). Individual calculations for regions of the cuff tear indicate significant differences in anterior third (P = .01), middle third (P < .01), and posterior third (P = .02) of the tear after transosseous equivalent fixation.

CONCLUSION

Completion of the construct with lateral anchors in the transosseous equivalent technique results in reduced but preserved blood flow in the tendon repair site. Further study is required to determine the implications for tendon healing.

CLINICAL RELEVANCE

Intratendinous blood flow is a variable that should be considered when evaluating repair methods in rotator cuff surgery.

Tenocyte contraction induces crimp formation in tendon-like tissue

Tendons are composed of longitudinally aligned collagen fibrils arranged in bundles with an undulating pattern, called crimp. The crimp structure is established during embryonic development and plays a vital role in the mechanical behaviour of tendon, acting as a shock-absorber during loading. However, the mechanism of crimp formation is unknown, partly because of the difficulties of studying tendon development in vivo. Here, we used a 3D cell culture system in which embryonic tendon fibroblasts synthesise a tendon-like construct comprised of collagen fibrils arranged in parallel bundles. Investigations using polarised light microscopy, scanning electron microscopy and fluorescence microscopy showed that tendon constructs contained a regular pattern of wavy collagen fibrils. Tensile testing indicated that this superstructure was a form of embryonic crimp producing a characteristic toe region in the stress-strain curves. Furthermore, contraction of tendon fibroblasts was the critical factor in the buckling of collagen fibrils during the formation of the crimp structure. Using these biological data, a finite element model was built that mimics the contraction of the tendon fibroblasts and monitors the response of the Extracellular matrix. The results show that the contraction of the fibroblasts is a sufficient mechanical impulse to build a planar wavy pattern. Furthermore, the value of crimp wavelength was determined by the mechanical properties of the collagen fibrils and inter-fibrillar matrix. Increasing fibril stiffness combined with constant matrix stiffness led to an increase in crimp wavelength. The data suggest a novel mechanism of crimp formation, and the finite element model indicates the minimum requirements to generate a crimp structure in embryonic tendon.

Effects of acute inflammation induced in the rat paw on the deep digital flexor tendon

The tendon is commonly affected by inflammation, and in such situations, the tissue undergoes a process of reorganization of the extracellular matrix to improve and regenerate the affected region. Little is known about the mechanisms that trigger inflammation in the tissues surrounding the affected area. The objective of this study was to biochemically and morphologically analyze the deep digital flexor tendon at the peak of acute inflammation in the rat paw. Wistar rats were divided into the following three groups: those that received injection of 1% carrageenan, those that received 0.9% NaCl, and those that received nothing. The deep digital flexor tendon was divided into the distal, proximal, and intermediate regions. For biochemical analysis, the tendons were treated with guanidine hydrochloride and analyzed by sodium dodecyl sulfate-polyacrilamide gel electrophoresis. Proteins, glycosaminoglycans (GAGs), and hydroxyproline were quantified, and metalloproteinases were analyzed. The GAGs were analyzed by agarose gel electrophoresis. Tissue sections were stained with hematoxylin-eosin, toluidine blue, and Ponceau SS. The content of proteins and GAGs was smaller in the group receiving the application of carrageenan. The concentration of hydroxyproline in the two tendon regions that respond to tension forces was higher in the inflammation group. The metalloproteinase-9 was detected in the distal region, and a thicker epitenon with cellular infiltrate was observed in the groups with inflamed paws. Meanwhile, a better organization of collagen bundles was observed in the two tension regions of that same group. Our results show that although the tendon was not directly inflamed, changes in the surrounding structural and biochemical parameters were observed.

Conversion of human bone marrow-derived mesenchymal stem cells into tendon progenitor cells by ectopic expression of scleraxis

Tendons and ligaments (T/L) are dense connective tissues of mesodermal origin. During embryonic development, the tendon-specific cells descend from a sub-set of mesenchymal progenitors condensed in the syndetome, a dorsolateral domain of the sclerotome. These cells are defined by the expression of the transcription factor scleraxis (Scx), which regulates tendon formation and several other characteristic genes, such as collagen type I, decorin, fibromodulin, and tenomodulin (Tnmd). In contrast to other mesenchymal progenitors, the genealogy and biology of the tenogenic lineage is not yet fully understood due to the lack of simple and efficient protocols enabling generation of progenitors in vitro. Here, we investigated whether the expression of Scx can lead to the direct commitment of mesenchymal stem cells (MSCs) into tendon progenitors. First, MSC derived from human bone marrow (hMSC) were lentivirally transduced with FLAG-Scx cDNA to establish 2 clonal cell lines, hMSC-Scx and hMSC-Mock. Subsequent to Scx transduction, hMSC underwent cell morphology change and had significantly reduced proliferation and clonogenicity. Gene expression analysis demonstrated that collagen type I and several T/L-related proteoglycans were upregulated in hMSC-Scx cells. When stimulated toward 3 different mesenchymal lineages, hMSC-Scx cells failed to differentiate into chondrocytes and osteoblasts, whereas adipogenic differentiation still occurred. Lastly, we detected a remarkable upregulation of the T/L differentiation gene Tnmd in hMSC-Scx. From these results, we conclude that Scx delivery results in the direct programming of hMSC into tendon progenitors and that the newly generated hMSC-Scx cell line can be a powerful and useful tool in T/L research.

Functional morphology of the thoracolumbar transversospinal muscles

STUDY DESIGN. A qualitative and semiquantitative study of the morphology of the human thoracolumbar transversospinal (TSP) muscles. OBJECTIVE. To further define the functional morphology of the thoracolumbar TSP muscles. SUMMARY OF BACKGROUND DATA. The TSP muscle group plays an important role in vertebral function but few studies have rigorously investigated their morphology throughout the thoracolumbar region and details on the location of motor endplates (MEPs) and fiber types are sparse. METHODS. Thoracolumbar TSP muscles were examined by microdissection in five cadavers (seven sides). MEPs were identified using acetylcholinesterase histochemistry in muscles between T5 and S4 unilaterally in two cadavers. The relative proportions of type I and type II skeletal muscle fibers were determined using immunohistochemistry on whole cross sections of every TSP muscle from one side of one cadaver (T5-S4). RESULTS.TSP morphology was homogeneous and consistent throughout the thoracolumbar region. Notable differences to standard descriptions included: (1) consistent attachments between muscles; (2) no discrete cleavage planes between muscles; and (3) attachment sites over the sacrum and to lumbar zygapophysial joints. Previously undescribed small muscles were found attaching to the medial sacrum. All TSP muscles were multipennate, with fibers arranged in parallel having one MEP per muscle fiber. Muscles were highly aerobic (mean proportion of type I fibers 89%), with the proportion of type I fibers decreasing caudally. A significantly greater proportion of type I fibers were found in the midthoracic compared to the low lumbar regions. CONCLUSION. The complex morphology of the TSP muscles indicates that they would be better classified as spinotransverse muscles. They are multipennate, highly aerobic, with fibers organized in parallel, an arrangement lending itself to "fine-tuning" of vertebral movements. Understanding their morphology has implications for investigation, treatment, motor control, and biomechanics.

Conversion of mechanical force into TGF-β-mediated biochemical signals

Mechanical forces influence homeostasis in virtually every tissue [1, 2]. Tendon, constantly exposed to variable mechanical force, is an excellent model in which to study the conversion of mechanical stimuli into a biochemical response [3-5]. Here we show in a mouse model of acute tendon injury and in vitro that physical forces regulate the release of active transforming growth factor (TGF)-β from the extracellular matrix (ECM). The quantity of active TGF-β detected in tissue exposed to various levels of tensile loading correlates directly with the extent of physical forces. At physiological levels, mechanical forces maintain, through TGF-β/Smad2/3-mediated signaling, the expression of Scleraxis (Scx), a transcription factor specific for tenocytes and their progenitors. The gradual and temporary loss of tensile loading causes reversible loss of Scx expression, whereas sudden interruption, such as in transection tendon injury, destabilizes the structural organization of the ECM and leads to excessive release of active TGF-β and massive tenocyte death, which can be prevented by the TGF-β type I receptor inhibitor SD208. Our findings demonstrate a critical role for mechanical force in adult tendon homeostasis. Furthermore, this mechanism could translate physical force into biochemical signals in a much broader variety of tissues or systems in the body.

On the anatomy and histology of the pubovisceral muscle enthesis in women

AIMS

The origin of the pubovisceral muscle (PVM) from the pubic bone is known to be at elevated risk for injury during difficult vaginal births. We examined the anatomy and histology of its enthesial origin to classify its type and see if it differs from appendicular entheses.

METHODS

Parasagittal sections of the pubic bone, PVM enthesis, myotendinous junction, and muscle proper were harvested from five female cadavers (51-98 years). Histological sections were prepared with hematoxylin and eosin, Masson's trichrome, and Verhoeff-Van Gieson stains. The type of enthesis was identified according to a published enthesial classification scheme. Quantitative imaging analysis was performed in sampling bands 2 mm apart along the enthesis to determine its cross-sectional area and composition.

RESULTS

The PVM enthesis can be classified as a fibrous enthesis. The PVM muscle fibers terminated in collagenous fibers that insert tangentially onto the periosteum of the pubic bone for the most part. Sharpey's fibers were not observed. In a longitudinal cross-section, the area of the connective tissue and muscle becomes equal approximately 8 mm from the pubic bone.

CONCLUSION

The PVM originates bilaterally from the pubic bone via fibrous entheses whose collagen fibers arise tangentially from the periosteum of the pubic bone.

Distribution patterns of fibre types in the triceps surae muscle group of chimpanzees and orangutans

Different locomotor and postural demands are met partly due to the varying properties and proportions of the muscle fibre types within the skeletal muscles. Such data are therefore important in understanding the subtle relationships between morphology, function and behaviour. The triceps surae muscle group is of particular interest when studying our closest living relatives, the non-human great apes, as they lack a significant external Achilles tendon, crucial to running locomotion in humans and other cursorial species. The aim of this study, therefore, was to determine the proportions of type I (slow) and type II (fast) fibres throughout these muscles in chimpanzees and orangutans using immunohistochemistry. The orangutan had a higher proportion of type I fibres in all muscles compared with the chimpanzees, related to their slower, more controlled movements in their arboreal habitat. The higher proportion of type II fibres in the chimpanzees likely reflects a compromise between their need for controlled mobility when arboreal, and greater speed and power when terrestrial. Overall, the proportion of slow fibres was greater in the soleus muscle compared with the gastrocnemius muscles, and there was some evidence of proximal to distal and medial to lateral variations within some muscles. This study has shown that not only do orangutans and chimpanzees have very different muscle fibre populations that reflect their locomotor repertoires, but it also shows how the proportion of fibre types provides an additional mechanism by which the performance of a muscle can be modulated to suit the needs of a species.

Retro-trochanteric sciatica-like pain: current concept

The aim of this manuscript is to review the current knowledge in terms of retro-trochanteric pain syndrome, make recommendations for diagnosis and differential diagnosis and offer suggestions for treatment options. The terminology in the literature is confusing and these symptoms can be referred to as 'greater trochanteric pain syndrome', 'trochanteric bursitis' and 'trochanteritis', among other denominations. The authors focus on a special type of sciatica, i.e. retro-trochanteric pain radiating down to the lower extremity. The impact of different radiographic assessments is discussed. The authors recommend excluding pathology in the spine and pelvic area before following their suggested treatment algorithm for sciatica-like retro-trochanteric pain.

Multi-finger interaction during involuntary and voluntary single finger force changes

Two types of finger interaction are characterized by positive co-variation (enslaving) or negative co-variation (error compensation) of finger forces. Enslaving reflects mechanical and neural connections among fingers, while error compensation results from synergic control of fingers to stabilize their net output. Involuntary and voluntary force changes by a finger were used to explore these patterns. We hypothesized that synergic mechanisms will dominate during involuntary force changes, while enslaving will dominate during voluntary finger force changes. Subjects pressed with all four fingers to match a target force that was 10% of their maximum voluntary contraction (MVC). One of the fingers was unexpectedly raised 5.0 mm at a speed of 30.0 mm/s. During finger raising the subject was instructed "not to intervene voluntarily". After the finger was passively lifted and a new steady-state achieved, subjects pressed down with the lifted finger, producing a pulse of force voluntarily. The data were analyzed in terms of finger forces and finger modes (hypothetical commands to fingers reflecting their intended involvement). The target finger showed an increase in force during both phases. In the involuntary phase, the target finger force changes ranged between 10.71 ± 1.89% MVC (I-finger) and 16.60 ± 2.26% MVC (L-finger). Generally, non-target fingers displayed a force decrease with a maximum amplitude of -1.49 ± 0.43% MVC (L-finger). Thus, during the involuntary phase, error compensation was observed--non-lifted fingers showed a decrease in force (as well as in mode magnitude). During the voluntary phase, enslaving was observed--non-target fingers showed an increase in force and only minor changes in mode magnitude. The average change in force of non-target fingers ranged from 21.83 ± 4.47% MVC for R-finger (M-finger task) to 0.71 ± 1.10% MVC for L-finger (I-finger task). The average change in mode of non-target fingers was between -7.34 ± 19.27% MVC for R-finger (L-finger task) and 7.10 ± 1.38% MVC for M-finger (I-finger task). We discuss a range of factors affecting force changes, from purely mechanical effects of finger passive lifting to neural synergic adjustments of commands to individual fingers. The data fit a recently suggested scheme that merges the equilibrium-point hypothesis (control with referent configurations) with the idea of hierarchical synergic control of multi-element systems.

Collagen type I amide I band infrared spectroscopy

Collagen fiber structure and organization have been found to vary in different tendon types. Differences have been reported in the FT-IR spectra of the amide I band of collagen-containing structures. In the present study, the FT-IR spectral characteristics of the amide I band of the bovine flexor tendon and the extended rat tail tendon were compared by using the diamond attenuated total reflectance technique. The objective was to associate FT-IR spectral characteristics in tendons with their different collagen fiber supraorganization and biomechanical properties. Nylon 6 and poly-L-lysine were used as polyamide models. Each of these materials was found to exhibit molecular order and crystallinity, as revealed by their birefringence. The following FT-IR parameters were evaluated: amide I band profile, absorption peaks and areas, and the 1655 cm⁻¹/1690 cm⁻¹ absorbance ratio. The amide I area and the 1655 cm⁻¹/1690 cm⁻¹ absorbance ratio were significantly higher for the bovine flexor tendon, indicating that its collagen fibers are richer in pyridinoline-type cross-linking, proline and/or hydroxyproline and H-bonding, and that these fibers are more packed and supraorganizationally ordered than those in the rat tail tendon. This conclusion is additionally supported by differences in collagen solubility and biochemical/biomechanical properties of the tendons.

Connecting muscles to tendons: tendons and musculoskeletal development in flies and vertebrates

The formation of the musculoskeletal system represents an intricate process of tissue assembly involving heterotypic inductive interactions between tendons, muscles and cartilage. An essential component of all musculoskeletal systems is the anchoring of the force-generating muscles to the solid support of the organism: the skeleton in vertebrates and the exoskeleton in invertebrates. Here, we discuss recent findings that illuminate musculoskeletal assembly in the vertebrate embryo, findings that emphasize the reciprocal interactions between the forming tendons, muscle and cartilage tissues. We also compare these events with those of the corresponding system in the Drosophila embryo, highlighting distinct and common pathways that promote efficient locomotion while preserving the form of the organism.

Novel strategies in tendon and ligament tissue engineering: Advanced biomaterials and regeneration motifs

Tendon and ligaments have poor healing capacity and when injured often require surgical intervention. Tissue replacement via autografts and allografts are non-ideal strategies that can lead to future problems. As an alternative, scaffold-based tissue engineering strategies are being pursued. In this review, we describe design considerations and major recent advancements of scaffolds for tendon/ligament engineering. Specifically, we outline native tendon/ligament characteristics critical for design parameters and outcome measures, and introduce synthetic and naturally-derived biomaterials used in tendon/ligament scaffolds. We will describe applications of these biomaterials in advanced tendon/ligament engineering strategies including the utility of scaffold functionalization, cyclic strain, growth factors, and interface considerations. The goal of this review is to compile and interpret the important findings of recent tendon/ligament engineering research in an effort towards the advancement of regenerative strategies.

The atypical homeodomain transcription factor Mohawk controls tendon morphogenesis

The Mohawk homeobox (Mkx) gene encodes a new atypical homeodomain-containing protein with transcriptional repressor activity. Mkx mRNA exhibited dynamic expression patterns during development of the palate, somite, kidney, and testis, suggesting that it may be an important regulator of multiple developmental processes. To investigate the roles of Mkx in organogenesis, we generated mice carrying a null mutation in this gene. Mkx(-/-) mice survive postnatally and exhibit a unique wavy-tail phenotype. Close examination revealed that the mutant mice had smaller tendons than wild-type littermates and that the rapid postnatal growth of collagen fibrils in tendons was disrupted in Mkx(-/-) mice. Defects in tendon development were detected in the mutant mouse embryos as early as embryonic day 16.5 (E16.5). Although collagen fibril assembly initially appeared normal, the tendons of Mkx(-/-) embryos expressed significantly reduced amounts of collagen I, fibromodulin, and tenomodulin in comparison with control littermates. We found that Mkx mRNA was strongly expressed in differentiating tendon cells during embryogenesis and in the tendon sheath cells in postnatal stages. In addition to defects in tendon collagen fibrillogenesis, Mkx(-/-) mutant mice exhibited abnormal tendon sheaths. These results identify Mkx as an important regulator of tendon development.

Tendon and ligament fibrillar crimps give rise to left-handed helices of collagen fibrils in both planar and helical crimps

Collagen fibres in tendons and ligaments run straight but in some regions they show crimps which disappear or appear more flattened during the initial elongation of tissues. Each crimp is formed of collagen fibrils showing knots or fibrillar crimps at the crimp top angle. The present study analyzes by polarized light microscopy, scanning electron microscopy, transmission electron microscopy the 3D morphology of fibrillar crimp in tendons and ligaments of rat demonstrating that each fibril in the fibrillar region always twists leftwards changing the plane of running and sharply bends modifying the course on a new plane. The morphology of fibrillar crimp in stretched tendons fulfills the mechanical role of the fibrillar crimp acting as a particular knot/biological hinge in absorbing tension forces during fibril strengthening and recoiling collagen fibres when stretching is removed. The left-handed path of fibrils in the fibrillar crimp region gives rise to left-handed fibril helices observed both in isolated fibrils and sections of different tendons and ligaments (flexor digitorum profundus muscle tendon, Achilles tendon, tail tendon, patellar ligament and medial collateral ligament of the knee). The left-handed path of fibrils represents a new final suprafibrillar level of the alternating handedness which was previously described only from the molecular to the microfibrillar level. When the width of the twisting angle in the fibrillar crimp is nearly 180 degrees the fibrils appear as left-handed flattened helices forming crimped collagen fibres previously described as planar crimps. When fibrils twist with different subsequent rotational angles (< 180 degrees ) they always assume a left-helical course but, running in many different nonplanar planes, they form wider helical crimped fibres.

Scientific bases and clinical utilisation of the calf-raise test

BACKGROUND

Athletes commonly sustain injuries to the triceps surae muscle-tendon unit. The calf-raise test (CRT) is frequently employed in sports medicine for the detection and monitoring of such injuries. However, despite being widely-used, a recent systematic review found no universal consensus relating to the test's purpose, parameters, and standard protocols.

OBJECTIVES

The purpose of this paper is to provide a clinical perspective on the anatomo-physiological bases underpinning the CRT and to discuss the utilisation of the test in relation to the structure and function of the triceps surae muscle-tendon unit.

DESIGN

Structured narrative review.

METHODS

Nine electronic databases were searched using keywords and MESH headings related to the CRT and the triceps surae muscle-tendon unit anatomy and physiology. A hand-search of reference lists and relevant journals and textbooks complemented the electronic search.

SUMMARY

There is evidence supporting the clinical use of the CRT to assess soleus and gastrocnemius, their shared aponeurosis, the Achilles tendon, and the combined triceps surae muscle-tendon unit. However, employing the same clinical test to assess all these structures and their associated functions remains challenging.

CONCLUSIONS

Further refinement of the CRT for the triceps surae muscle-tendon unit is needed. This is vital to support best practice utilisation, standardisation, and interpretation of the CRT in sports medicine.

Recruitment and maintenance of tendon progenitors by TGFbeta signaling are essential for tendon formation

Tendons and ligaments mediate the attachment of muscle to bone and of bone to bone to provide connectivity and structural integrity in the musculoskeletal system. We show that TGFbeta signaling plays a major role in the formation of these tissues. TGFbeta signaling is a potent inducer of the tendon progenitor (TNP) marker scleraxis both in organ culture and in cultured cells, and disruption of TGFbeta signaling in Tgfb2(-/-);Tgfb3(-/-) double mutant embryos or through inactivation of the type II TGFbeta receptor (TGFBR2; also known as TbetaRII) results in the loss of most tendons and ligaments in the limbs, trunk, tail and head. The induction of scleraxis-expressing TNPs is not affected in mutant embryos and the tendon phenotype is first manifested at E12.5, a developmental stage in which TNPs are positioned between the differentiating muscles and cartilage, and in which Tgfb2 or Tgfb3 is expressed both in TNPs and in the differentiating muscles and cartilage. TGFbeta signaling is thus essential for maintenance of TNPs, and we propose that it also mediates the recruitment of new tendon cells by differentiating muscles and cartilage to establish the connections between tendon primordia and their respective musculoskeletal counterparts, leading to the formation of an interconnected and functionally integrated musculoskeletal system.

The fascia of the limbs and back--a review

Although fasciae have long interested clinicians in a multitude of different clinical and paramedical disciplines, there have been few attempts to unite the ensuing diverse literature into a single review. The current article gives an anatomical perspective that extends from the gross to the molecular level. For expediency, it deals only with fascia in the limbs and back. Particular focus is directed towards deep fascia and thus consideration is given to structures such as the fascia lata, thoracolumbar fascia, plantar and palmar fascia, along with regional specializations of deep fascia such as retinacula and fibrous pulleys. However, equal emphasis is placed on general aspects of fascial structure and function, including its innervation and cellular composition. Among the many functions of fascia considered in detail are its ectoskeletal role (as a soft tissue skeleton for muscle attachments), its importance for creating osteofascial compartments for muscles, encouraging venous return in the lower limb, dissipating stress concentration at entheses and acting as a protective sheet for underlying structures. Emphasis is placed on recognizing the continuity of fascia between regions and appreciating its key role in coordinating muscular activity and acting as a body-wide proprioceptive organ. Such considerations far outweigh the significance of viewing fascia in a regional context alone.

Tubulin polymerization-promoting protein family member 3, Tppp3, is a specific marker of the differentiating tendon sheath and synovial joints

Tppp3, a member of the Tubulin polymerization-promoting protein family, is an intrinsically unstructured protein that induces tubulin polymerization. We show that Tppp3 is a distinct marker in the developing musculoskeletal system. In tendons, Tppp3 is expressed in cells at the circumference of the developing tendons, likely the progenitors of connective tissues that surround tendons: the tendon sheath, epitenon, and paratenon. These tissues form an elastic sleeve around tendons and provide lubrication to minimize friction between tendons and surrounding tissues. Tppp3 is the first molecular marker of the tendon sheath, opening the door for direct examination of these tissues. Tppp3 is also expressed in forming synovial joints. The onset of Tppp3 expression in joints coincides with cavitation, representing a molecular marker that can be used to indicate this stage in joint transition in joint differentiation. In late embryonic stages, Tppp3 expression highlights other demarcation lines that surround differentiating tissues in the forelimb.

Electron microscope 3D reconstruction of branched collagen fibrils in vivo

The ability of tendon to withstand tensile forces is largely attributable to an extracellular matrix containing parallel collagen fibrils organized into fascicles. A major belief is that force is transmitted between collagen fibrils via interactions of molecules at the fibril surface. However, there is existing evidence (reviewed here) for persistent connections between fibrils formed by interfibrillar fusion. Furthermore, in vitro studies have shown the ability of the ends of fibrils to fuse together. In this study, we show using serial section electron microscopy of embryonic mouse-tail tendon further evidence for interfibril fusion in vivo. We showed: (1) fibrils fused via Y-shaped branches without disruption of the 67 nm D-periodicity, (2) the frequency of the branches was approximately 1:20 000 D-periods, and (3) the small angle of the Y ranged from 4 degrees to 10 degrees, indicating a structure-based mechanism of branch formation. The regular occurrence of Y-shaped branches between collagen fibrils suggests direct force transmission between fibrils. Furthermore, the formation of the Y-shaped branches by tip-to-shaft fusion would explain the paucity of fibril tips in vivo.

Potential role of ginseng in the treatment of colorectal cancer

Colorectal cancer remains one of the most prevalent cancer and a leading cause of cancer related death in the US. Many currently used chemotherapeutic agents are derived from botanicals. Identifying herbal sources, including those from ginseng family, to develop better anti-cancer therapies remains an essential step in advancing the treatment of the cancer. In this article, potential roles of ginseng herbs, especially American ginseng and notoginseng, in colorectal cancer therapeutics are presented. The major pharmacologically active constituents of ginsengs are ginsenosides, which can be mainly classified as protopanaxadiol and protopanaxatriol groups. Structure-activity relationship between their chemical structures and pharmacological activities are discussed. In addition, various steaming temperature and time treatment of the ginseng herbs can change ginsenoside profiles, and enhance their anti-cancer activities. This heat treatment process may increase the role of ginseng in treating colorectal cancer.

A finite dissipative theory of temporary interfibrillar bridges in the extracellular matrix of ligaments and tendons

The structural integrity and the biomechanical characteristics of ligaments and tendons result from the interactions between collagenous and non-collagenous proteins (e.g. proteoglycans, PGs) in the extracellular matrix. In this paper, a dissipative theory of temporary interfibrillar bridges in the anisotropic network of collagen type I, embedded in a ground substance, is derived. The glycosaminoglycan chains of decorin are assumed to mediate interactions between fibrils, behaving as viscous structures that transmit deformations outside the collagen molecules. This approach takes into account the dissipative effects of the unfolding preceding fibrillar elongation, together with the slippage of entire fibrils and the strain-rate-dependent damage evolution of the interfibrillar bridges. Thermodynamic consistency is used to derive the constitutive equations, and the transition state theory is applied to model the rearranging properties of the interfibrillar bridges. The constitutive theory is applied to reproduce the hysteretic spectrum of the tissues, demonstrating how PGs determine damage evolution, softening and non-recoverable strains in their cyclic mechanical response. The theoretical predictions are compared with the experimental response of ligaments and tendons from referenced studies. The relevance of the proposed model in mechanobiology research is discussed, together with several applications from medical practice to bioengineering science.