Tendon Structure Research Articles

The Immediate Effect of Cumulative Transverse Strain via Exercise on the Achilles Tendon in Individuals with and Without Flat Feet.

Flat feet change lower extremity alignment, and it may change the load distribution on Achilles tendon during exercise. The purpose of the present study was to investigate the immediate effect of cumulative transverse strain via resistive ankle plantarflexion exercise on the Achilles tendon in individuals with flat feet. Fourteen individuals with flat feet and 14 age-matched individuals with normal foot posture were enrolled in the present study. Achilles tendon thickness was measured by an ultrasonography device with a linear probe at 3 points: 1 cm (AT-1), 2 cm (AT-2), and 3 cm (AT-3) proximal to the superior aspect of the calcaneus. Ultrasonography measurements were performed before and after participants completed 90 repetitions of double-leg calf raise exercises which included moving the foot from full ankle dorsiflexion to full ankle plantarflexion. Achilles tendon thickness at all points measured was thinner in the flat feet group at both pre- and post-exercise conditions compared with that of the control group (p<0.05). Achilles tendon thickness at AT-1, AT-2, and AT-3 decreased after the exercise in both groups (p<0.001). The differences in Achilles tendon thickness at all points measured between pre- and post-exercise conditions were lower in individuals with flat feet than those of the control group (p<0.05). There was a significant decrease in Achilles tendon thickness after exercise in both groups; however, the tendon thickness markedly diminished in individuals with normal foot posture. The results are thought to result from changes in tendon structure and in load distribution on the Achilles tendon.

Tendon Repair and Regeneration Using Bioinspired Fibrillation Engineering That Mimicked the Structure and Mechanics of Natural Tissue.

Replicating the controlled nanofibrillar architecture of collagenous tissue represents a promising approach in the design of tendon replacements that have tissue-mimicking biomechanics─outstanding mechanical strength and toughness, defect tolerance, and fatigue and fracture resistance. Guided by this principle, a fibrous artificial tendon (FAT) was constructed in the present study using an engineering strategy inspired by the fibrillation of a naturally spun silk protein. This bioinspired FAT featured a highly ordered molecular and nanofibrillar architecture similar to that of soft collagenous tissue, which exhibited the mechanical and fracture characteristics of tendons. Such similarities provided the motivation to investigate FAT for applications in Achilles tendon defect repair. In vitro cellular morphology and expression of tendon-related genes in cell culture and in vivo modeling of tendon injury clearly revealed that the highly oriented nanofibrils in the FAT substantially promoted the expression of tendon-related genes combined with the Achilles tendon structure and function. These results provide confidence about the potential clinical applications of the FAT.

Cell Guiding Multicomponent Nanoyarn Tendon Scaffolds with Tunable Morphology and Flexibility.

Nanofibrous scaffolds are widely investigated for tendon tissue engineering due to their porous structure, high flexibility, and the ability to guide cells in a preferred direction. Previous research has shown that providing a microenvironment similar to in vivo settings improves tissue regeneration. Therefore, in this work, ingenious multicomponent nanoyarn scaffolds that mimic the fibrillar and tubular structures of tendons are developed for the first time through electrospinning and bundling nanoyarns followed by electrospinning of a nanofibrous shell around the bundle. Multicomponent nanoyarn scaffolds out of poly(ε-caprolactone) with varying porosity, density, and diameter were successfully produced by coelectrospinning with water-soluble poly(2-ethyl-2-oxazoline) as a sacrificial component. The diameter and fiber orientation of the nanoyarns were successfully tuned based on parameter-morphology models obtained by the design of experiments. Cyclic bending tests were performed, indicating that the flexibility of the multicomponent nanoyarn scaffolds depends on the morphology and can be tuned through controlling the number of nanoyarns in the bundle and the porosity. Indirect and direct cell culture tests using mouse and equine tendon cells revealed excellent cytocompatibility of the nanofibrous products and demonstrated the potential of the nanoyarns to guide the growing cells along the nanofiber direction, which is crucial for tendon tissue engineering.

Achilles Tendinopathy Pathogenesis and Management: A Narrative Review.

The Achilles tendon is the thickest and strongest tendon of the human body, and it is frequently injured during sports activity. The incidence of Achilles tendon pathologies has increased over recent decades, especially in the last few years, because of increased sports participation among the general population and due to the diffusion of competitive sports at a high level. Tendinopathies are common in athletes and in middle-aged overweight patients. The term "tendinopathy" refers to a condition characterised clinically by pain and swelling, with functional limitations of tendon and nearby structures, and consequently to chronic failure of healing response process. Tendinopathies can produce marked morbidity, and at present, scientifically validated management modalities are limited. Despite the constantly increasing interest and number of studies about Achilles tendinopathy (AT), there is still not a consensual point of view on which is the best treatment, and its management is still controversial. AT can be treated conservatively primarily, with acceptable results and clinical outcomes. When this approach fails, surgery should be considered. Several surgical procedures have been described for both conditions with a relatively high rate of success with few complications and the decision for treatment in patients with AT should be tailored on patient's needs and level of activity. The aim of this article is to give insights about the pathogenesis and most used and recent treatment options for AT.

Deficits in neuromuscular control of increasing force in patients with chronic lateral epicondylitis.

Objective: This study investigated the neuromuscular control of increasing and releasing force in patients with chronic lateral epicondylitis (CLE). Methods: Fifteen patients with CLE (10 males, 5 females, 46.5 ± 6.3years) and fifteen healthy participants (9 males, 6 females, 45.3 ± 2.5years) participated in this study. In addition to power grip and maximal voluntary contraction (MVC) of wrist extension, force fluctuation dynamics and characteristics of inter-spike intervals (ISI) of motor units (MUs) with various recruitment thresholds in the extensor carpi radialis brevis (ECRB) and extensor carpi radialis longus (ECRL) during a designated force-tracking task with a trapezoidal target (0%-75%-0% MVC) were assessed. Results: Besides a smaller MVC of wrist extension, the patients exhibited significantly greater task errors (p = 0.007) and force fluctuations (p = 0.001) during force increment than the healthy counterparts. Nevertheless, no force variables significantly differed between groups during force release (p > 0.05). During force increment, the amplitudes of the motor unit action potential of the ECRB and ECRL muscles of the patients were smaller than those of the heathy counterparts (p < 0.001). The patient group also exhibited a higher percentage of motor units (MU) with lower recruitment threshold (<5% MVC) in the ECRL/ECRB muscles and a lower percentage of MU with higher recruitment threshold (>40% MVC) in the ECRB muscle, compared to the healthy group. During force increment, the patient group exhibited a higher rate of decrease in inter-spike intervals (ISIs) of motor units with lower recruitment thresholds (<10% MVC) in the ECRB and ECRL muscles, compared to the control group (p < 0.005). Conclusion: The patients with CLE exhibited more pronounced impairment in increasing force than in releasing force. This impairment in increasing force is attributed to deficits in tendon structure and degenerative changes in the larger motor units of the wrist extensors. To compensate for the neuromuscular deficits, the rate of progressive increase in discharge rate of the remaining smaller motor units (MUs) is enhanced to generate force. Significance: The deficits in neuromuscular control observed in CLE with degenerative changes cannot be fully explained by the experimental pain model, which predicts pain-related inhibition on low-threshold motor units.

Musculoskeletal Ultrasound: An Essential Tool in Diagnosing Patellar Tendon Injuries.

Musculoskeletal (MSK) ultrasound has emerged as a vital tool in diagnosing patellar tendon injuries. Traditional imaging techniques, such as X-rays and Magnetic Resonance Imaging, have certain limitations in assessing soft tissue structures or may not be easily accessible. MSK ultrasound, with its high-resolution, real-time imaging capabilities, offers a cost-effective, safe, and patient-friendly alternative. It allows for accurate visualization of the patellar tendon's structure and function, thereby facilitating the identification of pathological changes such as thickening, thinning, or disruption which aids in diagnosing conditions such as tendonitis, partial tears, and ruptures. Furthermore, MSK ultrasound serves as an invaluable tool for guiding interventions like injections, as it provides real-time imaging. This article explores the role and benefits of MSK ultrasound in diagnosing patellar tendon injuries, highlighting its cost-effectiveness, accessibility, real-time assessment capabilities, and reduced patient burden compared to other imaging modalities. Despite its numerous benefits, the need for ongoing research to enhance its utility is highlighted. As technology advances, MSK ultrasound is set to revolutionize the early detection and management of patellar tendon injuries.

Design of an optical fiber embedded smart artificial tendon for deformation monitoring

Advances in materials development provide new insights on smart structures as the ones presented in this work, which consists of multifunctional artificial tendons with structural applications and the ability of measuring deformations. The tendons are produced using Flexible UV cured and Polyurethane (heat-cured) resins. Silica optical fibers were applied as intensity variation sensors to measure the deformations in the tendons. The optical fibers have an additional capability to provide a reinforcement to the bioinspired tendon structure. The mechanical capabilities of the tendons are also analyzed, with the PU tendon reaching 30% strain and withstanding stresses up to 1.0 MPa without suffering damage. The tendons are also subject in dynamic tests, where they present sensitivity to the strain rate. Using linear regressions, intensity variation rates into the 2 ∼ 2.6 × 104 a.u. × s−1 range are estimated with determination coefficient (R2) higher than 0.9. Similarly, in the static bending test, the variation of the power as a function of the flexion can also be approximated by a linear behavior with a R2 of 0.97. Thus, the proposed approach resulted in an optical fiber-embedded biomimetic artificial tendon that can perform not only the structural behavior, but also can measure the deformations in the structure, which are important data for the control of robotic devices.

Calcification alters the viscoelastic properties of tendon fascicle bundles depending on matrix content.

Tendon fascicle bundles are often used as biological grafts and thus must meet certain quality requirements, such as excluding calcification, which alters the biomechanical properties of soft tissues. In this work, we investigate the influence of early-stage calcification on the mechanical and structural properties of tendon fascicle bundles with varying matrix content. The calcification process was modeled using sample incubation in concentrated simulated body fluid. Mechanical and structural properties were investigated using uniaxial tests with relaxation periods, dynamic mechanical analysis, as well as magnetic resonance imaging and atomic force microscopy. Mechanical tests showed that the initial phase of calcification causes an increase in the elasticity, storage, and loss modulus, as well as a drop in the normalized value of hysteresis. Further calcification of the samples results in decreased modulus of elasticity and a slight increase in the normalized value of hysteresis. Analysis via MRI and scanning electron microscopy showed that incubation alters fibrillar relationships within the tendon structure and the flow of body fluids. In the initial stage of calcification, calcium phosphate crystals are barely visible; however, extending the incubation time for the next 14 days results in the appearance of calcium phosphate crystals within the tendon structure and leads to damage in its structure. Our results show that the calcification process modifies the collagen-matrix relationships and leads to a change in their mechanical properties. These findings will help to understand the pathogenesis of clinical conditions caused by calcification process, leading to the development of effective treatments for these conditions. STATEMENT OF SIGNIFICANCE: This study investigates how calcium mineral deposition in tendons affects their mechanical response and which processes are responsible for this phenomenon. By analyzing the elastic and viscoelastic properties of animal fascicle bundles affected by calcification induced via incubation in concentrated simulated body fluid, the study sheds light on the relationship between structural and biochemical changes in tendons and their altered mechanical response. This understanding is crucial for optimizing tendinopathy treatment and preventing tendon injury. The findings provide insights into the calcification pathway and its resulting changes in the biomechanical behaviors of affected tendons, which have been previously unclear.

Ultrasonographic assessment of knee joint in patients with diabetes mellitus: comparison of sonographic changes in distal femoral cartilage and tendon structures with non-diabetics patients.

The aim of this study was to evaluate the adverse effects of diabetes mellitus on the knee joint by using ultrasonography. One hundred and two subjects with diabetes for 5 years and more were compared prospectively with 93 age and sex-matched healthy subjects. Individuals in both groups were aged between 40-55, had a body mass index below 30 kg/m2, and had no knee joint complaints. Femoral cartilage thickness, cartilage surface, quadriceps and patellar tendon thickness in both knees were assessed by ultrasonography using a 5-12 mHz linear transducer. According to ultrasonographic findings, thin and irregular femoral cartilage was more common in diabetic patients than in healthy controls (p<0.05). Diabetic patients had thinner quadriceps tendons compared to the control group (p<0.001). No statistically significant difference was recorded in patellar tendon thickness (right knee p=0.697, left knee p=0.639). The presence of effusion in the suprapatellar recess of the right knee was more common in diabetics than non-diabetics (p=0.006). Irregularity and thinning of the distal femoral cartilage in diabetics may indicate cartilage degeneration. In addition, the decrease in the thickness of the quadriceps tendon may lead to instability and adversely affect the knee joint. These sonographic findings may indicate early knee joint degeneration, so ultrasonography may help determine the possible risk of osteoarthritis in diabetic patients.

Functional Chimeric Double-barrel Fibula and Reinnervated Peroneus Brevis Osteomyocutaneous Flap for One-stage Forearm Reconstruction.

Reconstructing a mangled limb is complex and requires expertise in both bone and soft-tissue reconstruction, particularly when there is significant muscle loss. Typically, multistage surgery is necessary, starting with soft-tissue coverage, followed by bone grafting and tendon transfers. Sometimes, microsurgical techniques such as vascularized bone grafts and free functional muscle transfers are necessary, especially when there is a bone defect of over 6 cm; the soft-tissue environment is infected, scarred, or poorly vascularized; or there are extensive musculotendinous injuries. We treated a 34-year-old man who had a crushed left forearm resulting in an 18 × 8 cm open wound, 5-cm radius and 7-cm ulna bone defects, loss of the extensor pollicis longus and brevis muscles, and extensive injuries to the other musculotendinous structures of the forearm. To accomplish a one-stage reconstruction, we used a chimeric fibula osteomyocutaneous flap that included a 20 × 10 cm skin flap, peroneus brevis muscle with its motor nerve, and two segments of fibula. The proximal and distal fibula segments were used for ulnar and radial bone reconstruction, respectively, preserving forearm supination and pronation. The peroneus brevis tendon was sutured to the extensor pollicis longus tendon, and its motor nerve was coaptated with the posterior interosseous nerve to restore thumb extension. The skin flap provided complete coverage of all exposed bone and tendon structures. At the 12-month follow-up, the patient regained full extension of the thumb, and there were no difficulties with forearm supination and pronation or with foot eversion and plantar flexion at the donor leg.

Patellofemoral pain and musculoskeletal features in young pre- and post-pubertal female dancers

ABSTRACT The aim of this study was to examine associations between patellofemoral pain (PFP) and musculoskeletal features (such as tendon structure and bone properties) in young (pre- and post-pubertal) female dancers. A total of 49 dancers participated in this study (mean age 13.6 ± 2.9; weight 47.0 ± 13.2; height 153.7 ± 12.9 and body mass index (BMI) 19.4 ± 3.1) and were assessed for the following factors: dance background and Tanner stage through interviews; ultrasonography assessments of bone properties and patellar tendon structure through ultrasonographic tissue characterization and quantitative ultrasound, respectively; and anthropometric measurements, muscle strength, range of motion (ROM), hypermobility and PFP through physical examinations. PFP was found in 49% of the participants. Post-pubertal dancers with no-PFP were found to have greater muscle strength, greater radial and tibial properties, and better tendon structure compared to pre-pubertal dancers with PFP and compared to pre-pubertal dancers with no-PFP [F(2, 41) = 18.64, p < .001; F(2, 41) = 20.46, p < .001; F(2, 41) = 33.06, p < .001; and, F(2, 41) = 6.02, p = .007, respectively]. Logistic regression showed that tibial bone properties and range of movement (ROM) in hip external rotation were significantly associated with PFP [odds ratio (OR) = .889 and OR = 2.653, respectively; Cox & Snell R2 = .701]. The study revealed a high prevalence of PFP among young dancers, with low bone properties and hyperjoint ROM emerging as the main factors that are related to PFP. These findings should be addressed by medical teams, athletic trainers, and dance teachers regarding the need for implementing modifications to dance training programmes and injury-prevention strategies in young pre-pubertal dancers.

Influence of Staphylococcus epidermidis on Collagen Crimp Patterns of Soft Tissue Allograft

Background: Postoperative infections, commonly from Staphylococcus epidermidis, may result in anterior cruciate ligament graft failure and necessitate revision surgery. In biomechanical studies, S. epidermidis has been shown to establish biofilms on tendons and reduce graft strength. Purpose/Hypothesis: The goal of this study was to determine the effect of bacterial bioburden on the collagen structure of tendon. It was hypothesized that an increase in S. epidermidis biofilm would compromise tendon crimp, a pattern necessary for mechanical integrity, of soft tissue allografts. Study design: Controlled laboratory study. Methods: Cultures of S. epidermidis were used to inoculate tibialis anterior cadaveric tendons. Conditions assessed included 5 × 105 colony-forming units or concentrated spent media from culture (no living bacteria). Incubation times of 30 minutes, 3 hours, 6 hours, and 24 hours were utilized. Second-harmonic generation imaging allowed for visualization of collagen autofluorescence. Crimp lengths were determined using ImageJ and compared based on incubation time. Results: Incubation time positively correlated with increasing S. epidermidis bioburden. Both fine and coarse crimp patterns lengthened with increasing incubation time. Significant coarse crimp changes were observed after only 30-minute incubations (P < .029), whereas significant fine crimp lengthening occurred after 6 hours (P < .0001). No changes in crimp length were identified after incubation in media lacking living bacteria. Conclusion: The results of this study demonstrate that exposure to S. epidermidis negatively affects collagen crimp structure. Structural alterations at the collagen fiber level occur within 30 minutes of exposure to media containing S. epidermidis. Clinical Relevance: Our study highlights the need for antimicrobial precautions to prevent graft colonization and maximize graft mechanical strength.

Ultrasound Measurement of Local Deformation in the Human Free Achilles Tendon Produced by Dynamic Muscle-Induced Loading: A Systematic Review

Achilles tendinopathy is the most prevalent lower limb tendinopathy, yet it remains poorly understood, with mismatches between observed structure and reported function. Recent studies have hypothesised that Achilles tendon (AT) healthy function is associated with variable deformation across the tendon width during use, focusing on quantifying sub-tendon deformation. Here, the aim of this work was to synthesise recent advances exploring human free AT tissue-level deformation during use. Following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, PubMed, Embase, Scopus and Web of Science were systematically searched. Study quality and risk of bias were assessed. Thirteen articles were retained, yielding data on free AT deformation patterns. Seven were categorised as high-quality and six as medium-quality studies. Evidence consistently reports that healthy and young tendons deform non-uniformly, with the deeper layer displacing 18%-80% more than the superficial layer. Non-uniformity decreased by 12%-85% with increasing age and by 42%-91% in the presence of injury. There is limited evidence of large effect that AT deformation patterns during dynamic loading are non-uniform and may act as a biomarker of tendon health, risk of injury and rehabilitation impact. Better considered participant recruitment and improved measurement procedures would particularly improve study quality, to explore links between tendon structure, function, aging and disease in distinct populations.

Flexor hallucis longus tendon morphology in dancers clinically diagnosed with tendinopathy.

The unique demands of dance technique make dancers more prone to certain pathologies especially of the foot and ankle. Flexor hallucis longus (FHL) tendinopathy, colloquially known as "dancer's tendinopathy," is common in dancers and not well studied. The purpose of this study was to assess if morphological alterations in tendon structure occur as an adaptive response to dance activity by comparing the FHL tendon in dancers to non-dancers, and if pathology further alters tendon morphology in dancers clinically diagnosed with tendinopathy. Three groups of ten participants were recruited (healthy non-dancers, healthy dancers, and dancers with FHL tendinopathy). Ultrasound images of the FHL tendons were analyzed for macromorphology by measuring the tendon thickness. The micromorphology was analyzed by determining the peak spatial frequency radius of the tendon. Our study did find increased tendon proper and composite tendon thickness in dancers with tendinopathy but no difference between asymptomatic dancers and non-dancers. There was no significant difference in micromorphology found between any of the groups. As expected, dancers with tendinopathy demonstrated increased composite tendon and tendon proper thickness however, there was no evidence of adaptive thickening of the FHL tendon as might be expected for the dance population. There was also no evidence of micromorphological changes in the presence of clinically diagnosed FHL tendinopathy. Because of the limited normative data for this pathology, these results can help improve diagnosis and therefore treatment for dancers to decrease the impact of this injury on their careers.

Current progress in growth factors and extracellular vesicles in tendon healing.

Tendon injury healing is a complex process that involves the participation of a significant number of molecules and cells, including growth factors molecules in a key role. Numerous studies have demonstrated the function of growth factors in tendon healing, and the recent emergence of EV has also provided a new visual field for promoting tendon healing. This review examines the tendon structure, growth, and development, as well as the physiological process of its healing after injury. The review assesses the role of six substances in tendon healing: insulin-like growth factor-I (IGF-I), transforming growth factor β (TGFβ), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), and EV. Different growth factors are active at various stages of healing and exhibit separate physiological activities. IGF-1 is expressed immediately after injury and stimulates the mitosis of various cells while suppressing the response to inflammation. VEGF, which is also active immediately after injury, accelerates local metabolism by promoting vascular network formation and positively impacts the activities of other growth factors. However, VEGF's protracted action could be harmful to tendon healing. PDGF, the earliest discovered cytokine to influence tendon healing, has a powerful cell chemotaxis and promotes cell proliferation, but it can equally accelerate the response to inflammation and relieve local adhesions. Also useful for relieving tendon adhesion is TGF- β, which is active almost during the entire phase of tendon healing. As a powerful active substance, in addition to its participation in the field of cardiovascular and cerebrovascular vessels, tumour and chronic wounds, TGF- β reportedly plays a role in promoting cell proliferation, activating growth factors, and inhibiting inflammatory response during tendon healing.

A Critical Review on Tendon Structure and Load Remodeling

A Critical Review on Tendon Structure and Load Remodeling

Investigation of the Tissue Degenerative Impact of Increased BMI in Achilles Tendon via Strain Elastography and Finite Element Analysis.

This study is focused on establishing a relationship between poor muscle activity faced by obese individuals due to the change in stiffness of the intramuscular mass of the lower limb. This issue is also common among athletes and physically active teenagers. The study is aimed at a subject assessment diagnosis technique named as Strain Elastography (SE) to measure muscle strain. Further, Finite Element Modelling (FEM) technique is used to investigate the strain and/or deformations generated in the Achilles Tendon (AT) models, which were categorized according to their Body Mass Index (BMI) through computationally applied loadings. Total 54 volunteers with an average age of 21.85 ± 1.28 years were categorized into three groups according to their BMI (kg/m2); under BMI < 18.5 (n=14), normal BMI = 18.5-24.9 (n=20) and over BMI/obese > 25.0 (n=20). Additionally, multiple correlational analyses were performed between full range of BMI values and SE outcome. The presence of significant difference (p<0.05) was measured between different categories for BMI, BFMI, FFMI, DLFC, tendon length, tendon thickness and SR. Moreover, multiple correlational analyses and scatter plot strengthen the results. For FEM simulations, the maximum deformation was observed at the proximal end of the tendon in all three groups. It can be concluded that change in tendon stiffness and the resulting change in tendon structure was visualized with increased BMI. Moreover, obese individuals are more prone to tendon injury due to the increment in tendon thickness which causes bulging of the AT due to higher loads.

MiRNAs contributing to the repair of tendon injury.

Tendon injury is one of the most common disorders of the musculoskeletal system, with a higher likelihood of occurrence in elderly individuals and athletes. In posthealing tendons, two undesirable consequences, tissue fibrosis and a reduction in mechanical properties, usually occur, resulting in an increased probability of rerupture or reinjury; thus, it is necessary to propose an appropriate treatment. Currently, most methods do not sufficiently modulate the tendon healing process and restore the function and structure of the injured tendon to those of a normal tendon, since there is still inadequate information about the effects of multiple cellular and other relevant signaling pathways on tendon healing and how the expression of their components is regulated. microRNAs are vital targets for promoting tendon repair and can modulate the expression of biological components in signaling pathways involved in various physiological and pathological responses. miRNAs are a type of noncoding ribonucleic acid essential for regulating processes such as cell proliferation, differentiation, migration and apoptosis; inflammatory responses; vascularization; fibrosis; and tissue repair. This article focuses on the biogenesis response of miRNAs while presenting their mechanisms in tendon healing with perspectives and suggestions.

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

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

Effect of Symptom Duration on Injury Severity and Recovery in Patients With Achilles Tendinopathy.

Achilles tendinopathy is a common overuse condition. Distinguishing between early- and late-stage tendinopathy may have implications on treatment decisions and recovery expectations. To compare the effects of time and baseline measures of tendon health on outcomes among patients with varying symptom durations after 16 weeks of comprehensive exercise treatment. Cohort study; Level of evidence, 3. Participants (N = 127) were categorized into 4 groups based on the number of months since symptom onset: ≤3 months (n = 24); between >3 and ≤6 months (n = 25); between >6 and ≤12 months (n = 18); or >12 months (n = 60). All participants received 16 weeks of standardized exercise therapy and pain-guided activity modification. Outcomes representing symptoms, lower extremity function, tendon structure, mechanical properties, psychological factors, and patient-related factors were assessed at baseline and at 8 and 16 weeks after the initiation of exercise therapy. Chi-square tests and 1-way analysis of variance were used to compare baseline measures between groups.Time, group, and interaction effects were evaluated using linear mixed models. The mean age of the participants was 47.8 ± 12.6 years, 62 participants were women, and symptoms ranged from 2 weeks to 274 months. No significant differences were found among symptom duration groups at baseline for any measure of tendon health. At 16 weeks, all groups demonstrated improvements in symptoms, psychological factors, lower extremity function, and tendon structure, with no significant differences among the groups (P > .05). Symptom duration did not influence baseline measures of tendon health. Additionally, no differences were observed among the different symptom duration groups in response to 16 weeks of exercise therapy and pain-guided activity modification.