The aging tendon

Assessment of thoracic disc degeneration using dual-energy CT-based collagen maps

BACKGROUND

We evaluated the role of dual-energy computed tomography (DECT)-based collagen maps in assessing thoracic disc degeneration.

METHODS

We performed a retrospective analysis of patients who underwent DECT and magnetic resonance imaging (MRI) of the thoracic spine within a 2-week period from July 2019 to October 2022. Thoracic disc degeneration was classified by three blinded radiologists into three Pfirrmann categories: no/mild (grade 1-2), moderate (grade 3-4), and severe (grade 5). The DECT performance was determined using MRI as a reference standard. Interreader reliability was assessed using intraclass correlation coefficient (ICC). Five-point Likert scales were used to assess diagnostic confidence and image quality.

RESULTS

In total, 612 intervertebral discs across 51 patients aged 68 ± 16 years (mean ± standard deviation), 28 males and 23 females, were assessed. MRI revealed 135 no/mildly degenerated discs (22.1%), 470 moderately degenerated discs (76.8%), and 7 severely degenerated discs (1.1%). DECT collagen maps achieved an overall accuracy of 1,483/1,838 (80.8%) for thoracic disc degeneration. Overall recall (sensitivity) was 331/405 (81.7%) for detecting no/mild degeneration, 1,134/1,410 (80.4%) for moderate degeneration, and 18/21 (85.7%) for severe degeneration. Interrater agreement was good (ICC = 0.89). Assessment of DECT-based collagen maps demonstrated high diagnostic confidence (median 4; interquartile range 3-4) and good image quality (median 4; interquartile range 4-4).

CONCLUSION

DECT showed an overall 81% accuracy for disc degeneration by visualizing differences in the collagen content of thoracic discs.

RELEVANCE STATEMENT

Utilizing DECT-based collagen maps to distinguish various stages of thoracic disc degeneration could be clinically relevant for early detection of disc-related conditions. This approach may be particularly beneficial when MRI is contraindicated.

KEY POINTS

A total of 612 intervertebral discs across 51 patients were retrospectively assessed with DECT, using MRI as a reference standard. DECT-based collagen maps allowed thoracic disc degeneration assessment achieving an overall 81% accuracy with good interrater agreement (ICC = 0.89). DECT-based collagen maps could be a good alternative in the case of contraindications to MRI.

Current concept review of Achilles tendinopathy

Achilles tendinopathy is a common overuse injury affecting the ankle and foot. It manifests as a clinical condition that includes pain, edema, and decreased functionality. This condition can be broadly categorized into two main types based on anatomical location: insertional and noninsertional tendinopathy. The development of Achilles tendinopathy involves various factors, both internal and external. Patients with Achilles tendinopathy often experience stiffness worsened by prolonged rest, and pain exacerbated by physical activity. These symptoms can limit work activity and sports participation, with many patients facing discomfort while wearing shoes due to heel sensitivity. Diagnosis is primarily clinical, although MRI and ultrasound imaging can aid in differential diagnosis. Identifying risk factors and understanding the patient's biomechanics assist in accurate diagnosis and subsequent management. Management of Achilles tendinopathy involves a range of conservative and surgical options. However, due to varying results in clinical studies, a definitive gold standard treatment has not emerged. Eccentric exercises are a valuable tool in managing the condition. The recommend treatments such as shock wave therapy or nitric oxide patches are sought if symptoms do not improve. Peritendinous injections could be options if physical therapy proves ineffective. Surgical intervention is required after six months of conservative treatment. Recent research on Achilles tendinopathy emphasizes the need for individualized treatment plans that address its multifaceted nature. Combining biomechanical analysis, advanced imaging, and patient-specific factors is key to achieving optimal outcomes. Additionally, preventive strategies focusing on proper training techniques, load management, and addressing modifiable risk factors play a critical role in reducing the incidence of this condition. In conclusion, this article provides a current overview of Achilles tendinopathy. It highlights the importance of a comprehensive approach to understanding its causes, pathophysiology, diagnosis, and management strategies.

Clinical and Ultrasonographic Characteristics of the Achilles Tendon in Hemodialysis Patients

Background and Objectives: The early recognition of tendon alterations in chronic hemodialysis (HD) patients, an awareness of the factors that influence the condition, and active intervention have considerable clinical relevance. The aim of this study was to investigate the musculoskeletal ultrasound (MSUS) features of the Achilles tendon in chronic HD patients and determine the factors associated with tendon abnormalities. Materials and Methods: This study was conducted on 46 HD patients and 24 sex- and age-matched controls. All participants were evaluated clinically for any signs of Achilles tendon abnormalities. Then, the Achilles tendon was scanned bilaterally using MSUS. Results: Among the 92 Achilles tendons in the HD patients, there was tenderness and swelling of only two (2.2%). Regarding MSUS features, there were statistically significant higher thicknesses in the proximal end (p < 0.001), midpoint (p < 0.001), and distal end (p < 0.001) of the Achilles tendons in the HD patients when compared with the healthy controls. Tendinosis was found in 12 (13%) of the HD patients' Achilles tendons, which was statistically significant in comparison to the healthy controls (p = 0.008). There were statistically significant higher scores of structural abnormalities (p = 0.005), bone erosions (p = 0.017), and calcifications (p = 0.015) in the HD patients when compared to the healthy controls. According to the results of a univariate regression analysis, age and male gender were predictive for US abnormalities in HD patients (p = 0.002 and 0.025, respectively). Conclusions: The Achilles tendon in subjects on chronic HD showed frequent US abnormalities. These abnormalities in HD patients appear to be more related to age and gender and may be asymptomatic.

Correlation between the Coaptation and Regeneration of Tendon Stumps in Endoscopic Assisted Achilles Tendon Rupture Repair

OBJECTIVE

When the endoscopic Achilles tendon repair technique is utilized, direct stitching of the ruptured site is challenging due to the frayed tendon stumps. To explore whether undesirable coaptation of the tendon stumps influences the generation of the tendons.

METHODS

This study is a retrospective analysis of 46 patients who underwent a modified endoscopic Achilles tendon rupture repair from October 2018 to June 2020. Patients were divided into two groups according to the coaptation of tendon stumps on postoperative ultrasonography. Group 1 included 17 cases with undesirable coaptation (<50%), and Group 2 included 29 cases with appropriate coaptation (≥50%). Magnetic resonance imaging (MRI) was obtained postoperatively at 3, 6, and 12 months to evaluate the tendon morphological construction. Clinical evaluations were performed using the American Orthopedic Foot and Ankle Society (AOFAS) ankle-hind foot score, the Achilles Tendon Total Rupture Score (ATRS), muscle power, and the Achilles tendon resting angle at the final follow-up. Complications were also encountered. The Student's t-test and the Mann-Whitney U-test were used to assess differences among both groups.

RESULTS

The mean follow-up time was 37.5 ± 10.6 months in Group 1 and 39.0 ± 11.6 months in Group 2, respectively. The average age in Group 1 is slightly older than in Group 2 (37.3 ± 6.1 vs. 32.7 ± 6.3, p = 0.021). The tendon cross-section areas and thickness increased initially and decreased later on postoperative MRI evaluation. It also showed a significantly higher signal/noise quotient (SNQ) in Group 1 at postoperative 3 months. At postoperative 6 and 12 months, the SNQ between both groups was similar. The AOFAS score (95.9 ± 5.1 vs. 96.2 ± 4.9, p = 0.832), ATRS score (97.0 ± 3.6 vs. 97.7 ± 3.3, p = 0.527), and muscle power (21.38 vs. 24.74, p = 0.287) were not significantly different between both groups. However, the resting angle of Group 1 was significantly larger than that of Group 2 (4.6 ± 2.4 vs. 2.4 ± 2.3, p = 0.004). There was no difference in the complications (p = 0.628).

CONCLUSION

Although complete regeneration can be finally achieved, the early stage of tendon stump regeneration can be prolonged due to undesirable coaptation when endoscopic Achilles tendon repair technique is applied. The prolonged high signal duration on MRI indicates the less-than-ideal regeneration of the tendon, which might lead to elongation of the tendon.

Risk Factors for Failure of Conservative Management of Insertional Achilles Tendinosis

INTRODUCTION

While many patients benefit from nonoperative treatment of insertional Achilles tendinopathy (IAT), some elect for surgical debridement and reconstruction. The purpose of this study is to determine the relationship of patient demographic characteristics, comorbidity profiles, and radiological parameters with failure of conservative management of IAT.

METHODS

A retrospective chart review was performed to identify patients who received either surgical or nonsurgical treatment of IAT at an academic institution from September 2015 to June 2019 (N = 226). Demographic and comorbidity data, and the presence and magnitude of relevant radiological parameters were collected and compared between the surgically (n = 48) and nonsurgically (n = 178) treated groups.

RESULTS

No significant differences could be detected between groups regarding demographic factors or previous procedures. The surgery group was significantly more likely to have evidence of Haglund's deformity on clinical exam (83% vs 69%, P = .005), lower SF-12 physical scores (25.5 vs 35.5, P < .001), higher VAS pain scores (6.3 vs 5.3, P = .033), any mental illness (33% vs 20%, P = .044), and depression (27% vs 12%, P = .012).

DISCUSSION

Patients who received surgery for IAT were significantly more likely to have evidence of Haglund's deformity on clinical exam, depression, higher VAS pain scores, and lower SF-12 physical scores. Both patients and surgeons should be aware of the higher rates of failure of conservative treatment in these patients.

LEVEL OF EVIDENCE

Level III.

Quantitative Assessment of Tendon Backscatter Anisotropy in B-Mode Ultrasound

To test the anisotropy of human tendons in conventional B-mode ultrasound, we prospectively performed ultrasound scans of 40 normal patella tendons and 24 patella tendons with chronic tendinopathy in adults. We scanned all tendons in longitudinal orientation (parallel to tendon fibers) using a linear array transducer (8.5 MHz) with beam steering at 0°, 5°, 10°, 15° and 20°. We used ImageJ histogram analysis to process B-mode images offline for assessing backscatter as a function of angle, known as backscatter anisotropy, between normal tendons and the subcutaneous tissues and between normal tendons and tendons with tendinopathy. We compared the results using the slopes of linear regression lines drawn through the angle-dependent data, and we concluded that the tissue anisotropy was significantly different if the 95% confidence intervals of the line slopes for different tissues did not overlap. We observed significant differences between normal tendons and both the adjacent subcutaneous tissues and tendons with tendinopathy. However, the difference in the regression slopes between tendons with tendinopathy and the adjacent subcutaneous soft tissues was not significant. It appears that changes in anisotropic backscatter could be used to detect tendon abnormalities and in assessing the significance of disease and the effectiveness of therapy.

Tendon Aging

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

Targeting Senescent Tendon Stem/Progenitor Cells to Prevent or Treat Age-Related Tendon Disorders

Age-related tendon disorder, a primary motor system disease, is characterized by biological changes in the tendon tissue due to senescence and seriously affects the quality of life of the elderly. The pathogenesis of this disease is not well-understood. Tendon stem/progenitor cells (TSPCs) exhibit multi-differentiation capacity. These cells are important cellular components of the tendon because of their roles in tendon tissue homeostasis, remodeling, and repair. Previous studies revealed alterations in the biological characteristics and tenogenic differentiation potential of TSPCs in senescent tendon tissue, in turn contributing to insufficient differentiation of TSPCs into tenocytes. Poor tendon repair can result in age-related tendinopathies. Therefore, targeting of senescent TSPCs may restore the tenogenic differentiation potential of these cells and achieve homeostasis of the tendon tissue to prevent or treat age-related tendinopathy. In this review, we summarize the biological characteristics of TSPCs and histopathological changes in age-related tendinopathy, as well as the potential mechanisms through which TSPCs contribute to senescence. This information may promote further exploration of innovative treatment strategies to rescue TSPCs from senescence.

Trends in digital joint motion following surgical reconstruction of a tendon rupture after distal radius fracture

BACKGROUND

Tendon rupture has been recognized as a complication of distal radius fracture (DRF); however, the clinical outcome of reconstructive surgery for this injury remains unclear. We examined prognostic factors for the outcomes of reconstructive surgery in patients with a tendon rupture after DRF.

METHODS

This study was a retrospective review of a case series. Seventy-five consecutive patients were treated at our institution for tendon rupture after DRF. The cohort included 14 males and 61 females with a mean age of 67.7 years at the time of tendon reconstruction. Sixty-four and eighteen tendon ruptures occurred after non-operative management for DRF and palmar locking plate fixation, respectively. Seven ruptured tendons received a free tendon graft from the palmaris longus tendon, and the others underwent tendon transfers. All patients were managed postoperatively by our hand therapy unit according to a controlled active mobilization regime.

RESULTS

The mean follow-up period was 28 weeks (range: 12-80 weeks). Patients with extensor tendon ruptures were significantly younger than those with flexor tendon ruptures regardless of the initial DRF treatment. The mean percentage active range of motion of the injured digits relative to normal active motion (%AROM) at the final follow-up was 70% (range: 30-101%) in all patients. The %AROM after flexor tendon reconstruction for patients after non-operative management was significantly inferior to that of other patients. Multiple regression analysis revealed that aging and non-operative management of DRF are independent risk factors for poor %AROM.

CONCLUSIONS

This study confirmed that advanced age and non-operative management of DRF were prognostic factors for digital joint motion following surgical reconstruction for tendon rupture. Our results suggest that it may be difficult to achieve good clinical outcomes in elderly patients with tendon ruptures (particularly flexor tendon ruptures) following non-operative management of DRF.

Metabolic and molecular responses of human patellar tendon to concentric- and eccentric-type exercise in youth and older age

Exercise training can induce adaptive changes to tendon tissue both structurally and mechanically; however, the underlying compositional changes that contribute to these alterations remain uncertain in humans, particularly in the context of the ageing tendon. The aims of the present study were to determine the molecular changes with ageing in patellar tendons in humans, as well as the responses to exercise and exercise type (eccentric (ECC) and concentric (CON)) in young and old patellar tendon. Healthy younger males (age 23.5 ± 6.1 years; n = 27) and older males (age 68.5 ± 1.9 years; n = 27) undertook 8 weeks of CON or ECC training (3 times per week; at 60% of 1 repetition maximum (1RM)) or no training. Subjects consumed D₂O throughout the protocol and tendon biopsies were collected after 4 and 8 weeks for measurement of fractional synthetic rates (FSR) of tendon protein synthesis and gene expression. There were increases in tendon protein synthesis following 4 weeks of CON and ECC training (P < 0.01; main effect by ANOVA), with no differences observed between young and old males, or training type. At the transcriptional level however, ECC in young adults generally induced greater responses of collagen and extracellular matrix-related genes than CON, while older individuals had reduced gene expression responses to training. Different training types did not appear to induce differential tendon responses in terms of protein synthesis, and while tendons from older adults exhibited different transcriptional responses to younger individuals, protein turnover changes with training were similar for both age groups.

Clinical Impact of Metabolic Syndrome on Eccentric Exercises for Chronic Insertional Achilles Tendinopathy

Metabolic syndrome is one factor known to contribute to the development of tendinopathies. The aim of this study was to compare the clinical outcomes of eccentric calf-muscle exercise for treatment of chronic insertional Achilles tendinopathy in patients with or without metabolic syndrome. Twenty-eight patients with chronic insertional Achilles tendinopathy and metabolic syndrome who performed eccentric calf-muscle exercise were retrospectively compared with 28 age- and sex-matched controls without metabolic syndrome. Comparisons between the 2 groups were made by evaluating the Visual Analog Scale for pain, patient satisfaction, and amount of pain medications needed during 3 months of follow-up. Two-way analysis of variance with repeated measures showed that the pain scales in the metabolic syndrome group were higher than those in the control group during the follow-up period (F[1,54] = 24.45, p < .001). The patient satisfaction ratings were lower and the amount of required pain medication was higher in the metabolic syndrome group (p < .001 and p < .001, respectively). Eccentric calf-muscle exercises for chronic insertional Achilles tendinopathy were less effective in patients with metabolic syndrome. Therefore, these patients should be managed with a combination of other treatment modalities rather than eccentric exercise alone.

Aging and matrix viscoelasticity affect multiscale tendon properties and tendon derived cell behavior

Aging is the largest risk factor for Achilles tendon associated disorders and rupture. Although Achilles tendon macroscale elastic properties are suggested to decline with aging, less is known about the effect of maturity and aging on multiscale viscoelastic properties and their effect on tendon cell behavior. Here, we show dose dependent changes in native multiscale tendon mechanical and structural properties and uncover several nanoindentation properties predicted by tensile mechanics and echogenicity. Alginate hydrogel systems designed to mimic juvenile tendon microscale mechanics revealed that stiffness and viscoelasticity affected Achilles tendon cell aspect ratio and proliferation during aging. This knowledge provides further evidence for the negative impact of maturity and aging on tendon and begins to elucidate how viscoelasticity can control tendon derived cell morphology and expansion. STATEMENT OF SIGNIFICANCE: Aging is the largest risk factor for Achilles tendon associated disorders and rupture. Although Achilles tendon macroscale elastic properties are suggested to decline with aging, less is known about the effect of maturity and aging on multiscale viscoelastic properties and their effect on tendon cell behavior. Here, we show dose dependent changes in native multiscale tendon mechanical and structural properties and uncover several nanoindentation properties predicted by tensile mechanics and echogenicity. Alginate hydrogel systems designed to mimic juvenile tendon microscale mechanics revealed that stiffness and viscoelasticity affected Achilles tendon cell spreading and proliferation during aging. This knowledge provides further evidence for the negative impact of maturity and aging on tendon and begins to elucidate how viscoelasticity can control tendon derived cell morphology and expansion.

Epidemiology of Achilles Tendon Rupture in South Korea: Claims Data of the National Health Insurance Service from 2009 to 2017

Background

The incidence of Achilles tendon rupture and its trend has not been studied in Asia. The purpose of this nationwide study was to analyze the trend of incidence and surgical treatment of tendon ruptures in South Korea based on sex, age, and income level of patients, as well as seasonal variation.

Methods

A descriptive epidemiologic study was performed based on the data collected retrospectively from the Korea National Health Insurance Service. Data of all outpatients and inpatients were collected from approximately 52 million residents of South Korea, primarily diagnosed with Achilles tendon rupture from 2009 to 2017.

Results

A total of 112,350 patients had Achilles tendon rupture, of which 44,248 patients underwent surgical treatment during the study period. The overall, age-specific, and sex-specific incidence of Achilles tendon rupture and surgical treatment showed an increasing trend. Patients in the age group of 41 to 50 years showed the highest increase in incidence. Regarding season, higher incidence was reported during spring and summer, whereas the lowest incidence was found in winter. Higher income level was associated with increased incidence of the condition.

Conclusions

The incidence of Achilles tendon rupture and surgical treatments increased rapidly in patients between 41 and 50 years of age. Patients in the higher income quintile groups experienced more Achilles tendon injury than those in lower income groups, and fewer ruptures were observed during winter.

Quantitative evaluation of the Achilles tendon and supraspinatus tendon in end-stage kidney disease patients: A potential tool for predicting spontaneous tendon rupture

Many cases of spontaneous tendon rupture in end-stage kidney disease (ESKD) patients have been reported worldwide. Quantitative assessment of tendon has become an important way to improve the prognosis of patients. In the recruited healthy volunteers and ESKD patients, the thickness and shear wave velocity (SWV) of supraspinatus tendons and Achilles tendons were measured and compared among groups. Potential factors related to the tendon SWV of ESKD patients were screened in multiple linear regression. There was no significant difference in the tendon thickness and supraspinatus tendon SWV among groups. SWV of Achilles tendons in long-term dialysis ESKD patients were significantly lower than those in healthy volunteers (5.1 vs. 5.6 m/s, p < 0.01). Ca²⁺ , creatinine, body mass index, and genders are the significant factors related to the tendon SWV. Shear wave elastography can be used as a potential tool for predicting spontaneous tendon rupture in ESKD patients.

Basic Structure, Physiology, and Biochemistry of Connective Tissues and Extracellular Matrix Collagens

The physiology of connective tissues like tendons and ligaments is highly dependent upon the collagens and other such extracellular matrix molecules hierarchically organized within the tissues. By dry weight, connective tissues are mostly composed of fibrillar collagens. However, several other forms of collagens play essential roles in the regulation of fibrillar collagen organization and assembly, in the establishment of basement membrane networks that provide support for vasculature for connective tissues, and in the formation of extensive filamentous networks that allow for cell-extracellular matrix interactions as well as maintain connective tissue integrity. The structures and functions of these collagens are discussed in this chapter. Furthermore, collagen synthesis is a multi-step process that includes gene transcription, translation, post-translational modifications within the cell, triple helix formation, extracellular secretion, extracellular modifications, and then fibril assembly, fibril modifications, and fiber formation. Each step of collagen synthesis and fibril assembly is highly dependent upon the biochemical structure of the collagen molecules created and how they are modified in the cases of development and maturation. Likewise, when the biochemical structures of collagens or are compromised or these molecules are deficient in the tissues - in developmental diseases, degenerative conditions, or injuries - then the ultimate form and function of the connective tissues are impaired. In this chapter, we also review how biochemistry plays a role in each of the processes involved in collagen synthesis and assembly, and we describe differences seen by anatomical location and region within tendons. Moreover, we discuss how the structures of the molecules, fibrils, and fibers contribute to connective tissue physiology in health, and in pathology with injury and repair.

Low serum vitamin B12 levels are associated with degenerative rotator cuff tear

BACKGROUND

Vitamin B₁₂ (Vit B₁₂) deficiency results in elevated homocysteine levels and interference with collagen cross-linking, which may affect tendon integrity. The purpose of this study was to investigate whether serum Vit B₁₂ levels were correlated with degenerative rotator cuff (RC) tear.

METHODS

Eighty-seven consecutive patients with or without degenerative RC tear were enrolled as study participants. Possible risk factors (age, sex, medical history, bone mineral density, and serum chemistries including glucose, magnesium, calcium, phosphorus, zinc, homocysteine, Vitamin D, Vit B₁₂, homocysteine, and folate) were assessed. Significant variables were selected based on the results of univariate analyses, and a logistic regression model (backward elimination) was constructed to predict the presence of degenerative RC tear.

RESULTS

In the univariate analysis, the group of patients with degenerative RC tear had a mean concentration of 528.4 pg/mL Vit B₁₂, which was significantly lower than the healthy control group (627.1 pg/mL). Logistic regression analysis using Vit B₁₂ as an independent variable revealed that Vit B₁₂ concentrations were significantly correlated with degenerative RC tear (p = 0.044). However, Vit B₁₂ levels were not associated with tear size.

CONCLUSION

Low serum levels of Vit B₁₂ were independently related to degenerative RC tear. Further investigations are warranted to determine if Vit B₁₂ supplementation can decrease the risk of this condition.

Dual-energy CT collagen density mapping of wrist ligaments reveals tissue remodeling in CPPD patients: first results from a clinical cohort

OBJECTIVES

To evaluate differences in collagen density as detected by dual-energy computed tomography (DECT) of wrist ligaments between patients with calcium pyrophosphate-dihydrate deposition disease (CPPD) and a control group in order to gain insight into changes of the extracellular matrix in response to crystal deposition.

MATERIALS AND METHODS

This retrospective study included 28 patients (18 with CPPD, 10 controls) who underwent DECT of the wrist. Collagen density maps were reconstructed from the DECT datasets and used to measure densities in regions of interest (ROIs) placed in the scapholunate (SL) ligament (dorsal, palmar, proximal), lunotriquetral (LT) ligament, and extensor carpi radialis (ECR) tendon, (n = 260 measurements). The presence of calcifications on standard CT images in these regions was assessed by a blinded reader. Densities were compared with nonparametric tests, and linear regression analysis was performed to investigate the impact of age, sex, and CT- detected calcium deposition on collagen density.

RESULTS

Collagen density in the SL ligament was significantly higher in CPPD patients than in controls (overall mean: 265.4 ± 32.1 HU vs. 196.3 ± 33.8 HU; p < 0.001). In the ECR tendon, collagen densities did not differ significantly (p = 0.672): 161.3 ± 20.1 HU in CPPD vs. 163.6 ± 12.0 HU in controls. Regression analysis showed that diagnosis, but not age or calcification, had a significant impact on collagen density.

CONCLUSION

Collagen density of the SL ligament is significantly higher in CPPD patients than in control patients. Further research is needed to understand these changes in the extracellular matrix of ligaments in CPPD.

2017 Marathon of Rome: Anthropometry and Sport Profile in 350 Runners and Association With Achilles and Patellar Tendinopathy

BACKGROUND

Achilles and patellar tendinopathy are common in runners. Despite the relevance of the problem, causative factors remain poorly understood. This cross-sectional study evaluated the association between Achilles and patellar tendinopathy and age, sex, weight, height, number of marathons, and impact profile in runners who participated in the 2017 Marathon of Rome.

METHODS

At the 2017 Marathon of Rome, 350 athletes (256 men and 94 women; mean age: 44.8 years, range 12-80 years) filled in the VISA-A and VISA-P questionnaires. A fully trained orthopedic surgeon made a diagnosis of Achilles and patellar tendinopathy according to clinical criteria.

RESULTS

Ninety-five participants were diagnosed with Achilles tendinopathy and 96 with patellar tendinopathy. There was evidence of a statistically significant positive association between age and Achilles and patellar tendinopathy, with no effect of sex, weight, and height on the presence of Achilles tendinopathy. There was no evidence of a statistically significant positive association between the number of marathons and impact profile and VISA-A score. There was a statistically significant association between VISA-P score and impact profile. Finally, there was evidence of a statistically significant positive association between VISA-A score and VISA-P score (P = 0.007).

CONCLUSIONS

In marathon runners, there was no evidence of a statistically significant association between sex, weight, height, number of marathons, and Achilles and patellar tendinopathy. However, age was associated with Achilles and patellar tendinopathy, and impact profile was associated with patellar tendinopathy.

Ultrashort echo time (UTE) imaging reveals a shift in bound water that is sensitive to sub-clinical tendinopathy in older adults

OBJECTIVE

Use ultrashort echo time (UTE) magnetic resonance imaging to quantify bound water components of asymptomatic older Achilles tendons and investigate the relationship between UTE findings and imaging assessment of sub-clinical tendinopathy.

MATERIALS AND METHODS

Thirteen young (age 25 ± 4.8) and thirteen older (age 67 ± 4.7) adults were tested. A UTE sequence was used to quantify the transverse relaxation times of bound ([Formula: see text]) and free ([Formula: see text]) water and the bound water fraction (F_s) in the Achilles tendon. Anatomical images were collected and graded by a musculoskeletal radiologist to identify signs of sub-clinical tendinopathy. Two-sample t tests were used to compare [Formula: see text], [Formula: see text], and F_s between age groups and between adults with and without sub-clinical tendinopathy.

RESULTS

Older tendons exhibited a 60% longer [Formula: see text] (p = 0.004), similar [Formula: see text] (p = 0.86), and 5% smaller F_s (p = 0.048) than young tendons. Seven older adult tendons exhibited tendon thickening and increased signal intensity indicative of sub-clinical tendinopathy. This subset of tendons exhibited a 7% smaller bound water fraction (p = 0.02) and significantly longer [Formula: see text] (p < 0.001) than the normal tendons from young and older adults.

CONCLUSION

Older adult tendons exhibited unique UTE signatures that are consistent with disruption of the collagen fiber network and changes in macromolecular content. UTE imaging metrics were sensitive to early indicators of tissue degeneration identified on anatomical images and hence could provide a quantitative biomarker by which to track changes in tissue health resulting from injury, disease, and treatment.

Achilles tendon loading is lower in older adults than young adults across a broad range of walking speeds

The purpose of this study was to investigate age-related differences in Achilles tendon loading during gait. Fourteen young (7F/7M, 26 ± 5 years) and older (7F/7M, 67 ± 5 years) adults without current neurological or orthopaedic impairment participated. Shear wave tensiometry was used to measure tendon stress by tracking Achilles tendon wave speed. The wave speed-stress relationship was calibrated using simultaneously collected tensiometer and force plate measures during a standing sway task. Tendon stress was computed from the force plate measures using subject-specific ultrasound measures of tendon moment arm and cross-sectional area. All subjects exhibited a highly linear relationship between wave speed squared and tendon stress (mean R2 > 0.9), with no significant age-group differences in tensiometer calibration parameters. Tendon wave speed was monitored during treadmill walking at four speeds (0.75, 1.00, 1.25, and 1.50 m/s) and used to compute the stress experienced by the tendon. Relative to young adults, older adults exhibited 22% lower peak tendon wave speeds. Peak tendon stress during push-off in older adults (24.8 MPa) was 32% less than that in the young adults (36.7 MPa) (p = 0.01). There was a moderate increase (+11%) in peak tendon stress across both groups when increasing speed from 0.75 to 1.50 m/s (main effect of speed, p = 0.01). Peak tendon loading during late swing did not differ between age groups (mean 3.8 MPa in young and 4.2 MPa in older adults). These age-related alterations in tendon tissue loading may affect the mechanobiological stimuli underlying tissue remodeling and thereby alter the propensity for tendon injury and disease.

Identifying potential patient-specific predictors for anterior cruciate ligament reconstruction outcome - a diagnostic in vitro tissue remodeling platform

Purpose

Upon anterior cruciate ligament (ACL) rupture, reconstruction is often required, with the hamstring tendon autograft as most widely used treatment. Post-operative autograft remodeling enhances graft rupture risk, which occurs in up to 10% of the patient population, increasing up to 30% of patients aged under 20 years. Therefore, this research aimed to identify potential biological predictors for graft rupture, derived from patient-specific tissue remodeling-related cell properties in an in vitro micro-tissue platform.

Methods

Hamstring tendon-derived cells were obtained from remnant autograft tissue after ACL reconstructions (36 patients, aged 12–55 years), and seeded in collagen I gels on a micro-tissue platform. Micro-tissue compaction over time – induced by altering the boundary constraints – was monitored. Pro-collagen I expression was assessed using ELISA, and protein expression of tenomodulin and α-smooth muscle actin were measured using Western blot. Expression and activity of matrix metalloproteinase 2 were determined using gelatin zymography.

Results

Only micro-tissues corresponding to younger patients occasionally released themselves from the constraining posts. Pro-collagen I expression was significantly higher in younger patients. Differences in α-smooth muscle actin and tenomodulin expression between patients were found, but these were age-independent. Active matrix metalloproteinase 2 expression was slightly more abundant in younger patients.

Conclusions

The presented micro-tissue platform exposed patient-specific remodeling-related differences between tendon-derived cells, with the micro-tissues that released from constraining posts and pro-collagen I expression best reflecting the clinical age-dependency of graft rupture. These properties can be the starting point in the quest for potential predictors for identifying individual patients at risk for graft rupture.

In vivo assessment of material properties of muscles and connective tissues around the knee joint based on shear wave elastography

Previous studies on knee biomechanics have mainly focused on the joint structure itself, largely neglecting the material properties of the muscles and connective tissues around the knee joint. Therefore, this study was purposed to conduct a systematic in vivo examination of the material properties of muscles, tendons, and ligaments, and investigated the respective influences of gender and age on the material properties. The participants were 50 healthy males and females within the following four age groups: 21-30 years, 31-40 years, 41-50 years, and above 51 years. The Young's moduli of the muscles, tendons, and ligaments around the knee joint were measured by shear wave elastography (SWE). Analysis of the Young's modulus results showed that excellent repeatability could be achieved by using SWE. For muscles, the intraclass correlation coefficient (ICC) and 95% confidence interval (CI) ranged between 0.952 and 0.987, and 0.923 and 0.992, respectively. The ICC ranged from 0.920 to 0.941, and the 95% CI was between 0.872 and 0.969 for tendons and ligaments. Additionally, the Young's moduli of the muscles, tendons, and ligaments of males were greater than those of females. With the exception for medial patellar retinaculum (MPR), the Young's moduli of other observed tissues decreased with age for both males and females, indicating that age has a significant impact on the Young's moduli of muscles, tendons, and ligaments. Hence, SWE is a reliable and repeatable technique that can be used to assess the Young's moduli of the muscles, tendons, and ligaments around the knee joint. Furthermore, gender and age affects the material properties. The results of this study provide an in vivo database of the material properties of muscles and connective tissues, and thus may prove useful for the prevention and treatment of knee joint injuries and diseases.

Do Mast Cells Have a Role in Tendon Healing and Inflammation?

Understanding the links between the tendon healing process, inflammatory mechanisms, and tendon homeostasis/pain after tissue damage is crucial in developing novel therapeutics for human tendon disorders. The inflammatory mechanisms that are operative in response to tendon injury are not fully understood, but it has been suggested that inflammation occurring in response to nerve signaling, i.e., neurogenic inflammation, has a pathogenic role. The mechanisms driving such neurogenic inflammation are presently not clear. However, it has recently been demonstrated that mast cells present within the injured tendon can express glutamate receptors, raising the possibility that mast cells may be sensitive to glutamate signaling and thereby modulate neurogenic inflammation following tissue injury. In this review, we discuss the role of mast cells in the communication with peripheral nerves, and their emerging role in tendon healing and inflammation after injury.

Effect of preservation on the physical and chemical properties of the temporal fascia

OBJECTIVE

The temporal fascia has been widely used in tympanoplasty. In addition, the preserved fascia has been also used in the ear surgery. In this study, we planned the experiments to determine whether physical and chemical properties of the fascia preserved at a low temperature.

METHODS

Preserved temporal fasciae from 21 patients were used in this study. The thickness of the temporal fascia was measured under a 3D laser microscope. The tensile strength was evaluated using a tensile tester. In addition, the chemical property evaluated was the biologic antioxidative potential of samples.

RESULTS

The results showed that the strength of the fascia was not affected by the retention period. The thick fascia tended to show the less tensile strength. The intensity was highest in middle-aged donors when compared to young and older donor. The antioxidative potentials did not affect the preservation.

CONCLUSION

The results suggested that the preserved temporal fascia could be safely used for tympanoplasty.

Water-content related alterations in macro and micro scale tendon biomechanics

Though it is known that the water content of biological soft tissues alters mechanical properties, little attempt has been made to adjust the tissue water content prior to biomechanical testing as part of standardization procedures. The objective of this study was to examine the effects of altered water content on the macro and micro scale mechanical tissues properties. Human iliotibial band samples were obtained during autopsies to osmotically adapt their water content. Macro mechanical tensile testing of the samples was conducted with digital image correlation, and micro mechanical tests using atomic force microscopy. Analyses were conducted for elastic moduli, tensile strength, and strain at maximum force, and correlations for water content, anthropometric data, and post-mortem interval. Different mechanical properties exist at different water concentrations. Correlations to anthropometric data are more likely to be found at water concentrations close to the native state. These data underline the need for adapting the water content of soft tissues for macro and micro biomechanical experiments to optimize their validity. The osmotic stress protocol provides a feasible and reliable standardization approach to adjust for water content-related differences induced by age at death, post-mortem interval and tissue processing time with known impact on the stress-strain properties.

Spatial Patterns and Age-Related Changes of the Collagen Crimp in the Human Cornea and Sclera

Purpose

Collagen is the main load-bearing component of the eye, and collagen crimp is a critical determinant of tissue mechanical behavior. We test the hypothesis that collagen crimp morphology varies over the human cornea and sclera and with age.

Methods

We analyzed 42 axial whole-globe sections from 20 normal eyes of 20 human donors, ranging in age from 0.08 (1 month) to 97 years. The sections were imaged using polarized light microscopy to obtain μm-scale fiber bundle/lamellae orientation from two corneal and six scleral regions. Crimp morphology was quantified through waviness, tortuosity, and amplitude.

Results

Whole-globe median waviness, tortuosity, and amplitude were 0.127 radians, 1.002, and 0.273 μm, respectively. These parameters, however, were not uniform over the globe, instead exhibiting distinct, consistent patterns. All crimp parameters decreased significantly with age, with significantly different age-related decreases between regions. The crimp morphology of the limbus changed the most drastically with age, such that it had the largest crimp in neonates, and among the smallest in the elderly.

Conclusions

Age-related decreases in crimp parameters are likely one of the mechanisms underlying age-related stiffening of the sclera and cornea, potentially influencing sensitivity to IOP. Further work is needed to determine the biomechanical implications of the crimp patterns observed. The comparatively large changes in the crimp morphology of the limbus, especially in the early years of life, suggest that crimp in this region may play a role in eye development, although the exact nature of this is unclear.

Implications of Aging in Plastic Surgery

Given the rapidly aging population, investigating the effect of age on plastic surgery outcomes is imperative. Despite this, the topic has received relatively little attention. Furthermore, there appears to be little integration between the basic scientists investigating the mechanisms of aging and the plastic surgeons providing the majority of "antiaging" therapies. This review first provides a description of the effects and mechanisms of aging in 5 types of tissue: skin, adipose tissue, muscles, bones and tendons, and nervous tissue followed by an overview of the basic mechanisms underlying aging, presenting the currently proposed cellular and molecular theories. Finally, the impact of aging, as well as frailty, on plastic surgery outcomes is explored by focusing on 5 different topics: general wound healing and repair of cutaneous tissue, reconstruction of soft tissue, healing of bones and tendons, healing of peripheral nerves, and microsurgical reconstruction. We find mixed reports on the effect of aging or frailty on outcomes in plastic surgery, which we hypothesize to be due to exclusion of aged and frail patients from surgery as well as due to outcomes that reported no postsurgical issues with aged patients. As plastic surgeons continue to interact more with the growing elderly population, a better appreciation of the underlying mechanisms and outcomes related to aging and a clear distinction between chronological age and frailty can promote better selection of patients, offering appropriate patients surgery to improve an aged appearance, and declining interventions in inappropriate patients.

Are Ultrasound Measurements of Achilles Tendon Size Reliable? A Systematic Review of Rater Reliability

Ultrasound measurements of Achilles tendon size are used to assess the tendon's response to exercise, aging, rehabilitation, tendon loading and healing. It is important to understand and minimise the measurement error that occurs with these measurements. This review identified and synthesised studies reporting on intra- and inter-rater reliability of ultrasound measurements of Achilles tendon size. Analysis of 21 studies revealed that good to excellent intra- and inter-rater reliability can be achieved for ultrasound measurements of Achilles tendon size. Reliability can be optimised by using one experienced operator, standardising transducer pressure and orientation and averaging two or three measurements. There was a high risk of methodological bias across the included studies. Reporting of reliability studies needs to be improved by the use of existing reporting guidelines and expansion of these guidelines to include important elements of ultrasound imaging.

The role of muscle strength on tendon adaptability in old age

PURPOSE

The purpose of the study was to determine: (1) the relationship between ankle plantarflexor muscle strength and Achilles tendon (AT) biomechanical properties in older female adults, and (2) whether muscle strength asymmetries between the individually dominant and non-dominant legs in the above subject group were accompanied by inter-limb AT size differences.

METHODS

The maximal generated AT force, AT stiffness, AT Young's modulus, and AT cross-sectional area (CSA) along its length were determined for both legs in 30 women (65 ± 7 years) using dynamometry, ultrasonography, and magnetic resonance imaging.

RESULTS

No between-leg differences in triceps surae muscle strength were identified between dominant (2798 ± 566 N) and non-dominant limb (2667 ± 512 N). The AT CSA increased gradually in the proximo-distal direction, with no differences between the legs. There was a significant correlation (P < 0.05) of maximal AT force with AT stiffness (r = 0.500) and Young's modulus (r = 0.414), but only a tendency with the mean AT CSA. However, region-specific analysis revealed a significant relationship between maximal AT force and the proximal part of the AT, indicating that this region is more likely to display morphological adaptations following an increase in muscle strength in older adults.

CONCLUSIONS

These findings demonstrate that maximal force-generation capabilities play a more important role in the variation of AT stiffness and material properties than in tendon CSA, suggesting that exercise-induced increases in muscle strength in older adults may lead to changes in tendon stiffness foremost due to alterations in material rather than in its size.

Shear Wave Elastography Measures of the Achilles Tendon: Influence of Time of Day, Leg Dominance and the Impact of an Acute 30-Minute Bout of Running

The mechanical properties of human tendons are likely to be influenced by factors known to affect elastic structures, including patterns of loading and unloading during the day. However, the exact scale and relevance of these variables to tendon stiffness remains unclear. The aim of this study was to (1) measure Achilles tendon (AT) stiffness over the course of the day, (2) examine AT stiffness between dominant and non-dominant standing leg tendons and (3) assess the impact of previous activity on AT stiffness. To assess the impact of time of day and leg dominance, 15 healthy participants (6 females, 9 males; mean age 28 ± 4 year, mean VISA-A score 99.0 ± 1.2) had shear wave elastography (SWE) measures taken at 08:00 h, 12:30 h and 17:00 h on both dominant and non-dominant legs. To assess the impact of exercise, 24 tendons were analysed (7 females, 5 males; mean age 27 ± 4 year, mean VISA-A Score 99.1 ± 1.1) with participants randomly assigned to either a control (CONT) group or a running (RUN) group. The RUN group performed a 30-min run at a subjective intensity of 13–15 on rating of perceived exertion (RPE) scale and had SWE measures taken before, immediately after, 6 h 24 h, 48 h and 72 h following the run. There were no significant differences in AT stiffness over the course of a day or between dominant and non-dominant leg. Significant increases in AT stiffness were noted pre-post run (0.27 m/s, 2.95%, p = 0.037). Leg dominance does not affect SWE values from asymptomatic ATs or change throughout a day, but a 30-min run significantly increases AT stiffness. Leg dominance and timing of clinical appointments are unlikely to affect SWE results, however a prior bout of physical activity may cause changes within the AT resulting in a significantly different SWE measure. Clinicians and researchers should be cautious of interpreting SWE results if weight bearing exercise has been performed beforehand.

Increased enslaving in elderly is associated with changes in neural control of the extrinsic finger muscles

Aging has consequences for hand motor control, among others affecting finger force enslaving during static pressing tasks. The aim of this study was to assess whether the extent of finger force enslaving changes with aging during a task that involves both static and dynamic phases. Ten right-handed young (22-30 years) and ten elderly subjects (67-79 years) were instructed to first exert a constant force (static phase) and then flex their index finger while counteracting constant resistance forces orthogonal to their fingertips (dynamic phase). The other fingers (non-instructed) were held in extension. EMG activities of the flexor digitorum superficialis (FDS) and extensor digitorum (ED) muscles in the regions corresponding to the index, middle and ring fingers together with their forces and position of index finger were measured. In both elderly and young, forces exerted by the non-instructed fingers increased (around 0.6 N for both young and elderly) during isotonic flexion of the index finger, but with a different delay of on average 100 ± 72 ms in elderly and 334 ± 101 ms in young subjects. Results also suggest different responses in activity of FDS and ED muscle regions of the non-instructed fingers to index finger flexion between elderly and young subjects. The enslaving effect was significantly higher in elderly than in young subjects both in the static (12% more) and dynamic (14% more) phases. These differences in enslaving can at least partly be explained by changes in neuromuscular control.

Alterations in Leg Extensor Muscle-Tendon Unit Biomechanical Properties With Ageing and Mechanical Loading

Tendons transfer forces produced by muscle to the skeletal system and can therefore have a large influence on movement effectiveness and safety. Tendons are mechanosensitive, meaning that they adapt their material, morphological and hence their mechanical properties in response to mechanical loading. Therefore, unloading due to immobilization or inactivity could lead to changes in tendon mechanical properties. Additionally, ageing may influence tendon biomechanical properties directly, as a result of biological changes in the tendon, and indirectly, due to reduced muscle strength and physical activity. This review aimed to examine age-related differences in human leg extensor (triceps surae and quadriceps femoris) muscle-tendon unit biomechanical properties. Additionally, this review aimed to assess if, and to what extent mechanical loading interventions could counteract these changes in older adults. There appear to be consistent reductions in human triceps surae and quadriceps femoris muscle strength, accompanied by similar reductions in tendon stiffness and elastic modulus with ageing, whereas the effect on tendon cross sectional area is unclear. Therefore, the observed age-related changes in tendon stiffness are predominantly due to changes in tendon material rather than size with age. However, human tendons appear to retain their mechanosensitivity with age, as intervention studies report alterations in tendon biomechanical properties in older adults of similar magnitudes to younger adults over 12–14 weeks of training. Interventions should implement tendon strains corresponding to high mechanical loads (i.e., 80–90% MVC) with repetitive loading for up to 3–4 months to successfully counteract age-related changes in leg extensor muscle-tendon unit biomechanical properties.

Mechanobiology of young and aging tendons: In vivo studies with treadmill running

Tendons are unique in the sense that they are constantly subjected to large mechanical loads and that they contain tendon-specific cells, including tenocytes and tendon stem/progenitor cells. The responses of these cells to mechanical loads can be anabolic or catabolic and as a result, change the biological properties of the tendon itself that may be beneficial or detrimental. On the other hand, aging also induces aberrant changes in cellular expression of various genes and production of various types of matrix proteins in the tendon, and consequently lead to tendon degeneration and impaired healing in aging tendons; both could be improved by moderate physiological mechanical loading such as treadmill running. This article gives an overview on the mechanobiology research of young and aging animal tendons using treadmill running model. The challenges in such treadmill running studies are also discussed. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:557-565, 2018.

Compositional mapping of the mature anterior cruciate ligament-to-bone insertion

The anterior cruciate ligament (ACL)-to-bone interface constitutes a complex, multi-tissue structure comprised of contiguous ligament, non-mineralized fibrocartilage, mineralized fibrocartilage, and bone regions. This composite structure enables load transfer between structurally and functionally dissimilar tissues and is critical for ligament homeostasis and joint stability. Presently, there is a lack of quantitative understanding of the matrix composition and organization across this junction, especially after the onset of skeletal maturity. The objective of this study is to characterize the adult bovine ACL-to-bone interface using Fourier transform infrared spectroscopic imaging (FTIRI), testing the hypothesis that regional changes in collagen, proteoglycan, and mineral distribution, as well as matrix organization, persist at the mature insertion. It was observed that while collagen content increases continuously across the adult interface, collagen alignment decreases between ligament and bone. Proteoglycans were primarily localized to the fibrocartilage region and an exponential increase in mineral content was observed between the non-mineralized and mineralized regions. These observations reveal significant changes in collagen distribution and alignment with maturity, and these trends underscore the role of physiologic loading in postnatal matrix remodeling. Findings from this study provide new insights into interface organization and serve as benchmark design criteria for interface regeneration and integrative soft tissue repair. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2513-2523, 2017.

The Achilles tendon is mechanosensitive in older adults: adaptations following 14 weeks versus 1.5 years of cyclic strain exercise

The aging musculoskeletal system experiences a general decline in structure and function, characterized by a reduced adaptability to environmental stress. We investigated whether the older human Achilles tendon (AT) demonstrates mechanosensitivity (via biomechanical and morphological adaptations) in response to long-term mechanical loading. Thirty-four female adults (60-75 years) were allocated to either a medium-term (14 weeks; N=21) high AT strain cyclic loading exercise intervention or a control group (N=13), with 12 participants continuing with the intervention for 1.5 years. AT biomechanical properties were assessed using ultrasonography and dynamometry. Tendon cross-sectional area (CSA) was investigated by means of magnetic resonance imaging. A 22% exercise-related increment in ankle plantarflexion joint moment, along with increased AT stiffness (598.2±141.2 versus 488.4±136.9 N mm^-1 at baseline), Young's modulus (1.63±0.46 versus 1.37±0.39 GPa at baseline) and about 6% hypertrophy along the entire free AT were identified after 14 weeks of strength training, with no further improvement after 1.5 years of intervention. The aging AT appears to be capable of increasing its stiffness in response to 14 weeks of mechanical loading exercise by changing both its material and dimensional properties. Continuing exercise seems to maintain, but not cause further adaptive changes in tendons, suggesting that the adaptive time-response relationship of aging tendons subjected to mechanical loading is nonlinear.

Tendon injuries: Basic science and new repair proposals

Tendons connect muscles to bones, ensuring joint movement. With advanced age, tendons become more prone to degeneration followed by injuries. Tendon repair often requires lengthy periods of rehabilitation, especially in elderly patients. Existing medical and surgical treatments often fail to regain full tendon function.

The development of novel treatment methods has been hampered due to limited understanding of basic tendon biology. Recently, it was discovered that tendons, similar to other mesenchymal tissues, contain tendon stem/progenitor cells (TSPCs) which possess the common stem cell properties.

The current strategies for enhancing tendon repair consist mainly of applying stem cells, growth factors, natural and artificial biomaterials alone or in combination. In this review, we summarise the basic biology of tendon tissues and provide an update on the latest repair proposals for tendon tears.

Cite this article: EFORT Open Rev 2017;2:332-342. DOI: 10.1302/2058-5241.2.160075

Downregulation of CITED2 contributes to TGFβ-mediated senescence of tendon-derived stem cells

Tendon-derived stem cells (TDSCs) are multipotent adult stem cells with potential applications in tendon and tendon-bone junction repair. However, cellular characteristics change during in vitro passaging. Therefore, elucidation of the molecular and cellular mechanisms of tendon aging will be essential for the development of TDSC-based therapies. The aim of this study is to investigate the effect of CITED2, a nuclear regulator and transforming growth factor β2 (TGFβ2) on TDSC proliferation and senescence by comparing cells derived from Achilles tendon biopsies of young individuals (Y-TDSC) with those of older patients (O-TDSC). Our results showed that CITED2 mRNA and protein expression levels were significantly higher in Y-TDSCs than in O-TDSCs and O-TDSCs displayed decreased proliferation and increased senescence compared with Y-TDSCs. Furthermore, high levels of CITED2 protein expression in Y-TDSCs correlated with the downregulation of SP1 and p21 and the upregulation of MYC, potentially indicating the mechanism by which CITED2 upregulates TDSC proliferation. TGFβ2 was found to downregulate the expression of the CITED2 gene and knockdown of CITED2 abolished the effect of TGFβ2 on TDSC proliferation and senescence. Thus, the downregulation of CITED2 contributes to TGFβ-mediated senescence providing an insight into the molecular and cellular mechanisms that contribute to tendon aging and degeneration. Our findings may aid the development of cell-based therapies for tendon repair.

Micro- and Ultrastructural Characterization of Age-Related Changes at the Anterior Cruciate Ligament-to-Bone Insertion

There remains a lack of understanding of the structural changes that occur across the complex, multitissue anterior cruciate ligament (ACL)-to-bone insertion as a function of aging. The objective of this study is to provide a multiscale comparison of matrix properties across the skeletally immature and mature ACL-to-bone insertion. Using complementary imaging methods, micro- and ultrastructural analysis of the insertion revealed that collagen fiber orientation at the interface changes with age, though the degree of collagen organization is maintained over time. These changes are accompanied by a decrease in collagen fibril density and are likely driven by physiological loading. Mineral crystal structure and crystallinity are conserved over time, despite regional differences in crystallinity between the interface and bone. This suggests that mineral chemistry is established early in development and underscores its important functional role. Collectively, these findings provide new insights into interface development and set critical design benchmarks for integrative soft tissue repair.

Effect of aging and exercise on the tendon

Here, we review the literature on how tendons respond and adapt to ageing and exercise. With respect to aging, there are considerable changes early in life, but this seems to be maturation rather than aging per se. In vitro data indicate that aging is associated with a decreased potential for cell proliferation and a reduction in the number of stem/progenitor-like cells. Further, there is persuasive evidence that turnover in the core of the tendon after maturity is very slow or absent. Tendon fibril diameter, collagen content, and whole tendon size appear to be largely unchanged with aging, while glycation-derived cross-links increase substantially. Mechanically, aging appears to be associated with a reduction in modulus and strength. With respect to exercise, tendon cells respond by producing growth factors, and there is some support for a loading-induced increase in tendon collagen synthesis in humans, which likely reflects synthesis at the very periphery of the tendon rather than the core. Average collagen fibril diameter is largely unaffected by exercise, while there can be some hypertrophy of the whole tendon. In addition, it seems that resistance training can yield increased stiffness and modulus of the tendon and may reduce the amount of glycation. Exercise thereby tends to counteract the effects of aging.

Achilles Tendinopathy: Current Concepts about the Basic Science and Clinical Treatments

Achilles tendinopathy is one of the most frequently ankle and foot overuse injuries, which is a clinical syndrome characterized by the combination of pain, swelling, and impaired performance. The two main categories of Achilles tendinopathy are classified according to anatomical location and broadly include insertional and noninsertional tendinopathy. The etiology of Achilles tendinopathy is multifactorial including both intrinsic and extrinsic factors. Failed healing response and degenerative changes were found in the tendon. The failed healing response includes three different and continuous stages (reactive tendinopathy, tendon disrepair, and degenerative tendinopathy). The histological studies have demonstrated an increased number of tenocytes and concentration of glycosaminoglycans in the ground substance, disorganization and fragmentation of the collagen, and neovascularization. There are variable conservative and surgical treatment options for Achilles tendinopathy. However, there has not been a gold standard of these treatments because of the controversial clinical results between various studies. In the future, new level I researches will be needed to prove the effect of these treatment options.

Reduced Patellar Tendon Elasticity with Aging: In Vivo Assessment by Shear Wave Elastography

How aging affects the elasticity of tendons has long been debated, partly because of the limited methods for in vivo evaluation, which differ vastly from those for in vitro animal studies. In this study, we tested the reliability of shear wave elastography (SWE) in the evaluation of patellar tendons and their change in elasticity with age. We recruited 62 healthy participants in three age groups: 20-30 years (group 1), 40-50 years (group 2) and 60-70 years (group 3). Shear wave velocity and elastic modulus were measured at the proximal, middle and distal areas of the patellar tendon. Reliability was excellent at the middle area and fair to good at both ends. Compared with the other groups, group 3 had significantly decreased elastic modulus and shear wave velocity values (p ≤ 0.001 vs. group 1 or 2), with significant increased side-to-side differences. SWE may be valuable in detecting aging tendons before visible abnormalities are observed on B-mode ultrasonography.

Human Fetal Progenitor Tenocytes for Regenerative Medicine

Tendon injuries are very frequent and affect a wide and heterogeneous population. Unfortunately, the healing process is long with outcomes that are not often satisfactory due to fibrotic tissue appearance, which leads to scar and adhesion development. Tissue engineering and cell therapies emerge as interesting alternatives to classical treatments. In this study, we evaluated human fetal progenitor tenocytes (hFPTs) as a potential cell source for treatment of tendon afflictions, as fetal cells are known to promote healing in a scarless regenerative process. hFPTs presented a rapid and stable growth up to passage 9, allowing to create a large cell bank for off-the-shelf availability. hFPTs showed a strong tenogenic phenotype with an excellent stability, even when placed in conditions normally inducing cells to differentiate. The karyotype also indicated a good stability up to passage 12, which is far beyond that necessary for clinical application (passage 6). When placed in coculture, hFPTs had the capacity to stimulate human adult tenocytes (hATs), which are responsible for the deposition of a new extracellular matrix during tendon healing. Finally, it was possible to distribute cells in porous or gel scaffolds with an excellent survival, thus permitting a large variety of applications (from simple injections to grafts acting as filling material). All of these results are encouraging in the development of an off-the-shelf cell source capable of stimulating tendon regeneration for the treatment of tendon injuries.

Moderate Exercise Mitigates the Detrimental Effects of Aging on Tendon Stem Cells

Aging is known to cause tendon degeneration whereas moderate exercise imparts beneficial effects on tendons. Since stem cells play a vital role in maintaining tissue integrity, in this study we aimed to define the effects of aging and moderate exercise on tendon stem/progenitor cells (TSCs) using in vitro and in vivo models. TSCs derived from aging mice (9 and 24 months) proliferated significantly slower than TSCs obtained from young mice (2.5 and 5 months). In addition, expression of the stem cell markers Oct-4, nucleostemin (NS), Sca-1 and SSEA-1 in TSCs decreased in an age-dependent manner. Interestingly, moderate mechanical stretching (4%) of aging TSCs in vitro significantly increased the expression of the stem cell marker, NS, but 8% stretching decreased NS expression. Similarly, 4% mechanical stretching increased the expression of Nanog, another stem cell marker, and the tenocyte-related genes, collagen I and tenomodulin. However, 8% stretching increased expression of the non-tenocyte-related genes, LPL, Sox-9 and Runx-2, while 4% stretching had minimal effects on the expression of these genes. In the in vivo study, moderate treadmill running (MTR) of aging mice (9 months) resulted in the increased proliferation rate of aging TSCs in culture, decreased lipid deposition, proteoglycan accumulation and calcification, and increased the expression of NS in the patellar tendons. These findings indicate that while aging impairs the proliferative ability of TSCs and reduces their stemness, moderate exercise can mitigate the deleterious effects of aging on TSCs and therefore may be responsible for decreased aging-induced tendon degeneration.