The effects of aging, antiinflammatory drugs, and ultrasound on the in vitro response of tendon tissue

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.

Tendon healing: a concise review on cellular and molecular mechanisms with a particular focus on the Achilles tendon

Tendon is a bradytrophic and hypovascular tissue, hence, healing remains a major challenge. The molecular key events involved in successful repair have to be unravelled to develop novel strategies that reduce the risk of unfavourable outcomes such as non-healing, adhesion formation, and scarring. This review will consider the diverse pathophysiological features of tendon-derived cells that lead to failed healing, including misrouted differentiation (e.g. de- or transdifferentiation) and premature cell senescence, as well as the loss of functional progenitors. Many of these features can be attributed to disturbed cell-extracellular matrix (ECM) or unbalanced soluble mediators involving not only resident tendon cells, but also the cross-talk with immigrating immune cell populations. Unrestrained post-traumatic inflammation could hinder successful healing. Pro-angiogenic mediators trigger hypervascularization and lead to persistence of an immature repair tissue, which does not provide sufficient mechano-competence. Tendon repair tissue needs to achieve an ECM composition, structure, strength, and stiffness that resembles the undamaged highly hierarchically ordered tendon ECM. Adequate mechano-sensation and -transduction by tendon cells orchestrate ECM synthesis, stabilization by cross-linking, and remodelling as a prerequisite for the adaptation to the increased mechanical challenges during healing. Lastly, this review will discuss, from the cell biological point of view, possible optimization strategies for augmenting Achilles tendon (AT) healing outcomes, including adapted mechanostimulation and novel approaches by restraining neoangiogenesis, modifying stem cell niche parameters, tissue engineering, the modulation of the inflammatory cells, and the application of stimulatory factors.Cite this article: Bone Joint Res 2022;11(8):561-574.

Differences in cellular and microstructural properties of the semitendinosus muscle tendon between young and adult patients

BACKGROUND

Poor outcomes associated with anterior cruciate ligament reconstruction in paediatric patients are a major concern. The tendon structure and its cellular characteristics are key factors that affect the mechanical properties of tendons. This study aimed to evaluate the effects of growth on the cellular and microstructural properties of the tendon of the semitendinosus muscle in humans.

METHODS

Semitendinosus muscle tendon samples from 76 patients who underwent ligament reconstruction were examined and divided into three groups: immature (10.8 ± 2.7 years old), young (16.5 ± 1.8 years old), and adult (35.2 ± 8.6 years old), based on age and the state of the epiphyseal plate in the distal femur. The number of tendon cells per unit area was assessed, and the major-to-minor-length ratio of the tendon cell nuclei was calculated to evaluate the shape of the nuclei using haematoxylin and eosin staining. The collagen fibril diameter and distribution were determined using electron microscopy.

RESULTS

The major-to-minor-length ratio of the tendon cell nuclei significantly increased with age (p-value; immature vs. young: 0.018, young vs adult: 0.001, immature vs adult: 0.001). The shape of the tendon cell nuclei was rounder in the immature group and more elongated in the adult group. A significant decrease in the number of tendon cells was observed with age (immature: 565 ± 134/mm², young: 356 ± 105/mm², adult: 272 ± 81/mm²; p-value: immature vs young: 0.001, young vs adult: 0.012, immature vs adult: 0.001). The mean fibril diameter in the immature group was significantly smaller (p-value: immature vs young: 0.018, young vs adult: 0.001, immature vs adult: 0.001). The distribution of the collagen fibrils changed from right skewed in the immature group to flat in the adult group.

CONCLUSIONS

The characteristics of the tendon cells and the microstructure of collagen in muscle tendons significantly changed with age.

The Effect of Age and Intrinsic Aerobic Exercise Capacity on the Expression of Inflammation and Remodeling Markers in Rat Achilles Tendons

Old age, adiposity, and metabolic disorders are known as risk factors for chronic tendinopathy, which is a common problem in both athletes and the general population. However, the importance of these influencing factors has not yet been well understood. This study investigated alterations in gene expression and histology of Achilles tendons of young (10 weeks) and old (100 weeks) rats bred for low (low capacity runners, LCR) and high (high capacity runners, HCR) intrinsic aerobic exercise capacity. In this rat model, LCR displayed a phenotype of reduced exercise capacity, higher body weight, and metabolic dysfunctions compared to HCR. We hypothesized that the risk factors for tendinopathy in old LCR could lead to more pronounced impairments in Achilles tendon tissue. In quantitative real-time PCR (qPCR), age-related downregulation of tenocyte markers e.g., tenomodulin, genes related to matrix modeling and remodeling (e.g., collagens, elastin, biglycan, fibronectin, tenascin C) as well as transforming growth factor beta 3 (Tgfb3) have been detected. Inflammation marker cyclooxygenase 2 (Cox2) was downregulated in old rats, while microsomal prostaglandin E synthase 2 (Ptges2) was upregulated in old HCR and old LCR. In all groups, interleukin 6 (Il6), interleukin 1 beta (Il1b), and tumor necrosis factor alpha (Tnfa) showed no significant alteration. In histological evaluation, tendons of old rats had fewer and more elongated tenocyte nuclei than young rats. Even though a higher content of glycosaminoglycans, a sign of degeneration, was found in old HCR and LCR, no further signs of tendinopathy were detectable in tendons of old rats by histological evaluation. Low intrinsic aerobic exercise capacity and the associated phenotype did not show significant effects on gene expression and tendon histology. These findings indicate that aging seems to play a prominent role in molecular and structural alterations of Achilles tendon tissue and suggests that other risk factors associated with intrinsic aerobic exercise capacity are less influential in this rat model.

Distal semimembranosus tendinopathy: A narrative review

Distal semimembranosus tendinopathy is a relatively uncommon diagnosis that can be responsible for medial knee pain. The semimembranosus tendon inserts on the posteromedial knee and is surrounded by the semimembranosus bursa, with both the bursa and tendon potential sources of pain. Similar to other tendinopathies, semimembranosus tendinopathy often occurs with overuse of the musculotendinous unit and is commonly seen in runners. Diagnosis can be made clinically and may be substantiated with use of ultrasound or magnetic resonance imaging. Scant literature exists evaluating the efficacy of treatments for this condition. Consequently, best practice for treatment is inferred from other similar tendinopathies, clinical expertise, and smaller studies on semimembranosus tendinopathy. Extrapolating from other tendinopathies, rehabilitation should be the cornerstone of initial treatment, with focus on kinetic chain and gait abnormalities, hamstring strength and neuromuscular control, and progressive tendon loading. Recalcitrant cases with a coexisting bursopathy can be treated with an ultrasound-guided bursal corticosteroid injection. Future studies may help delineate the optimal treatment regimen for this relatively uncommon diagnosis.

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.

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.

Effect of young extrinsic environment stimulated by hypoxia on the function of aged tendon stem cell

Tendon stem cells (TSCs), recently identified as tendon cells, play an important role in maintaining the homeostasis of tendon tissue. Age-related decrease in the function of TSCs has been reported. Recent reports demonstrated that hypoxic condition is advantageous for efficient expansion of TSCs. Moreover, the impaired function of aged stem cells could be modulated by exposing them to a young environment. Therefore, we investigated the effects of hypoxic-conditioned culture medium (HCCM) from young TSCs on the proliferation, migration, senescence, and tenocyte phenotype of aged TSCs. TSCs were isolated, and the conditioned medium was collected. There were 4 groups: young TSCs, aged TSCs, aged TSCs + aged HCCM, and aged TSCs + young HCCM. The proliferative capacity, migration, β-galactosidase activity, and tenogenic differentiation potential of TSCs were assessed. Our results showed that HCCM enhanced the proliferation and migration potential of aged TSCs. Moreover, the senescence-associated β-galactosidase activity of aged TSCs was decreased by young HCCM. After being cultured in the young HCCM, the expressions of tenocyte-related genes in aged TSCs were significantly enhanced. Together, results of this study indicate that HCCM from young TSCs may represent an effective strategy to improve the impaired function of aged TSCs.

An overview of structure, mechanical properties, and treatment for age-related tendinopathy

Tendons transfer tensile loads from muscle to bone, which enable joint motions and stabilize joints. Tendons sustain large mechanical loads in vivo and as a result, tendons were frequently injured. Aging has been confirmed as a predisposing factor of tendinopathy and bad recovery quality following tendon repair. Current treatment methods are generally not effective and involve either symptomatic relief with non-steroidal antiinflammatory drugs and physical therapy or surgery when conservative treatments failed. The limitation in treatment options is due to our incomplete knowledge of age-related tendinopathy. Studies over the past decades have uncovered a number of important mechanical and cellular changes of aging tendon. However, the basis of aging as a major risk factor for tendon injury and impaired tendon healing remained poorly understood. The objectives of this review are to provide an overview of the current knowledge about the aging-associated changes of structure, mechanical properties and treatment in tendon and highlight causes and therapies for age-related tendinopathy.

NSAID therapy effects on healing of bone, tendon, and the enthesis

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used for the treatment of skeletal injuries. The ability of NSAIDs to reduce pain and inflammation is well-established. However, the effects of NSAID therapy on healing of skeletal injuries is less defined. NSAIDs inhibit cyclooxygenase activity to reduce synthesis of prostaglandins, which are proinflammatory, lipid-signaling molecules. Inhibition of cyclooxygenase activity can impact many physiological processes. The effects of NSAID therapy on healing of bone, tendon, and the tendon-to-bone junction (enthesis) have been studied in animal and cell culture models, but human studies are few. Use of different NSAIDs with different pharmacological properties, differences in dosing regimens, and differences in study models and outcome measures have complicated comparisons between studies. In this review, we summarize the mechanisms by which bone, tendon, and enthesis healing occurs, and describe the effects of NSAID therapy on each of these processes. Determining the impact of NSAID therapy on healing of skeletal tissues will enable clinicians to appropriately manage the patient's condition and improve healing outcomes.

Short-term acetaminophen consumption enhances the exercise-induced increase in Achilles peritendinous IL-6 in humans

Through an unknown mechanism, the cyclooxygenase inhibitor and antipyretic acetaminophen (APAP) alters tendon mechanical properties in humans when consumed during exercise. Interleukin-6 (IL-6) is produced by tendon during exercise and is a potent stimulator of collagen synthesis. In nontendon tissue, IL-6 is upregulated in the presence of cyclooxygenase inhibitors and may contribute to alterations in extracellular matrix turnover, possibly due to inhibition of prostaglandin E2 (PGE2). We evaluated the effects of APAP on IL-6 and PGE2 in human Achilles peritendinous tissue after 1 h of treadmill exercise. Subjects were randomly assigned to a placebo (n = 8, 26 ± 1 yr) or APAP (n = 8, 25 ± 1 yr) group. Each subject completed a nonexercise and exercise experiment consisting of 6 h of microdialysis. Drug (APAP, 1,000 mg) or placebo was administered in a double-blind manner during both experiments. PGE2 and IL-6 were determined via enzyme immunoassay and APAP via high-performance liquid chromatography. In subjects given APAP, peritendinous APAP levels increased to 4.08 ± 0.65 μg/ml (P < 0.05). PGE2 did not increase with exercise in either group (P > 0.05), nor was PGE2 significantly reduced in the APAP group. IL-6 levels increased with exercise in both groups (P < 0.05), but this increase was greater in the APAP group (P < 0.05). Our findings suggest that APAP enhances tendon IL-6 production after exercise. Peak levels of APAP obtained in the peritendinous space were twofold lower than values reported in plasma or skeletal muscle. These findings provide insight into the effects of APAP on tendon and provide novel information on the kinetics of APAP in tendon tissue after oral APAP consumption.

Inflamm-aging and arachadonic acid metabolite differences with stage of tendon disease

The contribution of inflammation to the pathogenesis of tendinopathy and high prevalence of re-injury is not well established, although recent evidence suggests involvement of prostaglandins. We investigated the roles of prostaglandins and inflammation-resolving mediators in naturally occurring equine tendon injury with disease stage and age. Levels of prostaglandins E₂ (PGE₂), F_2α (PGF_2α), lipoxin A₄ (LXA₄) and its receptor FPR2/ALX were analysed in extracts of normal, sub-acute and chronic injured tendons. To assess whether potential changes were associated with altered PGE₂ metabolism, microsomal prostaglandin E synthase-1 (mPGES-1), prostaglandin dehydrogenase (PGDH), COX-2 and EP₄ receptor expression were investigated. The ability of tendons to resolve inflammation was determined by assessing FPR2/ALX expression in natural injury and IL-1β stimulated tendon explants.

Alterations in the profile of lipid mediators during sub-acute injury included low PGE₂ and elevated LXA₄ levels compared to normal and chronic injuries. In contrast, PGF_2α levels remained unchanged and were three-fold lower than PGE₂. The synthetic capacity of PGE₂ as measured by the ratio of mPGES-1:PGDH was elevated in sub-acute injury, suggesting aberrations in tendon prostaglandin metabolism, whilst COX-2 and EP₄ receptor were unchanged. Paradoxically low tendon PGE₂ levels in early injury may be attributed to increased local clearance via PGDH or the class switching of lipid mediators from the prostaglandin to the lipoxin axis. PGE₂ is therefore implicated in the development of tendon inflammation and its ensuing resolution. Whilst there was no relationship between age and tendon LXA₄ levels, there was an age-associated decline in FPR2/ALX receptor expression with concurrent increased PGE₂ levels in injury. Furthermore, uninjured tendon explants from younger (<10 years) but not older horses (≥10 years) treated with IL-1β responded by increasing FPR2/ALX suggesting aged individuals exhibit a reduced capacity to resolve inflammation via FPR2/ALX, which may present a potential mechanism for development of chronic tendinopathy and re-injury.

Tendinosis: pathophysiology and nonoperative treatment

Tendinosis is a troublesome clinical entity affecting many active people. Its treatment remains a challenge to sports medicine clinicians. The etiopathophysiology of tendinosis has not been well delineated. The known pathophysiology and the recent advances in the understanding of the etiologic process of tendinosis are discussed here, including new concepts in mechanotransduction and the biochemical alterations that occur during tendon overload. The optimal, nonoperative treatment of tendinosis is not clear. This article reviews recent evidence of the clinical efficacy of the following interventions: eccentric exercise, extracorporal shock wave treatment, corticosteroid and nonsteroidal anti-inflammatory medications, sclerosing injections, nitric oxide, platelet-rich plasma injections, and matrix metalloproteinase inhibitors. Eccentric exercise has strongest evidence of efficacy. Extracorporal shock wave treatment has mixed evidence and needs further study of energy and application protocols. Sclerosing agents show promising early results but require long-term studies. Corticosteroid and nonsteroidal anti-inflammatory medications have not been shown to be effective, and many basic science studies raise possible concerns with their use. Nitric oxide has been shown in several basic science studies to be promising, but clinical efficacy has not been well established. More clinical trials are needed to assess dosing, indications, and clinical efficacy of nitric oxide. Platelet-rich plasma injections have offered encouraging short-term results. Larger and longer-term clinical trials are needed to assess this promising modality. Matrix metalloproteinase inhibitors have had few clinical studies, and their role in the treatment of tendinosis is still in the early phase of investigation.

The effect of aging on migration, proliferation, and collagen expression of tenocytes in response to ciprofloxacin

Quinolone-induced tendinopathy or tendon rupture tends to be age-related. However, the synergistic effects of quinolone and aging on tenocytes remained to be explored. Tenocytes intrinsic to rat Achilles tendon from two age groups (young: 2 months; and near senescent (old): 24 months) were treated with ciprofloxacin. Tenocyte migration and proliferation were assessed by transwell filter migration assay and MTT (3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay, respectively. Messenger RNA and protein expressions of types I and III collagen were determined by reverse transcription-polymerase chain reaction (RT/PCR) and Western blot analysis, respectively. Transwell filter migration assay revealed that ciprofloxacin inhibited tenocytes migration, which became more significant in old tenocytes (p < 0.05). The results of MTT assay revealed that tenocytes proliferation decreased after ciprofloxacin treatment (p < 0.05), which also became more significant in old tenocytes. The results of RT-PCR and Western blot analysis revealed that mRNA and protein expressions of type I collagen remained unchanged in either young or old tenocytes with ciprofloxacin treatment, whereas the expressions of type III collagen were down-regulated by ciprofloxacin, which was more significant in old tenocytes. In conclusion, aging potentiated the ciprofloxacin-mediated inhibition of migration, proliferation, and expression of type III collagen of tenocytes.

Lessons we can learn from gene expression patterns in rotator cuff tears and tendinopathies

Persistently high failure rates that are reported after rotator cuff repairs have encouraged greater understanding of the pathophysiology that underlies rotator cuff tears. Biologic changes that contribute to the pathogenesis of rotator cuff tears and tendinopathies, as well as adaptation after these changes, have been well described. A subset of patients with a genetic predisposition to early onset of rotator cuff tears and earlier symptom and disease progression have been identified. Many biologic changes occurring at the gene level have been identified. Pathways that are believed to contribute to rotator cuff tendinopathies include extracellular matrix remodeling, angiogenesis, changes in metabolism, apoptosis, and stress-related genes. Metaplasia of rotator cuff cells is contributed to by changes in gene expression. Modification of these gene changes may be possible through mechanical loading, drugs, or cellular manipulation. Gene changes may offer greater insight into why certain tears fail to heal and help to identify therapeutic targets.

Diagnosis and treatment of acute ankle injuries: development of an evidence-based algorithm

Acute ankle injuries are among the most common injuries in emergency departments. However, there are still no standardized examination procedures or evidence-based treatment. Therefore, the aim of this study was to systematically search the current literature, classify the evidence, and develop an algorithm for the diagnosis and treatment of acute ankle injuries. We systematically searched PubMed and the Cochrane Database for randomized controlled trials, meta-analyses, systematic reviews or, if applicable, observational studies and classified them according to their level of evidence. According to the currently available literature, the following recommendations have been formulated: i) the Ottawa Ankle/Foot Rule should be applied in order to rule out fractures; ii) physical examination is sufficient for diagnosing injuries to the lateral ligament complex; iii) classification into stable and unstable injuries is applicable and of clinical importance; iv) the squeeze-, crossed leg- and external rotation test are indicative for injuries of the syndesmosis; v) magnetic resonance imaging is recommended to verify injuries of the syndesmosis; vi) stable ankle sprains have a good prognosis while for unstable ankle sprains, conservative treatment is at least as effective as operative treatment without the related possible complications; vii) early functional treatment leads to the fastest recovery and the least rate of reinjury; viii) supervised rehabilitation reduces residual symptoms and re-injuries. Taken these recommendations into account, we present an applicable and evidence-based, step by step, decision pathway for the diagnosis and treatment of acute ankle injuries, which can be implemented in any emergency department or doctor's practice. It provides quality assurance for the patient and promotes confidence in the attending physician.

Decreased proliferation of aging tenocytes is associated with down-regulation of cellular senescence-inhibited gene and up-regulation of p27

Symptomatic tendinopathy tends to be age-related. However, the molecular mechanisms of ageing and its effects on tenocyte proliferation and cell cycle progression are unknown. We examined tenocytes from Achilles tendons in rats from three age groups (young, 2 months; middle-aged, 12 months, and near senescence, 24 months). Tenocyte proliferation was assessed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. Senescence-associated β-galactosidase (SA β-gal) staining was performed in all groups of tenocytes. mRNA and protein expression of cellular senescence-inhibited gene (CSIG) and p27 was measured by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively. The results of MTT assay revealed that tenocyte proliferation decreased with age (p < 0.05). Cell cycle progression was arrested at G0/G1 phase in senescent tenocytes. More senescent tenocytes expressed SA β-gal than young tenocytes did. By RT-PCR and Western blot analysis, the gene and protein expression of CSIG was found to be down-regulated, whereas that of p27 was up-regulated with age. In conclusion, the proliferation of tenocytes declines with age and is associated with the down-regulation of CSIG and up-regulation of p27.

Influence of acetaminophen and ibuprofen on in vivo patellar tendon adaptations to knee extensor resistance exercise in older adults

Millions of older individuals consume acetaminophen or ibuprofen daily and these same individuals are encouraged to participate in resistance training. Several in vitro studies suggest that cyclooxygenase-inhibiting drugs can alter tendon metabolism and may influence adaptations to resistance training. Thirty-six individuals were randomly assigned to a placebo (67 ± 2 yr old), acetaminophen (64 ± 1 yr old; 4,000 mg/day), or ibuprofen (64 ± 1 yr old; 1,200 mg/day) group in a double-blind manner and completed 12 wk of knee extensor resistance training. Before and after training in vivo patellar tendon properties were assessed with MRI [cross-sectional area (CSA) and signal intensity] and ultrasonography of patellar tendon deformation coupled with force measurements to obtain stiffness, modulus, stress, and strain. Mean patellar tendon CSA was unchanged (P > 0.05) with training in the placebo group, and this response was not influenced with ibuprofen consumption. Mean tendon CSA increased with training in the acetaminophen group (3%, P < 0.05), primarily due to increases in the mid (7%, P < 0.05) and distal (8%, P < 0.05) tendon regions. Correspondingly, tendon signal intensity increased with training in the acetaminophen group at the mid (13%, P < 0.05) and distal (15%, P = 0.07) regions. When normalized to pretraining force levels, patellar tendon deformation and strain decreased 11% (P < 0.05) and stiffness, modulus, and stress were unchanged (P > 0.05) with training in the placebo group. These responses were generally uninfluenced by ibuprofen consumption. In the acetaminophen group, tendon deformation and strain increased 20% (P < 0.05) and stiffness (-17%, P < 0.05) and modulus (-20%, P < 0.05) decreased with training. These data suggest that 3 mo of knee extensor resistance training in older adults induces modest changes in the mechanical properties of the patellar tendon. Over-the-counter doses of acetaminophen, but not ibuprofen, have a strong influence on tendon mechanical and material property adaptations to resistance training. These findings add to a growing body of evidence that acetaminophen has profound effects on peripheral tissues in humans.

Effects of maturation on the mechanical properties of regenerated and residual tissues in the rabbit patellar tendon after resection of its central one-third

BACKGROUND

The central one-third portion of the patellar tendon is commonly used as a graft for the reconstruction of the anterior cruciate ligament. Although several studies have been carried out on mechanical properties of healing tendons in mature animals, there have been no studies on regenerated and residual tissues in the immature patellar tendon after the removal of its central portion.

METHODS

An entire one-third defect was made in the patellar tendon of 2-, 3- and 6-month-old rabbits. After 3 weeks, the tissue regenerated in the defect and the residual tissue were biomechanically and histologically evaluated.

FINDINGS

The length of patellar tendons in 6-month-old animals after the resection of its central one-third was significantly longer than that in age-matched controls. The cross-sectional area of all operated tendons was significantly larger compared to age-matched controls. There were no significant effects of maturation on the mechanical properties of regenerated and residual tissues in operated tendons, although tensile strength and tangent modulus of normal tendons were significantly greater in 6-month rabbits than in immature ones. The histology of each of regenerated and residual tissues was similar in the three groups.

INTERPRETATION

There were no remarkable effects of maturation on regenerated and residual tissues after the removal of the central one-third tendon. However, the strength and the modulus of normal tendons are significantly lower in immature patients than in mature ones. Therefore, surgeons should take account of the inferior mechanical properties of the tendon in skeletally immature patients at the time of surgeries for the reconstruction of the anterior cruciate ligament.

Role of biomechanics in the understanding of normal, injured, and healing ligaments and tendons

Ligaments and tendons are soft connective tissues which serve essential roles for biomechanical function of the musculoskeletal system by stabilizing and guiding the motion of diarthrodial joints. Nevertheless, these tissues are frequently injured due to repetition and overuse as well as quick cutting motions that involve acceleration and deceleration. These injuries often upset this balance between mobility and stability of the joint which causes damage to other soft tissues manifested as pain and other morbidity, such as osteoarthritis.

The healing of ligament and tendon injuries varies from tissue to tissue. Tendinopathies are ubiquitous and can take up to 12 months for the pain to subside before one could return to normal activity. A ruptured medial collateral ligament (MCL) can generally heal spontaneously; however, its remodeling process takes years and its biomechanical properties remain inferior when compared to the normal MCL. It is also known that a midsubstance anterior cruciate ligament (ACL) tear has limited healing capability, and reconstruction by soft tissue grafts has been regularly performed to regain knee function. However, long term follow-up studies have revealed that 20–25% of patients experience unsatisfactory results. Thus, a better understanding of the function of ligaments and tendons, together with knowledge on their healing potential, may help investigators to develop novel strategies to accelerate and improve the healing process of ligaments and tendons.

With thousands of new papers published in the last ten years that involve biomechanics of ligaments and tendons, there is an increasing appreciation of this subject area. Such attention has positively impacted clinical practice. On the other hand, biomechanical data are complex in nature, and there is a danger of misinterpreting them. Thus, in these review, we will provide the readers with a brief overview of ligaments and tendons and refer them to appropriate methodologies used to obtain their biomechanical properties. Specifically, we hope the reader will pay attention to how the properties of these tissues can be altered due to various experimental and biologic factors. Following this background material, we will present how biomechanics can be applied to gain an understanding of the mechanisms as well as clinical management of various ligament and tendon ailments. To conclude, new technology, including imaging and robotics as well as functional tissue engineering, that could form novel treatment strategies to enhance healing of ligament and tendon are presented.

Tissue specific characteristics of cells isolated from human and rat tendons and ligaments

Background

Tendon and ligament injuries are common and costly in terms of surgery and rehabilitation. This might be improved by using tissue engineered constructs to accelerate the repair process; a method used successfully for skin wound healing and cartilage repair. Progress in this field has however been limited; possibly due to an over-simplistic choice of donor cell. For tissue engineering purposes it is often assumed that all tendon and ligament cells are similar despite their differing roles and biomechanics. To clarify this, we have characterised cells from various tendons and ligaments of human and rat origin in terms of proliferation, response to dexamethasone and cell surface marker expression.

Methods

Cells isolated from tendons by collagenase digestion were plated out in DMEM containing 10% fetal calf serum, penicillin/streptomycin and ultraglutamine. Cell number and collagen accumulation were by determined methylene blue and Sirius red staining respectively. Expression of cell surface markers was established by flow cytometry.

Results

In the CFU-f assay, human PT-derived cells produced more and bigger colonies suggesting the presence of more progenitor cells with a higher proliferative capacity. Dexamethasone had no effect on colony number in ACL or PT cells but 10 nM dexamethasone increased colony size in ACL cultures whereas higher concentrations decreased colony size in both ACL and PT cultures. In secondary subcultures, dexamethasone had no significant effect on PT cultures whereas a stimulation was seen at low concentrations in the ACL cultures and an inhibition at higher concentrations. Collagen accumulation was inhibited with increasing doses in both ACL and PT cultures. This differential response was also seen in rat-derived cells with similar differences being seen between Achilles, Patellar and tail tendon cells. Cell surface marker expression was also source dependent; CD90 was expressed at higher levels by PT cells and in both humans and rats whereas D7fib was expressed at lower levels by PT cells in humans.

Conclusion

These data show that tendon & ligament cells from different sources possess intrinsic differences in terms of their growth, dexamethasone responsiveness and cell surface marker expression. This suggests that for tissue engineering purposes the cell source must be carefully considered to maximise their efficacy.

Glucocorticoids inhibit tenocyte proliferation and Tendon progenitor cell recruitment

Corticosteroid injection is commonly used to treat tendon injuries but is often associated with tendon rupture and impaired tendon healing. The effects of dexamethasone on tenocytes have been studied in vitro but only using high concentrations of dexamethasone in monolayer cultures of tenocytes over short periods of time. We have therefore investigated the effects of physiological and pharmacological concentrations of dexamethasone on monolayer cultures of tenocytes over extended time periods. We have also used fibroblastic-colony forming unit cultures to examine the effects of dexamethasone on a progenitor cell population located in tendons. Culturing tenocytes in the presence of dexamethasone for a period of 24 days resulted in a concentration-related decrease in cell number and collagen synthesis as compared to control cultures. This effect was time dependent with cell number in both dexamethasone-treated and control cultures leveling off after 14 days with the control cultures reaching higher cell densities. In contrast in control cultures, collagen accumulation continued to increase until week 4, whereas in the presence of dexamethasone, this tended to level off after 14 days. To study the role of progenitor cell recruitment, the effects of dexamethasone were investigated using the fibroblastic-colony forming unit assay. Treatment with dexamethasone at concentrations of 0.1 nM to 10 microM leads to a progressive reduction in mean colony size as compared to control cultures. Colony number remained constant at concentrations below 10 nM but fell progressively at concentrations above this. In conclusion, dexamethasone reduces both cell number and collagen synthesis in tenocyte cultures in a concentration-dependent manner by both direct effects on tenocyte proliferation and collagen accumulation, and also by modulating the recruitment of tendon progenitor cells.

Etiology of Patellar Tendinopathy in Athletes

Objective:

To review the etiology of patellar tendinopathy as it relates to clinical management of chronic patellar-tendon disease in athletes.

Data Sources:

Information was gathered from a MEDLINE search of literature in English using the key wordspatellar tendinitis, patellar tendonitis, patellar tendinosis, patellar tendinopathy,andjumper’s knee.

Study Selection:

All relevant peer-reviewed literature in English was reviewed.

Data Synthesis:

The etiology of patellar tendinopathy is multifactorial, incorporating both intrinsic and extrinsic factors. Age, muscle flexibility, training program, and knee-joint dynamics have all been associated with patellar tendinopathy. The roles of gender, body morphology, and patellar mobility in patellar tendinopathy are unclear.

Conclusions:

The pathoetiology of patellar tendinopathy is a complex process that results from both an inflammatory response and degenerative changes. There is a tremendous need for research to improve our understanding of the pathoetiology of patellar tendinopathy and its clinical management.

Effect of hyperbaric oxygen therapy on patellar tendinopathy in a rabbit model

BACKGROUND

Hyperbaric oxygen therapy is a method for augmenting oxygen availability to tissues. This study investigated the effect of hyperbaric oxygen therapy on the collagenase-induced tendinopathy in the rabbit patellar tendon.

METHODS

In this study, 13 rabbits were treated by ultrasound-guided injection of 0.025 mL collagenase into the patellar tendon at the right knee, with the left knee serving as a control condition. The rabbits were randomly divided into two groups. After tendinopathy had been confirmed by histologic examination 3 weeks after treatment, hyperbaric oxygen therapy was initiated for group 1. The hyperbaric oxygen therapy involved 30 daily sessions of 2.5 ATA for 120 minutes starting 6 weeks after treatment. The rabbits in group 2 were put in normobaric room air. Both groups were killed 10 weeks after treatment. Histologic examinations as well as mechanical and biochemical tests were performed after the animals were killed.

RESULTS

The ultimate tensile load in the tendon that had hyperbaric oxygen therapy was 34.8% greater than that in the control tendon 10 weeks after treatment (p < 0.05). Hydroxyproline concentrations increased 82.2% simultaneously in the tendons that had hyperbaric oxygen therapy, as compared with the concentrations in the control tendons (p < 0.05). However, no statistical difference was found between the two groups in terms of pyridinoline concentration at the 10th week (p > 0.05). The histologic examination demonstrated an increase in blastlike tenocytes in group 1, with more mature phenotype, more organized collagen matrix, absence of myxoid degeneration, and increased vascularity at the 10th week, as compared with the control knee.

CONCLUSIONS

The results validate the effectiveness of hyperbaric oxygen therapy in the treatment of tendinopathy. Hyperbaric oxygen therapy may increase collagen synthesis and collagen cross-link formation during the early healing process.

Repetitively stretched tendon fibroblasts produce inflammatory mediators

We studied the expression of cytosolic phospholipase-A2 and activity of secretory phospholipase-A2 by human patellar tendon fibroblasts subjected to cyclic mechanical stretching. The effect of different stretching frequencies on the production of prostaglandin-E2 and expression of cyclooxygenase enzyme were also examined. An in vitro system that can control alignment, shape, and mechanical loading conditions of tendon fibroblasts was used for this study. Cyclic stretching of fibroblasts increased the expression level of cytosolic phospholipase-A2 by 88% and activity level of secretory phospholipase-A2 by 190%, compared with those of nonstretched fibroblasts. Cyclic stretching of tendon fibroblasts at 0.1 Hz and 1.0 Hz also increased prostaglandin-E2 production by 40% and 69%, respectively. Furthermore, cyclooxygenase-1 and cyclooxygenase-2 expression levels were increased in a stretching frequency-dependent manner, but cyclooxygenase-2 expression was increased more than that of cyclooxygenase-1. Because cytosolic phospholipase-A2 and secretory phospholipase-A2 are involved in the production of prostaglandin-E2 and other inflammatory mediators, this study suggests that regulation of phospholipase-A2 expression level may be an alternative approach to control in vivo tendon inflammation. The results of this study also may explain in part why activities that involve repetitive motion and high frequency loading of tendons are more likely to result in tendon inflammation.

Achilles rupture in the athlete. Current science and treatment

Achilles tendon ruptures became increasingly common in the latter half of the 20th century. Once the diagnosis is made, the patient's goals and objectives should be clearly stated. The treatment choice should incorporate the patient's needs, desires, objectives, and functional goals to assure an optimal result.

Effects of Age on the Spinal Stretch Reflex

The spinal stretch reflex consists of a relatively simple neuronal network. The Ia afferent fiber of the muscle spindle communicates to the alpha motoneuron via a single synapse. This basic pathway has been studied extensively over the past century, yet considerable information continues to emerge concerning the manner in which this pathway adapts to aging. It is well accepted that the amplitude of the spinal stretch reflex declines with normal aging, and it is intuitively agreed that these changes have a detrimental impact on the motor output of aging individuals. Understanding the changes observed in the spinal stretch reflex pathway due to aging requires a recognition of the changes that can occur in each component of this spinal network. This review will address these changes by following the spinal stretch reflex from initiation to completion. The components that result in the sensory input to the motoneuron will be covered first, followed by a review of the physiological changes that can occur to the motoneuron soma that can affect the processing of the sensory input. The output of the motoneuron encompasses the remaining components from the motor axon itself, to the neuromuscular junction, and then to the characteristic changes in the muscle. Finally, the functional effect that these changes have on the reflex as a fundamental motor behavior will be addressed, especially in terms of its impact on posture and balance.

Sports and other soft tissue injuries, tendinitis, bursitis, and occupation-related syndromes

Three topics are reviewed: iliopsoas bursitis (IPB), iliotibial band frictional syndrome (ITBFS), and Achilles tendinopathy. Although not frequently diagnosed, IPB may be more prevalent than what is commonly thought. Several excellent review articles are presented. Imaging studies are usually needed for confirmation of the diagnosis, and a report on magnetic resonance imaging is presented. Successful treatment of IPB with home exercise is reviewed. Because an increasing number of people are exercising, there is an increasing need to know the syndromes that can result from overuse, such as ITBFS. Several articles on the use of diagnostic ultrasonography and magnetic resonance imaging to aid in the confirmation of this entity are reviewed; one article explores the pathology of ITBFS in a cadaveric study. In the section of the treatment of ITBFS the authors review one article on exercise and one on surgery. Use of ultrasound to aid in the diagnosis of Achilles tendinopathy is reviewed, as well as risk factors related to developing it. Two articles on surgical treatment are reviewed.

Tenology: a new frontier

Tendons were long given little recognition by rheumatologists. Yet, their complex structure and distinctive functional characteristics have been demonstrated by an abundance of histological, biochemical, and biomechanical studies: clearly, tendons are not inert cords linking muscles to bones. The current wave of popularity of sporting activities has brought with it an epidemic of disorders of the tendons, thus focusing attention on these structures. At the same time, modern imaging techniques (particularly magnetic resonance imaging) have allowed clinicians to improve their knowledge of and classification schemes fortendon disorders. Several risk factors, including technical factors, have been identified, so that preventive treatment is now as important as curative treatment. Culture systems for tenocytes (the specialized fibroblasts found in tendons) are now available and have been used to develop experimental models, paving the way for significant advances in tendon repair techniques.