Structural and biomechanical changes in the Achilles tendon after chronic treatment with statins

Animal models of tendon calcification: Past, present, and future

Tendon calcification is a common clinical condition that frequently occurs as a complication after tendon injury and surgery, or as an expression of fibrodysplasia ossificans progressiva. This condition can be referred to by various names in clinical practice and literature, including tendon ossification, tendon mineralization, heterotopic ossification, and calcific tendonitis. The exact pathogenesis of tendon calcification remains uncertain, but current mainstream research suggests that calcification is mostly cell mediated. To further elucidate the pathogenesis of tendon calcification and to better simulate the overall process, selecting appropriate experimental animal models is important. Numerous animal models have been utilized in various clinical studies, each with its own set of advantages and limitations. In this review, we have discussed the advancements made in research on animal models of tendon calcification, with a focus on the selection of experimental animals, the sites of injury in these models, and the methods employed for modeling.

Current Research on the Influence of Statin Treatment on Rotator Cuff Healing

Rotator cuff tears are a condition characterized by damage to the muscles and tendons that connect the scapula and humerus, which are responsible for shoulder rotation and arm lifting. Metabolic factors such as diabetes, thyroid disease, high cholesterol, vitamin D deficiency, obesity, and smoking have been associated with an increased risk of rotator cuff tears. Interestingly, patients with hyperlipidemia, a condition characterized by high levels of cholesterol and other fats in the blood, have been found to have a higher incidence of rotator cuff tears and breakdown of tendon matrix. As a result, statin therapy, which is commonly used to lower cholesterol levels in hyperlipidemia, has been explored as a potential treatment to improve clinical outcomes in rotator cuff tears. However, the results of preclinical and clinical studies on the effects of statins on tendon healing in rotator cuff tears are limited and not well-defined. Moreover, since hyperlipidemia and rotator cuff tears are more prevalent in older individuals, a literature review on the efficacy and safety of statin therapy in this population is needed.

Bilateral Spontaneous Supraspinatus Tendon Rupture Under Prolonged BRAF/MEK Targeting Treatment in a Melanoma Patient

The B-Raf proto-oncogene, serine/threonine kinase (BRAF)/ mitogen-activated protein kinase kinase (MEK) targeting agents have become the treatment of choice for BRAF-mutated melanoma during the last decade. However, it is possible that some long-term adverse events of these drugs have not yet been reported. A case of bilateral spontaneous, non-traumatic, supraspinatus tendon rupture in a 65-year-old Caucasian male suffering metastatic melanoma under prolonged and successful combination treatment with dabrafenib plus trametinib is presented. These damages could not be attributed to some other probable cause. The ruptured tendons were promptly restored arthroscopically. Oncologists should remain vigilant for the early detection of potential side effects of BRAF/MEK targeting agents that have not been systematically recorded yet but may appear and affect patients in the long run.

Progress in studying the impact of hyperlipidemia and statins on rotator cuff injury and repair

This review delves into the intersection of two prevalent conditions, hyperlipidemia and rotator cuff injuries, both of which bear substantial healthcare burdens. Our investigation begins with an exploration of rotator cuff injuries, common musculoskeletal disorders that severely impair shoulder functionality and quality of life. These injuries are notably pervasive among sports enthusiasts and the older adult, with an incidence rate estimated at 5-10% in the general population. Despite their widespread occurrence and the diverse, multifactorial etiological factors, effective treatment strategies remain elusive. We then examine hyperlipidemia, a metabolic disorder affecting approximately 40% of the global adult population. Characterized by elevated levels of cholesterol and triglycerides, hyperlipidemia can precipitate severe cardiovascular complications and presents a significant socioeconomic burden. Although current management strategies encompass lifestyle modifications and pharmacological interventions, the condition remains a formidable health challenge. Central to this review is the exploration of a potential association between hyperlipidemia and rotator cuff injuries. We aim to synthesize the current understanding of hyperlipidemia's role in the pathophysiology of rotator cuff injuries, thereby offering fresh insights into their common etiological underpinnings, potential therapeutic targets, and drugs, such as Statins. The influence of other lipid-lowering therapeutics on tendon health is also considered, and further research into the molecular pathways and potential therapeutic benefits of these drugs is required. This pursuit aligns with broader efforts to enhance patient outcomes, minimize healthcare burdens, and contribute to the global understanding of these prevalent conditions.

An indentation-based framework for probing the glycosaminoglycan-mediated interactions of collagen fibrils

Microscale deformation processes, such as reorientation, buckling, and sliding of collagen fibrils, determine the mechanical behavior and function of collagenous tissue. While changes in the structure and composition of tendon have been extensively studied, the deformation mechanisms that modulate the interaction of extracellular matrix (ECM) constituents are not well understood, partly due to the lack of appropriate techniques to probe the behavior. In particular, the role of glycosaminoglycans (GAGs) in modulating collagen fibril interactions has remained controversial. Some studies suggest that GAGs act as crosslinkers between the collagen fibrils, while others have not found such evidence and postulate that GAGs have other functions. Here, we introduce a new framework, relying on orientation-dependent indentation behavior of tissue and computational modeling, to evaluate the shear-mediated function of GAGs in modulating the collagen fibril interactions at a length scale more relevant to fibrils compared to bulk tests. Specifically, we use chondroitinase ABC to enzymatically deplete the GAGs in tendon; measure the orientation-dependent indentation response in transverse and longitudinal orientations; and infer the microscale deformation mechanisms and function of GAGs from a microstructural computational model and a modified shear-lag model. We validate the modeling approach experimentally and show that GAGs facilitate collagen fibril sliding with minimal crosslinking function. We suggest that the molecular reconfiguration of GAGs is a potential mechanism for their microscale, strain-dependent viscoelastic behavior. This study reveals the mechanisms that control the orientation-dependent indentation response by affecting the shear deformation and provides new insights into the mechanical function of GAGs and collagen crosslinkers in collagenous tissue.

Optimizing repair of tendon ruptures and chronic tendinopathies: Integrating the use of biomarkers with biological interventions to improve patient outcomes and clinical trial design

Tendons are dense connective tissues of the musculoskeletal system that link bones with muscles to foster mobility. They have complex structures and exist in varying biomechanical, metabolic and biological environments. In addition, tendon composition and mechanical properties can change over the lifespan as an individual ages. Many tendons function in high stress conditions with a low vascular and neuronal supply, conditions often leading to development of chronic tendinopathies, and in some cases, overt rupture of the tissues. Given their essential nature for human mobility and navigation through the environment, the effective repair and regeneration of different tendons after injury or damage is critical for quality of life, and for elite athletes, the return to sport participation at a high level. However, for mainly unknown reasons, the outcomes following injury are not always successful and lead to functional compromise and risk for re-injury. Thus, there is a need to identify those patients who are at risk for developing tendon problems, as well those at risk for poor outcomes after injury and to design interventions to improve outcomes after injury or rupture to specific tendons. This review will discuss recent advances in the identification of biomarkers prognostic for successful and less successful outcomes after tendon injury, and the mechanistic implications of such biomarkers, as well as the potential for specific biologic interventions to enhance outcomes to improve both quality of life and a return to participation in sports. In addition, the implication of these biomarkers for clinical trial design is discussed, as is the issue of whether such biomarkers for successful healing of one tendon can be extended to all tendons or are valid only for tendons in specific biomechanical and biological environments. As maintaining an active lifestyle is critical for health, the successful implementation of these advances will benefit the large number of individuals at risk.

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

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

Isotretinoin induced achilles tendinopathy: Histopathological and biomechanical evaluation on rats

OBJECTIVE

The aim of the present study was to evaluate histopathological and biomechanical effects of isotretinoin on Achilles tendon.

MATERIALS & METHODS

Sixteen rats were divided into two groups including the control group (n = 8) and isotretinoin group (n = 8). The control group received 1.42 ml/kg soy oil per day whereas the isotretinoin group received 15 mg/kg/day (gavage dose 1.42 ml/kg) isotretinoin dissolved in soy oil through gavage method for 6 weeks. Achilles tendons were excised at the end of week 6. The tendon samples were evaluated by hematoxylin-eosin under a light microscope. Quantitative evaluation was performed via Movin and Bonar scoring. A computer-monitored tensile testing machine was utilised for biomechanical testing. Biomechanical characteristics of the tendon samples (elastic modulus, yield force, ultimate tensile force) were measured.

RESULTS

Histopathological evaluation revealed a significantly higher Movin and Bonar scores in histopathological evaluation. Movin score in isotretinoin group was 4.1 ± 2.5 and it was 2.3 ± 1.0 in control group (p = 0.032). Bonar score in isotretinoin group was 2.9 ± 1.4 and it was 1.6 ± 0.7 in control group (p = 0.022). In line with histopathological evaluation, biomechanical measurements in isotretinoin group (elastic modulus, yield force, ultimate tensile force) were significantly lower than the control group. Elastic modulus in isotretinoin group was 227 ± 27.7 N/mm² and in control group it was 281.7 ± 38.7 N/mm² (p = 0.006). In isotretinoin group; yield force was 33.7 ± 4.3 Pa and in control group it was 40.8 ± 5.9 Pa (p = 0.021). Ultimate tensile force in isotretinoin group was 35.7 ± 4.2 Pa and in control group it was 44 ± 7 Pa (p = 0.009).

CONCLUSION

The present study detected histopathological and biomechanical negative effect of isotretinoin on Achilles tendon. Therefore, isotretinoin should be questioned in medical history of patients with tendinopathy.

Exploring the In Vivo Anti-Inflammatory Actions of Simvastatin-Loaded Porous Microspheres on Inflamed Tenocytes in a Collagenase-Induced Animal Model of Achilles Tendinitis

Tendon rupture induces an inflammatory response characterized by release of pro-inflammatory cytokines and impaired tendon performance. This study sought to investigate the therapeutic effects of simvastatin-loaded porous microspheres (SIM/PMSs) on inflamed tenocytes in vitro and collagenase-induced Achilles tendinitis in vivo. The treatment of SIM/PMSs in lipopolysaccharide (LPS)-treated tenocytes reduced the mRNA expressions of pro-inflammatory cytokines (Matrix metalloproteinase-3 (MMP-3), cyclooxygenase-2 (COX-2), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α)). In addition, the local injection of SIM/PMSs into the tendons of collagenase-induced Achilles tendinitis rat models suppressed pro-inflammatory cytokines (MMP-3, COX-2, IL-6, TNF-α, and MMP-13). This local treatment also upregulated anti-inflammatory cytokines (IL-4, IL-10, and IL-13). Furthermore, treatment with SIM/PMSs also improved the alignment of collagen fibrils and effectively prevented collagen disruption in a dose-dependent manner. Therefore, SIM/PMSs treatment resulted in an incremental increase in the collagen content, stiffness, and tensile strength in tendons. This study suggests that SIM/PMSs have great potential for tendon healing and restoration in Achilles tendinitis.

Activation of AKT-mTOR Signaling Directs Tenogenesis of Mesenchymal Stem Cells

Tendon repair is a clinical challenge because of the limited understanding on tenogenesis. The synthesis of type I collagen (Collagen I) and other extracellular matrix are essential for tendon differentiation and homeostasis. Current studies on tenogenesis focused mostly on the tenogenic transcriptional factors while the signaling controlling tenogenesis on translational level remains largely unknown. Here, we showed that mechanistic target of rapamycin (mTOR) signaling was activated by protenogenic growth factor, transforming growth factors beta1, and insulin-like growth factor-I. The expression of mTOR was upregulated during tenogenesis of mesenchymal stem cells (MSCs). Moreover, mTOR was downregulated in human tendinopathy tissues and was inactivated upon statin treatment. Both inhibition and depletion of AKT or mTOR significantly reduced type I collagen production and impaired tenogenesis of MSCs. Tendon specific-ablation of mTOR resulted in tendon defect and reduction of Collagen I. However, there is no evident downregulation of tendon associated collagens at the transcription level. Our study demonstrated that AKT-mTOR axis is a key mediator of tendon differentiation and provided a novel therapeutic target for tendinopathy and tendon injuries. Stem Cells 2018;36:527-539.

What is the role of systemic conditions and options for manipulation of bone formation and bone resorption in rotator cuff tendon healing and repair?

Rotator cuff pathology is a significant cause of shoulder pain. Operative repair of rotator cuff is an established standard of care for these patient, however, failure of the procedure is common. Systemic conditions such as diabetes mellitus, hypocholesteremia, thyroid disease, and smoking significantly affect the outcomes of rotator cuff repair and have significant implications for the management of these patients. Diabetes mellitus has been proposed to damage tendons through non-enzymatic glycosylation of collagen with advanced glycation end product formation and impaired microcirculation. Hypocholesteremia may lead to fatty infiltration and subsequent pro-inflammatory degenerative enzymatic degeneration. Thyroid disease may disrupt tendon homeostasis through the alteration of collagen production and the accumulation of glycosaminoglycans. Lastly, smoking inhibits tendon healing through the induction of hypovascularity and hypoperfusion. Understanding of the implications these systemic conditions have on the outcomes is important in the management of rotator cuff disease.

Sonographic evaluation of the immediate effects of eccentric heel drop exercise on Achilles tendon and gastrocnemius muscle stiffness using shear wave elastography

BACKGROUND

Mechanical loading is crucial for muscle and tendon tissue remodeling. Eccentric heel drop exercise has been proven to be effective in the management of Achilles tendinopathy, yet its induced change in the mechanical property (i.e., stiffness) of the Achilles tendon (AT), medial and lateral gastrocnemius muscles (MG and LG) was unknown. Given that shear wave elastography has emerged as a powerful tool in assessing soft tissue stiffness with promising intra- and inter-operator reliability, the objective of this study was hence to characterize the stiffness of the AT, MG and LG in response to an acute bout of eccentric heel drop exercise.

METHODS

Forty-five healthy young adults (36 males and nine females) performed 10 sets of 15-repetition heel drop exercise on their dominant leg with fully-extended knee, during which the AT and gastrocnemius muscles, but not soleus, were highly stretched. Before and immediately after the heel drop exercise, elastic moduli of the AT, MG and LG were measured by shear wave elastography.

RESULTS

After the heel drop exercise, the stiffness of AT increased significantly by 41.8 + 33.5% (P < 0.001), whereas the increases in the MG and LG stiffness were found to be more drastic by 75 + 47.7% (P < 0.001) and 71.7 + 51.8% (P < 0.001), respectively. Regarding the AT, MG and LG stiffness measurements, the inter-operator reliability was 0.940, 0.987 and 0.986, and the intra-operator reliability was 0.916 to 0.978, 0.801 to 0.961 and 0.889 to 0.985, respectively.

DISCUSSION

The gastrocnemius muscles were shown to bear larger mechanical loads than the AT during an acute bout of eccentric heel drop exercise. The findings from this pilot study shed some light on how and to what extent the AT and gastrocnemius muscles mechanically responds to an isolated set of heel drop exercise. Taken together, appropriate eccentric load might potentially benefit mechanical adaptations of the AT and gastrocnemius muscles in the rehabilitation of patients with Achilles tendinopathy.

Statin-induced calcific Achilles tendinopathy in rats: comparison of biomechanical and histopathological effects of simvastatin, atorvastatin and rosuvastatin

PURPOSE

Accumulating clinical evidence indicates the risk of tendinopathy and spontaneous and/or simultaneous tendon ruptures associated with statin use. This experimental study was designed to evaluate and compare the biomechanical and histopathological effects of the three most commonly prescribed statins (simvastatin, atorvastatin and rosuvastatin) on the Achilles tendon in rats.

METHODS

Statins were administered by gavage to rats at daily doses of 20 and 40 mg/kg for 3 weeks. One week later, the Achilles tendons were dissected and their biomechanical properties, including ultimate tensile force, yield force and elastic modulus, were determined. The samples were stained with haematoxylin-eosin and examined under a light microscope. The biomechanical properties of the tibia were tested by three-point bending test. Bone mineral density (BMD) and the lengths of tibias were measured by computed tomography.

RESULTS

All the statins caused deterioration of the biomechanical parameters of the Achilles tendon. Histopathological analysis demonstrated foci of dystrophic calcification only in the statin-treated groups. However, the number and the total area of calcific deposits were similar between the statin groups. The biomechanical parameters of tibias were improved in all the statin groups. BMD in the statin-treated groups was not significantly different from the control group.

CONCLUSION

All the statins tested are associated with calcific tendinopathy risk of which full awareness is required during everyday medical practice. However, statin-associated improvement of bone biomechanical properties is a favourable feature which may add to their beneficial effects in atherosclerotic cardiovascular disease, especially in the elderly.

Simvastatin and atorvastatin reduce the mechanical properties of tendon constructs in vitro and introduce catabolic changes in the gene expression pattern

Treatment with lipid-lowering drugs, statins, is common all over the world. Lately, the occurrence of spontaneous tendon ruptures or tendinosis have suggested a negative influence of statins upon tendon tissue. But how statins might influence tendons is not clear. In the present study, we investigated the effect of statin treatment on mechanical strength, cell proliferation, collagen content and gene expression pattern in a tendon-like tissue made from human tenocytes in vitro. Human tendon fibroblasts were grown in a 3D tissue culture model (tendon constructs), and treated with either simvastatin or atorvastatin, low or high dose, respectively, for up to seven days. After seven days of treatment, mechanical testing of the constructs was performed. Collagen content and cell proliferation were also determined. mRNA levels of several target genes were measured after one or seven days. The maximum force and stiffness were reduced by both statins after 7 days (p<0.05), while the cross sectional area was unaffected. Further, the collagen content was reduced by atorvastatin (p = 0.01) and the cell proliferation rate was decreased by both types of statins (p<0.05). Statin treatment also introduced increased mRNA levels of MMP-1, MMP-3, MMP-13, TIMP-1 and decreased levels of collagen type 1 and 3. In conclusion, statin treatment appears to have a negative effect on tendon matrix quality as seen by a reduced strength of the tendon constructs. Further, activated catabolic changes in the gene expression pattern and a reduced collagen content indicated a disturbed balance in matrix production of tendon due to statin administration.

Do different tendons exhibit the same response following chronic exposure to statins?

Over the past few years, a number of cases of tendon injuries associated with statin therapy have been reported. In this study, we assessed whether statins can affect the extracellular matrix (ECM) of the deep digital flexor tendon (DDFT) and patellar tendon (PT). Wistar rats were assigned to groups treated with atorvastatin (A20, A80), treated with simvastatin (S20, S80), and control. Zymography, Western blotting for collagen I, non-collagenous proteins (NCP), glycosaminoglycans (GAGs), and hydroxyproline quantifications were performed. DDFT findings: NCP were increased in A20 and A80; higher concentration of hydroxyproline was found in S80; levels of GAGs was increased in all statin-treated groups; collagen I was increased in S80 and pro-MMP-2 activity was reduced in A80, S20, and S80. PT findings: NCP were reduced in A20, A80, and S80; GAGs was reduced in A80 and S20; collagen I was increased in A20 and pro-MMP-2 activity was reduced in the S20. Both the statins provoked marked changes in both tendons. All these changes may make the tendons more prone to microdamage and ruptures. Therefore, a better understanding of the behavior of the tendon ECM components under statin therapy may provide important insights into the mechanisms behind statin-induced tendon injuries.

Effect of simvastatin on rat supraspinatus tendon mechanical and histological properties in a diet-induced hypercholesterolemia model

Hypercholesterolemia is a common condition and is a risk factor for tendon rupture, specifically in the supraspinatus tendon. In the clinic, statins are commonly prescribed to lower cholesterol, but little information is available examining the effect of statin treatment on the musculoskeletal system. Therefore, the objective of this study was to determine the biomechanical and histological effects of statin treatment in a diet-induced hypercholesterolemia model. We hypothesized that hypercholesterolemic rats treated with statins would have improved tendon biomechanical and histological properties compared to hypercholesterolemic rats not receiving daily statin treatment. Thirty adult male Sprague-Dawley rats ate either high-cholesterol (HC) diet (n = 20) or normal chow (CTL, n = 10). After 6 months, a subset of HC rats began daily oral simvastatin dosing (HC+S) at 20 mg/kg. All rats were sacrificed after a total of 9 months (3 months of statin treatment) and evaluated for histology and mechanics. For mechanics, at the insertion region, HC+S group had increased tendon cross-sectional area decreased and modulus. No differences were noted in mechanical properties at the midsubstance. For histology, no differences were noted in the insertion region. In the midsubstance region, HC+S group had more spindle shaped cells. Our results suggest that 3 months of simvastatin treatment in a diet-induced hypercholesterolemia rat model alters some tendon mechanical and histological properties, although a strong conclusion in support of improved parameters cannot be drawn. Therefore, we conclude that simvastatin treatment does not negatively affect tendon properties. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2009-2015, 2016.

Bilateral patellar tendon rupture associated with statin use

Patellar tendon rupture is an uncommon clinical presentation, which generally affects the under 40s who are active in sport. Bilateral rupture of both tendons is much rarer. It occurs most frequently in patients with predisposing factors such as corticosteroid use or systemic diseases. The authors present the case of a 56-year-old male on long-term statin therapy who sustained this injury following a fall on ice. He had no known risk factors for tendon rupture. Surgical treatment involved tendon repair using Krakow suture via bony tunnels in the patella. Statins have previously been associated with tendon ruptures at other sites but there have been no published cases of bilateral patellar tendon rupture linked to statin use. We review the literature regarding the association between statins and tendon rupture.

Lovastatin-Mediated Changes in Human Tendon Cells

Statins are among the most widely prescribed drugs worldwide. Numerous studies have shown their beneficial effects in prevention of cardiovascular disease through cholesterol-lowering and anti-atherosclerotic properties. Although some statin patients may experience muscle-related symptoms, severe side effects of statin therapy are rare, primarily due to extensive first-pass metabolism in the liver. Skeletal muscles appear to be the main site of side effects; however, recently some statin-related adverse effects have been described in tendon. The mechanism behind these side effects remains unknown. This is the first study that explores tendon-specific effects of statins in human primary tenocytes. The cells were cultured with different concentrations of lovastatin for up to 1 week. No changes in cell viability or morphology were observed in tenocytes incubated with therapeutic doses. Short-term exposure to lovastatin concentrations outside the therapeutic range had no effect on tenocyte viability; however, cell migration was reduced. Simvastatin and atorvastatin, two other drug family members, also reduced the migratory properties of the cells. Prolonged exposure to high concentrations of lovastatin induced changes in cytoskeleton leading to cell rounding and decreased levels of mRNA for matrix proteins, but increased BMP-2 expression. Gap junctional communication was impaired but due to cell shape change and separation rather than direct gap junction inhibition. These effects were accompanied by inhibition of prenylation of Rap1a small GTPase. Collectively, we showed that statins in a dose-dependent manner decrease migration of human tendon cells, alter their expression profile and impair the functional network, but do not inhibit gap junction function.