The impact of mild hypercholesterolemia on injury repair in the rat patellar tendon
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Abstract Hypercholesterolemia is associated with tendon pathology and injury prevalence. Lipids can accumulate in the tendon's extracellular spaces, which may disrupt its hierarchical structure and the tenocytes physicochemical environment. We hypothesized that the tendon's ability to repair after injury would be attenuated with elevated cholesterol levels, leading to inferior mechanical properties. Fifty wild‐type (sSD) and 50 apolipoprotein E knock‐out rats ( ApoE −/ − ) were given a unilateral patellar tendon (PT) injury at 12 weeks old; the uninjured limb served as a control. Animals were euthanized at 3‐, 14,‐ or 42‐days postinjury and PT healing was investigated. ApoE −/ − serum cholesterol was double that of SD rats (mean: 2.12 vs. 0.99 mg/mL, p < 0.001) and cholesterol level was related to the expression of several genes after injury; notably rats with higher cholesterol demonstrated a blunted inflammatory response. There was little physical evidence of tendon lipid content or differences in injury repair between groups, therefore we were not surprised that tendon mechanical or material properties did not differ between strains. The young age and the mild phenotype of our ApoE −/ − rats might explain these findings. Hydroxyproline content was positively related to total blood cholesterol, but this result did not translate to observable biomechanical differences, perhaps due to the narrow range of cholesterol levels observed. Tendon inflammatory and healing activity is modulated at the mRNA level even with a mild hypercholesterolemia. These important initial impacts need to be investigated as they may contribute to the known consequences of cholesterol on tendons in humans.Keywords:
Hydroxyproline
Apolipoprotein E
Collagen fibril
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Tendon is important structure of the human body, since it can sustain tensile loading. The primary function of this tissue is to stabilize the joints they attached to it during daily activities. As well as, tendon has viscoelastic properties that can determine their response to loading and restrict the potential of injuries. One of the major points that this paper works with is the study of the biomechanical behaviour of tendon in response to tensile loading to describe their biological behaviour. Also, conclude the mathematical expression that may illustrate the tendon behaviour. All of the experiments were made in Physiology laboratories / Medical College/ Al- Nahrain University on ten rats "Rattus Norvegicus" of [108- 360] gm weight for in- vitro tensile test. So that 20 specimens were dissected from the rat knees, for the patellar tendons which always hydrated to prevent the tissue dryness. The results of the study, shows the behaviour of the tendon in response to tensile loading with two techniques; the dead loads technique and the continuous loads technique. The stress- strain relationships were also evaluated, as well as, the modified superposition theory was applied at different strain levels to the patellar tendon. The obtained results show that the modified superposition theory gives good results that are partly similar to the experimental results. Also, the tendon shows longer initial pattern than that for the ligament due to the presence of higher elastin content in the tendon than in the ligament.
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Collagen fibres
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Patellar ligament
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Previous studies by our laboratory have demonstrated that implanting a stiffer tissue engineered construct at surgery is positively correlated with repair tissue stiffness at 12 weeks. The objective of this study was to test this correlation by implanting a construct that matches normal tissue biomechanical properties. To do this, we utilized a soft tissue patellar tendon autograft to repair a central-third patellar tendon defect. Patellar tendon autograft repairs were contrasted against an unfilled defect repaired by natural healing (NH). We hypothesized that after 12 weeks, patellar tendon autograft repairs would have biomechanical properties superior to NH. Bilateral defects were established in the central-third patellar tendon of skeletally mature (one year old), female New Zealand White rabbits (n = 10). In one limb, the excised tissue, the patellar tendon autograft, was sutured into the defect site. In the contralateral limb, the defect was left empty (natural healing). After 12 weeks of recovery, the animals were euthanized and their limbs were dedicated to biomechanical (n = 7) or histological (n = 3) evaluations. Only stiffness was improved by treatment with patellar tendon autograft relative to natural healing (p = 0.009). Additionally, neither the patellar tendon autograft nor natural healing repairs regenerated a normal zonal insertion site between the tendon and bone. Immunohistochemical staining for collagen type II demonstrated that fibrocartilage-like tissue was regenerated at the tendon-bone interface for both repairs. However, the tissue was disorganized. Insufficient tissue integration at the tendon-to-bone junction led to repair tissue failure at the insertion site during testing. It is important to re-establish the tendon-to-bone insertion site because it provides joint stability and enables force transmission from muscle to tendon and subsequent loading of the tendon. Without loading, tendon mechanical properties deteriorate. Future studies by our laboratory will investigate potential strategies to improve patellar tendon autograft integration into bone using this model.
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Patellar ligament
Biomechanics
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Patellar ligament
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The high failure rate of rotator cuff repair is often attributed to the fact that a normal zonal insertion site is not regenerated between tendon and bone. [1,2] Interestingly, a previous study in our laboratory demonstrated that a patellar tendon autograft (PTA) used to repair a central-third patellar tendon (PT) defect also does not regenerate a normal zonal insertion site at 12 weeks following surgery. Therefore, using our model of tendon healing, our objective was to design a biologic augmentation (BA) that could be implemented at the insertion site between tendon and bone to help promote integration. The results of this study have potential application in developing new techniques for rotator cuff repair.
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Strain is one of the parameters determining tendon adaptation to mechanical stimuli. The aim of this study was to test whether the patellar tendon strain induced during recreational alpine skiing would affect tendon mechanical properties in older individuals. Twenty‐two older males and females (67 ± 2 years) were assigned to a 12‐week guided skiing programe (IG) and 20 aged‐matched volunteers served as controls (CG). Patellar tendon mechanical properties and cross‐sectional area (CSA) were measured before and after training, with combined dynamometry and ultrasonography scanning. None of the variables changed significantly in the CG after training. In the IG, tendon stiffness and Young's modulus were increased (respectively, 14% and 12%, P <0.01), without any significant change in tendon CSA. In addition, changes in tendon stiffness were blunted in women (9%) compared with men (19%). Serum IGF‐1 concentration tended to be lower in women (−19%, P =0.07). These results demonstrate that the mechanical stimulus induced by alpine skiing is sufficient to elicit adaptive changes in patellar tendon mechanical and material properties in older subjects. Furthermore, the present sex‐specific adaptations are consistent with previous reports of lower collagen metabolic responsiveness in women and may be underpinned by anthropometric and metabolic differences.
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Patellar ligament
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Aponeurosis
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