Achilles Tendon Healing Research Articles

Unraveling the link: locomotor activity exerts a dual role in predicting Achilles tendon healing and boosting regeneration in mice.

Tendon disorders present significant challenges in the realm of musculoskeletal diseases, affecting locomotor activity and causing pain. Current treatments often fall short of achieving complete functional recovery of the tendon. It is crucial to explore, in preclinical research, the pathways governing the loss of tissue homeostasis and its regeneration. In this context, this study aimed to establish a correlation between the unbiased locomotor activity pattern of CRL:CD1 (ICR) mice exposed to uni- or bilateral Achilles tendon (AT) experimental injuries and the key histomorphometric parameters that influence tissue microarchitecture recovery. The study involved the phenotyping of spontaneous and voluntary locomotor activity patterns in male mice using digital ventilated cages (DVC®) with access to running wheels either granted or blocked. The mice underwent non-intrusive 24/7 long-term activity monitoring for the entire study period. This period included 7 days of pre-injury habituation followed by 28 days post-injury. The results revealed significant variations in activity levels based on the type of tendon injury and access to running wheels. Notably, mice with bilateral lesions and unrestricted wheel access exhibited significantly higher activity after surgery. Extracellular matrix (ECM) remodeling, including COL1 deposition and organization, blood vessel remodeling, and metaplasia, as well as cytological tendon parameters, such as cell alignment and angle deviation were enhanced in surgical (bilateral lesion) and husbandry (free access to wheels) groups. Interestingly, correlation matrix analysis uncovered a strong relationship between locomotion and microarchitecture recovery (cell alignment and angle deviation) during tendon healing. Overall, this study highlights the potential of using mice activity metrics obtained from a home-cage monitoring system to predict tendon microarchitecture recovery at both cellular and ECM levels. This provides a scalable experimental setup to address the challenging topic of tendon regeneration using innovative and animal welfare-compliant strategies.

Micro- and nanostructure specific X-ray tomography reveals less matrix formation and altered collagen organization following reduced loading during Achilles tendon healing

Recovery of the collagen structure following Achilles tendon rupture is poor, resulting in a high risk for re-ruptures. The loading environment during healing affects the mechanical properties of the tendon, but the relation between loading regime and healing outcome remains unclear. This is partially due to our limited understanding regarding the effects of loading on the micro- and nanostructure of the healing tissue. We addressed this through a combination of synchrotron phase-contrast X-ray microtomography and small-angle X-ray scattering tensor tomography (SASTT) to visualize the 3D organization of microscale fibers and nanoscale fibrils, respectively. The effect of in vivo loading on these structures was characterized in early healing of rat Achilles tendons by comparing full activity with immobilization. Unloading resulted in structural changes that can explain the reported impaired mechanical performance. In particular, unloading led to slower tissue regeneration and maturation, with less and more disorganized collagen, as well as an increased presence of adipose tissue. This study provides the first application of SASTT on soft musculoskeletal tissues and clearly demonstrates its potential to investigate a variety of other collagenous tissues. Statement of significanceCurrently our understanding of the mechanobiological effects on the recovery of the structural hierarchical organization of injured Achilles tendons is limited. We provide insight into how loading affects the healing process by using a cutting-edge approach to for the first time characterize the 3D micro- and nanostructure of the regenerating collagen. We uncovered that, during early healing, unloading results in a delayed and more disorganized regeneration of both fibers (microscale) and fibrils (nanoscale), as well as increased presence of adipose tissue. The results set the ground for the development of further specialized protocols for tendon recovery.

Histopathological and histomorphometric investigation of the effects of different irrigation solutions on Achilles tendon healing in rats.

This study aimed to examine the effect of irrigation fluids containing povidone-iodine (PVP-I), rifampicin (RF), and chlorhexidine gluconate (CHG) used during surgery on healing on a rat Achilles tendon model. Twenty-eight male Sprague-Dawley rats (range, 300 to 400 g) were used in the experiment carried out between November 2022 and December 2022. The rats were divided into PVP-I, RF, CHG, and control groups, with seven rats in each group. Following the tenotomy and repair of the right Achilles tendon, the surgical site was irrigated using PVP-I, RF, CHG, or normal saline (the control group) for 2 min. All rats were sacrificed on the 21st postoperative day. The samples were evaluated histomorphometrically using the scoring system modified by Svensson, Soslowsky, and Cook and histopathologically using the Bonar and Movin classifications. The RF group gave better results in all three scoring systems compared to the control, PVP-I, and CHG groups (p=0.008, p=0.002, and p=0.006, respectively). Cellularity, rounding, and tenocyte morphology showed a significant difference in favor of the RF group (p=0.004). While the distribution of ground substance glycosaminoglycans showed a significant difference in favor of the RF group, there was no significant difference among the other groups (p=0.22). Irrigation solutions containing PVP-I, RF, or CHG show no negative effect on Achilles tendon healing. Moreover, the findings suggest that RF irrigation can accelerate the healing process.

The Correlation of Dynamic Magnetic Resonance Imaging Evaluation With Histological, Biochemical, and Biomechanical Properties in Healing Progress After Achilles Tendon Injury: A Review.

Achilles tendon injury is a common sports injury, and an in-depth understanding of its healing process is essential for improving rehabilitation strategies. As a non-invasive imaging technology with excellent anatomical and functional information extraction abilities, magnetic resonance imaging (MRI) has been widely used in the evaluation and monitoring of Achilles tendon injury. MRI scans at different stages of Achilles tendon healing can provide information about the structure of the Achilles tendon tissue, blood supply, composition, and metabolism. The change pattern on dynamic MRI evaluation is closely related to the specific stage of Achilles tendon healing and tissue characteristics. For example, the signal strength of dynamic enhanced MRI sequences can reflect blood supply to the Achilles tendon, whereas some quantitative MRI techniques can provide information on the recovery of water and collagen contents in the Achilles tendon. This article discusses the pathophysiological changes after Achilles tendon injury and summarizes the clinical and research status of the MRI techniques used for monitoring Achilles tendon healing. The feasibility of various MRI techniques for monitoring Achilles tendon healing and their correlation with histology, biochemistry, and biomechanics are reviewed, along with the challenges, limitations, and potential opportunities for their application. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 2.

The Co-Use of Stromal Vascular Fraction and Bone Marrow Concentrate for Tendon Healing.

The Achilles tendon is the most frequently injured tendon in the human body, despite being the strongest. Many conventional treatments including medication, surgical interventions, and physical therapy are available, however, the desired results are often not achieved. Stromal vascular fraction (SVF) and bone marrow concentrate (BMC) are two additional cellular treatment options. The purpose of this study is to evaluate the effect of SVF and BMC, used as a combination, for the treatment of Achilles tendon injuries. Five male New Zealand rabbits were used for each of the 6 study groups. A 3-mm of SVF and BMC were injected on the Achilles tendons at certain ratios. The histological results were classified by the Movin grading system for tendon healing. The collagen type-I and type-III structures in the tendons were examined by immunohistochemical evaluation. The expressions of tendon-specific genes were also examined by using the RT-PCR method to analyze tendon healing. Histological and immunohistochemical evaluation indicated that tendons receiving the SVF and BMAC mixture performed better than control and individual groups (p < 0.05). Moreover, RT-PCR evaluation showed that mixture-receiving groups were the closest similar to the uninjured group (p < 0.05). The combined use of BMC and SVF improved Achilles tendon healing when compared to the individual use of each mixture.

An Atelocollagen Injection Enhances the Healing of Nonoperatively Treated Achilles Tendon Tears: An Experimental Study in Rats.

There is growing interest in nonoperative treatment for the management of Achilles tendon ruptures (ATRs). However, nonoperative treatment is limited by the risk of tendon reruptures and low satisfaction rates. Recently, atelocollagen injections have been reported to have beneficial effects on tendon healing. To evaluate the beneficial effects of injected atelocollagen on Achilles tendon healing and investigate the mechanism of atelocollagen on tendon healing. Controlled laboratory study. Percutaneous tenotomy of the right Achilles tendon in 66 rats was performed. The animals were equally divided into the noninjection group (NG) and the collagen injection group (CG). At 1, 3, and 6 weeks, the Achilles functional index, cross-sectional area, load to failure, stiffness, stress, and the modified Bonar score were assessed. Transmission electron microscopy, western blotting, and immunohistochemistry were also performed. The Achilles functional index (-6.8 vs -43.0, respectively; P = .040), load to failure (42.1 vs 27.0 N, respectively; P = .049), and stiffness (18.8 vs 10.3 N/mm, respectively; P = .049) were higher in the CG than those in the NG at 3 weeks. There were no significant differences in histological scores between the 2 groups. Transmission electron microscopy analysis showed that the mean diameter of collagen fibrils in the CG was greater than that in the NG at 3 weeks (117.2 vs 72.6 nm, respectively; P < .001) and 6 weeks (202.1 vs 144.0 nm, respectively; P < .001). Western blot analysis showed that the expression of collagen type I in the CG was higher than that in the NG at 1 week (P = .005) and 6 weeks (P = .001). An atelocollagen injection had beneficial effects on the healing of nonoperatively treated Achilles tendon injuries. The Achilles tendon of CG rats exhibited better functional, biomechanical, and morphological outcomes compared with NG rats. The molecular data indicated that the mechanism of atelocollagen injections may be associated with an increased amount of collagen type I. An atelocollagen injection might be a good adjuvant option for the nonoperative treatment of ATRs.

The Effects of Fibroblast Growth Factor-2 (FGF-2) on Achilles Tendon Injury

Category: Basic Sciences/Biologics; Ankle Introduction/Purpose: Achilles tendon defects are a challenging problem, and there is a need for new treatments. We investigated the use of Platelet-rich fibrin (PRF), a dense fibrin scaffold containing many growth factors and cytokines, for Achilles tendon injuries. The study found that PRF accelerates healing by promoting the proliferation and activation of tenocytes via FGF receptor/AKT signaling and TGF-β/SMAD3 signaling. While FGF-2, a growth factor in PRF, has been shown to promote tenocyte differentiation and proliferation, its effect on Achilles tendon injuries has not been reported. Therefore, this study aimed to investigate the effect of FGF-2 on Achilles tendon healing when administered alone and to determine its specific contribution to the healing process. Methods: We used a rat model of Achilles tendon defect. A 4-mm portion of the right Achilles tendon, 4 mm proximal to the calcaneal insertion, was resected to create a tendon defect. Gelatin hydrogel sheet (MedGel PI5) as a scaffold for PBS, FGF-2 (Rigroth®), and FGF receptor inhibitor (FGFRI: Pemigatinib) was placed into the gap before suturing it with nylon sutures. We observed HE-stained specimens at 200x and assessed histological healing by counting cells and vessels and grading cell morphology. The motor function was evaluated by the Basso, Beattie, and Bresnahan (BBB) score and the treadmill test. We compared the effects of FGF-2 on tenocytes isolated from rat Achilles tendons in the control, FGF2, and FGFRI groups. The proliferation and migration of tenocytes were measured by MTS assay and wound closure assay, respectively. Protein expression, such as Tenomodulin (Tnmd), Collagen Ⅰ, Ⅲ, and Screlaxis-A in cells, were evaluated by Western Blotting. Results: In the rat model, the number of cells, vessels and cell morphology scores at the defect sites increased in the FGF-2 group and decreased in the FGFRI group at 2 and 4 weeks postoperatively. In the motor functional evaluation, the FGF-2 group showed earlier improvement in the BBB score and the treadmill test compared to the control and FGFRI groups. The MTS assay showed that the number of viable cells was higher in the FGF-2 group and lower in the FGFRI group than in the control. Wound closure assay showed tenocyte migration was increased in the FGF-2 group and decreased in the FGFRI group. Regarding protein expression, Tnmd, Collagen I, III, and Screlaxis-A were increased in the FGF-2 group and decreased in the FGFRI group. Conclusion: In vivo, FGF-2 promoted healing of Achilles tendon injury, and FGFRI impeded it in terms of motor function and histology. Additionally, in vitro, FGF-2 promoted the proliferation and migration of tenocytes and enhanced extracellular matrix production, while FGFRI diminished these effects. Although native FGF-2 is produced at the injured site, further administration of FGF-2 accelerated Achilles tendon injury healing, while inhibiting the FGF receptor delayed recovery in this study. Therefore, FGF- 2 is very important in Achilles tendon injury healing and may promote recovery by enhancing angiogenesis, proliferation, and extracellular matrix production of tenocytes.

Histopathological Study of the Effect of Xenogeneic Platelet-Rich Fibrin on Achilles Tendon Healing in Rabbit

Tendon is a mechanical bridge that transforms the force generated by muscle contraction into movement. This tissue is well known for its low cellularity and vascularity; therefore, any tendon damage is characterized by a slow and inefficient healing process resulting in mechanically, structurally, and functionally inferior tissue. The current study aimed to evaluate the effect of the regenerative capacity of xenogeneic platelet-rich fibrin on the acceleration of Achilles tendon healing in rabbits. 24 adult rabbits weighing (1.5-2) kg were used in this study. The animals were divided equally into three groups: A-PRF group, in which the tendon defect was treated with xenogeneic Advance-platelet rich fibrin; L-PRF group, which used xenogeneic for tendon defect treatment; and control groups treated with normal saline. Clinical investigation of the rabbits during the experiment period revealed improvement of lameness and disappearance of swelling and redness at the operation site in the A-PRF and L-PRF groups compared to the control group at the same period. Histopathological examination revealed a good tendon healing process in the A-PRF group characterized by a highly organized Achilles tendon and lightly stained collagen fibers arranged in parallel. At the same time, these are less evident in the L-PRF group. In conclusion, this study suggests that xenogeneic Advanced platelet-rich fibrin treatment can be useful as a biomaterial for accelerating Achilles tendon healing in rabbits and this biomaterial. Keywords: Xenogeneic platelet-rich fibrin; Rabbit Achilles tendon; tendon healing; Advanced platelet-rich fibrin; Iraq.

Network proteomic analysis identifies inter-alpha-trypsin inhibitor heavy chain 4 during early human Achilles tendon healing as a prognostic biomarker of good long-term outcomes.

http://clinicaltrials.gov, identifiers NCT02318472, NCT01317160.

Spatiotemporal and microstructural characterization of heterotopic ossification in healing rat Achilles tendons.

Achilles tendon rupture is a common debilitating medical condition. The healing process is slow and can be affected by heterotopic ossification (HO), which occurs when pathologic bone-like tissue is deposited instead of the soft collagenous tendon tissue. Little is known about the temporal and spatial progression of HO during Achilles tendon healing. In this study we characterize HO deposition, microstructure, and location at different stages of healing in a rat model. We use phase contrast-enhanced synchrotron microtomography, a state-of-the-art technique that allows 3D imaging at high-resolution of soft biological tissues without invasive or time-consuming sample preparation. The results increase our understanding of HO deposition, from the early inflammatory phase of tendon healing, by showing that the deposition is initiated as early as one week after injury in the distal stump and mostly growing on preinjury HO deposits. Later, more deposits form first in the stumps and then all over the tendon callus, merging into large, calcified structures, which occupy up to 10% of the tendon volume. The HOs were characterized by a looser connective trabecular-like structure and a proteoglycan-rich matrix containing chondrocyte-like cells with lacunae. The study shows the potential of 3D imaging at high-resolution by phase-contrast tomography to better understand ossification in healing tendons.

Pro-inflammatory activity of long noncoding RNA FOXD2-AS1 in Achilles tendinopathy

Achilles tendinopathy is a prevalent clinical problem that plagues athletes and general populations. Achilles tendon healing is a complex process, and so far, there is no successful long-term solution to Achilles tendinopathy in the field of microsurgery due to its poor natural regeneration ability. Limitations in understanding the pathogenesis of Achilles tendon development and Achilles tendon injury hinder clinical treatment developments. There is an increasing demand for innovative conservative treatments that can improve Achilles tendon injury. In this study, a Sprague–Dawley rat model of Achilles tendinopathy was established. Lentiviral vectors that interfere with the expression of FOXD2-AS1, miR-21-3p, or PTEN were injected every 3 days. Rats were euthanized after 3 weeks, and the effect of FOXD2-AS1, miR-21-3p, or PTEN on Achilles tendon healing was analyzed by histological observation, biomechanical test, and examinations of inflammatory factors and tendon markers. As measured, downregulating FOXD2-AS1 or upregulating miR-21-3p improved histological structure, suppressed inflammation, promoted the expression of tendon markers, and optimized the biomechanical properties of Achilles tendon. Upregulating PTEN was capable of reversing the promoting effect of inhibition of FOXD2-AS1 on Achilles tendon healing. As concluded, deficiency of FOXD2-AS1 accelerates the healing of Achilles tendon injury and improves tendon degeneration by regulating the miR-21-3p/PTEN axis and promoting the activation of the PI3K/AKT signaling pathway.

Pdgfrβ+ Lineage Cells Transiently Increase at the Site of Achilles Tendon Healing.

The purpose of this study was to track platelet-derived growth factor receptor-beta (Pdgfr-β) lineage cells at the site of Achilles tendon injury over time. Pdgfr-β-CreERT2 :Ai9 mice were generated in order to track Pdgfr-β lineage cells in adult mice. A surgical Achilles transection injury model was employed to examine the presence of Pdgfr-β lineage cells in the healing tendon over time, with 5 mice per time point at 3, 7, 14, 28, and 56 days postoperatively. Histology and immunohistochemistry for tdTomato (Pdgfr-β lineage cells), PCNA (proliferating cell nuclear antigen, cell proliferation), and α-SMA (alpha smooth muscle actin, myofibroblasts) were performed. The percentage of cells at the healing tendon site staining positive for tdTomato and PCNA were quantified. Over 75% of cells at the injury site were Pdgfr-β lineage cells at days 3, 7, and 14, and this percentage decreased significantly by days 28 and 56 post-injury. Cell proliferation at the injury site peaked on day 7 and decreased thereafter. Immunohistochemistry for α-SMA demonstrated minimal co-localization of myofibroblasts with Pdgfr-β lineage cells. This study demonstrates that in a mouse model of Achilles tendon injury, Pdgfr-β lineage cells' presence at the injury site is transient. Thus, we conclude that they are unlikely to be the cells that differentiate into myofibroblasts and directly contribute to tendon fibrous scar formation. This article is protected by copyright. All rights reserved.

Platelet Rich Plasma's Use on Recovering Achilles Tendon Ruptures of Wistar Strain White Mouse

Achilles tendon is the most common site of lower extremity tendon rupture. Current treatment has not been able to restore the biological and mechanical properties of the tendon to pre-injure condition. One of the treatments used to improve Achilles tendon healing is the application of PRP. The research would like to determine the effect of using Platelet Rich Plasma (PRP) on the recovery of tendon rupture in animals model (wistar strain white rats). This is an experimental study with a post-test only control group design using animals model (white rats). This study was conducted at the INA Lab Laboratory, Padang in November 2022. The samples were divided into two groups, the control group and the treatment group where both of these groups were injured and sutured to the tendons. The control group was not given PRP, while the treatment group was given 0.1 cc of PRP. The PRP used was heterologous from healthy human blood. Observations were made after 1 week both groups were maintained and treated. There were 12 white rats which were divided into the PRP group and the control group. The PRP group had a lower histopathological score (5.83) than the control group (10.50). In this study, there was a significant difference between the recovery of tendon ruptures in animal model (white rats) that were given Human Platelet Rich Plasma (PRP) and experimental animals (rats) that were not given PRP (p value 0.007). PRP improves healing in Achilles tendon rupture.

Investigation of the effects of umbilical cord-derived mesenchymal stem cells and curcumin on Achilles tendon healing - can they act synergistically?

It is known that curcumin and umbilical cord-derived mesenchymal stem cells (UC-MSCs) positively affect experi-mental tendon injury healing. This study investigated individual effects and potential synergistic effects of using curcumin and UC-MSCs alone and together. Eighty female Wistar albino rats were randomly divided into five groups: Control, curcumin, sesame oil, MSCs, and Curcumin+MSCs groups. In all rats, punch tendon defect was created in both right and left Achilles tendons. While no additional treatment was applied to the control group, curcumin, sesame oil used as a solvent for curcumin, MSCs, and MSCs and curcumin com-bination were applied locally to the injury site, respectively, in the other groups. Curcumin was solved in sesame oil before application. In each group, half of the animals were euthanized in the post-operative 2nd week while the other half were euthanized in the post-operative 4th week. The right Achilles was used for biomechanical testing, while the left Achilles was used for histological evaluation and immunohistochemical analysis of type I, Type III collagen, and tenomodulin. Histologically, significant improvement was observed in the curcumin, MSCs, and Curcumin+ MSCs groups compared to the control Group in the 2nd week. In the 2nd and 4th weeks, Type III collagen was significantly increased in the curcumin group com-pared to the control group. In week 4, tenomodulin increased significantly in the curcumin and MSCs groups compared to the control group. Tendon tensile strength increased significantly in MSCs and Curcumin+MSCs groups compared to the control group in the 4th week. No superiority was observed between the treatment groups regarding their positive effects on recovery. Locally used curcumin and UC-MSCs showed positive effects that were not superior to each other in the healing of injury caused by a punch in the Achilles tendons of rats. However, synergistic effects on healing were not observed when they were applied together.

Leucine rich repeat containing 32 accelerates tenogenic differentiation of tendon-derived stem cells and promotes Achilles tendon repair in rats.

Although many surgical or non-operative therapies have been developed to treat Achilles tendon injuries, the prognosis of which is often unsatisfactory. Recently, biologic approaches using multipotent stem cells like tendon-derived stem cells (TDSCs) pose a possible treatment option. To evaluate whether the Leucine rich repeat containing 32 (Lrrc32) affects the tenogenic differentiation of TDSCs and thus promotes Achilles tendon healing. TDSCs were infected with the recombinant Lrrc32-overexpressing lentivirus (LV-Lrrc32) and then locally injected into the injured site of rat. Four weeks after surgery, the Achilles tendon tissue (~0.5 cm) around the injured area was harvested for analysis. Pathological results showed that Lrrc32-overexpressing TDSCs significantly improved the morphological changes of the injured tendons. Specifically, the increased collagen-I expression and hydroxyproline content in extracellular matrix, and more orderly arrangement of the regenerated collagen fibers were observed in the Lrrc32 overexpression group. Moreover, 4 weeks after injection of Lrrc32-overexpressing TDSCs, the expression of tenocyte-related genes such as tenomodulin (Tnmd), scleraxis (Scx) and decorin (Dcn) were upregulated in the area of the healing tendon. These findings indicated that Lrrc32 promoted the tenogenic differentiation of TDSCs in vivo. Additionally, Lrrc32 overexpression also increased the expression of TGF-β1 and p-SMAD2/3, suggesting that the beneficial effects of Lrrc32 on tendon repair might be associated with the expression of TGF-β1 and p-SMAD2/3. Our findings collectively revealed that Lrrc32-overexpressed TDSCs promoted tendon healing more effectively than TDSCs alone.

Effects of L-carnitine on healing of Achilles tendon in rats.

In this experimental study, we aimed to analyze the effects of levocarnitine (L-carnitine) on tendon healing after surgical repair of Achilles tendon rupture in a rat model. The study included 40 Wistar Albino rats divided into four groups: Group 1, neither surgical intervention nor substance applications were performed for the Achilles tendons. In the other groups, the right Achilles tendons were cut using a scalpel and repaired with a modified Kessler-type technique with 3/0 monofilament polydioxanone suture. In Group 2, the rats did not receive any additional treatment, except for surgical repair. In Group 3, the same volume similar to Group 4 of saline solution was administered intraperitoneally for seven days. In Group 4, each rat received 300 mg/kg of L-carnitine intraperitoneally for seven days. At Week 6, all rats were sacrificed. All right Achilles tendons were used for biomechanical tests and histopathological evaluations. Biochemical analysis of the matrix metalloproteinase was also performed using the blood specimens. There were no significant differences among the groups in terms of the histopathological parameters. Although the mean matrix metalloproteinase level was low in the L-carnitine group, it did not reach statistical significance. A significant increase in maximum force, tensile strength, and strength to 2-mm gap was observed in the L-carnitine group. The significant effects of L-carnitine on biomechanical parameters may indicate favorable effects on Achilles tendon healing in rats by reducing matrix metalloproteinase 2 and 9. To improve Achilles tendon healing, further investigation for these markers is needed. Since the effects of L-carnitine on the Achilles tendon cannot be clearly distinguished histopathologically, further studies involving L-carnitine-induced effects are warranted.

Investigation into the effect of systemic single high-dose erythropoietin on the healing of Achilles tendons in rats.

This study aimed to examine systemic erythropoietin's effect on the Achilles tendon's healing in a rat model. Twenty-five adult Wistar rats were randomly assigned to one of two groups. The Achilles tendon of each rat was transected 5 mm proximal to its insertion to the calcaneus. All Achilles tendons were then repaired using modified Kessler methods. A single dose (5000 U/kg) of intraperitoneal erythropoietin (EPO) was administered to group I. Group II was a control group and did not receive an EPO injection. Four rats from each group were sacrificed at 1, 3 and 6 weeks after injection. Histopathological assessments were performed by observers blinded to the treatment. Groups I and II showed a similar increase in fibroblast cytoplasmic content and fibrillar collagen in the extracellular matrix. Collagen deposition, cellular proliferation, number of lipid vacuoles and capillary increases were similar between the groups. Evidence from this study has shown no direct effect of a single systemic high dose of EPO on the histological properties of the Achilles tendon in rats.

Predicting the formation of different tissue types during Achilles tendon healing using mechanoregulated and oxygen-regulated frameworks

During Achilles tendon healing in rodents, besides the expected tendon tissue, also cartilage-, bone- and fat-like tissue features have been observed during the first twenty weeks of healing. Several studies have hypothesized that mechanical loading may play a key role in the formation of different tissue types during healing. We recently developed a computational mechanobiological framework to predict tendon tissue production, organization and mechanical properties during tendon healing. In the current study, we aimed to explore possible mechanobiological related mechanisms underlying formation of other tissue types than tendon tissue during tendon healing. To achieve this, we further developed our recent framework to predict formation of different tissue types, based on mechanobiological models established in other fields, which have earlier not been applied to study tendon healing. We explored a wide range of biophysical stimuli, i.e., principal strain, hydrostatic stress, pore pressure, octahedral shear strain, fluid flow, angiogenesis and oxygen concentration, that may promote the formation of different tissue types. The numerical framework predicted spatiotemporal formation of tendon-, cartilage-, bone- and to a lesser degree fat-like tissue throughout the first twenty weeks of healing, similar to recent experimental reports. Specific features of experimental data were captured by different biophysical stimuli. Our modeling approach showed that mechanobiology may play a role in governing the formation of different tissue types that have been experimentally observed during tendon healing. This study provides a numerical tool that can contribute to a better understanding of tendon mechanobiology during healing. Developing these tools can ultimately lead to development of better rehabilitation regimens that stimulate tendon healing and prevent unwanted formation of cartilage-, fat- and bone-like tissues.

Periostin modulates extracellular matrix behavior in tendons

Periostin, originally named osteoblast-specific factor 2 (OSF-2) has been identified primarily in collagen rich, biomechanically active tissues where its role has been implicated in mechanisms to maintain the extracellular matrix (ECM), including collagen fibrillogenesis and crosslinking. It is well documented that periostin plays a role in wound healing and scar formation after injury, in part, by promoting cell proliferation, myofibroblast differentiation, and/or collagen fibrillogenesis. Given the significance of periostin in other scar forming models, we hypothesized that periostin will influence Achilles tendon healing by modulating ECM production. Therefore, the objective of this study was to elucidate the effects of periostin during Achilles tendon healing using periostin homozygous (Postn−/−) and heterozygous (Postn+/-) mouse models. A second experiment was included to further examine the influence of periostin on collagen composition and function using intact dorsal tail tendons. Overall, Postn−/− and Postn+/- Achilles tendons exhibited impaired healing as demonstrated by delayed wound closure, increased type III collagen production, decreased cell proliferation, and reduced tensile strength. Periostin ablation also reduced tensile strength and stiffness, and altered collagen fibril distribution in the intact dorsal tail tendons. Achilles tendon outcomes support our hypothesis that periostin influences healing, while tail tendon results indicate that periostin also affects ECM morphology and behavior in mouse tendons.

Effect of Particulate Matter on Achilles Tendon Healing: An Experimental Study in Rats

Category: Basic Sciences/Biologics; Ankle; Sports; Trauma Introduction/Purpose: Exposure of particulate matter (PM) has been linked to several diseases including pulmonary, cardiovascular, oncology, neurology system, and etc. Even though tendon injury has become increasingly common recently, there has been no study of relationship between tendon healing and PM. Hence, we performed experimental study in rats to evaluate whether PM has significant effect on tendon healing. We hypothesized that PM exposure may substantially influence Achilles tendon healing. Here, we evaluated whether PM exposure led to deleterious effect on tendon healing in a rat model of Achilles tendon rupture (ATR). Methods: All experiments with rats were approved by the Institutional Animal Care and Use Committee. The Achilles tendons of 20 Sprague-Dawley rats were transected by open tenotomy. The animals were divided into two groups according to exposure of PM 2.5 (particulate matter less than 2.5µm): control group (Non-PM group) or PM exposure group (PM group). 30 minutes of PM inhalational exposure was performed 3 days a week for 6 weeks in closed chamber systems. After 6 weeks, histologic study of lung, laboratory test and enzyme-linked immunosorbent assay (ELISA) of blood samples, histologic study, transmission electron microscopy (TEM) analysis, biomechanical study, RNA sequencing, and western blot analysis of Achilles tendon was performed. Results: Hematoxylin and eosin (H&amp;E) stain of lung tissue in PM group showed inflammation of alveolar wall and increased macrophage. Laboratory test and ELISA of blood samples from PM group showed significantly higher expression of white blood cell count and tissue necrosis factor alpha (TNF-α) than those from non-PM group, respectively. Histologic study of Achilles tendon in PM group exhibited increased lymphocyte and ossification findings with inflammatory change of cell morphology. TEM analysis showed decreased collagen fibril in PM group than non-PM group. Load to failure was decreased in the PM group than non-PM group. RNA sequencing and ingenuity pathway analysis showed increased cAMP-PKA-CREB signal pathway in PM group and the results were consistent with western blot outcomes. Conclusion: Achilles tendon healing was substantially affected by the PM exposure. Based on the present data, PM exposure induces detrimental histological and biomechanical results on Achilles tendon healing through cAMP-PKA-CREB pathway. Further in-vitro study and larger in-vivo study with longer time period are needed to support the present data.