Rat Achilles Tendon Healing Research Articles

Deprivation of loading during rat Achilles tendon healing affects extracellular matrix composition and structure, and reduces cell density and alignment.

Tendon healing involves mechanosensitive cells that adapt to mechanical stimuli through mechanotransduction, resulting in increased tissue strength. However, detailed insights into this process in response to different loads remain limited. We aimed to investigate how different loading regimes impact the spatial composition of elastin and collagens during Achilles tendon healing. Histological analysis was conducted on healing rat Achilles tendons exposed to (1) full loading, (2) reduced loading, or (3) minimal loading. Histological analysis included Hematoxylin & Eosin and immunohistochemical staining targeting elastin, Collagen1, Collagen3, and CD31. Our results showed that the impact of mechanical stimuli on healing tendons varied with the degree of loading. Unexpectedly, minimal loading led to higher staining intensity for collagens and elastin. However, tendons exposed to minimal loading appeared thinner and exhibited a less organized matrix structure, with fewer, less aligned, and more rounded cells. Additionally, our findings indicated an inverse correlation between angiogenesis and load level, with more blood vessels in tendons subjected to less loading. Tissue integrity improved by 12 weeks post-injury, but the healing process continued and did not regain the structure seen in intact tendons even after 20 weeks. This study reveals a load-dependent effect on matrix alignment, cell density, and cell alignment.

The effects of zinc sulfate mineral supplementation on Achilles tendon healing in rats.

The Achilles tendon is the most commonly injured and ruptured tendon in the body and typically occurs during participation in sports or recreational activities in men between 30 and 50 years of age. Treatment options for Achilles tendon rupture include conservative and surgical approaches. Conservative treatment is associated with a higher risk of rerupture, while surgical treatment carries a risk of wound site complications. Generally, both methods result in a prolonged tendon healing time. Studies are ongoing to identify biomolecules that aid tendon repair. The main objective of our study is to investigate the effects of zinc sulfate (ZnSO4) mineral supplementation on Achilles tendon healing in rats. Forty-eight female Sprague-Dawley rats were divided into four equal groups (C-15, C-30, ZnSO4-15, and ZnSO4-30) after standard Achilles tendon repair surgery. The ZnSO4-15 and ZnSO4-30 groups received an oral zinc sulfate monohydrate solution (50 mg/kg/day) for 15 and 30 days, respectively. The C-15 and C-30 groups were given 1 mL of distilled water per day orally during the experimental periods. Rats were sacrificed on the 15th and 30th day depending on their groups, and the healing of the operated tendons was evaluated using Movin and Bonar histopathologic scoring. For biomechanical analyses, the operated and intact Achilles tendons of all groups were removed, and tensile tests were performed to determine the tensile strength and toughness values for each tendon. Movin and Bonar scores were significantly lower in the ZnSO4-15 group than in the C-15 group and in the ZnSO4-30 group than in the C-30 group (p<0.05). Although we did not find the biomechanical results statistically significant, the intact tendons of the ZnSO4-15 group exhibited higher toughness than those of the C-15 group, and the tensile strength and toughness values of the operated and intact tendons of the ZnSO4-30 group were also higher than those of the C-30 group. Zinc sulfate monohydrate mineral supplementation had histopathologically positive effects on the proliferation and remodeling stages of Achilles tendon healing and may biomechanically benefit both operated and intact tendons.

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.

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.

The effects of Tendoflex® (polytendon complex) and Hypericum perforatum (St. John's wort oil) on repaired Achilles tendon healing in rats.

Objectives This experimental study aims to examine the effects of Tendoflex® and Hypericum perforatum on tendon healing in rat models undergoing iatrogenic Achilles tendon rupture and similar surgical treatments.Materials and methods Eighty Wistar albino rats weighing 250 to 350 g were randomly divided into four groups. Group A: Tendoflex® was administered orally as 1 capsule/2.5 kg daily by gavage. Group B: Hypericum perforatum was administered orally as 300 mg/kg daily by gavage. Group C: Tendoflex® and Hypericum perforatum were co-administered orally by gavage at the prespecified doses. Group D: No medication was given to the control group. Five rats from each group were sacrificed weekly, and the tissue samples were examined histologically, followed by the biomechanical tests of the Achilles tendon.Results In the mechanical testing, pulling forces were superior in all intervention groups and in all weeks over the control group. In particular, in the early periods (Weeks 1, 2, and 3), the mixed group showed the most favorable results, followed by the Hypericum perforatum group (p=0.010, p=0.591, and p=0.130, respectively). The most favorable collagen type I and type III expression values were found in the mixed and Hypericum perforatum groups at Weeks 2 and 3, respectively (p=0.025 and p=0.018). In the immunohistochemical and Western Blot examinations, extreme collagen type I and type III expression were detected in the mixed and Hypericum perforatum groups at Weeks 2, 3, and 4.Conclusion Tensile strength of the Achilles tendon increased by using Hypericum perforatum and Tendoflex® following rupture and repair of the Achilles tendon in rats. The combined use of these two agents yielded the most favorable mechanical and histological results, particularly in the early period. This result may be related to the higher level of collagen type I and type III immunity in all groups, compared to the control group.

Tendon Transection Healing Can Be Improved With Adipose-Derived Stem Cells Cultured With Growth Differentiation Factor 5 and Platelet-Derived Growth Factor.

As hand surgeons, tendon injuries and lacerations are a particularly difficult problem to treat, as poor healing potential and adhesions hamper optimal recovery. Adipose-derived stem cells (ADSCs) have been shown to aid in rat Achilles tendon healing after a puncture defect, and this model can be used to study tendon healing in the upper extremity. We hypothesized that ADSCs cultured with growth differentiation factor 5 (GDF5) and platelet-derived growth factor (PDGF) would improve tendon healing after a transection injury. Rat Achilles tendons were transected and then left either unrepaired or repaired. Both groups were treated with a hydrogel alone, a hydrogel with ADSCs, or a hydrogel with ADSCs that were cultured with GDF5 and PDGF prior to implantation. Tissue harvested from the tendons was evaluated for gene expression of several genes known to play an important role in successful tendon healing. Histological examination of the tendon healing was also performed. In both repaired and unrepaired tendons, those treated with ADSCs cultured with GDF5/PDGF prior to implantation showed the best tendon fiber organization, the smallest gaps, and the most organized blood vessels. Treatment with GDF5/PDGF increased expression of the protenogenesis gene SOX9, promoted cell-to-cell connections, improved cellular proliferation, and enhanced tissue remodeling. Adipose-derived stem cells cultured with GDF5/PDGF prior to implantation can promote tendon repair by improving cellular proliferation, tenogenesis, and vascular infiltration. This effect results in a greater degree of organized tendon healing.

Liquid Poly-N-acetyl Glucosamine (sNAG) Improves Achilles Tendon Healing in a Rat Model.

The Achilles tendon, while the strongest and largest tendon in the body, is frequently injured. Even after surgical repair, patients risk re-rupture and long-term deficits in function. Poly-N-acetyl glucosamine (sNAG) polymer has been shown to increase the rate of healing of venous leg ulcers, and use of this material improved tendon-to-bone healing in a rat model of rotator cuff injury. Therefore, the purpose of this study was to investigate the healing properties of liquid sNAG polymer suspension in a rat partial Achilles tear model. We hypothesized that repeated sNAG injections throughout healing would improve Achilles tendon healing as measured by improved mechanical properties and cellular morphology compared to controls. Results demonstrate that sNAG has a positive effect on rat Achilles tendon healing at three weeks after a full thickness, partial width injury. sNAG treatment led to increased quasistatic tendon stiffness, and increased tangent and secant stiffness throughout fatigue cycling protocols. Increased dynamic modulus also suggests improved viscoelastic properties with sNAG treatment. No differences were identified in histological properties. Importantly, use of this material did not have any negative effects on any measured parameter. These results support further study of this material as a minimally invasive treatment modality for tendon healing.

Diminishing effects of mechanical loading over time during rat Achilles tendon healing.

Mechanical loading affects tendon healing and recovery. However, our understanding about how physical loading affects recovery of viscoelastic functions, collagen production and tissue organisation is limited. The objective of this study was to investigate how different magnitudes of loading affects biomechanical and collagen properties of healing Achilles tendons over time. Achilles tendon from female Sprague Dawley rats were cut transversely and divided into two groups; normal loading (control) and reduced loading by Botox (unloading). The rats were sacrificed at 1, 2- and 4-weeks post-injury and mechanical testing (creep test and load to failure), small angle x-ray scattering (SAXS) and histological analysis were performed. The effect of unloading was primarily seen at the early time points, with inferior mechanical and collagen properties (SAXS), and reduced histological maturation of the tissue in unloaded compared to loaded tendons. However, by 4 weeks no differences remained. SAXS and histology revealed heterogeneous tissue maturation with more mature tissue at the peripheral region compared to the center of the callus. Thus, mechanical loading advances Achilles tendon biomechanical and collagen properties earlier compared to unloaded tendons, and the spatial variation in tissue maturation and collagen organization across the callus suggests important regional (mechano-) biological activities that require more investigation.

Comparison on effects of platelet-rich plasma versus autologous conditioned serum on Achilles tendon healing in a rat model

The aim of this study was to compare the effects of local administrations of platelet-rich plasma (PRP) with autologous conditioned serum (ACS) on Achilles tendon healing in a rat model. In this study, 40 male Sprague-Dawley rats, aged 12 months and weighing 350 to 400 g were used. The rats were divided into three groups (n=10 in each group): a control group and two treatment groups (PRP vs ACS). A standardized procedure was applied for the complete rupture and repair of the Achilles tendon in each group. The PRP group received one dose of PRP on the operative area, and ACS group received ACS at 24, 48, and 72 hours after the surgery. The control group received no injection. Animals were sacrificed 30 days after the operation, and tendon healing in each group was assessed histopathologically based on Bonar's semi-quantitative score and Movin's semi-quantitative grading scale. For the biomechanical analyses, unoperated Achilles tendons of all rats in the control and ACS groups were also harvested, and pulling tests were applied to the specimen to measure the longitudinal axis strength. The highest force value among the data obtained was defined as the maximum strength value (Fmax). The mean Bonar's score was significantly lower in the PRP group (3.8±0.8) than in the ACS (4.8±0.45) and control groups (5.2±0.837) (p=0.0028). The mean Movin's score was significantly lower in the PRP group (7.80±1.49) than in the ACS (9.8±1) and control groups (11.2±2.4) (p=0.029). The ratio of type I collagen was significantly higher in the PRP group (60±6) than in the ACS (52±4.5) and control groups (42±9) (p=0.005). Biomechanical results obtained from operated sites were comparable in terms of Fmax among groups (PRP, 33.93±2.61; ACS, 35.24±3.26; control, 35.69±3.62) (p=0.674). Similarly, the results obtained from unoperated sites were comparable among groups (PRP, 47.71±1.21; ACS, 48.14±2; control, 49.14.69±1.88) (p=0.395). In terms of histopathological results, PRP seems to be more effective than ACS for Achilles tendon healing in rats.

Response to mechanical loading in rat Achilles tendon healing is influenced by the microbiome

We have previously shown that changes in the microbiome influence how the healing tendon responds to different treatments. The aim of this study was to investigate if changes in the microbiome influence the response to mechanical loading during tendon healing. 90 Sprague-Dawley rats were used. Specific Opportunist and Pathogen Free (SOPF) rats were co-housed with Specific Pathogen Free (SPF) rats, carrying Staphylococcus aureus and other opportunistic microbes. After 6 weeks of co-housing, the SOPF rats were contaminated which was confirmed by Staphylococcus aureus growth. Clean SOPF rats were used as controls. The rats were randomized to full loading or partial unloading by Botox injections in their calf muscles followed by complete Achilles tendon transection. Eight days later, the healing tendons were tested mechanically. The results were analysed by a 2-way ANOVA with interaction between loading and contamination on peak force as the primary outcome and there was an interaction for both peak force (p = 0.049) and stiffness (p = 0.033). Furthermore, partial unloading had a profound effect on most outcome variables. In conclusion, the response to mechanical loading during tendon healing is influenced by changes in the microbiome. Studies aiming for clinical relevance should therefore consider the microbiome of laboratory animals.

Multiscale computational model of Achilles tendon wound healing: Untangling the effects of repair and loading.

Mechanical stimulation of the healing tendon is thought to regulate scar anisotropy and strength and is relatively easy to modulate through physical therapy. However, in vivo studies of various loading protocols in animal models have produced mixed results. To integrate and better understand the available data, we developed a multiscale model of rat Achilles tendon healing that incorporates the effect of changes in the mechanical environment on fibroblast behavior, collagen deposition, and scar formation. We modified an OpenSim model of the rat right hindlimb to estimate physiologic strains in the lateral/medial gastrocnemius and soleus musculo-tendon units during loading and unloading conditions. We used the tendon strains as inputs to a thermodynamic model of stress fiber dynamics that predicts fibroblast alignment, and to determine local collagen synthesis rates according to a response curve derived from in vitro studies. We then used an agent-based model (ABM) of scar formation to integrate these cell-level responses and predict tissue-level collagen alignment and content. We compared our model predictions to experimental data from ten different studies. We found that a single set of cellular response curves can explain features of observed tendon healing across a wide array of reported experiments in rats–including the paradoxical finding that repairing transected tendon reverses the effect of loading on alignment–without fitting model parameters to any data from those experiments. The key to these successful predictions was simulating the specific loading and surgical protocols to predict tissue-level strains, which then guided cellular behaviors according to response curves based on in vitro experiments. Our model results provide a potential explanation for the highly variable responses to mechanical loading reported in the tendon healing literature and may be useful in guiding the design of future experiments and interventions.

Effects of Short Term Oral Administration of Curcumin on Achilles Tendon Healing in Rats

Objective- Tendon healing, in terms of histologic and functional characteristics, is always inferior to its normal level due to the poor vascularity and low metabolic rate. Curcumin possesses anti-inflammatory, anti-oxidant and healing effects. This study aimed to investigate effects of curcumin on Achilles tendon experimental injury using histopathology, biomechanical and functional evaluationsDesign- Experimental studyProcedures- Twenty four adult male rats were divided into control and treatment groups. After aseptic preparation, complete transverse tenotomy through the middle section of right Achilles tendon, followed by modified Kessler suture placement was performed. Normal saline and curcumin (100 mg kg-1) were administered orally for seven days after surgery in control and treatment groups, respectively. Sampling was done six weeks later.Results- Lower peri-tendinous adhesion was found in the treatment group. Histopathology revealed significant increase in density and arrangement of collagen fibers, decrease in fibroblast and inflammatory cells and lower vascularity in treatment group compared to control groups which indicates earlier maturation of granulation tissue by curcumin. Significant increase in maximum load, yield load, stress and absorbed energy in the treatment group were noted by biomechanical analysis. Improved functionality was also found in the treatment group according to hind paw print analysis.Conclusion and Clinical Relevance- The present study indicated that oral administration of curcumin resulted in improved structural, biomechanical properties and functionality of the Achilles tendon in rats.

Stimulation of Tendon Healing With Delayed Dexamethasone Treatment Is Modified by the Microbiome

Background: The immune system reflects the microbiome (microbiota). Modulation of the immune system during early tendon remodeling by dexamethasone treatment can improve rat Achilles tendon healing. The authors tested whether changes in the microbiota could influence the effect of dexamethasone treatment. Hypothesis: A change in microbiome would influence the response to dexamethasone on regenerate remodeling, specifically tendon material properties (peak stress). Study Design: Controlled laboratory study. Methods: Specific opportunist and pathogen-free female rats were housed separately (n = 41) or together with specific pathogen-free rats carrying opportunistic microbes such as Staphylococcus aureus (n = 41). After 6 weeks, all co-housed rats appeared healthy but now carried S aureus. Changes in the gut bacterial flora were tested by API and RapID biochemical tests. All rats (clean and contaminated) underwent Achilles tendon transection under aseptic conditions. Flow cytometry was performed 8 days postoperatively on tendon tissue. Sixty rats received subcutaneous dexamethasone or saline injections on days 5 through 9 after transection. The tendons were tested mechanically on day 12. The predetermined primary outcome was the interaction between contamination and dexamethasone regarding peak stress, tested by 2-way analysis of variance. Results: Dexamethasone increased peak stress in all groups but more in contaminated rats (105%) than in clean rats (53%) (interaction, P = .018). A similar interaction was found for an estimate of elastic modulus (P = .021). Furthermore, dexamethasone treatment reduced transverse area but had small effects on peak force and stiffness. In rats treated with saline only, contamination reduced peak stress by 16% (P = .04) and elastic modulus by 35% (P = .004). Contamination led to changes in the gut bacterial flora and higher levels of T cells (CD3+CD4+) in the healing tendon (P < .05). Conclusion: Changes in the microbiome influence tendon healing and enhance the positive effects of dexamethasone treatment during the early remodeling phase of tendon healing. Clinical Relevance: The positive effect of dexamethasone on early tendon remodeling in rats is strikingly strong. If similar effects could be shown in humans, immune modulation by a few days of systemic corticosteroids, or more specific compounds, could open new approaches to rehabilitation after tendon injury.

Adipose-derived Human Perivascular Stem Cells May Improve Achilles Tendon Healing in Rats.

Achilles tendon rupture is a common injury and the best treatment option remains uncertain between surgical and nonoperative methods. Biologic approaches using multipotent stem cells such as perivascular stem cells pose a possible treatment option, although there is currently a paucity of evidence regarding their clinical therapeutic use. The purpose of this study was to determine whether injected perivascular stem cells (PSCs) would (1) improve histologic signs of tendon healing (such as percent area of collagen); and (2) improve biomechanical properties (peak load or stiffness) in a rat model of Achilles tendon transection. Two subtypes of PSCs were derived from human adipose tissue: pericytes (CD146CD34CD45CD31) and adventitial cells (CD146CD34CD45CD31). Thirty-two athymic rats underwent right Achilles transection and were randomized to receive injection with saline (eight tendons), hydrogel (four tendons), pericytes in hydrogel (four tendons), or adventitial cells in hydrogel (eight tendons) 3 days postoperatively with the left serving as an uninjured control. Additionally, a subset of pericytes was labeled with CM-diI to track cell viability and localization. At 3 weeks, the rats were euthanized, and investigators blinded to treatment group allocation evaluated tendon healing by peak load and stiffness using biomechanical testing and percent area of collagen using histologic analysis with picrosirius red staining. Histologic analysis showed a higher mean percent area collagen for pericytes (30%) and adventitial cells (28%) than hydrogel (21%) or saline (26%). However, a nonparametric statistical analysis yielded no statistical difference. Mechanical testing demonstrated that the pericyte group had a higher peak load than the saline group (41 ± 7 N versus 26 ± 9 N; mean difference 15 N; 95% confidence interval [CI], 4-27 N; p = 0.003) and a higher peak load than the hydrogel group (41 ± 7 N versus 25 ± 3 N; mean difference 16; 95% CI, 8-24 N; p = 0.001). The pericyte group demonstrated higher stiffness than the hydrogel group (36 ± 12 N/mm versus 17 ± 6 N/mm; mean difference 19 N/mm; 95% CI, 5-34 N/mm; p = 0.005). Our results suggest that injection of PSCs improves mechanical but not the histologic properties of early Achilles tendon healing. This is a preliminary study that provides more insight into the use of adipose-derived PSCs as a percutaneous therapy in the setting of Achilles tendon rupture. Further experiments to characterize the function of these cells may serve as a pathway to development of minimally invasive intervention aimed at improving nonoperative management while avoiding the complications associated with surgical treatment down the line.

Different mechanisms activated by mild versus strong loading in rat Achilles tendon healing.

BackgroundMechanical loading stimulates Achilles tendon healing. However, various degrees of loading appear to have different effects on the mechanical properties of the healing tendon, and strong loading might create microdamage in the tissue. This suggests that different mechanisms might be activated depending on the magnitude of loading. The aim of this study was to investigate these mechanisms further.MethodsFemale rats had their right Achilles tendon cut transversely and divided into three groups: 1) unloading (calf muscle paralysis by Botox injections, combined with joint fixation by a steel-orthosis), 2) mild loading (Botox only), 3) strong loading (free cage activity). Gene expression was analyzed by PCR, 5 days post-injury, and mechanical testing 8 days post-injury. The occurrence of microdamage was analyzed 3, 5, or 14 days post-injury, by measuring leakage of injected fluorescence-labelled albumin in the healing tendon tissue.ResultsPeak force, peak stress, and elastic modulus of the healing tendons gradually improved with increased loading as well as the expression of extracellular matrix genes. In contrast, only strong loading increased transverse area and affected inflammation genes. Strong loading led to higher fluorescence (as a sign of microdamage) compared to mild loading at 3 and 5 days post-injury, but not at 14 days.DiscussionOur results show that strong loading improves both the quality and quantity of the healing tendon, while mild loading only improves the quality. Strong loading also induces microdamage and alters the inflammatory response. This suggests that mild loading exert its effect via mechanotransduction mechanisms, while strong loading exert its effect both via mechanotransduction and the creation of microdamage.ConclusionIn conclusion, mild loading is enough to increase the quality of the healing tendon without inducing microdamage and alter the inflammation in the tissue. This supports the general conception that early mobilization of a ruptured tendon in patients is advantageous.

Histopathological, immunohistochemical, and biomechanical effects of splenectomy on Achilles tendon healing in rats

ABSTRACTPurpose: This study aimed to assess Achilles tendon repair in rats following splenectomy to simulate patients with musculoskeletal system injury who had splenectomy after spleen injury, a situation often seen in orthopedics and traumatology practice.Materials and Methods: The study included 32 male Sprague–Dawley rats (10 months old; average weight, 394.5 ± 28.3 g). The rats were fed with standard rodent food ad libitum at 22°C in a dark environment for 12 h. They were divided into two groups, namely the splenectomy (total splenectomy and Achilles tendon repair) and control groups (only Achilles tendon repair; n = 16). Four weeks after the surgery, the rats were euthanized, and their Achilles tendons were examined histopathologically, immunohistochemically, and biomechanically.Results: In the splenectomy group, proinflammatory cytokines, such as interleukin-1β, tumor necrosis factor-α, and interferon-γ, showed significantly lower values than those in the control group (p ˂0.01); moreover, the levels of anti-inflammatory cytokines like vascular endothelial growth factor, transforming growth factor-β1, interleukin-2, interleukin-10, and hepatocyte growth factor were significantly higher than in the control group (p ˂ 0.001). The average ultimate tensile strengths were 2.58 ± 0.5 in the splenectomy and 2.78 ± 0.3 in the control group (p = 0.043). The average values were 0.33 ± 0.5 in the splenectomy and 0.44 ± 0.1 in the control group (p = 0.021).Conclusion: Splenectomy may positively influence Achilles tendon healing through modification of the proinflammatory/anti-inflammatory ratio in favor of anti-inflammatory cytokines by causing a decrease in spleen-originated inflammatory cells.

Effects of low molecular weight heparin and rivaroxaban on rat Achilles tendon healing.

This study aims to compare the histopathological and biomechanical effects of low molecular weight heparin (LMWH) and rivaroxaban, which are frequently used in orthopedic surgery for thromboembolic prophylaxis, on rat Achilles tendon healing. In the study, 36 adult, male Sprague Dawley rats weighing between 300 g and 400 g were used. Three groups were formed including 12 rats in each. Achilles tendons of all rats were cut and repaired. Nadroparin calcium was administered subcutaneously for 21 days at a dose of 170 IU AXa to the first group (LMWH group). Rivaroxaban was administered daily at a dose of 3 mg/kg for 21 days as gastric lavage to the second group (rivaroxaban group). The third group was identified as the control group and no medication was administered in this group. At the end of three weeks, tendons extracted from the groups were examined histopathologically and biomechanically. Bonar's and Movin's scores obtained as a result of histopathological examination were statistically significantly higher in the control group (p=0.003 and p=0.004, respectively) (high scores indicate that tendon healing is not sufficient). When type I and type III collagen ratios were examined, type I collagen ratio, which should be found at a higher ratio in mature tendon, was statistically significantly higher in rivaroxaban and LMWH groups compared with the control group (p=0.002). As a result of biomechanical examination, higher mean maximum force values were obtained from the rivaroxaban group compared with the LMWH group (p=0.31). Mean maximum force values obtained from the control group were higher than those obtained from the LMWH group (p=0.03) and the rivaroxaban group (p=0.18). Histopathological examination revealed that both LMWH and rivaroxaban have positive effects on tendon healing. However, the same positive effects were not detected in biomechanical examination.

EFFECTS OF HIGH-DOSE VITAMIN C AND HYALURONIC ACID ON TENDON HEALING.

ABSTRACTObjective:To assess the histopathologic and biomechanical effects of hyaluronic acid (HA) and high-dose vitamin C (VC) on rat Achilles tendon healing. Methods:Forty-eight Sprague-Dawley rats were randomized to HA and VC and control groups with equal numbers. Each group was further divided into two subgroups to be sacrificed on Day 15 (n=8) and Day 30 (n=8). The Achilles tendons were cut and repaired. While the control rats remained untreated, HA and VC were administered after repair. The repaired tendons were removed for biomechanical and histopathologic analyses. In the biomechanical tests, the tendons were stretched to failure and maximum forces were measured. For histopathologic examination, the specimens were interpreted semiquantitatively using Movin’s grading scale and Bonar scores. Results:The highest mean forces were obtained in the HA group on Day 15 and in the VC group on Day 30, with a significant difference between HA and VC on Day 15 between control and VC on Day 30 (p<0.05). Histological examination showed both Movin and Bonar scores decreased in all groups on Day 30, with significant improvements in the HA and VC groups (p<0.05). Conclusion:Our results demonstrated that both VC and HA had therapeutic effects on tendon healing, especially in the late phase. Level of Evidence I; High quality randomized trial with statistically significant difference.

Different gene response to mechanical loading during early and late phases of rat Achilles tendon healing.

Mechanical loading stimulates tendon healing both when applied in the inflammatory phase and in the early remodeling phase of the process, although not necessarily via the same mechanisms. We investigated the gene response to mechanical loading in these two phases of tendon healing. The right Achilles tendon in rats was transected, and the hindlimbs were unloaded by tail suspension. The rats were exposed to 5 min of treadmill running 3 or 14 days after tendon transection. Thereafter, they were resuspended for 15 min or 3 h until euthanasia. The controls were suspended continuously. Gene analysis was first performed by microarray analysis followed by quantitative RT-PCR on selected genes, focusing on inflammation. Fifteen minutes after loading, the most important genes seemed to be the transcription factors EGR1 and C-FOS, regardless of healing phase. These transcription factors might promote tendon cell proliferation and differentiation, stimulate collagen production, and regulate inflammation. Three hours after loading on day 3, inflammation was strongly affected. Seven inflammation-related genes were upregulated according to PCR: CCL20, CCL7, IL-6, NFIL3, PTX3, SOCS1, and TLR2. These genes can be connected to macrophages, T cells, and recruitment of leukocytes. According to Ingenuity Pathway Analysis, the recruitment of leukocytes was increased by loading on day 3, which also was confirmed by histology. This inflammation-related gene response was not seen on day 14 Our results suggest that the immediate gene response after mechanical loading is similar in the early and late phases of healing but the late gene response is different.NEW & NOTEWORTHY This study investigates the direct effect of mechanical loading on gene expression during different healing phases in tendon healing. One isolated episode of mechanical loading was studied in otherwise unloaded healing tendons. This enabled us to study a time sequence, i.e., which genes were the first ones to be regulated after the loading episode.

A high-glucose diet affects Achilles tendon healing in rats

Chronic and acute tendinopathies are difficult to treat and tendon healing is generally a very slow and incomplete process and our general understanding of tendon biology and regeneration lags behind that of muscle or bone. Although still largely unexplored, several studies suggest a positive effect of nutritional interventions on tendon health and repair. With this study, we aim to reveal effects of a high-glucose diet on tendon neoformation in a non-diabetic rat model of Achilles tenotomy. After surgery animals received either a high-glucose diet or a control diet for 2 and 4 weeks, respectively. Compared to the control group, tendon repair tissue thickness and stiffness were increased in the high-glucose group after 2 weeks and gait pattern was altered after 1 and 2 weeks. Cell proliferation was up to 3-fold higher and the expression of the chondrogenic marker genes Sox9, Col2a1, Acan and Comp was significantly increased 2 and 4 weeks post-surgery. Further, a moderate increase in cartilage-like areas within the repair tissue was evident after 4 weeks of a high-glucose diet regimen. In summary, we propose that a high-glucose diet significantly affects tendon healing after injury in non-diabetic rats, potentially driving chondrogenic degeneration.