The effect of dry needling and treadmill running on inducing pathological changes in rat Achilles tendon

Focused ultrasound as an alternative to dry needling for the treatment of tendinopathies: A murine model

Tendinopathies account for 30% of 102 million annual musculoskeletal injuries occurring annually in the United States. Current treatments, like dry needling, induce microdamage to promote healing but produce mixed success rates. Previously, we showed focused ultrasound can noninvasively create microdamage while preserving mechanical properties in ex vivo murine tendons. This present study compared growth factor, histological, and mechanical effects after focused ultrasound or dry needling treatments in an in vivo murine tendon injury model. Partial Achilles tenotomy was performed in 26 rats. One-week postsurgery, tendons were treated with focused ultrasound (1.5 MHz, 1-ms pulses at 10 Hz for 106 s, p+  = 49 MPa, p-  = 19 MPa) or dry needling (30 G needle, 5 fenestrations over 20 s) and survived for 1 additional week. Blood was collected immediately before and after treatment and before euthanasia; plasma was assayed for growth factors. Treated tendons and contralateral controls were harvested for histology or mechanical testing. No differences were found between treatments in release of insulin growth factor 1 and transforming growth factor beta; vascular endothelial growth factor A concentrations were too low for detection. Histologically, focused ultrasound and dry needling tendons displayed localized fibroblast infiltration without collagen proliferation with no detectable differences between treatments. Mechanically, stiffness and percent relaxation of dry needling tendons were lower than controls (p = 0.0041, p = 0.0441, respectively), whereas stiffness and percent relaxation of focused ultrasound tendons were not different from controls. These results suggest focused ultrasound should be studied further to determine how this modality can be leveraged as a therapy for tendinopathies.

Animal model for tendinopathy

Background

Tendinopathy is a common motor system disease that leads to pain and reduced function. Despite its prevalence, our mechanistic understanding is incomplete, leading to limited efficacy of treatment options. Animal models contribute significantly to our understanding of tendinopathy and some therapeutic options. However, the inadequacies of animal models are also evident, largely due to differences in anatomical structure and the complexity of human tendinopathy. Different animal models reproduce different aspects of human tendinopathy and are therefore suitable for different scenarios. This review aims to summarize the existing animal models of tendinopathy and to determine the situations in which each model is appropriate for use, including exploring disease mechanisms and evaluating therapeutic effects.

Methods

We reviewed relevant literature in the PubMed database from January 2000 to December 2022 using the specific terms ((tendinopathy) OR (tendinitis)) AND (model) AND ((mice) OR (rat) OR (rabbit) OR (lapin) OR (dog) OR (canine) OR (sheep) OR (goat) OR (horse) OR (equine) OR (pig) OR (swine) OR (primate)). This review summarized different methods for establishing animal models of tendinopathy and classified them according to the pathogenesis they simulate. We then discussed the advantages and disadvantages of each model, and based on this, identified the situations in which each model was suitable for application.

Results

For studies that aim to study the pathophysiology of tendinopathy, naturally occurring models, treadmill models, subacromial impingement models and metabolic models are ideal. They are closest to the natural process of tendinopathy in humans. For studies that aim to evaluate the efficacy of possible treatments, the selection should be made according to the pathogenesis simulated by the modeling method. Existing tendinopathy models can be classified into six types according to the pathogenesis they simulate: extracellular matrix synthesis-decomposition imbalance, inflammation, oxidative stress, metabolic disorder, traumatism and mechanical load.

Conclusions

The critical factor affecting the translational value of research results is whether the selected model is matched with the research purpose. There is no single optimal model for inducing tendinopathy, and researchers must select the model that is most appropriate for the study they are conducting.

The translational potential of this article

The critical factor affecting the translational value of research results is whether the animal model used is compatible with the research purpose. This paper provides a rationale and practical guide for the establishment and selection of animal models of tendinopathy, which is helpful to improve the clinical transformation ability of existing models and develop new models.

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-β (Pdgfr-β) lineage cells at the site of Achilles tendon injury over time. Pdgfr-β-CreERT2 :Ai9 mice were generated 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 five 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 (α-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 postinjury. Cell proliferation at the injury site peaked on Day 7 and decreased thereafter. Immunohistochemistry for α-SMA demonstrated minimal colocalization 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. Clinical Significance: This study provides some insight into the presence of Pdgfr-β lineage cells (including pericytes) following Achilles injury, furthering our understanding of tendon healing.

Development and application of a novel in vivo overload model of the Achilles tendon in rat

Repetitive overload is a primary factor in tendon injury, causing progressive accumulation of matrix damage concurrent with a cellular response. However, it remains unclear how these events occur at the initial stages of the disease, making it difficult to identify appropriate treatment approaches. Here, we describe the development of a new model to cyclically load the Achilles tendon (AT) of rats in vivo and investigate the initial structural and cellular responses. The model utilizes controlled dorsiflexion of the ankle joint applied near maximal dorsiflexion, for 10,000 cycles at 3 Hz. Animals were subjected to a single bout of in vivo loading under anaesthesia, and either culled immediately (without recovery from anaesthesia), or 48 h or 4-weeks post-loading. Macro strains were assessed in cadavers, whilst tendon specific microdamage was assessed through collagen-hybridizing peptide (CHP) immunohistochemistry which highlighted a significant rise in CHP staining in loaded ATs compared to contralateral controls, indicating an accumulation of overload-induced damage. Staining for pro-inflammatory mediators (IL-6 and COX-2) and matrix degradation markers (MMP-3 and -13) also suggests an initial cellular response to overload. Model validation confirmed our approach was able to explore early overload-induced damage within the AT, with microdamage present and no evidence of broader musculoskeletal damage. The new model may be implemented to map the progression of tendinopathy in the AT, and thus study potential therapeutic interventions.

Comparison of cortical versus cancellous bone fixation in tendon-to-bone healing with a rat trans-calcaneal suture model for Achilles tendon sleeve avulsion

BACKGROUND

Trans-calcaneal suture technique is an economical and effective method for repairing Achilles tendon sleeve avulsion. Whether cancellous bone fixation upon this technique could accelerate tendon-to-bone healing is unknown. The purpose of this study is to compare the effect of cortical versus cancellous bone fixation on tendon-bone healing with a novel rat trans-calcaneal suture model.

METHODS

Trans-calcaneal suture treatment was carried out on the right hindlimb in male Sprague-Dawley rats (N = 80). They were randomly divided into the cortical group (Achilles fixed to the calcaneal cortical bone, n = 40) and the cancellous group (Achilles fixed to the calcaneal cancellous bone, n = 40). Gait analysis and immunohistochemistry were performed 1, 4, 7, and 14 days after the operation. Gross observation, biomechanical analysis, micro-CT, and histological analysis were performed 4 and 8 weeks after surgery. Independent-samples t tests were used for comparison between groups.

RESULTS

At 1, 4, and 7 days, the swing time of the affected limb in the cancellous group decreased, while the duty cycle, the maximum contact area, the print area, and the mean intensity increased significantly. The cross-sectional area of the tendon-bone junction in the cancellous group was smaller, and the failure load and stiffness were higher 4 weeks after the operation. The cancellous group showed more proportion of new bone and a relatively well-organized and dense connective tissue interface with better fibrocartilage-like tissue at 4 weeks after the operation. The ratio of ED2 + macrophages in the cancellous group was significantly higher than in the cortical group on 1, 4, 7, and 14 days. There were no significant differences in gait at 2 weeks, in appearance, biomechanics, new bone formation, and histology at 8 weeks after surgery between the two groups.

CONCLUSION

In the new rat trans-calcaneal suture model, cancellous fixation can accelerate tendon-to-bone healing in the early stage, which perhaps is related to the abundant bone marrow tissue in the cancellous bone that modulates the inflammatory processes.

A combination of omega-3 and exercise reduces experimental Achilles tendinopathy induced with a type-1 collagenase in rats

This study aimed to evaluate the effectiveness of omega-3 supplementation with exercise in a collagenase-induced Achilles tendinopathy (AT) rat model. Experimental groups (healthy control (HC), AT, exercise (Ex), omega-3 (W), and Ex+W) were randomly allocated. After a week of adaptation, oral omega-3 was initiated for 8 weeks (5 days/week). The exercise groups performed treadmill running for 30 min/day (5 days/week, 20 m/min, 8 weeks) following one week of adaptation (10 m/min, 15 min/day). Matrix metalloproteinase-13 (MMP-13), interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and total antioxidant-oxidant status (TAS) levels were determined in serum samples. Tendon samples were obtained for biomechanical, histopathological, and immunohistochemical assessments. Ultimate tensile force, yield force, stiffness values, collagen type-I alpha 1 expression, and serum TAS significantly decreased (P < 0.05) in AT vs. HC. These values and expression significantly increased in the Ex+W group vs. AT. Serum MMP-13, IL-1β, and TNF-α levels decreased in all treatment groups vs. AT. The most significant decrease was found in the Ex+W group (P < 0.01). Histopathologically, the improvement in degeneration was statistically significant in the Ex+W group (P < 0.05). Immunohistochemically, MMP-13, IL-1β, TNF-α, and nitric oxide synthase-2 expression was decreased in all treatment groups vs. AT. In conclusion, omega-3 and exercise might be recommended in AT patients.

Quantitative analysis of tendon histopathology using digital pathology in rat models with Achilles tendon injury

Although digital image analysis methods that quantify histopathologic features have emerged, no validated quantitative methods are available to evaluate tendon injury. This study aimed to propose and validate a quantitative analysis method to identify the histopathologic features of tendon injuries. The histopathologic features of two Achilles tendon injury models (a partial full-thickness defect model and a collagenase injection model) using Sprague-Dawley rats were evaluated by semiquantitative grading and a quantitative analysis method using a digital pathology software at weeks 1 and 4 after tendon injury (six tendons per group at each time point). The outcome variables between tendon injury models and between time points were compared, and the correlation between semiquantitative scores and the results of the quantitative analysis was investigated. The proposed analysis method quantified the severity of the histopathological features after tendon injury. Quantitative analysis differentiated the cell morphology between tendon injury models and time points better than semiquantitative scoring. The results from quantitative measurements correlated significantly with the semiquantitative scores. The proposed quantitative method can be effective in evaluating the histopathology of tendon injuries.

Effects of focused ultrasound and dry needling on tendon mechanical properties

Tendon injuries are extremely common, resulting in mechanically weaker tendons that could lead to tendon rupture. Dry needling (DN) is widely used to manage pain and function after injury. However, DN is invasive and high inter-practitioner variability has led to mixed success rates. Focused ultrasound (fUS) is a non-invasive medical technology that directs ultrasound energy into a well-defined focal volume. fUS can induce thermal ablation or mechanical fractionation, with bioeffect type controlled through ultrasound parameters. Tendons must withstand high physiological loads, thus treatments maintaining tendon mechanical properties while promoting healing are needed. Our objective was to evaluate mechanical effects of DN and 3 fUS parameter sets, chosen to prioritize mechanical fractionation, on Achilles and supraspinatus tendons. Ex vivo rat Achilles and supraspinatus tendons (50 each) were divided into sham, DN, fUS-1, fUS-2, and fUS-3 (n = 10/group). Following treatment, tendons were mechanically tested. Elastic modulus of supraspinatus tendons treated with DN (126.64 ± 28.1 MPa) was lower than sham (153.02 ± 29.3 MPa; p = 0.0280). Stiffness and percent relaxation of tendons treated with DN (Achilles: 114.40 ± 31.6 N/mm; 49.10 ± 6.1%; supraspinatus: 109.53 ± 30.8 N/mm; 50.17 ± 7.6%) were lower (all p < 0.0334) than sham (Achilles: 141.34 ± 20.9 N/mm; 60.30 ± 7.7%; supraspinatus: 135.14 ± 30.2 N/mm; 60.85 ± 15.4%). Modulus of Achilles and supraspinatus tendons treated with fUS-1 (159.88 ± 25.7 MPa; 150.12 ± 22.0 MPa, respectively) were similar to sham (156.35 ± 23.0 MPa; 153.02 ± 29.3 MPa, respectively). These results suggest that fUS preserves mechanical properties better than DN, with fUS-1 performing better than fUS-2 and fUS-3. fUS should be studied further to fully understand its mechanical and healing effects to help evaluate fUS as an alternative, non-invasive treatment for tendon injuries.

Effects of Human Placenta Extract (Laennec) on Ligament Healing in a Rodent Model

Rich in bioactive substances such as amino acids and peptides, Laennec (human placenta hydrolysate) has been widely used to control various types of musculoskeletal pain. However, the effects of Laennec on tendon and ligament injuries are not clearly understood. In the present study, Laennec was tested to identify its in vivo effects on ligament injury in an animal model and its in vitro effects on tendon-derived fibrocytes. A total of 99 Sprague Dawley rats were divided into the negative control (normal) group (n = 11) and the ligament injury group (n = 88). The ligament injury group was subdivided into normal saline-treated group, Laennec-treated group, polydeoxyribonucleotide-treated group, and 20% dextrose-treated group. Ligaments were collected at 1 week and 4 weeks after treatment. Histologic and biomechanical properties were analyzed. In vitro effects of Laennec and polydeoxyribonucleotide on fibrocytes were also analyzed. Although all other treatment groups showed increased inflammatory cells, the Laennec-treated group maintained cell counts and activated macrophage levels that were similar to the normal group. Unlike the saline-treated group and dextrose-treated group, the Laennec-treated group had low levels of degenerative changes at 4 weeks after treatment. Supportively, in vitro results showed that the Laennec-treated group had increased collagen type I, scleraxis (Scx) and tenomodulin (Tnmd) expression (p < 0.05). Our study demonstrates that Laennec treatment enhances wound healing of damaged ligament by suppressing immune responses and reducing degenerative changes of damaged ligament. In addition, we found that Laennec induces the gene expression of type I collagen, Scx and Tnmd in fibrocytes, suggesting that Laennec may facilitate regeneration of damaged ligaments. Therefore, we expect that Laennec can be a useful drug to treat injured ligament.

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

BACKGROUND

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.

QUESTIONS/PURPOSES

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

Our results suggest that injection of PSCs improves mechanical but not the histologic properties of early Achilles tendon healing.

CLINICAL RELEVANCE

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.

Movement and joints: effects of overuse on anuran knee tissues

Movement plays a main role in the correct development of joint tissues. In tetrapods, changes in normal movements produce alterations of such tissues during the ontogeny and in adult stages. The knee-joint is ideal for observing the influence of movement disorders, due to biomechanical properties of its components, which are involved in load transmission. We analyze the reaction of knee tissues under extreme exercise in juveniles and adults of five species of anurans with different locomotor modes. We use anurans as the case study because they undergo great mechanical stress during locomotion. We predicted that (a) knee tissues subjected to overuse will suffer a structural disorganization process; (b) adults will experience deeper morphological changes than juveniles; and (c) morphological changes will be higher in jumpers compared to walkers. To address these questions, we stimulated specimens on a treadmill belt during 2 months. We performed histological analyses of the knee of both treated and control specimens. As we expected, overuse caused structural changes in knee tissues. These alterations were gradual and higher in adults, and similar between jumpers and walkers species. This study represents a first approach to the understanding of the dynamics of anuran knee tissues during the ontogeny, and in relation to locomotion. Interestingly, the alterations found were similar to those observed in anurans subjected to reduced mobility and also to those described in joint diseases (i.e., osteoarthritis and tendinosis) in mammals, suggesting that among tetrapods, changes in movement generate similar responses in the tissues involved.

[Effect of different intensity treadmill training on repair of micro-injured Achilles tendon in rats]

Objective

To explore the effect of different intensity treadmill training on the repair of micro-injured Achilles tendon induced by collagenase in rats.

Methods

Seventy-two 8-week-old male Sprague Dawley rats (weighing, 200-250 g) were selected. After adaptive treadmill training for 1 week, rats were injected with 30 μL type I collagenase solution (10 mg/mL) into both Achilles tendons to make micro-injured Achilles tendon models. After 1 week of cage feeding, the rats were randomly divided into 3 groups: the control group, the low-intensity group, and the high-intensity group, 24 rats each group. The rats in control group could move freely, and the rats underwent daily treadmill training at the intensity of 13 m/min and 20 min/d in the low-intensity group and at the intensity of 17 m/min and 60 min/d in the high-intensity group. At immediate, 1 week, and 4 weeks after training, bilateral Achilles tendons were collected from 8 rats of each group for gross observation, histological analysis, and mechanical testing.

Results

At immediate after training, there was no significant difference in the gross observation, histological observation, and biomechanical properties of the Achilles tendon between groups ( P>0.05). The gross observation showed connective tissue hyperplasia near Achilles tendon and lackluster tendon in each group at 1 week; hyperplasia significantly reduced in the low-intensity group when compared with the control group, and there were more connective tissue and a large number of neovascularization in the high-intensity group at 4 weeks. At 1 week, there was no significant difference in the semi-quantitative histological total score between groups ( P>0.05), but there were significant differences in vascularity between low-intensity group or high-intensity group and control group ( P<0.05). At 4 weeks, the semi-quantitative histological total score was significantly higher in high-intensity group than control group and low-intensity group ( P<0.05), and in control group than low-intensity group ( P<0.05). There were significant differences in collagen arrangement, cell morphology, abnormal cells, and vascularity between low-intensity group and high-intensity group or control group ( P<0.05). And there was significant difference in abnormal cells between high-intensity group and control group ( P<0.05). The mechanical testing showed that there was no significant difference in cross-sectional area of the Achilles tendon, the ultimate force, tensile strength, and elastic modulus between groups at 1 week ( P>0.05); the low-intensity group was significantly higher than the control group in the ultimate force and the tensile strength ( P<0.05), and than high-intensity group in the ultimate force and elastic modulus ( P<0.05), but no significant difference was found in the other indexes between groups ( P>0.05) at 4 weeks.

Conclusion

Low-intensity treadmill training can promote the repair of rat micro-injured Achilles tendon induced by collagenase.