Collagen denaturation in post-run Achilles tendons and Achilles tendinopathy: In vivo mechanophysiology and magnetic resonance imaging

Clinical benefits of early-stage autologous conditioned serum and injectable platelet-rich fibrin on healing superficial digital flexor tendonitis in donkeys

Injectable platelet-rich fibrin (I-PRF) has been explored for its regenerative potential, but its application in tendon healing remains unstudied. Autologous conditioned serum (ACS), commonly used in joint therapies, inhibits interleukin 1-mediated inflammation, though its role in tendon healing is not well established. This study aimed to evaluate the clinical benefits of I-PRF alone and in combination with ACS in tendon healing. Twenty-three donkeys with forelimb superficial digital flexor (SDF) tendonitis were examined at admission (T0) and randomly assigned to PRF/ACS treated group (n  = 10), PRF group (n  = 7), or included as a control group (n  = 6). Among clinical parameters, tendon shape and weight-bearing scores at T150 were significantly improved (P  < 0.001) in the PRF/ACS group compared to the control group. Regardless of the tendon cross-sectional area (T-CSA), all other ultrasonographic parameters showed significant improvement in the PRF/ACS group compared to the control group. T-CSA increased throughout the study in PRF group but significantly decreased at T150 in control and PRF/ACS groups. The combination therapy had a significant improvement in fiber alignment score (FAS) and T-CSA compared to PRF group. Early lesion resolution in PRF/ACS at T90 and later in PRF at T150 suggests superior healing in PRF/ACS group. Persistent increase in T-CSA in the PRF group indicates ongoing healing, while its reduction in the PRF/ACS groups reflects more progressed healing stages and superior outcomes. Conversely, the presence of hyperechoic dots and misaligned tendon fibers in the control group suggests inferior healing outcomes. Intralesional I-PRF combined with ACS significantly enhanced clinical and ultrasonographic healing characteristics in donkeys with SDF tendonitis.

Sixteen weeks of high-speed treadmill running is insufficient to induce Achilles tendinopathy in a rat model

Despite the high prevalence of Achilles tendinopathy, clinically relevant animal models of Achilles tendinopathy are lacking. Previous studies have demonstrated possible tendinopathic cell and matrix changes with high-speed treadmill running, but the consistency as well as functional and mechanical consequences of these changes were unclear. We sought to determine the applicability of this protocol as a tendinopathy model by defining changes in Achilles tendon structure, function, and mechanics associated with 16 wk of high-speed treadmill running (26.8 m/min, 60 min/day, and 5 days/wk). We expected that high-speed running would induce detrimental structural, functional, and mechanical changes that worsen over the course of the 16-wk protocol. Treadmill running did influence body weight, hindlimb gait, and tendon cross-sectional area. However, contrary to our hypothesis, treadmill running did not induce tendinopathic changes in matrix organization, cell morphology, or tendon mechanics. As such, alternative strategies for robust and reproducible induction of Achilles tendinopathy in preclinical animal models are needed.NEW & NOTEWORTHY We demonstrated that 16 wk of high-speed treadmill running did not induce structural, functional, or mechanical changes consistent with Achilles tendinopathy in the rat. These findings underscore the importance of exploring alternative approaches to generating reliable and clinically relevant animal models of Achilles tendinopathy.

Filamented light (FLight) biofabrication of mini-tendon models show tunable matrix confinement and nuclear morphology

One hallmark of healthy tendon tissue is the high confinement of tenocytes between tightly packed, highly aligned collagen fibers. During tendinopathy, this organization becomes dysregulated, leading to cells with round-shaped morphology and collagen fibers which exhibit crimping and misalignment. The elongated nuclei in healthy tendons are linked to matrix homeostasis through distinct mechanotransduction pathways, and it is believed that the loss of nuclear confinement could upregulate genes associated with abnormal matrix remodeling. Replicating the cell and nuclear morphology of healthy and diseased states of tendon, however, remains a significant challenge for engineeredin vitrotendon models. Here we report on a high throughput biofabrication of mini-tendons that mimick the tendon core compartment based on the filamented light (FLight) approach. Each mini-tendon, with a length of 4 mm, was composed of parallel hydrogel microfilaments (2-5µm diameter) and microchannels (2-10µm diameter) that confined the cells. We generated four distinct matrices with varying stiffness (7-40 kPa) and microchannel dimensions. After 14 d of culture, 29% of tenocytes in the softest matrix with the largest microchannel diameter were aligned, exhibiting an average nuclear aspect ratio (nAR) of 2.1. In contrast, 84% of tenocytes in the stiffest matrix with the smallest microchannel diameter were highly aligned, with a mean nAR of 3.4. When tenocytes were culturedonthe FLight hydrogels (2D) as opposed to within the hydrogels three-dimensional (3D), the mean nAR was less than 1.9, indicating that nuclear morphology is significantly more confined in 3D environments. By tuning the stiffness and microarchitecture of the FLight matrix, we demonstrated that mechanical confinement can be modulated to exert control over the extent of nuclear confinement. This high-throughput, tunable platform offers a promising approach for studying the mechanobiology of healthy and diseased tendons and for eventual testing of drug compounds against tendinopathy.

Platelet-rich plasma and corticosteroid injection for tendinopathy: a systematic review and meta-analysis

OBJECTIVE

In this systematic review and meta-analysis, we evaluated and compared the efficacy and safety of platelet-rich plasma injection into corticosteroid injection in the treatment of tendinopathy.

METHODS

We searched PUBMED, EMBASE, Cochrane Library, SCOPUS, and Web of Science to identify randomized controlled trials on the PRP injection versus CS injection in treatment of tendinopathy.The meta-analysis was performed using the Revman 5.4 software.

RESULT

We found 27 RCT studies with a total of 1779 patients enrolled. 8 rotator cuff injuries, 7 humeral external epicondylitis, 10 plantar fasciitis, and 2 tenosynovitis. The results of the meta-analysis showed that there were no significant group differences in the results of patients with rotator cuff injury comparing the pain visual analog scale score and functional measures at 1 month after receiving injection treatment. After three months of receiving PRP treatment, the VAS scores showed greater improvement compared to the CS group(OR = -1.64,95%CI [-2.97,-0.31],P = 0.02), while there was no statistically significant difference in shoulder joint function between the two groups at the 3-6 month post-treatment mark. Patients with plantar fasciitis showed no significant differences in VAS and AOFAS scores after receiving PRP or CS injections at 1 and 3 months. However, at the 6-month mark, the PRP group demonstrated significantly better VAS and AOFAS scores compared to the CS group(OR = -1.41,95%CI [-1.88,-0.44],P < 0.00001; OR = 7.19,95%CI [2.41,11.91],P = 0.003). 1 month after CS injection in patients with tenosynovitis, the VAS score was lower than that of the PRP group; patients with elbow epicondylitis had better improved upper limb function rating scale scores 1 month after CS injection compared to the PRP group. In patients with tenosynovitis, the VAS scores were superior to the CS group six months after PRP treatment(OR = -0.72,95%CI [-1.04,-0.40],P < 0.00001); similarly, patients with lateral epicondylitis exhibited better VAS, DASH scores than the CS group three and twelve months post-PRP treatment(OR = -9.76,95%CI [-10.89,-8.63],P = 0.0002; OR = -0.97,95%CI [-1.87,-0.06],P < 0.0001; OR = -18.03,95%CI [-31.61,-4.46],P = 0.009).

CONCLUSION

PRP can effectively improve pain and functional impairment in patients with tendinopathy, and its mid-term efficacy is superior to that of corticosteroids. However, the long-term efficacy remains to be further clinically verified.

Moderate- and High-Speed Treadmill Running Exercise Have Minimal Impact on Rat Achilles Tendon

Exercise influences clinical Achilles tendon health in humans, but animal models of exercise-related Achilles tendon changes are lacking. Moreover, previous investigations of the effects of treadmill running exercise on rat Achilles tendon demonstrate variable outcomes. Our objective was to assess the functional, structural, cellular, and biomechanical impacts of treadmill running exercise on rat Achilles tendon with sensitive in and ex vivo approaches. Three running levels were assessed over the course of 8 weeks: control (cage activity), moderate-speed (treadmill running at 10 m/min, no incline), and high-speed (treadmill running at 20 m/min, 10° incline). We hypothesized that moderate-speed treadmill running would beneficially impact tendon biomechanics through increased tenocyte cellularity, metabolism, and anabolism whereas high-speed treadmill running would cause a tendinopathic phenotype with compromised tendon biomechanics due to pathologic tenocyte differentiation, metabolism, and catabolism. Contrary to our hypothesis, treadmill running exercise at these speeds had a nominal effect on the rat Achilles tendon. Treadmill running modestly influenced tenocyte metabolism and nuclear aspect ratio as well as viscoelastic tendon properties but did not cause a tendinopathic phenotype. These findings highlight the need for improved models of exercise- and loading-related tendon changes that can be leveraged to develop strategies for tendinopathy prevention and treatment.