Consensus on equine tendon disease: Building on the 2007 Havemeyer symposium

Treatment of Naturally Occurring Tendon Disease with Allogeneic Multipotent Mesenchymal Stromal Cells: A Randomized, Controlled, Triple-Blinded Pilot Study in Horses

The treatment of tendinopathies with multipotent mesenchymal stromal cells (MSCs) is a promising option in equine and human medicine. However, conclusive clinical evidence is lacking. The purpose of this study was to gain insight into clinical treatment efficacy and to identify suitable outcome measures for larger clinical studies. Fifteen horses with early naturally occurring tendon disease were assigned to intralesional treatment with allogeneic adipose-derived MSCs suspended in serum or with serum alone through block randomization (dosage adapted to lesion size). Clinicians and horse owners remained blinded to the treatment during 12 months (seven horses per group) and 18 months (seven MSC-group and five control-group horses) of follow-up including clinical examinations and diagnostic imaging. Clinical inflammation, lameness, and ultrasonography scores improved more over time in the MSC group. The lameness score difference significantly improved in the MSC group compared with the control group after 6 months. In the MSC group, five out of the seven horses were free of re-injuries and back to training until 12 and 18 months. In the control group, three out of the seven horses were free of re-injuries until 12 months. These results suggest that MSCs are effective for the treatment of early-phase tendon disease and provide a basis for a larger controlled study.

Intralesional bone marrow and superior check desmotomy is superior to conservative treatment of equine superficial digital flexor tendonitis

BACKGROUND

Superficial digital flexor tendon (SDFT) injury is common in racehorses and a significant cause of lost training days and wastage in the industry.

OBJECTIVES

To compare the post-injury performance of Thoroughbred and Standardbred racehorses diagnosed with SDFT tendonitis treated with intralesional bone marrow and superior check desmotomy or managed conservatively and further to compare this performance with that of uninjured racehorses.

STUDY DESIGN

Retrospective and case-controlled.

METHODS

Medical and race records of racehorses treated surgically or managed conservatively for SDFT tendonitis were collated. Signalment, lesion severity and treatment were identified and performance post-injury compared. Performance of the treatment groups was further assessed by comparison with uninjured racehorses matched for age, sex, number of starts pre-injury and randomly selected from the cases' last races.

RESULTS

The study population comprised 114 racehorses divided into surgical (39/114), conservative (38/114) and control groups (37/114). Horses that had surgery were more likely to return to racing than those managed conservatively (OR 4.7 95% CI [1.6-14.3], P = .006). Standardbreds were more likely to return to race compared with Thoroughbreds (OR 4.0 95% CI [1.2-13.3], P = .03). There was no statistically significant difference in the average number of placings, average number of wins and post-injury earnings between the surgically treated and conservatively managed groups (P = .9, P = .9 and P = .7, respectively). The average number of lifetime starts post-injury/post-selection between surgery, conservative and control groups were not statistically significantly different (P = .2). Surgically treated horses had a statistically significantly shorter time to start post-injury compared with the conservative group (P = .04).

MAIN LIMITATIONS

The retrospective nature of the study precludes an actual fit as a nonrandomised clinical trial and the nonrandomised nature of the allocation of the treatment groups is biased.

CONCLUSIONS

Surgical intervention of superficial digital flexor tendonitis in racehorses suffering flexor tendon injury showed a higher likelihood of return to racing than conservative treatment.

Applicability of ARFI elastography in detecting elasticity changes of the equine superficial digital flexor tendon with induced injury

The objectives of this prospective, experimental study were to describe changes in the stiffness of the equine superficial digital flexor tendon (SDFT) after induced injury, deep digital flexor tendon (DDFT), accessory ligament (AL-DDFT), and suspensory ligament (SL) during 90 days of healing using acoustic radiation force impulse (ARFI) elastography. Eight healthy horses were selected. Preinjury B mode and ARFI evaluations were performed bilaterally in the palmar metacarpal region. Injury was induced only on the left forelimb (G2) by a single injection of collagenase in SDFT, 15 cm distal to the accessory carpal bone. The right forelimb was used as a control (G1). Evaluations were performed at eight timepoints: one before injury (T0) and seven (T1-T7) after injury (3, 15, 30, 40, 60, 75, and 90 days post-induction). Tendinopathies were visualized as hypoechoic areas with loss of parallel tendon fiber pattern. Injured SDFTs presented mainly cool colors (soft) from T1 to T3, and from T4, there was an increase in warm colors (hard), close to the appearance of tendons of G1. In the first four timepoints, there was a decrease in stiffness compared to G1 (P < 0.001). On T1 and T2, a cutoff value <6.21 m/s to determine tendinopathy of the SDFT was established (75.8% sensitivity and 92.03% specificity). Stiffness changes in the DDFT, AL-DDFT, and SL of injured limbs occurred at different timepoints. Tendinopathy significantly altered the stiffness of the injured tendon and the adjacent tissues. ARFI made it possible to detect these changes, helping to monitor the reparation of this injury.

Who Is Healthy? A Review of How Equine Control Groups Are Defined in Clinical Orthopaedic Research 1999-2021

INTRODUCTION

 Proper identification of healthy subjects is essential in case-control studies. However, standardized definitions of healthy controls are lacking in equine orthopaedic research.

OBJECTIVES

 The aim of this study was to define the non-invasive methods used for selecting healthy control horses in osteoarthritis (OA), desmitis and tendinitis research.

METHODS

 Systematic review. Case-control studies with a healthy control group and longitudinal studies where horses had to be healthy at the start were included. Studies where joints were visualized by arthroscopy or post-mortem examination were excluded.

RESULTS

From 2,472 OA papers and 2,746 desmitis/tendinitis papers, 127 and 84 papers met the inclusion criteria respectively. For OA, 11 methods were identified for defining healthy subjects with a median of three methods used per paper. Dynamic examination, radiographic evaluation and clinical examination were the most frequent. Eight different methods were identified in the desmitis/tendinitis papers with a median of three methods per paper; ultrasonography, clinical- and dynamic examination were the most frequent.

CONCLUSIONS

 Overall, the OA and desmitis/tendinitis studies used similar methods for defining subjects as healthy, but the way the examinations were performed and interpreted was inconsistent. In several studies, healthy controls were not examined for lameness. The most common methods have limitations for detecting horses with early OA, which may have implications for interpretation of results. Standardized use of more sensitive and objective methods could be beneficial.

"One Health" in tendinopathy research: Current concepts

Tendinopathy remains one of the most common musculoskeletal disorders affecting both human and equine athletes and presents a considerable therapeutic challenge. The following workshop report comes from the third Dorothy Havemeyer Symposium of Tendinopathy which provided a unique overview of our current understanding of both the basic science and the clinical challenges for diagnosing and treating tendinopathy in both species. Pathologically, tendon demonstrates alterations in both cellular, molecular, structural, and biomechanical features, leading to a spectrum of pathological endotypes. To develop novel interventions to manage, treat or prevent tendinopathies it is vital to understand the underlying mechanisms that lead to both tendon failure, and also regeneration and resolution of inflammation. The horse shows analogous pathology with both human Achilles tendinopathy (superficial digital flexor tendon) and intrathecal rotator cuff tears (deep digital flexor tendon tears) enabling scientists and clinicians from both medical and veterinary fields to work jointly on matching naturally occurring disease models. The experience in human medicine on the design, conduct, and impact of clinical trials has much to inform clinical trials in horses. There is a need to design appropriate studies to address clear questions, socialize the study to achieve good enrollment, and consider the significance and impact of the clinical question as well as the cost of addressing it. Because economics is often a limitation in equine medicine the use of observational studies, and specifically registries, should be given careful consideration.

Biplanar High-Speed Fluoroscopy of Pony Superficial Digital Flexor Tendon (SDFT)-An In Vivo Pilot Study

The superficial digital flexor tendon (SDFT) is the most frequently injured structure of the musculoskeletal system in sport horses and a common cause for early retirement. This project's aim was to visualize and measure the strain of the sound, injured, and healing SDFTs in a pony during walk and trot. For this purpose, biplanar high-speed fluoroscopic kinematography (FluoKin), as a high precision X-ray movement analysis tool, was used for the first time in vivo with equine tendons. The strain in the metacarpal region of the sound SDFT was 2.86% during walk and 6.78% during trot. When injured, the strain increased to 3.38% during walk and decreased to 5.96% during trot. The baseline strain in the mid-metacarpal region was 3.13% during walk and 6.06% during trot and, when injured, decreased to 2.98% and increased to 7.61%, respectively. Following tendon injury, the mid-metacarpal region contributed less to the overall strain during walk but showed increased contribution during trot. Using this marker-based FluoKin technique, direct, high-precision, and long-term strain measurements in the same individual are possible. We conclude that FluoKin is a powerful tool for gaining deeper insight into equine tendon biomechanics.

Biomechanical and wearability testing of novel legwear for variably limiting extension of the metacarpophalangeal joint of horses

OBJECTIVE

To evaluate the ability of novel legwear designed to limit extension of the metacarpophalangeal joint (MCPJ) to redirect loading forces from the flexor apparatus during walk, trot, and canter on a treadmill and during unrestrained and restrained activity in a stall.

ANIMALS

6 adult horses without musculoskeletal disease.

PROCEDURES

Legwear-derived force data were recorded under 4 conditions: inactive state (unlimited legwear extension) and 3 active (restrictive) states (mild, 30° extension; moderate, 20° extension; or maximum, 10° extension). Associations between peak legwear loads and torques among legwear states and treadmill gaits and stall activities were assessed. The hair coat and skin of the forelimbs were examined for any legwear-induced adverse effects after testing.

RESULTS

During the treadmill exercises, moderate restriction of legwear extension resulted in significantly higher peak load and torque than mild restriction, and faster speeds (canter vs walk or trot and trot vs walk) yielded significantly higher peak load and torque. During in-stall activity, maximum restriction of legwear extension yielded significantly higher peak load and torque than moderate restriction. Unrestrained in-stall activity resulted in significantly higher peak load and torque than restrained activity. The legwear caused minimal adverse effects on the hair coat and skin of the forelimbs.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings suggested that the legwear variably reduced peak loads on the flexor apparatus. Extension of the MCPJ may be incrementally adjusted through the legwear such that return to activity may be controlled, and controlled return to activity is crucial for rehabilitating flexor apparatus injuries.

Variation in the MRI signal intensity of naturally occurring equine superficial digital flexor tendinopathies over a 12-month period

BACKGROUND

Signal intensity (SI) of equine tendinopathies in MRI differs between the superficial digital flexor tendon (SDFT) and the deep digital flexor tendon (DDFT). In DDFT lesions, short tau inversion recovery (STIR) SI decreases earlier than T2-weighted (T2w) SI, while the latter decreases earlier in SDFT lesions, but long-term results using STIR sequences are lacking.

METHODS

Standing MRI of eight horses with naturally occurring SDFT lesions was performed at the day of treatment as well as 2, 6 and 12 months after treatment.

RESULTS

After 12 months, six horses were sound and showed complete resolution of increased SI in T2w fast spin echo (FSE) images, but increased SI was found in STIR images in three horses and persisted in T1w and T2*w gradient recall echo images of all horses. In contrast, hyperintense areas were still visible in the SDFT in T2w FSE images in two horses presenting with re-injury. In the six horses without re-injury, percentage of cross-sectional areas affected and SI decreased over time in all sequences.

CONCLUSIONS

This study suggests that SI in naturally occurring SDFT lesions decreases earlier in T2w FSE than in STIR images, in contrast to the DDFT.

In Vivo Magic Angle Magnetic Resonance Imaging for Cell Tracking in Equine Low-Field MRI

The magic angle effect increases the MRI signal of healthy tendon tissue and could be used for more detailed evaluation of tendon structure. Furthermore, it could support the discrimination of hypointense artefacts induced by contrast agents such as superparamagnetic iron oxide used for cell tracking. However, magic angle MRI of the equine superficial digital flexor tendon has not been accomplished in vivo in standing low-field MRI so far. The aim of this in vivo study was to evaluate the practicability of this magic angle technique and its benefit for tracking superparamagnetic iron oxide-labelled multipotent mesenchymal stromal cells. Six horses with induced tendinopathy in their forelimb superficial digital flexor tendons were injected locally either with superparamagnetic iron oxide-labelled multipotent mesenchymal stromal cells or serum. MRI included standard and magic angle image series in T1- and T2∗-weighted sequences performed at regular intervals. Image analysis comprised blinded evaluation and quantitative assessment of signal-to-noise ratio. The magic angle technique enhanced the tendon signal-to-noise ratio (P < 0.001). Hypointense artefacts were observable in the cell-injected superficial digital flexor tendons over 24 weeks and artefact signal-to-noise ratio differed significantly from tendon signal-to-noise ratio in the magic angle images (P < 0.001). Magic angle imaging of the equine superficial digital flexor tendon is feasible in standing low-field MRI. The current data demonstrate that the technique improves discrimination of superparamagnetic iron oxide-induced artefacts from the surrounding tendon tissue.

Power Doppler to investigate superficial digital flexor tendinopathy in the horse

Background:

Recent advances in tendinopathy research have focused on tendon vascularization detected with Color Doppler (CD) ultrasound. The use of CD has also been described in horses in a study on chronic lesions of superficial digital flexor tendon and suspensory ligament.

Aim:

The aim of this study was to investigate the occurrence and distribution of power Doppler (PD) signal in horses with superficial digital flexor tendinopathy.

Methods:

Twenty-five horses with tendinopathy were included and 10 healthy horses with no lameness and no ultrasonographic abnormalities were used for comparison.

Results:

In all horses with tendinopathy, the PD signal was visible while normal tendons with no abnormalities in B-mode were PD signal-free.

Conclusion:

We can speculate that PD could provide essential information about the healing process than the grayscale ultrasound.

Effects of mesenchymal stromal cells versus serum on tendon healing in a controlled experimental trial in an equine model

BACKGROUND

Mesenchymal stromal cells (MSC) have shown promising results in the treatment of tendinopathy in equine medicine, making this therapeutic approach seem favorable for translation to human medicine. Having demonstrated that MSC engraft within the tendon lesions after local injection in an equine model, we hypothesized that they would improve tendon healing superior to serum injection alone.

METHODS

Quadrilateral tendon lesions were induced in six horses by mechanical tissue disruption combined with collagenase application 3 weeks before treatment. Adipose-derived MSC suspended in serum or serum alone were then injected intralesionally. Clinical examinations, ultrasound and magnetic resonance imaging were performed over 24 weeks. Tendon biopsies for histological assessment were taken from the hindlimbs 3 weeks after treatment. Horses were sacrificed after 24 weeks and forelimb tendons were subjected to macroscopic and histological examination as well as analysis of musculoskeletal marker expression.

RESULTS

Tendons injected with MSC showed a transient increase in inflammation and lesion size, as indicated by clinical and imaging parameters between week 3 and 6 (p < 0.05). Thereafter, symptoms decreased in both groups and, except that in MSC-treated tendons, mean lesion signal intensity as seen in T2w magnetic resonance imaging and cellularity as seen in the histology (p < 0.05) were lower, no major differences could be found at week 24.

CONCLUSIONS

These data suggest that MSC have influenced the inflammatory reaction in a way not described in tendinopathy studies before. However, at the endpoint of the current study, 24 weeks after treatment, no distinct improvement was observed in MSC-treated tendons compared to the serum-injected controls. Future studies are necessary to elucidate whether and under which conditions MSC are beneficial for tendon healing before translation into human medicine.

Clinical findings and prognosis of interference injuries to the palmar aspect of the forelimbs in Standardbred racehorses: A study on 74 cases

BACKGROUND

Information on interference injuries in racehorses is lacking.

OBJECTIVE

To describe clinical findings and prognosis of palmar forelimb interference injuries in Standardbreds.

STUDY DESIGN

Retrospective cohort study.

METHODS

Records of 74 racehorses sustaining palmar forelimb interference injuries were studied; 7 occurred during training and 67 during racing. The number of starts before injury, hind shoeing status, gait penalties and racing speeds in cases occurring during racing were compared with negative controls (67 age, sex and speed category matched horses) from the same races. The number of starts and racing speed in 30 racing days preceding recruitment were compared with those following recruitment (negative controls) or return to racing (cases). Clinical aspects and outcome in interference-induced superficial digital flexor (SDF) tendonitis were compared with 77 horses with overstrain-induced SDF tendonitis.

RESULTS

In 89% of cases, there was SDF tendonitis and this was associated with a longer time to return to racing (6 months vs. 1 months; P<0.001). The presence of gait penalties (odds ratio (OR) 11.13; 95% CI 3.74, 41.64; P<0.001) and unshod hind feet (OR = 6.26, 95% CI 2.26, 19.62; P<0.001) increased risk of interference injuries. After recruitment/return to racing, horses with interference injuries participated in a lower number of races (24 starts per racing day, interquartile range [IQR] 20-32) compared with controls (49, IQR 43-55, P<0.0001). Interference-induced tendonitis cases (n = 58) had a shorter time to return to racing (245 ± 137 days) than overstrain-induced tendonitis cases (331 ± 118 days, P<0.001).

MAIN LIMITATIONS

Data were collected retrospectively; time of ultrasonographic assessment varied and health status of the racing controls is unknown.

CONCLUSIONS

SDF tendonitis is common with palmar forelimb interference injuries in Standardbreds and increases time to return to racing. Interference-induced SDF tendonitis has a better prognosis than overstrain-induced tendonitis.

Randomized controlled trial demonstrates the benefit of RGTA® based matrix therapy to treat tendinopathies in racing horses

A randomized controlled trial was performed on racing horses, to evaluate the efficacy of a new class of therapeutic agents in regenerative medicine—ReGeneraTing Agents^® (RGTA^®), to treat tendinopathies. Preliminary uncontrolled studies on tendon healing in racing horses with RGTA^® (OTR4131)—Equitend^® showed encouraging results, justifying performing a randomized, controlled, multicenter study with a two-year racing performance follow up. The objective of this study was to evaluate the effect of Equitend^® versus placebo on acute superficial digital flexor tendonitis in racing French Standardbred Trotters (ST). Twenty-two ST were randomly and blindly assigned to receive with a ratio of 2 to 1, a single Equitend^® (n = 14) or placebo (n = 8) intralesional injection under ultrasonographic guidance. Horses were evaluated over 4 months, by clinical and ultrasonographic evaluations (day 0, months 1, 2, 4), and their racing performances followed up over the 2 years after treatment. During the first month of treatment, a significant decrease in the cross-sectional area (CSA) was found in the Equitend^® group (p = 0.04). After 4 months, the number of Equitend^® treated horses with an improved CSA was significantly higher than the placebo-treated horses (p = 0.03571). The Equitend^® group returned to their pre-injury performance level, racing in, and winning, significantly more races than the placebo group (p = 0.01399 and 0.0421, respectively). Furthermore, recurrence was significantly higher in the placebo group than in the Equitend^® group (71.4% vs 16.6%, p = 0.02442). In conclusion, we measured a significant, short-term, reduction effect on CSA and demonstrated a long-term beneficial effect of intralesional injection of Equitend^® for the treatment of superficial digital flexor tendonitis on racing ST, racing 2. 3 times more often than placebo, with 3.3 times fewer recurrences maintaining pre-injury performance level. This study may open the way for the development of a human treatment of tendonitis.

Clinical findings, treatment, and outcome in 11 dairy heifers with breakdown injury due to interosseous medius muscle rupture

OBJECTIVE

To describe the diagnosis, treatment, and prognosis of fetlock breakdown due to interosseus medius muscle rupture in cattle.

STUDY DESIGN

Retrospective clinical study.

ANIMALS

Dairy heifers with unilateral or bilateral interosseus medius muscle rupture (n = 11).

METHODS

Breakdown injury due to rupture of the interosseus medius muscle was documented clinically, radiographically, and ultrasonographically. Breakdown was bilateral in 4 heifers (3 in forelimbs, 1 in hind limbs) and unilateral in 7 (all hind limbs). One heifer with severe bilateral hind limb breakdown was slaughtered and the remaining 10 were treated by transfixation pin cast (1 heifer), box rest (n = 2), and/or a cast and splint (7).

RESULTS

Hyperextension of the fetlock and hyperflexion of the proximal interphalangeal joints during weight bearing were characteristic for interosseus muscle breakdown. Ultrasonographically, the origin and body of the interosseus muscle and the branches to the sesamoid bones were primarily affected by the rupture. Conservative treatment was successful (used for their intended purpose) in 8 of 9 heifers with a median lifespan of 32 months after discharge from the clinic (range 6-83).

CONCLUSION

Rupture of the interosseus medius muscle in young cattle may be more common than previously suggested in the literature. Imaging with ultrasound allowed more detailed localization of lesions of the musculo-tendinous structure. Interosseus medius muscle rupture had a favorable prognosis when treated conservatively in these heifers.

Long-Term Cell Tracking following Local Injection of Mesenchymal Stromal Cells in the Equine Model of Induced Tendon Disease

Tendon disease has been treated with multipotent mesenchymal stromal cells (MSCs) in the equine large-animal model with promising success. The aim of this study was to gain more insight into the fate and biodistribution of MSCs after local application into tendon lesions by long-term cell tracking in this large-animal model. Superficial digital flexor tendon lesions were induced in all limbs in six horses and injected with 10 × 10 6 Molday ION Rhodamine B™-labeled MSCs suspended in serum or serum alone. Follow-up was performed using low-field magnetic resonance imaging (MRI), flow cytometry, and histology. Cell tracking based on the hypointense artifacts induced by the superparamagnetic iron oxide (SPIO) labeling agent in MRI as well as based on Rhodamine B fluorescence was feasible. However, Prussian blue staining for assessment of histology was not entirely specific for SPIO. Labeled cells could be traced at their injection site by MRI as well as histology for the whole follow-up period of 24 weeks. Although the numbers of labeled cells within the injected tendon lesions decreased over time, part of the applied cells appeared to remain viable and integrated within the injured tissue. Furthermore, small numbers of labeled cells were identified in peripheral blood within the first 24 h after cell injection and could also be found until week 24 within the contralateral control tendon lesions that had been injected with serum. The present findings unveil details on MSC biodistribution and persistence after their local application, which are of clinical relevance with regard to MSC safety and mechanisms of action.

Comparison of treatment outcomes for superficial digital flexor tendonitis in National Hunt racehorses

Superficial digital flexor (SDF) tendonitis is a common injury in Thoroughbred racehorses. Injuries require prolonged rehabilitation, with unpredictable outcomes and a high incidence of re-injury. This observational case-control study aimed to compare race outcomes after commonly advocated treatments for tendon healing. Clinical and racing records were evaluated for 127 National Hunt racehorses treated between 2007 and 2011 for an SDF tendon injury. Two age- and sex-matched control horses were selected for each case horse to analyse the effect on post-injury racing outcomes of pre-injury data, lesion severity and treatment group [controlled exercise alone, bar firing, intralesional platelet-rich plasma (PRP), tendon splitting, tendon splitting combined with bar firing]. Control horses raced more often than case horses, with higher maximum racing post rating (RPRmax) and longer racing distances. Pre-injury racing performance was not associated with treatment group. Rate of return to racing was not associated with lesion severity or treatment group. Number of races, total distance raced post-injury and RPRmax were not associated with lesion severity or treatment group. Controlled exercise alone offered similar post-injury racing outcomes in National Hunt racehorses with SDF tendonitis to the other treatment options examined. Bar firing, either alone or in conjunction with tendon splitting, provided no additional benefit in rate of return to racing and race performance.

Freeze-thaw cycles enhance decellularization of large tendons

The use of decellularized tendon tissue as a scaffold for tendon tissue engineering provides great opportunities for future clinical and current research applications. The aim of this study was to assess the effect of repetitive freeze-thaw cycles and two different detergents, t-octyl-phenoxypolyethoxyethanol (Triton X-100) and sodium dodecyl sulfate (SDS), on decellularization effectiveness and cytocompatibility in large tendons. Freshly collected equine superficial and deep digital flexor tendons were subjected to decellularization according to four different protocols (1 and 2: freeze-thaw cycles combined with either Triton X-100 or SDS; 3 and 4: Triton X-100 or SDS). Decellularization effectiveness was assessed based on the reduction of vital cell counts, histologically visible nuclei, and DNA content. Transmission electron microscopy was performed to evaluate cellular and extracellular matrix integrity. Further, cytocompatibility of scaffolds that had been decellularized according to the protocols including freeze-thaw cycles (protocols 1 and 2) was assessed by seeding the scaffolds with superparamagnetic iron oxide labeled mesenchymal stromal cells and monitoring the cells histologically and by magnetic resonance imaging for two weeks. Decellularization was significantly more effective when using the protocols including freeze-thaw cycles, leaving only roughly 1% residual nuclei and 20% residual DNA, whereas samples that had not undergone additional freeze-thaw cycles contained roughly 20% residual nuclei and 40% residual DNA. No morphological extracellular matrix alterations due to decellularization could be observed. Scaffolds prepared by both protocols including freeze-thaw cycles were cytocompatible, but the cell distribution into the scaffold tended to be better in scaffolds that had been decellularized using freeze-thaw cycles combined with Triton X-100 instead of SDS.

Imaging horse tendons using multimodal 2-photon microscopy

Injuries and damage to tendons plague both human and equine athletes. At the site of injuries, various cells congregate to repair and re-structure the collagen. Treatments for collagen injury range from simple procedures such as icing and pharmaceutical treatments to more complex surgeries and the implantation of stem cells. Regardless of the treatment, the level of mechanical stimulation incurred by the recovering tendon is crucial. However, for a given tendon injury, it is not known precisely how much of a load should be applied for an effective recovery. Both too much and too little loading of the tendon could be detrimental during recovery. A mapping of the complex local environment imparted to any cell present at the site of a tendon injury may however, convey fundamental insights related to their decision making as a function of applied load. Therefore, fundamentally knowing how cells translate mechanical cues from their external environment into signals regulating their functions during repair is crucial to more effectively treat these types of injuries. In this paper, we studied systems of tendons with a variety of 2-photon-based imaging techniques to examine the local mechanical environment of cells in both normal and injured tendons. These tendons were chemically treated to instigate various extents of injury and in some cases, were injected with stem cells. The results related by each imaging technique distinguish with high contrast and resolution multiple morphologies of the cells' nuclei and the alignment of the collagen during injury. The incorporation of 2-photon FLIM into this study probed new features in the local environment of the nuclei that were not apparent with steady-state imaging. Overall, this paper focuses on horse tendon injury pattern and analysis with different 2-photon confocal modalities useful for wide variety of application in damaged tissues.