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Aging is hypothesized to be associated with changes in tendon matrix composition which may lead to alteration of tendon material properties and hence propensity to injury. Altered gene expression may offer insights into disease pathophysiology and thus open new perspectives toward designing pathophysiology‐driven therapeutics. Therefore, the current study aimed at identifying naturally occurring differences in tendon micro‐morphology and gene expression of newborn, young and old horses. Age‐related differences in the distribution pattern of tendon fibril thickness and in the expression of the tendon relevant genes collagen type 1 (Col1), Col3, Col5, tenascin‐C, decorin, tenomodulin, versican, scleraxis and cartilage oligomeric matrix protein were investigated. A qualitative and quantitative gene expression and collagen fibril diameter analysis was performed for the most frequently injured equine tendon, the superficial digital flexor tendon, in comparison with the deep digital flexor tendon. Most analyzed genes (Col1, Col3, Col5, tenascin‐C, tenomodulin, scleraxis) were expressed at a higher level in foals (age ≤ 6 months) than in horses of 2.75 years (age at which flexor tendons become mature in structure) and older, decorin expression increased with age. Decorin was previously reported to inhibit the lateral fusion of collagen fibrils, causing a thinner fibril diameter with increased decorin concentration. The results of this study suggested that reduction of tendon fibril diameters commonly seen in equine tendons with increasing age might be a natural age‐related phenomenon leading to greater fibril surface areas with increased fibrillar interaction and reduced sliding at the fascicular/fibrillar interface and hence a stiffer interfascicular/interfibrillar matrix. This may be a potential reason for the higher propensity to tendinopathies with increasing age., TEM pictures and histograms showing collagen fibril distribution changes for the SDFT and DDFT with age. Whereas a Gaussian‐like distribution of fibril diameters was observed in tendons of foals up to 6 months of age, a marked shift towards much thinner fibrils was seen in tendons of horses 2.75 years of age or older.

Background Osteoarthritis, a chronic and progressive degenerative joint disorder, ranks amongst the top five causes of disability. Given the high incidence, associated socioeconomic costs and the absence of effective disease-modifying therapies of osteoarthritis, cell-based treatments offer a promising new approach. Owing to their paracrine, differentiation and self-renewal abilities, mesenchymal stem cells (MSCs) have great potential for regenerative medicine, which might be further enhanced by targeted gene therapy. Hence, the development of systems allowing transgene expression, particularly when regulated by natural disease-dependent occuring substances, is of high interest. Methods Bone marrow-isolated equine MSCs were stably transduced with an HIV-1 based lentiviral vector expressing the luciferase gene under control of an inducible nuclear factor κB (NFκB)-responsive promoter. Marker gene expression was analysed by determining luciferase activity in transduced cells stimulated with different concentrations of interleukin (IL)-1β or tumour necrosis factor (TNF)α. Results A dose-dependent increase in luciferase expression was observed in transduced MSCs upon cytokine stimulation. The induction effect was more potent in cells treated with TNFα compared to those treated with IL-1β. Maximum transgene expression was obtained after 48 h of stimulation and the same time was necessary to return to baseline luciferase expression levels after withdrawal of the stimulus. Repeated cycles of induction allowed on-off modulation of transgene expression without becoming refractory to induction. The NFκB-responsive promoter retained its inducibility also in chondrogenically differentiated MSC/Luc cells. Conclusions The results of the present study demonstrate that on demand transgene expression from the NFκB-responsive promoter using naturally occurring inflammatory cytokines can be induced in undifferentiated and chondrogenically differentiated equine MSCs. Copyright © 2016 John Wiley & Sons, Ltd.

Objectives To evaluate knot security for 3 knot types created in 3 commonly used 5 metric suture materials incubated in physiological and pathological fluids. Study Design In vitro mechanical study. Sample Population Knotted suture loops (n = 5/group). Methods Loops of 3 different suture materials (glycolide/lactide copolymer; polyglactin 910; polydioxanone) were created around a 20 mm rod using 3 knot types (square [SQ], surgeon's [SK], and triple knot [TK]) and were tested to failure in distraction (6 mm/min) after tying (day 0) and after being incubated for 14 and 28 days in phosphate buffered saline (PBS) or inflamed peritoneal fluid. Failure load (N) and mode were recorded and compared. Results For polydioxanone, significant differences in force to knot failure were found between SQ and SK/TK but not between SK and TK. The force required to break all constructs increased after incubation in phosphate buffered saline (PBS). With glycolide/lactide copolymer no differences in force to knot failure were observed. With polyglactin 910, a significant difference between SQ and TK was observed, which was not seen between the other knot types. Incubation in inflamed peritoneal fluid caused a larger and more rapid decrease in force required to cause knot failure than incubation in PBS. Conclusions Mechanical properties of suture materials have significant effects on knot security. For polydioxanone, SQ is insufficient to create a secure knot. Additional wraps above a SK confer extra stability in some materials, but this increase may not be clinically relevant or justifiable. Glycolide/lactide copolymer had excellent knot security.

Summary Reasons for performing study Selection of suture material in equine surgery is often based on costs or subjective factors, such as the surgeon's personal experience, rather than objective facts. The amount of objective data available on durability of suture materials with regard to specific equine physiological conditions is limited. Objectives To evaluate the effect of various equine physiological and pathological fluids on the rate of degradation of a number of commonly used suture materials. Study design In vitro material testing. Methods Suture materials were exposed in vitro to physiological fluid, followed by biomechanical analysis. Three absorbable suture materials, glycolide/lactide copolymer, polyglactin 910 and polydioxanone were incubated at 37°C for 7, 14 or 28 days in phosphate-buffered saline, equine serum, equine urine and equine peritoneal fluid from an animal with peritonitis. Five strands of each suture material type were tested to failure in a materials testing machine for each time point and each incubation medium. Yield strength, strain and Young's modulus were calculated, analysed and reported. Results For all suture types, the incubation time had a significant effect on yield strength, percentage elongation and Young's modulus in all culture media (P

REASONS FOR PERFORMING STUDY: Equine embryogenesis post implantation is not well studied, and only two-dimensional illustrations are available. A thorough appreciation of the complex three-dimensional relationship between tissues and organs and their development is, however, crucial for understanding physiological and pathological mechanisms. OBJECTIVES: The goals were 2-fold: 1) to establish a freely accessible online atlas as a reference tool for the scientific and pedagogic communities; and 2) to create a framework for integration of data with known spatiotemporal distribution, such as gene expression or cell lineage. STUDY DESIGN: Descriptive anatomical study. METHODS: Magnetic resonance microscopy was performed on embryos of 28, 32, 35, 37, 39, 40, 42, 45, 50 and 65 days gestation using a 9.4 T magnet. Equine embryos were staged according to the Carnegie system. Acquired images were optimised using histogram optimisation and processed for easy online access. RESULTS: Magnetic resonance microscopy protocols for imaging of equine embryos and fetuses were developed. The wider spread of signal intensity values achieved by histogram equalisation increased visual contrast considerably. Despite their longer gestation, equine conceptuses appeared to reach the various Carnegie staging benchmarks earlier than human embryos. CONCLUSIONS: The equine atlas is designed to serve as an online reference tool for research and teaching. POTENTIAL RELEVANCE: The equine atlas may serve as a foundation and scaffold for improved anatomical labelling, spatial and temporal data integration and further understanding of physiological and pathophysiological processes involved in development and disease.

Objective: To determine the physiologic response of the equine navicular bone to core decompression surgery in healthy horses. Study Design: Experimental in vivo study. Materials: Healthy adult horses (n=6). Methods: Core decompression was completed by creating three 2.5-mm-diameter drill channels into the navicular bone under arthroscopic control. The venous (PV), arterial (PA), articular (PDIPJ), and intraosseous pressures (IOP) were recorded before and after decompression drilling. Each IOP measurement consisted of a baseline (IOPB) and a stress test (intramedullary injection of saline solution, IOPS) recording. Lameness was assessed subjectively and using force plate gait analysis. Fluorochrome bone labeling was performed. Horses were euthanatized at 12 weeks. Navicular bone mineral density (BMD) was measured, and bone histology evaluated. Results: Peak IOP (IOPmax) after stress testing was significantly (P

Objective: To determine the effect of core decompression surgery and bone mineral density (BMD) on the mechanical properties of equine navicular bones. Study Design: Experimental, in vitro study. Sample Population: Fore limb navicular bones (n=36 pairs) from sound 2–5-year-old horses with no radiographic abnormalities of the distal aspect of the forelimbs. Methods: Navicular BMD was measured using dual energy X-ray absorptiometry. One randomly assigned navicular bone from each pair served as control. The contralateral test specimen was allocated to 1 of 6 treatment groups defined by drill bit size (3.2 versus 2.5 mm diameter) and by the number of drill channels (1, 2, or 3) created in the proximal border of the bone. Bones were then tested until failure in 3-point bending. Data were statistically analyzed using ANOVA and regression analysis. Results: There were significant (P .05) influence the extent of the reduction in mechanical strength. Conclusion: In vitro core decompression significantly decreases the breaking strength of the equine navicular bone.

REASONS FOR PERFORMING STUDY: Articular cartilage regeneration is the focus and goal of considerable research effort. Since articular chondrocytes descend from a distinct cohort of progenitor cells located in embryonic nascent joints (interzones), establishing the timing of equine interzone formation is an essential first step towards understanding equine joint and articular cartilage development. OBJECTIVES: To establish the time frame during which the equine femorotibial interzone forms. STUDY DESIGN: Descriptive anatomical study. METHODS: Equine embryos were harvested at 37 (E37), 40, 42, 45, 50 and 65 days' gestation. The femorotibial interzone was examined using high-resolution episcopic microscopy of E37, E42, E45, E50 and E65. Additional histology and collagen-II-immunohistochemistry were performed on E42. RESULTS: At E37, the femorotibial interzone is first visible as a uniform layer, while at E42 the interzone is fully formed and consists of 3 morphologically distinct layers. The first evidence of cavitation was seen at E45. At E50, the cruciate ligaments were well formed and by E65, joint formation appeared complete. CONCLUSIONS: The embryogenesis of the equine femorotibial joint is similar to the developmental timeline of stage-matched human and murine embryos. Further studies looking at interzone formation on a cellular and molecular level may further our understanding of the intricate developmental patterns and pathways of articular cartilage development.

Summary A comminuted fracture of the central tarsal bone, fragmentation of the fourth tarsal bone and associated joint instability was diagnosed in a 14-year-old Sport Horse mare who presented for investigation of acute nonweightbearing hindlimb lameness. The mare responded well to conservative management and, unlike previously reported cases of similar injuries, returned to a similar level of athletic activity.