Macroscale and microscale mechanical and biochemical properties of the equine superficial digital flexor tendon are regionally dependent.

The distal equine SDFT has higher GAG content, lower stiffness, and disorganized collagen, informing regional tendinopathy understanding.

This study investigated regional variations in mechanical, biochemical, and histological properties along the length of the equine superficial digital flexor tendon (SDFT), a structure commonly affected by tendinopathy in performance horses. Using postmortem SDFTs from 9 equine donors, researchers divided each tendon into proximal, middle, and distal regions defined by the musculotendinous and osteotendinous junctions. Macroscale mechanical properties were assessed via tensile testing, microscale properties via atomic force microscopy, and biochemical composition through glycosaminoglycan (GAG), collagen, and DNA content assays, supplemented by histological staining. Key findings revealed significant regional differences, particularly between the middle and distal regions. The distal region demonstrated a approximately 3-fold higher GAG content and a 1.67-fold lower tensile modulus compared to the middle region, indicating reduced stiffness and altered matrix composition. Histological analysis confirmed a more disorganized collagen fibril arrangement in the distal region. Microscale mechanical properties did not show statistically significant regional differences. These findings suggest that the distal SDFT has inherently distinct structural and biomechanical characteristics, including a fibrocartilaginous-like matrix, which may predispose it to different injury patterns or affect healing responses. This regional characterization of normal SDFT properties provides an important baseline for understanding the pathophysiology of tendinopathy and may inform region-specific diagnostic and therapeutic strategies in equine practice.

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