Focal experimental injury leads to widespread gene expression and histologic changes in equine flexor tendons.
Authors: Jacobson Else, Dart Andrew J, Mondori Takamitsu, Horadogoda Neil, Jeffcott Leo B, Little Christopher B, Smith Margaret M
Journal: PloS one
Summary
# Editorial Summary: Widespread Tendon Changes Following Focal Flexor Tendon Injury When the superficial digital flexor tendon (SDFT) sustains a localised injury, the pathological response extends far beyond the initial damage site—a finding with significant implications for how we manage and rehabilitate these injuries in horses. Researchers surgically hemi-transected the SDFT in six horses and examined tissue samples from multiple regions along the entire tendon length six weeks post-injury, analysing both histological changes and gene expression patterns using real-time PCR, whilst comparing findings to sham-operated and unoperated control tendons. Histopathology scores were substantially elevated throughout the injured tendon (with the exception of the most distal region), and importantly, the response was uniform across both the overstressed medial and stress-deprived lateral halves, indicating that mechanical load alone did not dictate the extent of change. Gene expression revealed upregulation of multiple extracellular matrix components (aggrecan, versican, biglycan, collagen types I–III) and certain matrix metalloproteinases, alongside downregulation of ADAMTS4, MMP3, and TIMP3—patterns that strongly correlated with the severity of histological damage seen on microscopy. These findings suggest that focal tendon injuries trigger a rapid, widespread inflammatory and remodelling cascade throughout the entire structure within just six weeks, which may explain why clinically injured horses frequently experience poor functional recovery and re-injury despite apparently appropriate local healing; practitioners should therefore consider that effective treatment protocols need to address pathology throughout the whole tendon rather than focusing solely on the injury site, and that developing better non-invasive monitoring methods for tracking these systemic changes will be essential for optimising rehabilitation strategies.
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Practical Takeaways
- •A small localized tendon injury triggers pathologic changes along the entire length of the tendon—treating only the injury site may be insufficient for optimal healing and recovery
- •By 6 weeks post-injury, widespread degenerative changes are already established in the tendon, suggesting early intervention and monitoring of the whole tendon is critical to prevent re-injury
- •Current treatment protocols should consider addressing tendinopathy throughout the entire tendon length, not just the focal lesion, and new diagnostic tools are needed to track these widespread changes
Key Findings
- •Focal surgical injury to equine SDFT caused significant histopathologic changes throughout the entire tendon length at 6 weeks, not just at the injury site
- •Gene expression for proteoglycans (aggrecan, versican, biglycan) and collagen types I, II, and III was upregulated across all regions, while ADAMTS4, MMP3, and TIMP3 were downregulated
- •Increased proteoglycan immunostaining (aggrecan, biglycan, versican) was detected in all but the most proximal region, suggesting widespread extracellular matrix remodeling
- •Gene expression changes correlated with histopathology scores, indicating active and rapid tendinopathy development throughout the entire tendon within 6 weeks of focal injury