Study finds regional differences in equine flexor tendon properties
Bottom line
Regional differences in the equine superficial digital flexor tendon may help explain why some parts of the tendon are more vulnerable to injury, according to a new American Journal of Veterinary Research study. Researchers examined superficial digital flexor tendons collected postmortem from nine horses and compared proximal, middle, and distal regions using tensile testing, atomic force microscopy, and biochemical analysis. The team found that mechanical and biochemical properties varied by region, adding evidence that the tendon isn't uniform from end to end. That finding lands alongside newer imaging work showing 2D shear wave elastography can distinguish clinically healthy from injured superficial digital flexor tendons and may serve as a supplementary diagnostic tool. (researchgate.net)
Why it matters: For equine veterinarians, the study adds useful context to a tendon that's already known to be injury-prone, especially in performance horses. Prior reviews and clinical references describe the superficial digital flexor tendon as an energy-storing structure with high injury risk, with many lesions occurring in the mid-metacarpal region. If tendon properties differ by location at both the macro and micro level, that could shape how clinicians interpret imaging, assess lesion significance, and eventually tailor rehabilitation or regenerative approaches by region rather than treating the tendon as mechanically identical throughout. (beva.onlinelibrary.wiley.com)
What to watch: Watch for follow-up studies linking these regional property differences to live-horse imaging findings, injury patterns, and treatment outcomes. (researchgate.net)
Key facts
- Study type
- American Journal of Veterinary Research study
- Species
- Equine superficial digital flexor tendon
- Sample size
- Nine horses
- Design
- Postmortem tendons divided into proximal, middle, and distal regions
- Methods
- Tensile testing, atomic force microscopy, and biochemical analysis
- Main finding
- Mechanical and biochemical properties varied by region
- Clinical context
- The tendon is known to be injury-prone in horses, especially in performance horses
- Related imaging finding
- 2D shear wave elastography can distinguish clinically healthy from injured superficial digital flexor tendons
A new AJVR study suggests the equine superficial digital flexor tendon, one of the most clinically important tendons in equine sports medicine, behaves differently depending on where you look along its length. Investigators reported that macroscale mechanical, microscale mechanical, and biochemical properties were regionally dependent in the tendon, based on postmortem samples divided into proximal, middle, and distal segments. (researchgate.net)
That matters because the superficial digital flexor tendon is already a familiar source of lameness and lost performance in horses, particularly equine athletes. Background literature describes it as an energy-storing tendon that is highly susceptible to injury during high-speed exercise, and clinical references note that superficial digital flexor tendinitis is commonly associated with overextension, fatigue, poor conditioning, and persistent work through early inflammation. Reviews of equine tendon imaging have also highlighted that most superficial digital flexor tendon injuries occur in the mid-metacarpal region, making regional biology more than an academic question. (beva.onlinelibrary.wiley.com)
In the new study, researchers collected superficial digital flexor tendons from nine equine donors after death and separated them into proximal, middle, and distal regions using the musculotendinous and osteotendinous junctions as landmarks. They then used tensile testing to assess macroscale mechanics, atomic force microscopy to measure microscale properties, and biochemical assays to compare regional composition. The paper's central conclusion was that these properties are regionally dependent, supporting the idea that different parts of the tendon may face different mechanical demands and may not respond to injury or repair in the same way. (researchgate.net)
The finding also fits with a broader shift toward more nuanced tendon assessment. In a 2025 Equine Veterinary Journal study, investigators found that 2D shear wave elastography was feasible, repeatable, and reproducible for evaluating healthy and pathologic forelimb superficial digital flexor tendons. In that cohort of 30 horses, clinically healthy tendons had lower shear wave velocity and Young's modulus values than injured tendons, suggesting less stiffness, and the authors positioned 2D-SWE as a supplementary diagnostic method for tendinopathy detection. (lifescience.net)
Direct expert reaction to the new AJVR paper was limited in publicly accessible sources, but outside commentary underscores why the work is relevant. In coverage by The Horse, Claire O'Brien described the superficial digital flexor tendon as a structure that stores and releases energy efficiently, but pays a price for that specialization because it doesn't regenerate tissue back to a true pre-injury state. NC State has also highlighted related work from Lauren Schnabel's group on stem cell-based tendon repair, noting reduced reinjury in naturally occurring superficial digital flexor tendon injuries, which helps frame why a more precise understanding of tendon region-specific biology could matter for future therapies. (thehorse.com)
Why it matters: For veterinary professionals, the practical takeaway is that "normal" may need to be defined by tendon region, not just by tendon type. If proximal, middle, and distal portions differ in structure and mechanics, then imaging interpretation, lesion monitoring, rehabilitation plans, and biologic treatment strategies may all benefit from a more location-specific approach. That could be especially important in cases where ultrasound or elastography findings don't neatly match clinical signs, or where recurrence risk is concentrated in the same high-load region. This is still preclinical work, but it strengthens the rationale for pairing advanced imaging with region-aware biomechanics in equine tendon care. (researchgate.net)
What to watch: The next step is translational: studies that connect these postmortem regional differences to in vivo imaging, naturally occurring lesion distribution, and outcomes after rehabilitation or regenerative treatment. If those links hold up, region-specific reference values and treatment protocols could become more realistic targets for equine practice. (researchgate.net)