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American journal of veterinary research2026; 87(8); 1-9; doi: 10.2460/ajvr.26.02.0059

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

Abstract: To examine regional mechanical and biochemical differences across the length of the equine superficial digital flexor tendon (SDFT). Unassigned: Equine SDFTs were collected postmortem from 9 donors and divided into proximal, middle, and distal regions based on the location of the musculotendinous and osteotendinous junctions. Tensile testing was performed on samples to obtain macroscale mechanical properties, and atomic force microscopy was done to obtain microscale mechanical properties. Biochemical assays and histological staining were done to assess glycosaminoglycan (GAG), collagen, and DNA content in each region. Unassigned: Regional differences were present in macroscale mechanical properties and biochemical properties. Differences were primarily seen between the middle and distal region, with the distal region having a 3-fold increased GAG content (Δ14.15 µg GAG/mg sample; 95% CI, -0.32 to 28.62) and a 1.67-fold decreased macroscopic tensile modulus (Δ-68.2 MPa; 95% CI, -107.9 to -28.5). A more disorganized collagen fibril matrix was seen in the distal region through histological staining. Unassigned: Mechanical, biochemical, and histological regional differences exist with the equine SDFT. In particular, the distal region showed a disorganized matrix with higher GAG content and decreased modulus in comparison to the proximal and middle regions. Unassigned: Our data provide information that helps better understand normal SDFT function and presentation of tendinopathy by providing regional structural and biochemical and mechanical information within the SDFT.
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Publication Date: 2026-05-15 PubMed ID: 42140271PubMed Central: PMC13234756DOI: 10.2460/ajvr.26.02.0059Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigates how the mechanical and biochemical properties of the equine superficial digital flexor tendon (SDFT) vary along different regions of the tendon.
  • The researchers analyzed the proximal, middle, and distal regions to understand differences in tendon structure and function.

Purpose and Background

  • The superficial digital flexor tendon (SDFT) in horses is critical for limb movement and bears large mechanical loads.
  • Understanding regional differences in the tendon’s properties can clarify how it functions normally and how it may be vulnerable to injury or tendinopathy.
  • The study aims to examine both mechanical properties at multiple scales and biochemical composition throughout the length of the equine SDFT.

Methodology

  • Sample Collection: SDFTs were collected postmortem from 9 horses.
  • Division of Regions: Each tendon was segmented into proximal, middle, and distal regions, based on anatomical landmarks:
    • Proximal: Near the musculotendinous junction
    • Middle: Mid-length of the tendon
    • Distal: Near the osteotendinous junction
  • Mechanical Testing:
    • Macroscale mechanical properties were measured using tensile testing techniques to assess characteristics like tensile modulus.
    • Microscale mechanical properties were examined with atomic force microscopy (AFM) to gain insights into the microscopic stiffness and organization of the tendon matrix.
  • Biochemical Analysis:
    • Biochemical assays measured the content of glycosaminoglycans (GAGs), collagen, and DNA in each region to assess biochemical composition.
    • Histological staining techniques were used to observe the organization and distribution of collagen fibrils within the tendon regions.

Key Findings

  • Regional Differences in Mechanical Properties:
    • The distal region exhibited a significantly lower macroscopic tensile modulus (approximately 1.67 times decreased) compared to proximal and middle regions, indicating reduced stiffness and mechanical strength.
    • Microscale mechanical properties also varied regionally, though the main reported changes were at the macroscale.
  • Biochemical and Structural Variations:
    • The distal region showed roughly a 3-fold increase in glycosaminoglycan (GAG) content compared to the middle region.
    • Histological staining revealed that the collagen fibril matrix in the distal region was more disorganized than in proximal and middle parts, suggesting altered structural integrity.
    • These biochemical and structural changes likely contribute to the mechanical differences observed.

Significance and Implications

  • The research demonstrates that the properties of the SDFT are not uniform along its length; the distal region specifically stands out with distinct mechanical weakness and altered biochemical makeup.
  • These findings are important for understanding normal tendon biomechanics, as regional specialization may be linked to specific functional roles or vulnerabilities within the tendon.
  • The observed differences also provide insights into tendinopathy development, as regions with disorganized matrix and altered biochemical profiles may be more prone to injury or degeneration.
  • This study’s data could inform veterinary diagnosis and treatment strategies by highlighting areas of the tendon that may require focused attention or different management approaches.
  • Further research might explore how these regional variations change with age, training, or injury to improve preventative and rehabilitative protocols in equine athletes.

Cite This Article

APA
Watson SL, Davis ZG, Koch DW, Connard SS, Brown AC, Schnabel LV, Fisher MB. (2026). Macroscale and microscale mechanical and biochemical properties of the equine superficial digital flexor tendon are regionally dependent. Am J Vet Res, 87(8), 1-9. https://doi.org/10.2460/ajvr.26.02.0059

Publication

American journal of veterinary research
ISSN: 1943-5681
NlmUniqueID: 0375011
Country: United States
Language: English
Volume: 87
Issue: 8
Pages: 1-9
PII: ajvr.26.02.0059

Researcher Affiliations

Watson, Samantha L
  • Lampe Joint Department of Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill, Raleigh, NC.
Davis, Zachary G
  • Lampe Joint Department of Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill, Raleigh, NC.
  • Comparative Medicine Institute, North Carolina State University, Raleigh, NC.
Koch, Drew W
  • Comparative Medicine Institute, North Carolina State University, Raleigh, NC.
  • Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC.
Connard, Shannon S
  • Comparative Medicine Institute, North Carolina State University, Raleigh, NC.
  • Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC.
Brown, Ashley C
  • Lampe Joint Department of Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill, Raleigh, NC.
  • Comparative Medicine Institute, North Carolina State University, Raleigh, NC.
Schnabel, Lauren V
  • Comparative Medicine Institute, North Carolina State University, Raleigh, NC.
  • Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC.
Fisher, Matthew B
  • Lampe Joint Department of Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill, Raleigh, NC.
  • Comparative Medicine Institute, North Carolina State University, Raleigh, NC.
  • Department of Orthopaedics, UNC School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC.

MeSH Terms

  • Animals
  • Horses / physiology
  • Horses / anatomy & histology
  • Tendons / physiology
  • Tendons / anatomy & histology
  • Tendons / chemistry
  • Biomechanical Phenomena
  • Tensile Strength
  • Microscopy, Atomic Force / veterinary
  • Collagen / analysis
  • Glycosaminoglycans / analysis
  • DNA / analysis
  • Forelimb / physiology
  • Forelimb / anatomy & histology

Grant Funding

  • T32 OD011130 / NIH HHS

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