Effect of maturation and aging on material and ultrasonographic properties of equine superficial digital flexor tendon

Carol Gillis From the Veterinary Medical Teaching Hospital (Gillis), Departments of Anatomy, Physiology, and Cell Biology (Stover), Pathology, Microbiology, and Immunology (Pool), and Surgical and Radiological Sciences (Meagher), School of Veterinary Medicine, Department of Orthopaedic Surgery, School of Medicine (Sharkey), and Division of Statistics (Willits), University of California, Davis, CA 95616.

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Neil Sharkey From the Veterinary Medical Teaching Hospital (Gillis), Departments of Anatomy, Physiology, and Cell Biology (Stover), Pathology, Microbiology, and Immunology (Pool), and Surgical and Radiological Sciences (Meagher), School of Veterinary Medicine, Department of Orthopaedic Surgery, School of Medicine (Sharkey), and Division of Statistics (Willits), University of California, Davis, CA 95616.

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Susan M. Stover From the Veterinary Medical Teaching Hospital (Gillis), Departments of Anatomy, Physiology, and Cell Biology (Stover), Pathology, Microbiology, and Immunology (Pool), and Surgical and Radiological Sciences (Meagher), School of Veterinary Medicine, Department of Orthopaedic Surgery, School of Medicine (Sharkey), and Division of Statistics (Willits), University of California, Davis, CA 95616.

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Roy R. Pool From the Veterinary Medical Teaching Hospital (Gillis), Departments of Anatomy, Physiology, and Cell Biology (Stover), Pathology, Microbiology, and Immunology (Pool), and Surgical and Radiological Sciences (Meagher), School of Veterinary Medicine, Department of Orthopaedic Surgery, School of Medicine (Sharkey), and Division of Statistics (Willits), University of California, Davis, CA 95616.

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Dennis M. Meagher From the Veterinary Medical Teaching Hospital (Gillis), Departments of Anatomy, Physiology, and Cell Biology (Stover), Pathology, Microbiology, and Immunology (Pool), and Surgical and Radiological Sciences (Meagher), School of Veterinary Medicine, Department of Orthopaedic Surgery, School of Medicine (Sharkey), and Division of Statistics (Willits), University of California, Davis, CA 95616.

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Neil Willits From the Veterinary Medical Teaching Hospital (Gillis), Departments of Anatomy, Physiology, and Cell Biology (Stover), Pathology, Microbiology, and Immunology (Pool), and Surgical and Radiological Sciences (Meagher), School of Veterinary Medicine, Department of Orthopaedic Surgery, School of Medicine (Sharkey), and Division of Statistics (Willits), University of California, Davis, CA 95616.

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SUMMARY

Results of studies in human beings and other species have indicated that aging significantly influences the strength, modulus of elasticity, and energy storage ability of tendon. We wanted to determine the effects of aging on the material and ultrasonographic properties of equine superficial digital flexor (sdf) tendon. Ultrasonographic measurements of left forelimb sdf tendon cross-sectional area and mean echogenicity were made in 23 standing horses ranging in age from 2 to 23 years. All horses had not been in work for a minimum of 6 months prior to the study. After euthanasia, left forelimb bone-muscle-tendon-bone specimens were mounted in a materials testing system. The sdf tendon was cyclically loaded sinusoidally 100 times at 0.5 Hz from 1.5 to 5.0% strain, then was submitted to 10-minute creep-and-stress relaxation tests. Modulus of elasticity, load at 3% strain, and creep-and-stress relaxation were determined for each specimen. A significant positive correlation was found between elastic modulus and age. Correlation was not found between age and sdf tendon cross-sectional area or mean echogenicity. When 2-year-old horses were compared with older horses, the latter had tendons with a significantly (P = 0.007) greater modulus of elasticity. The authors conclude that increasing age through maturity is associated with a corresponding increase in equine sdf tendon elastic modulus.

SUMMARY

Results of studies in human beings and other species have indicated that aging significantly influences the strength, modulus of elasticity, and energy storage ability of tendon. We wanted to determine the effects of aging on the material and ultrasonographic properties of equine superficial digital flexor (sdf) tendon. Ultrasonographic measurements of left forelimb sdf tendon cross-sectional area and mean echogenicity were made in 23 standing horses ranging in age from 2 to 23 years. All horses had not been in work for a minimum of 6 months prior to the study. After euthanasia, left forelimb bone-muscle-tendon-bone specimens were mounted in a materials testing system. The sdf tendon was cyclically loaded sinusoidally 100 times at 0.5 Hz from 1.5 to 5.0% strain, then was submitted to 10-minute creep-and-stress relaxation tests. Modulus of elasticity, load at 3% strain, and creep-and-stress relaxation were determined for each specimen. A significant positive correlation was found between elastic modulus and age. Correlation was not found between age and sdf tendon cross-sectional area or mean echogenicity. When 2-year-old horses were compared with older horses, the latter had tendons with a significantly (P = 0.007) greater modulus of elasticity. The authors conclude that increasing age through maturity is associated with a corresponding increase in equine sdf tendon elastic modulus.

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