EFFECT OF MATURATION AND AGING ON MATERIAL AND ULTRASONOGRAPHIC PROPERTIES OF EQUINE SUPERFICIAL DIGITAL FLEXOR TENDON

Results of studies in human beings and other species have indicated th at aging significantly influences the strength, modulus of elasticity, and energy storage ability of tendon. We wanted to determine the effe cts of aging on the material and ultrasonographic properties of equine superficial digital flexor (SDF) tendon. Ultrasonographic measurement s of left forelimb SDF tendon cross-sectional area and mean echogenici ty 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 specim ens were mounted in a materials testing system. The SDF tendon was cyc lically loaded sinusoidally 100 times at 0.5 Hz from 1.5 to 5.0% strai n, then was submitted to 10-minute creep-and-stress relaxation tests. Modulus of elasticity, load at 3% strain, and creep-and-stress relaxat ion were determined for each specimen. A significant positive correlat ion was found between elastic modulus and age. Correlation was not fou nd between age and SDF tendon cross-sectional area or mean echogenicit y. When 2-year-old horses were compared with older horses, the latter had tendons with a significantly (P = 0.007) greater modulus of elasti city. The authors conclude that increasing age through maturity is ass ociated with a corresponding increase in equine SDF tendon elastic mod ulus.