FUNCTIONAL-SIGNIFICANCE OF THE MORPHOLOGY AND MICROMECHANICS OF COLLAGEN-FIBERS IN RELATION TO PARTIAL RUPTURE OF THE SUPERFICIAL DIGITAL FLEXOR TENDON IN RACEHORSES

The high incidence of partial rupture of the superficial digital flexo r tendor in the equine athlete represents a major cause for concern in the racing industry. Frequently, the lesion is localised to the centr al core of the tendon. This study tested the hypothesis that the site specific structural failure results from differences in the collagen f ibre morphology and associated micromechanics between central and peri pheral regions of the tendon. Bundles of collagen fibres were dissecte d from central and peripheral sites in the mid-metacarpal region of th e tendon. Crimp morphology was quantified by polarised light microscop y and mechanical characteristics determined using a fibre tensometer. In older horses, centrally located fibres showed significantly lower v alues for crimp angle, crimp length and toe limit strain than seen per ipherally. There were no significant differences in these features bet ween corresponding sites in the younger horses. No significant differe nce between sites was found in elastic modulus in either group. These data indicate a non-uniform functional stress distribution which may r esult from ageing or be related to the exercise history as a feature o f accumulated damage. These observations may explain the location of c entral core lesions seen on clinical examination.