IN-VITRO MECHANICAL-PROPERTIES OF THE ACCESSORY LIGAMENT OF THE DEEP DIGITAL FLEXOR TENDON IN HORSES IN RELATION TO AGE

The material properties of the accessesory ligament of the deep digita l flexor tendon (AL) of 21 forelimbs from horses between ages one day and 15 years were determined. The force (634-11416 N), failure stress (45-138 N/mm2), failure strain (7-24%) and tangent modulus (33-1639 MP a) are presented in relation to age. Tangent modulus did not indicate changes in elasticity due to age. The results demonstrate that complet e ligament failures (CLF) of ALs of older horses (mean 7835 N) occur a t lower forces than ALs of young adult horses (mean 8894 N). Sudden de creases, 'dips', in the force-time curves were noticed in ligaments fr om foals and yearlings and in ligaments from horses > 10 years. They w ere interpreted as the failure of a number of fibres which either fail at lower forces or are subject to higher forces than the rest. These differences in mechanical properties could be the result of age relate d differences in the material properties of ALs of older horses simila r to alterations in collagenous tissue in other species. When analysin g the data of the proximal, middle and distal regions of the ligaments separately, higher strain and elasticity were found in the distal com pared to the proximal parts. It is suggested that the clinical occurre nce of desmitis of the AL of older horses could be due to fibrillar fa ilure caused by differences in the material properties of the ligament s.