Collagen fibril diameter distributions in ligaments and tendons of the carpal region of the horse

Since horses bred for the racing industry are subject to rigorous training procedures there is a real need to understand how the stresses experienced by their tendons and ligaments in vivo relate to the major load-bearing elements-the collagen fibrils. Consequently, an age-related study has been made of the collagen fibril diameter distributions of nine ligaments in and around the equine carpus. This is the first stage of a larger study aimed at understanding the ultrastructural changes that occur as a result of exercise. Most of the ligaments showed a bimodal diameter distribution at maturity, and decreased diameters at old age as the fibrils break down. The scaphocapitate ligament, however, was unique in that the constituent fibrils were small, almost invariant in diameter with age, and had a unimodal distribution of sizes. The mechanical attributes of these tissues, as deduced from a theoretical analysis of the diameter distributions, are consistent with observation.