Abstract
The distal sesamoidean impar ligament (DSIL) is a key component of the equine podotrochlear apparatus, yet its role in conditions such as caudal heel pain and navicular syndrome remains poorly understood. The objective of this study was to characterize the histological properties of the DSIL and evaluate how it is influenced by breed and age. Eighty-four cadaveric forelimb DSIL samples were collected from young, athletic Quarter horses (QHs), Thoroughbreds (TBs), and older, retired Quarter horses. Samples were stained and assessed for vessel size and count, number of nerve fascicles, and the relative density of collagen and adipose tissue. Data were analyzed using general linear models and Kruskal-Wallis tests for continuous variables and Poisson regression for count data, with significance set at P < 0.05. The number of vessels in the DSIL was significantly higher in both young TBs and QHs compared to older QHs (P < 0.0001). In addition, TB horses had a higher vessel count than QHs (P < 0.0001). These findings underscore the DSIL's rich vascularity and its potential role in supporting the navicular bone. Histological characteristics of the DSIL appear to be influenced by both age and breed, offering insights relevant to the pathogenesis of navicular disease.