Edema and Structural Remodeling in Equine Suspensory Ligament Injury: A Severity Gradient Associated with Microvascular Dysfunction

Suspensory ligament injury is a major cause of lameness in sport horses, yet its underlying mechanisms remain incompletely understood. The aim of this study was to characterize histopathological alterations of the equine suspensory ligament and to evaluate their association with imaging features. A comparative descriptive study was performed on sport horses with forelimb lameness, combining clinical evaluation, ultrasonography, magnetic resonance imaging, and histopathological analysis. Ligament samples were collected post-mortem from anatomically defined regions selected based on imaging findings to allow regional imaging–histopathology correlation. The results showed a consistent presence of edema in perivascular, interfascicular, and intrafascicular compartments, indicating a diffuse disturbance of tissue fluid balance. Lesions with lower severity were characterized by increased vascular permeability and mild extracellular matrix expansion, whereas lesions with greater structural severity demonstrated vascular remodeling, including endothelial thickening, vascular wall changes, and perivascular connective tissue proliferation, associated with collagen disorganization. Regional differences were observed, with more pronounced alterations in the proximal region compared to the branch region. These findings are consistent with a pattern of structural changes associated with microvascular alterations, demonstrating variation in lesion severity across samples and supporting an association between imaging categories and semi-quantitative histological features. However, given the cross-sectional design, causality cannot be established.