Accessory ligament of the deep digital flexor tendon of the horse forelimb and its relationship with the superficial digital flexor tendon: A plastination, histological, and morphometry study

Abstract

Simple Summary Numerous studies have examined the accessory ligament of the deep digital flexor tendon (AL-DDFT), focusing on both its normal and pathological anatomy. However, limited information is available regarding the precise relationship between the AL-DDFT and its surrounding structures. Clinically, this ligament is often implicated in desmitis and the formation of adhesions, yet the mechanisms driving these pathological changes are not fully understood. While previous investigations have suggested potential contributing factors, detailed descriptive studies are still necessary. In this study, macroscopic, microscopic, and morphometric analyses of the AL-DDFT were carried out. Through dissection and examination of E12 plastinated sections, we provide novel insights into the structural organization and interactions of the AL-DDFT with adjacent tissues. These findings enhance the current understanding of the anatomical and clinical aspects of the AL-DDFT, building upon and integrating previous research.Abstract The accessory ligament of the deep digital flexor tendon (AL-DDFT) plays a crucial role in the stay apparatus of the horse. This study aimed to investigate the anatomical relationship between the AL-DDFT, the superficial digital flexor tendon (SDFT), and other structures in the metacarpal region. Sixteen distal forelimbs from eight horses, aged 1 to 6 years, were evaluated through macroscopic, microscopic, and morphometric analyses, utilizing detailed dissection, E12 plastinated sections, and histological analysis. During lateral dissection, a connection was observed between the AL-DDFT and the SDFT. Histological evaluation revealed that this connection was a fibrous band (FB), extending the common synovial sheath (CSS) to the SDFT, along with associated collagen fibrils of the epiligament and peritenon. Additionally, two distinct forms of the AL-DDFT were identified, Type I and Type II, with Type II showing a greater cross-sectional area (CSA) than Type I. While numerous morphological and morphometric studies have explored the AL-DDFT and related structures, research incorporating plastination-based morphological and histological evaluations remains scarce. The findings provide valuable insights for both the morphological and clinical assessment of structures within the metacarpal region.