INTRODUCTION
The physiological function of the human wrist is strictly dependent on the complex anatomy of the carpal bones and the ligaments providing stability to these bones (Andersson, 2017). The human scapholunate interosseous ligament (SLIL) is a C-shape structure connecting the scaphoid and lunate carpal bones, and it is considered as the primary stabilizer of the scapholunate joint (Johnson et al., 2013). SLIL disruption due to trauma or degeneration is considered the most common cause of carpal instability, which can significantly compromise hand function and lead to wrist arthrosis (Kitay & Wolfe, 2012; Wolff & Wolfe, 2016). The regenerative capability of the human SLIL is very limited, and injuries in this structure cannot heal by themselves and typically require surgical treatment (Mullikin et al., 2020). Although, numerous surgical procedures have been described (Lui et al., 2019; Mullikin et al., 2020), reconstruction of the dorsal component of the SLIL is the usual surgical treatment for SLIL injuries, underestimating the biomechanical role of the membranous and palmar portions of this structure (Naqui et al., 2018).
Despite its key role in carpal physiology, the exact structure and composition of the human SLIL are not fully understood. The gross morphology of the SLIL was originally defined by Berger and cols. (Berger, 1996), who described three major zones in the human SLIL: the dorsal, membranous, and palmar regions. The dorsal region is transversely oriented, whereas the palmar region is oblique, allowing significant relative movement between the two bones (Sokolow & Saffar, 2001). Numerous reports focused on the study of the SLIL from the anatomical, kinematical and biomechanical standpoints (Kitay & Wolfe, 2012; Rajan & Day, 2015; Wolff & Wolfe, 2016).
Histologically, the human SLIL is thought to be composed of collagen fascicles infiltrated by loosely organized connective tissue, as it is the case of most other intraarticular ligaments, although the SLIL could also share some similarities with human fibrocartilage (Berger, 1996; Sokolow & Saffar, 2001). However, the detailed histological structure of the human SLIL remains to be elucidated.
In the present work, we carried out a comprehensive histological characterization of the human SLIL using an array of histochemical and immunohistochemical methods in order to determine the main extracellular matrix molecules and cells which form part of this ligament.