Purpose: Understanding the muscular structure of the anal canal is crucial for the diagnosis and treatment of anorectal diseases. Treitz muscle is a vital yet poorly understood component. It supports the anal venous plexus and contributes to anal cushion formation. However, its anatomical details remain unclear, and various theories suggest different origins for its muscle bundles, which affects our understanding of the pathophysiology of hemorrhoids. In this study, we sought to clarify the origin and localization of Treitz muscle to provide an anatomical foundation for understanding anal function. Methods: In this descriptive cadaveric study of 11 cadavers, we performed macroscopic examinations and immunohistological analyses on tissues from the anterior, lateral, and posterior walls of the anal canal. The origin and localization of Treitz muscle were qualitatively evaluated. Results: Treitz muscle is a smooth muscle formed by a directional change in the muscle bundles of the internal anal sphincter, running longitudinally along its surface. A shift in the direction of muscle bundles originating from the internal anal sphincter, giving rise to Treitz muscle, was frequently observed in the anterolateral wall of the anal canal. Conclusion In summary, Treitz muscle, a smooth muscle extending from the internal anal sphincter, is considered part of the muscularis propria. Its directional shift was localized to the anterolateral wall, indicating that Treitz muscle is not uniformly distributed around the anal canal. This site-specific localization may influence the risk of hemorrhoids or cancer invasion depending on its anatomical position.

Anterior talofibular ligament (ATFL) injuries are the most common cause of ankle sprains. To ensure anatomically accurate surgery and ultrasound imaging of the ATFL, anatomical knowledge of the bony landmarks around the ATFL attachment to the distal fibula is required. The purpose of the present study was to anatomically investigate the ATFL attachment to the fibula with respect to bone morphology and attachment structures. First, we analyzed 36 feet using microcomputed tomography. After excluding 9 feet for deformities, the remaining 27 feet were used for chemically debrided bone analysis and macroscopic and histological observations. Ten feet of living specimens were observed using ultrasonography.We found that a bony ridge was present at the boundary between the attachments of the ATFL and calcaneofibular ligament (CFL) to the fibula. These two attachments could be distinguished based on a difference in fiber orientation. Histologically, the ATFL was attached to the anterodistal part of the fibula via fibrocartilage anterior to the bony ridge indicating the border with the CFL attachment. Using ultrasonography in living specimens, the bony ridge and hyperechoic fibrillar pattern of the ATFL could be visualized. We established that the bony ridge corresponded to the posterior margin of the ATFL attachment itself. The ridge was obvious, and the superior fibers of the ATFL have directly attached anteriorly to it. This bony ridge could become a valuable and easy-to-use landmark for ultrasound imaging of the ATFL attachment if combined with the identification of the fibrillar pattern of the ATFL.