3D intermittent loop structure of external anal sphincter muscle complex observed through consequential dissection of pelvic floor

Objective To analyze the contraction direction and distribution of external anal sphincter muscle complex by observing its 3D intermittent loop structure through consequential dissection of pelvic floor. Methods Intact external anal sphincter muscle complex samples were taken from 18 cadavers without anorectal disease and 1 neonate cadaver with congenital anorectal malformation using self-designed consequential dissection method of pelvic floor.The characteristics of direction and distribution of external anal sphincter muscle complex were observed under magnifier and anatomic microscope. Results The following were observed,including intact pelvic and its associated structures,pelvic and its associated muscles,semi-open pelvic,pelvic muscles completely isolated from pelvic bone structure,intact external anal sphincter muscle complex,intermittent loop fibers of external anal sphincter muscle complex crossing posterior to the anal canal with small U image lateral to the anal canal,strong and dense muscle fibers crossing anterior to the anal canal with anterior paries loosely connected,slim and loose posterior fibers filled with connective fibers and tightly connected with anal canal posterior wall. Conclusion Intact external anal sphincter muscle complex samples can be taken by consequential dissection of pelvic floor.Intermittent loop fibers of external anal sphincter muscle complex surround the anal canal anterior wall and then cross at the anal canal posterior wall with its lateral muscle bundles terminated at the anal canal walls characterized by small U fibers and compression on the anal canal walls.The contraction of intermittent loop fibers depend on the end action point of muscles tightly attached to the muscle fibers and the anal canal posterior wall.