Pelvic floor functional anatomy

Biomechanical analysis of pelvic floor disorders depends on precise understanding of geometry, attachment points, material properties, and loading conditions of pelvic floor structures. The pelvic organs are supported by combined actions of the levator ani muscles, perineal structures, and the connective tissues that attach the organs to the pelvic sidewalls. This arrangement divides the pelvis into anterior and posterior compartments. In the upper portion of this system (Level I), the attachments are relatively long mesenteries (cardinal and uterosacral ligament). The mid-vagina in Level II is more directly attached to the pelvic walls. Distally (Level III), the vagina is fused to the levator ani, perineal membrane, and perineal body, which surround and close the urogenital hiatus. When hiatal closure is normal, there is little loading on the Level I and II structures. With birth-related damage, the organs are pushed downward through the hiatus, Level I structures lengthen, and Level II connections fail.