A unified pelvic floor conceptual model for studying morphological changes with prolapse, age, and parity

Several two-dimensional and three-dimensional measurements have been used to assess changes in pelvic floor structures and shape. These include assessment of urogenital and levator hiatus dimensions, levator injury grade, levator bowl volume, and levator plate shape. We argue that each assessment reflects underlying changes in an individual aspect of the overall changes in muscle and fascial structures. Vaginal delivery, aging, and interindividual variations in anatomy combine to affect pelvic floor structures and their connections in different ways. There is presently no unifying conceptual model that permits evaluation of how these many measures relate to one another or that reflects overall pelvic floor structure and function. The aim of this article, therefore, is to describe a unified pelvic floor conceptual model to better understand how the above changes to the pelvic floor structures and their biomechanical interactions affect pelvic organ support with vaginal birth, prolapse, and age. In this model, the pelvic floor is comprised of five key anatomical structures: the 1) pubovisceral, 2) puborectal, and 3) iliococcygeal muscles with their superficial and inferior fascia; 4) the perineal membrane/body; and 5) the anal sphincter complex. Schematically, these structures are considered to originate from pelvic sidewall structures and meet medially at important connection points that include the anal sphincter complex, perineal body, and anococcygeal raphé. The pubovisceral muscle contributes primarily to urogenital hiatus closure, while the puborectal muscle is mainly related to levator hiatus closure, although each contributes to the other. Dorsally and laterally, the iliococcygeal muscle forms a shelf-like structure in women with normal support that spans the remaining area between these medial muscles and attachments to the pelvic sidewall. Other features include the levator plate, bowl volume, and anorectal angle. The pelvic floor conceptual model integrates existing observations and points out evident knowledge gaps in how parturition, injury, disease, and aging can contribute to changes associated with pelvic floor function caused by the detachment of one or more important connection points or pubovisceral muscle failure.