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Anatomy of Pelvic Floor Dysfunction Marlene M. Corton, MD NORMAL PELVIC ORGAN SUPPORT The main support of the uterus and vagina is provided by the interaction between the levator ani (LA) muscles (Fig. 1) and the connective tissue that attaches the cervix and vagina to the pelvic walls (Fig. 2). 1 The relative contribution of the connective tissue and levator ani muscles to the normal support anatomy has been the subject of controversy for more than a century. 2–5 Consequently, many inconsistencies in termi- nology are found in the literature describing pelvic floor muscles and connective tissue. The information presented in this article is based on a current review of the literature. LEVATOR ANI MUSCLE SUPPORT The LA muscles are the most important muscles in the pelvic floor and represent a crit- ical component of pelvic organ support (see Fig. 1). The normal levators maintain a constant state of contraction, thus providing an active floor that supports the weight of the abdominopelvic contents against the forces of intra-abdominal pressure. 6 This action is thought to prevent constant or excessive strain on the pelvic ‘‘ligaments’’ and ‘‘fascia’’ (Fig. 3A). The normal resting contraction of the levators is maintained by the action of type I (slow twitch) fibers, which predominate in this muscle. 7 This baseline activity of the levators keeps the urogenital hiatus (UGH) closed and draws the distal parts of the urethra, vagina, and rectum toward the pubic bones. Type II (fast twitch) muscle fibers allow for reflex muscle contraction elicited by sudden increases in abdominal pressure (Fig. 3B). The levators can also be voluntarily contracted as with Kegel exercises. Relaxation of the levators occurs only briefly and intermittently during the processes of evacuation (voiding, defecation) and parturition. The LA muscle is a complex unit that consists of several muscle components with different origins and insertions, and therefore, different functions. Knowing the precise Division of Female Pelvic Medicine and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center 5323 Harry Hines Boulevard, Dallas, Texas 75390 9032, USA E-mail address: [email protected]KEYWORDS Pelvic floor Levator ani muscles Pelvic connective tissue Ureter Retropubic space Prevesical space Obstet Gynecol Clin N Am 36 (2009) 401–419 doi:10.1016/j.ogc.2009.09.002 obgyn.theclinics.com 0889-8545/09/$ – see front matter ª 2009 Elsevier Inc. All rights reserved.
