Anatomy of the Pelvic Floor

The bones of the pelvis provide the foundation to which all of the pelvic structures are ultimately anchored (Figures 2-1 and 2-2). In the standing position, forces are dispersed to minimize the pressures on the pelvic viscera and musculature and to distribute forces to the bones that are better suited for the long-term, cumulative stresses of daily life. In the upright position, the iliopubic rami are oriented in an almost vertical plane. This orientation directs the pressure of the intraabdominal and pelvic contents toward the bones of the pelvis instead of the muscles and endopelvic fascia attachments of the pelvic floor. The pubic rami are nearly horizontal where they articulate in the midline. The weights of the abdominal viscera and some of the pelvic viscera are inferiorly supported by the bony articulation. Numerous ligaments are attached to the pelvic bones, many of which are used in reconstructive pelvic surgery (Figure 2-3).

Figure 2-1 The pelvic bone consists of the ilium, ischium, and pubis. The ilium is bound to the sacrum at the sacroiliac joints. This anterior aspect of the pelvis shows the pubic arch, symphysis, and obturator foramen from a head-on view.

(From Baggish MS, Karram MM: Atlas of pelvic anatomy and gynecologic surgery, ed 3, St Louis, 2011, Elsevier.)

Figure 2-2 Posterior view of the pelvis is combined with an outlet “looking-in” perspective. The ischial tuberosity, ischial spine, and greater and lesser sacrosciatic notches are best observed from this vantage point. Posterior sacrum highlights include the sacral hiatus, sacral canal, and posterior sacral foramina.

(From Baggish MS, Karram MM: Atlas of pelvic anatomy and gynecologic surgery, ed 3, St Louis, 2011, Elsevier.)

Figure 2-3 Inguinal ligament stretches between the anterior superior iliac spine and the pubic tubercle. From the latter is reflected the lacunar ligament, which forms the medial boundary of the femoral canal. Cooper ligament is a stout structure that clings to the iliopectineal line (see inset). Between the ischial spines and the lateral aspect of the sacrum is the sacrospinous ligament. This ligament also creates the greater and lesser sacrosciatic foramina.

(From Baggish MS, Karram MM: Atlas of pelvic anatomy and gynecologic surgery, ed 3, St Louis, 2011, Elsevier.)

The pelvic floor is made up of muscular and fascial structures that enclose the abdominal-pelvic cavity, the external vaginal opening, and the urethra and rectum (Figures 2-4 and 2-5). The two types of fascial components are parietal and visceral endopelvic fascia. The parietal fascia covers the pelvic skeletal muscles and provides attachment of muscles to the bony pelvis. It is histologically characterized by regular arrangements of collagen. Visceral endopelvic fascia is less discrete and exists throughout the pelvis as a mesh network made of loosely arranged collagen, elastin, and adipose tissue, through which blood vessels, lymphatic vessels, and nerves travel to reach the pelvic organs. Examples of visceral endopelvic fascia are discrete ligaments such as the cardinal and uterosacral ligaments. Figure 2-6 demonstrates the relationship of the vagina to other structures in the pelvis and also illustrates how the uterosacral and cardinal ligaments support the upper vagina.

Figure 2-4 Intact levator ani muscle is arising along the length of the arcus tendineus. The exposed retropubic space is demonstrated, together with the cut edges of the urethra and vagina.

(From Baggish MS, Karram MM: Atlas of pelvic anatomy and gynecologic surgery, ed 3, St Louis, 2011, Elsevier.)

Figure 2-5 Frontal view of the funnel-like levator ani and its relationship to the vulva and superficial muscles of the perineum are illustrated. The levator arises, in part, from the inferior margins of the pubic bone. The artist has superimposed the arcus tendineus (dashed white line) onto the obturator internus and pubic bone.

(From Baggish MS, Karram MM: Atlas of pelvic anatomy and gynecologic surgery, ed 3, St Louis, 2011, Elsevier.)

Figure 2-6 This three-dimensional drawing illustrates the relationship of the vagina to other structures in the pelvis. The lower figure also shows the superimposed outline of the urinary bladder, relative to the vagina. The upper vagina shares support with the uterus and bladder. Principally, the upper vagina consists of the deep cardinal ligament and, to a lesser extent, the uterosacral ligaments. In the upper illustration, the schematically drawn location of a portion of the uterosacral ligaments is attached to the vagina. The lower vagina is clearly supported by the levator ani muscle, anal sphincter, and deep vascular structures located beneath the bulbocavernosus muscle, as well as by the commonly shared connective tissue, smooth muscle, and vessels found in the tissues between the rectum and vagina and, likewise, between the bladder and vagina. Between these anchors, the lateral vaginal wall is not attached and opens into a fat-filled paravaginal space. If the lateral wall is cut and the fat being dissected is removed, then the anatomist will be looking into a retropubic (extraperitoneal) space filled with fat. If the fat is cleaned away, the obturator internus muscle is visible.

(From Baggish MS, Karram MM: Atlas of pelvic anatomy and gynecologic surgery, ed 3, St Louis, 2011, Elsevier.)

The pelvic side walls are made up of the obturator internus and piriformis muscles. The obturator membrane is a fibrous membrane that covers the obturator foramen (Figure 2-7). The obturator internus originates on the inferior margin of the superior pubic ramus and passes through the lesser sciatic foramen to insert onto the greater trochanter of the femur to rotate the thigh laterally. The piriformis is dorsal and lateral to the coccygeus. It extends from the anterior lateral portion of the sacrum to pass through the greater sciatic foramen and to insert onto the greater trochanter. The pelvic diaphragm consists of the levator ani and coccygeus muscles. The levator ani muscles are divided into the puborectalis, pubococcygeus, and iliococcygeus, which are all skeletal muscles. Other skeletal muscles in the pelvic floor include the external anal sphincter, the striated urethral sphincter, and the superficial perineal muscles (e.g., bulbocavernosus, ischiocavernosus, superficial transverse perinei).

Figure 2-7 The large obturator internus muscle covered with tough obturator fascia forms the pelvic sidewall. The arcus tendineus, or white line, is produced by a thickened area of obturator fascia. The levator ani muscle arises from the arcus. The cut edge of the levator is shown on the patient’s right side (viewer’s left side). The left levator has been removed. The piriformis and coccygeus muscles complete the enclosure of the pelvis.

(From Baggish MS, Karram MM: Atlas of pelvic anatomy and gynecologic surgery, ed 3, St Louis, 2011, Elsevier.)

The pelvic diaphragm is a term that has been used to describe the hammocklike structure that these muscles create between the pubic bone from the front and the coccyx from behind. The pelvic diaphragm is attached along the lateral pelvic walls to a thickened linear band of obturator fascia called the arcus tendineus fascia pelvis. This thickened band forms an identifiable line from the ischial spine to the posterior surface of the ipsilateral symphysis pubis. The puborectalis portion of the levator ani originates on the posterior inferior pubic ramus and arcus and passes posteriorly, forming a sling around the vagina, rectum, and perineal body to form the anorectal angle. Some muscle fibers may blend with the muscularis of the vagina, rectum, and external anal sphincter (see Figure 2-5). The pubococcygeus has a similar origin but inserts in the midline onto the anococcygeal raphe and the anterolateral borders of the coccyx. The iliococcygeus originates along the arcus tendineus from the back of the pubis to the ischial spine and inserts on the anococcygeal raphe to form the levator plate. The space through which the rectum, vagina, and urethra pass is called the genital hiatus (see Figure 2-7). The coccygeus muscle, who some would consider as part of the levator ani complex, makes up the posterior part of the pelvic floor and also plays a role in support. It originates on the ischial spine, overlies the sacrospinous ligament, and inserts on the lateral lower sacrum and coccyx. As one ages, the coccygeus becomes thinner and more fibrous, often blending with the sacrospinous ligament. At times, distinguishing the two is difficult because of the fact that they have the same origin and insertion. The coccygeus sacrospinous ligament complex (C-SSL) is a very common anchoring point for a variety of prolapse repairs that are discussed and illustrated throughout this text. Appreciating the close proximity of the many vascular structures and nerves to the C-SSL is extremely important (Figure 2-8). Posterior to the complex are the gluteus maximus muscle and the ischiorectal fossa. The pudendal nerves and vessels lie directly posterior to the ischial spine, and the sciatic nerve lies superior and lateral to the ischial spine. An abundant vascular supply, which includes the inferior gluteal and the hypogastric venous plexus, also lies superior to the ischial spine. The C-SSL complex can be exposed via a posterior perirectal dissection, as well as by anterior paravaginal dissection. The ability of the surgeon to palpate and identify this structure safely is mandatory to avoid significant bleeding or nerve damage.

Figure 2-8 Sagittal section through the pelvis (inset). The muscles enclosing the pelvis include the sidewall muscles; that is, the obturator internus, coccygeus, and piriformis. The white line, or arcus tendineus, stretches between the ischial spine and the lower margin of the pubic bone. The levator ani takes its origin from the thickened obturator internus fascia (the arcus tendineus), as well as from the lower margin of the pubic ramus. The bifurcation of the common iliac vessels is demonstrated. The internal iliac, or hypogastric, vessels supply the pelvic viscera via several branches and tributaries. The hypogastric artery divides into the superoposterior and inferoanterior divisions. From the posterior division, the superior gluteal, lateral sacral, and iliolumbar vessels emanate. The anterior division includes the lateral umbilical, superior and inferior vesicles, obturator, uterine, and vaginal branches. Terminal branches of the anterior division include the inferior gluteal and internal pudendal vessels. The posterior division of the hypogastric artery will lead the dissector to the sacral nerve roots and sciatic nerve. The obturator neurovascular bundle is best exposed by the retraction of the external iliac vein. The lateral umbilical vessels ascend the anterior abdominal wall, supported superficially to the external iliac vessels on either side of the urachus (not shown here).

(From Baggish MS, Karram MM: Atlas of pelvic anatomy and gynecologic surgery, ed 3, St Louis, 2011, Elsevier.)