Mechanisms of Support

The normal axis of the pelvic organs in the standing woman places the vagina and rectum directly over the levator plate. The levator plate and muscles of the pelvic floor therefore support the pelvic organs. The remainder of this section will describe the structures and attachments that keep the pelvic organs in the proper orientation so that they may be supported by the pelvic floor musculature.

The endopelvic fascia is the loose connective tissue network appearance of the retroperitoneum that envelops all of the organs of the pelvis and connects them loosely to the supportive musculature and bones of the pelvis. The term endopelvic fascia is used here to describe the tissues located between the surfaces of the peritoneum, muscles, and pelvic organs. Histologically, it is composed of colla gen, elastin, adipose tissue, nerves, vessels, lymph channels, and smooth muscle. Its properties provide stabilization and support, yet allow for the mobility of the viscera to permit storage of urine and stool, coitus, parturition, and defecation.

Several areas of the endopelvic fascia (and its associated peritoneum) have been named by anatomists. These are really condensations of the endopelvic fascia and not true ligaments: uterosacral ligament, cardinal ligament, broad ligament, mesovarium, mesosalpinx, and the round ligament. The broad ligament, mesovarium, mesosalpinx, and round ligament do not have a role in support of the pelvic organs.

DeLancey5 described vaginal support in three levels (see Figure 4-1.4 in Chapter 4-1). Level I refers to the uterosacral ligament/cardinal ligament complex and is the most cepha-lad supporting structures. Level II support is provided by the paravaginal attachments along the length of the vagina. Level III support describes the most inferior or distal portions of the vagina including the perineum. Each of these areas has a significant role in maintaining pelvic organ support and will be discussed individually. It is, however, important to remember that levels I, II, and III are all connected through continuation of the endopelvic fascia.

Comprising level I support, the cardinal and uterosacral ligaments attach to the cervix from the lateral and posterior sides, respectively, with fibers intermingling. The cardinal ligament blends with the uterosacral ligament and they are difficult, if not impossible, to precisely delineate from one another. Fibers traveling predominately laterally make up the cardinal ligament, whereas fibers going to the sacrum make up the uterosacral ligament. These fibers form a three-dimensional complex attaching the upper vagina, cervix, and lower uterine segment to the sacrum and lateral pelvic sidewalls at the piriformis, coccygeus, and the levator ani and perhaps the obturator internus fascia overlying the ischial spine. Together, the uterosacral/ cardinal ligament complex supports the cervix and upper vagina to maintain vaginal length and keep the vaginal axis nearly horizontal so that it rests on the rectum and can be supported by the levator plate. This keeps the cervix just superior to the level of the ischial spine.

Contiguous with the uterosacral/cardinal ligament complex at the location of the ischial spine is level II support - the paravaginal attachments. These are the connections of the lateral vagina and endopelvic fascia to the arcus tendineus fascia pelvis anteriorly and the arcus tendineus rectovaginalis posteriorly - level II support functions to keep the vagina midline directly over the rectum.

The arcus tendineus fascia pelvis is similar in composition to the arcus tendineus levator ani. It, however, arises from the levator ani fascia rather than that of the obturator internus. Similar to the arcus tendineus levator ani, it originates on the ischial spine; however, as it approaches the pubic symphysis, the arcus tendineus fascia pelvis travels medially and inferiorly to the arcus tendineus levator ani, inserting on the inferior aspect of the superior pubic rami over the origin of the puborectalis muscle. The arcus tendineus fascia pelvis or "white line" is a thickened condensation of the parietal fascia into which the paravaginal endopelvic fascia connects, supporting and creating the anterior lateral vaginal sulci. Furthermore, the axis of both of the arcus tendineus levator ani and the arcus tendineus fascia pelvis are nearly horizontal in the standing woman, creating the normal axis of the vagina. Anteriorly, the endopelvic fascia blends with the vaginal muscularis and is continuous with the supportive structures of the urethra (see Chapter 4-1).

Similar to the anterior paravaginal supports, there are posterior lateral supports as well (Figure 4-1.4 Figure 4-2.7). These fibers blend with the vaginal muscularis anteriorly, rectal muscularis posteriorly, and the perineal body inferiorly. The lateral endopelvic fascia attachments of the posterior vaginal wall do not have significant connections across the midline. Rather, they anchor the posterior lateral vaginal sulci to the ipsilateral levator ani.4

The endopelvic fascia extends from posterior lateral vagina sulci posteriorly around the rectum to attach the vagina to the pelvic floor. The posterior vaginal muscularis is attached through this endopelvic fascia to the fascia of the levator ani laterally at the arcus tendineus rectovagi-nalis.6 The arcus tendineus rectovaginalis represents a condensation of the parietal fascia of the levator ani coursing from the perineal body inferiorly, along the levator ani laterally, where it intersects the midpoint of the arcus tendineus fascia pelvis. The arcus tendineus rectovaginalis is approximately 4 cm in length. The connection to the arcus tendineus rectovaginalis creates the change in axis toward vertical of the distal vagina.

Figure 4-2.7. Photomicrograph of posterior wall attachments. Note the fibers of the endopelvic fascia that are attached (outlined by dots) to the lateral sulcus of the posterior vaginal wall. OI, obturator internus muscle; LAM, levator ani muscle. (Reprinted from American Journal of Obstetrics and Gynecology,Vol 180,JOL DeLancey,Structural anatomy of the posterior pelvic compartment as it relates to rectocele, p 815-823,© 1999 Mosby,with permission from Elsevier)

Figure 4-2.7. Photomicrograph of posterior wall attachments. Note the fibers of the endopelvic fascia that are attached (outlined by dots) to the lateral sulcus of the posterior vaginal wall. OI, obturator internus muscle; LAM, levator ani muscle. (Reprinted from American Journal of Obstetrics and Gynecology,Vol 180,JOL DeLancey,Structural anatomy of the posterior pelvic compartment as it relates to rectocele, p 815-823,© 1999 Mosby,with permission from Elsevier)

Figure 4-2.8. Perineal attachments of the perineal membrane to the inferior pubic rami and direction of tension on fibers uniting through the perineal body (arrows).(Reprinted from American Journal of Obstetrics and Gynecology,Vol 180, JOL Delancey, © Structural anatomy of the posterior pelvic compartment as it relates to rectocele, p 815-823 1999 Mosby, with permission from Elsevier)

Figure 4-2.8. Perineal attachments of the perineal membrane to the inferior pubic rami and direction of tension on fibers uniting through the perineal body (arrows).(Reprinted from American Journal of Obstetrics and Gynecology,Vol 180, JOL Delancey, © Structural anatomy of the posterior pelvic compartment as it relates to rectocele, p 815-823 1999 Mosby, with permission from Elsevier)

Level III support is provided by the perineal body, perineal membrane, superficial and deep perineal muscles, and endopelvic fascia. These structures support and maintain the normal anatomic position of the distal one-third of the vagina. The condensation of connective tissue at the point of convergence of the level III structures, distal rectum, levator ani, and distal level II attachments forms the perineal body. The perineal body is critical for support of the lower part of the vagina and proper function of the anal canal. The perineal membrane anchors the perineal body and distal vagina laterally and anteriorly to the ischiopubic rami (Figure 4-2.8). According to DeLancey,4 "When the distal rectum is subjected to increased force directed caudally, the fibers of the perineal membrane become tight and resist further displacement." Separation of the perineal body from the perineal membrane results in perineal decent and can contribute to defecatory dysfunction.

The three levels of support are connected and interdependent. Level III structures are connected to the endopelvic fascia that surrounds the vagina and rectum and are therefore continuous with level II support. Level II support is connected to level I support through the confluence of the lateral endopelvic fascia attachments and the uterosacral ligament/cardinal ligament complex. Adequate support at all levels maintains the pelvic organs in their normal anatomic positions.

When the vagina, bladder, and rectum are kept in the horizontal plane over the levator plate and pelvic floor muscles, intraabdominal and gravitational forces are applied perpendicular to the vagina and pelvic floor while the pelvic floor musculature counters those forces with its constant tone. It is this horizontal position and support by the levator ani that maintain pelvic organ support. With proper tone of the pelvic floor muscles (levator ani), the stress is relieved from the lateral paravaginal attachments. Furthermore, in times of acute stress, such as a cough or sneeze, there is a reflex contraction of the pelvic floor musculature countering and further stabilizing the viscera. The genital hiatus responds by narrowing to maintain level III support. With pelvic floor weakness, such as with neuropathic injury or mechanical muscular damage, the endopelvic fascia then becomes the primary mechanism of support. Over time,this stress can overcome the endopelvic fascial attachments and result in loss of the normal anatomic position through breaks, stretching, or attenuation of endopelvic fascia supports. This can result in changes in the vector forces applied to the viscera and may lead to pelvic organ prolapse and/or dysfunction. Recreation of these supportive connections and proper position of the organs while maintaining adequate vaginal length to keep the vaginal apex in a natural position should be the goal of pelvic reconstructive surgery.

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