Found deep to the anterior and posterior triangles, this broad muscular sling provides substantial support to the pelvic viscera. The pelvic diaphragm is composed of the levator ani and the coccygeus muscles. The levator ani, in turn, contains the pubococcygeus, puborectalis, and iliococcygeus muscles. The pubococcygeus muscle is also termed the pubovisceral muscle and is subdivided based on points of insertion and function. These include the pubovaginalis, puboperinealis, and puboanalis muscles, which insert into the vagina, perineal body, and anus, respectively (Kearney, 2004).
Vaginal birth conveys signiicant risk for damage to the levator ani or to its innervation (DeLancey, 2003; Weidner, 2006). Evidence supports that levator ani avulsion may predispose women to greater risk of pelvic organ prolapse (Dietz, 2008; Schwertner-Tiepelmann, 2012). For this reason, current research eforts are aimed at minimizing these injuries.
his triangle contains the ischioanal fossae, anal canal, and anal sphincter complex, which consists of the internal anal sphincter, external anal sphincter, and puborectalis muscle. Branches of the pudendal nerve and internal pudendal vessels are also found within this triangle.
Ischioanal Fossae. Also known as ischiorectal fossae, these two fat-filled wedge-shaped spaces are found on either side of the anal canal and comprise the bulk of the posterior triangle (Fig. 2-7). Each fossa has skin as its supericial base, whereas its deep apex is formed by the junction of the levator ani and obturator internus muscles. Other borders include: laterally, the obturator internus muscle fascia and ischial tuberosity; inferomedially, the anal canal and sphincter complex; superomedially, the inferior fascia of the downwardly sloping levator ani; posteriorly, the gluteus maxim us muscle and sacrotuberous ligament; and anteriorly, the inferior border of the anterior tri angle.
The fat found within each fossa provides support to surrounding organs yet allows rectal distention during defecation and vaginal stretching during delivery. Clinically, injury to vessels in the posterior triangle can lead to hematoma formation in the ischioanal fossa, and the potential for large accumulation in these easily distensible spaces. Moreover, the two fossae communicate dorsally, behind the anal canal. This can be especially important because an episiotomy infection or hematoma may extend from one fossa into the other.
Anal Canal. his distal continuation of the rectum begins at the level of levator ani attachment to the rectum and ends at the anal skin. Along this 4-to 5-cm length, the mucosa consists of columnar epithelium in the uppermost portion. However, at the pectinate line, also termed dentate line, simple stratified squamous epithelium begins and continues to the anal verge. At the verge, keratin and skin adnexa join the squamous epithelium.
The anal canal has several tissue layers (see Fig. 2-7). Inner layers include the anal mucosa, the internal anal sphincter, and an intersphincteric space that contains continuation of the rectum's longitudinal smooth muscle layer. An outer layer contains the puborectalis muscle as its cephalad component and the external anal sphincter caudally.