Handa 9781496386441 Full Sample Chap 1

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SECTION I  Preparing for Surgery

I encircling ring around the anal canal. It is responsible for the characteristic radially oriented folds in the peri- anal skin. The superficial part attaches to the coccyx posteriorly, contributing to the anococcygeal body, and sends a few fibers into the perineal body anteriorly. The superficial part of the external anal sphincter forms the bulk of the anal sphincter when seen separated in third-degree midline obstetric tears. The fibers of the deep part generally encircle the rectum and blend indis- tinguishably with the puborectalis, which forms a loop under the dorsal surface of the anorectum and which is attached anteriorly to the pubic bone (see FIG. 1.19 ). The internal anal sphincter is a thickening in the cir- cular smooth muscle of the anal wall. It lies just inside the external anal sphincter and is separated from it by a visible intersphincteric groove. It extends downward inside the external anal sphincter to within a few mil- limeters of the external sphincter’s caudal extent. The internal sphincter can be identified just outside the anal submucosa in repair of a chronic fourth-degree lac- eration as a rubbery white layer that is often erroneously been referred to as fascia during obstetrical repair of fourth-degree laceration. The longitudinal smooth muscle layer of the bowel, along with some fibers of the levator ani, separates the external and internal sphincters as they descend in the intersphincteric groove. Levator Ani Muscles The typical depiction of the levator ani muscles in anat- omy textbooks is unfortunately distorted by the extreme

abdominal pressures generated during embalming that forces them downward. Many of these illustrations therefore fail to give a true picture of the horizon- tal nature of this strong supportive shelf of muscle. Examination of the normal standing patient is the best way to appreciate the nature of this closure mechanism, because the lithotomy position causes some relaxation of the musculature. During routine pelvic examination of the nullipara, the effectiveness of this closure can be appreciated, because it is often difficult to insert a spec- ulum if the muscles are contracted. The bony pelvis is spanned by the levator muscles of the pelvic diaphragm. This diaphragm consists of two components: (a) a thin horizontal shelflike layer formed by the iliococcygeus muscle and (b) a thicker “U”-shaped sling of muscles that surround the levator hiatus that include the pubococcygeus and puborectalis muscles ( FIG. 1.20 ). The open area within the U (through which the urethra, vagina, and rectum pass) is called the leva- tor hiatus, and the portion of the hiatus anterior to the perineal body is called the urogenital hiatus. The pubococcygeus muscle arises from a thin apo- neurotic attachment to the inner surface of the pubic bone and inserts to the distal lateral vagina, perineal body, and anus. Some fibers also attach to the superior surface of the coccyx, hence the name pubococcygeus. Because the majority of the attachments, however, are to the vagina and anus, the term pubovisceral muscle is replacing this older term. The puborectalis muscle is distinct from the pubo- coccygeus muscle and lies lateral to it (see FIG. 1.20 ).

Pubic symphysis

Superior pubic ramus

Urethra

Tendinous arch of levator ani

Vagina Inferior pubic ramus

Acetabulum

Anus

Ischial tuberosity

Ischial spine Copyright © 2019 Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited.

Obturator internus m.

Iliococcygeus m. Pubococcygeus m.

Coccygeus m.

Gluteus maximus m.

Pelvic diaphragm

Piriformis m.

FIGURE 1.20  Anatomy of the pelvic floor, perineal view.

Coccyx

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