Chapter 2: The Pelvic Floor

THE PELVIC FLOOR

The pelvic floor (Fig. 2-1) is a muscular diaphragm that separates the pelvic cavity above from the perineal space below. It is formed by the levator ani and coccygeus muscles and is covered completely by parietal fascia.

The urogenital hiatus is an anterior gap through which the urethra and vagina pass. The rectal hiatus is posterior, and through which the rectum and anal canal pass.

PELVIC FLOOR FUNCTIONS

1. The pelvic floor supports the pelvic viscera in humans

2. To build up effective intra-abdominal pressure, the muscles of the diaphragm, abdominal wall, and pelvic floor must contract together

3. During parturition, the pelvic floor helps the anterior rotation of the presenting part and directs it downward and forward along the birth passage

PELVIC FLOOR MUSCLES

1. Levator ani, each composed of two muscles:

   1. Pubococcygeus, which has three divisions: pubovaginalis, puborectalis, and pubococcygeus proper

   2. Iliococcygeus

   3. Coccygeus (ischiococcygeus)

Levator Ani Muscle

The levator ani muscle has a lateral origin and a central insertion, where it joins with the corresponding muscle from the other side. The direction of the muscle from origin to insertion is inferior and medial. The origin of each levator ani is from the:

1. Posterior side of the pubis

2. Arcuate tendon of the pelvic fascia (the white line of the pelvic fascia)

3. Pelvic aspect of the ischial spine

The insertion, from anterior to posterior, is into:

1. Vaginal walls

2. Central point of the perineum

3. Anal canal

4. Anococcygeal body

5. Lateral border of the coccyx

Pubococcygeus Muscle

The pubococcygeus is the most important, most dynamic, and most specialized part of the pelvic floor. It lies in the midline; is perforated by the urethra, vagina, and rectum; and is often damaged during delivery. It originates from the posterior side of the pubis and from the white line of the pelvic fascia anterior to the obturator canal. The muscle passes posterior and medially in three sections: (1) pubovaginalis, (2) puborectalis, and (3) pubococcygeus proper.

Pubovaginalis Muscle

The most medial section of the pubococcygeus is shaped like a horseshoe and is open anteriorly. The fibers make contact and blend with the muscles of the urethral wall, after which they form a loop around the vagina. They insert into the sides and back of the vagina and into the central point of the perineum.

The principal function of the pubovaginalis is to act as a sling for the vagina. Since the vagina helps to support the uterus and appendages, bladder and urethra, and rectum, this muscle is the main support of the female pelvic organs. Tearing ...