Pelvic Wall 2 Lecture – Anatomy Lectures – MBBS Lectures

• The abdominopelvic cavity extends superiorly into the thoracic cage and inferiorly into the pelvis, so that its superior and inferior parts are relatively protected
• The funnel-shaped pelvic cavity is the inferoposterior part of the abdominopelvic cavity.
• The pelvic cavity is limited inferiorly by the musculofascial pelvic diaphragm, forming a bowl-like pelvic floor.

• The pelvic cavity contains the terminal parts of the ureters, the urinary bladder, rectum, pelvic genital organs, blood vessels, lymphatics, and nerves
• It also contains loops of small intestine (mainly ileum) and, large intestine (appendix and transverse and/or sigmoid colon).

Walls of pelvic cavity

• Bones and ligaments that are partly lined with muscles covered with fascia and parietal peritoneum form the walls of the pelvis.
• The pelvis has anterior, posterior, and lateral walls and an inferior wall or floor.

Anterior Pelvic Wall

• The anterior pelvic wall is the shallowest wall and is formed by:

1. Bodies of the pubic bones
2. Pubic rami
3. Symphysis pubis

Posterior Pelvic Wall

• The posterior pelvic wall is extensive and is formed by:

1. Sacrum
2. Coccyx 
3. Piriformis muscle and their covering of parietal pelvic fascia

Piriformis

Lateral Pelvic Wall

• The lateral pelvic wall is formed by:

1. Part of the hip bone below the pelvic inlet
2. Obturator membrane
3. Sacrotuberous and sacrospinous ligaments
4. Obturator internus muscle and its covering fascia.

Obturator Membrane:

• The obturator membrane is a fibrous sheet that almost completely closes the obturator foramen, leaving a small gap, the obturator canal, for the passage of the obturator nerve and vessels as they leave the pelvis to enter the thigh.

Obturator fascia:

• This fascia lines the internal surface of the obturator internus muscle which is thickened centrally as a tendinous arch (archous tendinous/white line) that provides attachment for the pelvic diaphragm

Inferior Pelvic Wall (Pelvic Floor)

•The floor of the pelvis supports the pelvic viscera and is formed by the pelvic diaphragm and associated fascia.

•The pelvic floor stretches across the pelvis and divides it into the main pelvic cavity above, which contains the pelvic viscera, and the perineum below.

PELVIC DIAPHRAGM:

•The pelvic floor is formed by the bowl- or funnel-shaped pelvic diaphragm, which consists of the coccygeus and levator ani muscles and the fascias covering the superior and inferior aspects of these muscles

•It is incomplete anteriorly to allow passage of the urethra in males and the urethra and the vagina in females

Levator ani:

• The levator ani muscle is a wide, thin sheet forming the larger, more anterior part of the pelvic diaphragm.
• It has a linear origin from the back of the body of the pubis, a tendinous arch formed by a thickening of the fascia covering the obturator internus, and the spine of the ischium.

Its insertion is as follows:

1. Anterior fibers:

                The levator prostatae or sphincter vaginae form a sling around the prostate gland or vagina and insert into a mass of fibrous tissue, called the perineal body, in front of the anal canal.

2. Intermediate fibers:

                The puborectalis forms a sling around the junction of the rectum and anal canal.

                The pubococcygeus passes posteriorly to insert into a small fibrous mass, called the anococcygeal body, between the tip of the coccyx and the anal canal.

3. Posterior fibers:

                The iliococcygeus inserts into the anococcygeal body and the coccyx.

• The pelvic diaphragm thus stretches between the anterior, the lateral, and the posterior walls of the lesser pelvis, giving it the appearance of a hammock suspended from these attachments, closing much of the ring of the pelvic girdle.
• An anterior gap between the medial borders of the levator ani muscles of each side—the urogenital hiatus—gives passage to the urethra and, in females, the vagina

Actions:

• Dynamic floor
• Tonically contracted most of the time
• Actively contracted during strenuous activity
• Maintaining fecal urinary continence

Coccygeus muscle:

• The coccygeus muscles arise from the lateral aspects of the inferior sacrum and coccyx, their fleshy fibers lying on and attaching to the deep surface of the sacrospinous ligament

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