Pelvic Walls & Diaphragm

Pelvic Girdle Femur

Key Points:

The muscles of the pelvis form a bowl that provides structure and support for the pelvic organs.
Two muscles form the pelvic walls: Obturator internus and piriformis.

Obturator internus:

Originates on the obturator membrane and ischiopubic ramus of the pelvis Inserts on the greater trochanter of the femur.
Obturator internus acts on the femur and forms the lateral walls of the pelvis.
The fascia that covers obturator internus thickens to form the tendinous arch of levator ani.
Obturator canal is an opening in the antero-superior border of the muscle; the obturator nerve, artery, and vein pass through this small opening.

Piriformis:

Originates on the anterior surface of the sacrum
Inserts on the greater trochanter of the femur
It forms the posterolateral wall of the pelvis (the biomechanical functions of obturator internus and piriformis are described in a separate tutorial).

Pelvic diaphragm

Lines the floor of the pelvis: Coccygeus and Levator ani (which is subdivided further).

Coccygeus:

Originates on the ischial spine and sacrospinous ligament
Inserts on the lateral margin of the coccyx and the sacrum
It supports the pelvic organs and pulls the coccyx anteriorly after defecation or parturition.

Levator ani = 3 muscles that support the pelvic organs.

– Originates on the tendinous arch of levator ani and the ischial spine – Inserts on the coccyx and anococcygeal ligament at the midline.

– Originates on the body of the pubic bone – Inserts on the coccyx and anococcygeal ligament.

– Originates on the body of the pubic bone – Inserts into the puborectal sling at the midline.

– Posteriorly, the anorectal hiatus (aka, anal aperture/opening). – Anteriorly, the urogenital hiatus, though which the vagina and/or urethra pass.

Misc notes:

Anococcygeal ligament connects right and left sides of iliococcygeus and pubococcygeus at the midline.

Pelvic Girdle