Muscles of the pelvic diaphragm are the levator ani and coccygeus muscles. These muscles are both the roof of the perineum and the floor of the pelvis.
Pelvic diaphragm, superior view, female. All of the viscera have been removed to reveal the muscles forming the pelvic floor, with apertures for the rectum/anus, vagina, and urethra. The most medial and largest muscle in this area is the pubococcygeus, with its subdivisions puborectalis and pubovaginalis shown as well. Further posterior, on each side, is the iliococcygeus muscle. The posterior margin of this muscle is at the level of the sacrospinous ligament, with which the coccygeus muscle is often blended. The iliococcygeus muscle is also unique in originating from the ischial spine and along the fibrous arcus tendineus, on the medial surface of the obturator internus muscle. The piriformis muscle appears to “fill in” the gap between the posterior edge of the coccygeus and the sacrum but is not a true pelvic floor muscle.
LEVATOR ANI MUSCLE
The levator ani muscle originates anteriorly from the body of the pubis, the tendinous arch, and the ischial spine. The four components of this muscle are listed in Table.
The nerve supply includes branches of the third, fourth, and fifth sacral nerves, and the inferior rectal nerves. The function is to elevate the pelvic floor, increase intraabdominal pressure during forced respiration, and assist in defecation and vomiting.
Components of the Levator Ani Muscle
|Pubovaginalis||Pubic bone||Perineal body||Constriction of the vagina|
|Puborectalis||Pubic bone||Posterior rectum||Sphincter of anal canal|
|Pubococcygeus||Tendon of obturator fascia||Anococcygealligament||Constriction of the anal canal|
|lliococcygeus||Tendon of obturator fascia||Anococcygealligament||Constriction of the anal canal|
The coccygeus originates from the ischial spine and inserts into the lower border of the sacrum and coccyx. This muscle tends to be fibrous and is incorporated in the sacrospinous ligament. It is supplied by the fifth sacral nerve and has no significant function.
The obturator internus arises from the medial, inferior, and lateral margins of the obturator foramen and inserts into the medial side of the greater trochanter of the femur. It is covered by the obturator fascia, which is thickened to form the tendinous arch for the attachment of the levator ani muscle. The fascia, as previously mentioned, forms the pudendal canal. Its function is the same as that of the piriformis muscle.
The piriformis originates from the second, third, and fourth segments of the sacrum, leaving the pelvis through the greater sciatic foramen, and is inserted into the upper border of the greater trochanter of the femur. It laterally rotates and abducts the hip.