Levator ani

Where is the levator ani?

With the coccygeus (ischiococcygeus) it forms the pelvic diaphragm, which makes up most of the floor of the pelvic cavity. Its fibers reach from the pubis in front back to the coccyx. (OpenStax A&P 2e, 11.4; StatPearls, Pelvic Floor; Gray 1918, 6e. Muscles of the Pelvis)

Just below it lies the perineum, the diamond-shaped region at the outlet of the pelvis. Its deep boundaries are the pubic arch in front, the tip of the coccyx behind, and on each side the rami of the pubis and ischium and the sacrotuberous ligament. (OpenStax A&P 2e, 11.4; Gray 1918, Muscles of the Perineum; StatPearls, Pelvic Floor)

What are the parts of the levator ani?

StatPearls describes three muscles that merge to form it: the puborectalis, the pubococcygeus and the iliococcygeus. (StatPearls, Levator Ani Muscle)

The iliococcygeus arises from the tendinous arch of the levator ani, a thickening of the fascia over the obturator internus. Its back fibers insert into the coccyx and its front fibers into the anococcygeal raphe. (StatPearls, Levator Ani Muscle)

The pubococcygeus arises from the back of the inferior pubic rami and the front of the obturator fascia and runs back to the anococcygeal raphe. The puborectalis arises from the lower pubic symphysis and loops behind the rectum to meet its partner, forming a sling. (StatPearls, Levator Ani Muscle)

What does the levator ani do?

Its main job is to support and raise the pelvic organs. It also helps hold intra-abdominal pressure and aids defecation and urination; part of it helps position the baby’s head in childbirth. (OpenStax A&P 2e, 11.4; StatPearls, Levator Ani Muscle; Gray 1918, 6e. Muscles of the Pelvis)

It narrows the lower end of the rectum and the vagina. The puborectalis sling works with the internal and external anal sphincters in defecation, and the pubococcygeus controls the flow of urine. (OpenStax A&P 2e, 11.4; StatPearls, Levator Ani Muscle; Gray 1918, 6e. Muscles of the Pelvis)

It moves with each breath, relaxing as you breathe in and contracting as you breathe out. The pelvic diaphragm drops as the respiratory diaphragm descends. (StatPearls, Levator Ani Muscle and Pelvic Floor)

Which nerves and vessels supply the levator ani?

Its main nerve supply comes from S3 and S4, with fibers from S2 and the coccygeal plexus. The nerve to levator ani, from the fourth sacral nerve, and the inferior rectal branch of the pudendal nerve both reach it. (StatPearls, Levator Ani Muscle)

Branches of the inferior gluteal, inferior vesical and internal pudendal arteries supply it. A 2012 study found a band of connective tissue in the ischioanal fossa that joins it to the gluteus maximus. (StatPearls, Levator Ani Muscle; FMA, Internal pudendal artery)

How does the levator ani vary?

MRI studies in women have found parts of it thinned or missing. With age in women, the genital hiatus widens and the back of the puborectalis thins. (StatPearls, Levator Ani Muscle and Pelvic Floor)

Where the sources differ

OpenStax describes the levator ani as two muscles, the pubococcygeus and the iliococcygeus. StatPearls’ levator ani article counts three, adding the puborectalis, and its pelvic floor article puts the coccygeus in the same complex. (OpenStax A&P 2e, 11.4; StatPearls, Levator Ani Muscle and Pelvic Floor)

StatPearls’ levator ani article has the iliococcygeus arising from the tendinous arch of the levator ani, the pubococcygeus from the back of the inferior pubic rami and the obturator fascia, and the puborectalis from the lower pubic symphysis, with insertion on the coccyx and anococcygeal raphe. Its pelvic floor article has the iliococcygeus and pubococcygeus arising from the pectineal line of the pubis and the obturator internus fascia and the puborectalis from the inferior pubic ramus. It gives the insertion as the coccyx, ischial spine, sacrum and urogenital diaphragm. (StatPearls, Levator Ani Muscle and Pelvic Floor)