Kathy Dooley: The Iliacus

Iliacus comes from the iliac fossa. That’s this deep fossa here. I want you to feel that for yourselves.

Find that ASIS we found earlier talking about the obliques. Go past these obliques, and gently dig your hand underneath that, just medial and deep.

For those of us who sit a lot, we might feel this to be a little tender. For those of us who have intra-abdominal pressure-building problems, we feel the other side.

See if they are equal. Maybe. Maybe, not equal.

This iliac fossa is pretty expansive. This muscle attaches to this area. Does the psoas attach to this area? No. Where does psoas attach?

T12, all the way down to L4, the body’s intervertebral disc, completely bypasses the pelvis for the most part to co-insert with the iliacus. We’ll talk about the in a second.

They do not come from the same place up top, making them very different.

The iliacus is also attached to something the psoas doesn’t. It attached to this thing called the “iliolumbar ligament.” The quadratus lumborum muscle also attaches to it.

I did a makeshift one to show you, because Dr. Jake doesn’t want to be dissected today.

It usually goes from L4 and L5, transverse processes. It’s coming down and around to insert onto the iliac crest here. This particular ligament, although extremely difficult to palpate unless you use a scalpel—this particular ligament has a massive attachment at the anterior layer of thoracolumbar fascia.

What do we know about this deep layer of thoracolumbar fascia? What did we learn today with that?

It’s attached to the internal abdominal oblique. The intrinsic muscles, as Dr. Anna described, that are exhalation muscles have to attach to that in order to be called “intrinsic muscles.” The only muscles that get a pass are the diaphragm and pelvic floor, because they’re inhalation muscles.

The iliolumbar ligament is an attachment for iliacus and the anterior layer of thoracolumbar fascia.

Does that make iliacus an intrinsic core muscle? No. In itself, it doesn’t attach to the anterior layer of thoracolumbar fascia, but man does it attach to the ligament that does!

Why do you think that’s important? It’s how intrinsics send things to the outside world—to the limb, to the lower extremity. Look at the size of Jake’s lower extremity. It needs force, baby.

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