Piriformis Anatomy: Origin, Insertion & Action

Hi everyone, welcome to Bodyworks Prime.  Today we're going over the origin, insertion and action the piriformis muscle. Here we can see a posterior view of the  piriformis muscle and the piriformis is connecting onto the femur here and as it works  its way up, it then passes through a gap between two ligaments. The gap is called the greater  sciatic foramen as it passes through the gap, it attaches onto the anterior side of the sacrum.  So the anterior side would be the side that's facing away

from us right now. I'll swap to a  different view in just a moment to show you that. In terms of its positioning, the piriformis  is deep to the gluteus maximus muscle; meaning the gluteus maximus covers the surface of the  piriformis. It's also just inferior to the gluteus medius muscle; so it's just a bit further down  than where the gluteus medius muscles located. I've got videos on all the gluteal muscles as  well and I'll put a link in the description box for them. So take a look at them af

ter this video  as well. So now we've swapped to an anterior view, you can see how the piriformis is coming up  here behind the hip and then coming through that gap and connecting onto the sacrum here.  The sacrum is divided into different sections, you can see I've labelled them here, S1  all the way down to S5. Each section is determined by these holes here, so if you draw  a line between them, that would divide each of these sections of the sacrum. So you'll see  that the piriformis is locate

d on S2 S3 and S4. You can see now I've marked out the origin point  here in red and specifically that origin point is on the anterior surface of the sacrum between  S2 and S4. Swapping back to a posterior view, we can see another origin point which  some people have and that's going to be on the gluteal surface of the ilium. This is  towards the posterior and inferior iliac spine, so this would be the posterior iliac spine right  here, that'd be the superior portion of the iliac spine and then

this would be the inferior portion  of that. Another origin point is going to be the sacrotuberous ligament which you can see I've  just brought into view right here and it's going to be the superior portion of this sacrotuberous  ligament where the piriformis can connect onto. Swapping back to an anterior view, you can  see I've marked out the insertion here in blue that's going to be on the greater  trochanter of the femur. Specifically, it's going to be on the medial side  of it and the super

ior aspect. Medial side meaning close to the middle and the  superior aspect meaning the top of it. So let's have a look at the actions next. Now  the femur at the moment is in an internally (or medially) rotated position depending how you  want to call it. So it's rotated towards the front of the body here and as the piriformis  contracts, it can rotate this femur so that rotates towards the posterior of the body. That  would be called lateral (or external) rotation of the femur (or the hip joi

nt). So the hip joint  is externally rotating when the piriformis is contracting. So that would be our first action  of the piriformis muscle. Now, another action would be abduction of the hip joint, so at the  moment the hip is abducted. As it comes inward, that would be adduction. This abduction of the  hip joint can only occur when the hip is past 60 degrees of flexion. So where I've got the  femur right now, this would be about 60 degrees and as it comes up into this range of motion, this  w

ould be the active area where the piriformis can contribute to that abduction movement. But as it  moves past that 60 degrees and comes into that straightened position, it loses its ability to  contribute to abduction of the hip joint. Another action which it can do though is stabilizing the  hip joint. So it's going to stabilize the head of the femur here in the acetabulum and that's going  to be another action of the piriformis muscle. So if you found this video helpful or you've  enjoyed it,

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