Okay!
So the next part of this tutorial is on the deep muscles of the gluteal region.
These are small, little muscles, which mainly act as lateral rotators of the femur at the
hip joint.
So unfortunately, this model here isn't actually that accurate, so I'll do a bit of flicking
between diagrams and this 3D model just to try and explain things clearly.
I used to find this quite a tricky area because there's a lot of small muscles with precise
origins and insertions.
So I'll just talk you through that now.
So these muscles obviously lie under the gluteus maximus -- the gluteus maximus, medius and
minimus.
These muscles laterally rotate and abduct the hip joint.
I've just switched over to one of these old diagrams, which shows things a bit more accurately.
So we're looking posteriorly at the same view we were just looking at.
So this is the cut, gluteus maximus, medius and minimus and we're looking at these group
of muscles here, which lie under the superficial group.
So I'm going to work from superior to inferior talking about the muscles.
I'll just quickly cover them first.
The most superior one is the piriformis muscle.
This originates on the anterolateral surface of the sacrum between the anterior sacral
foramina and it inserts on the greater trochanter of the femur.
Below that, you've got the gemellus superior.
Below that, you've got the obturator internus.
This is the tendon of the obturator internus because the actual muscle lies a bit more
medial (I'll show you that in a second).
So then you've got the gemellus inferior.
So in Latin, the word 'gemellus' is twin.
So these muscles are little triangular muscles and they lie above and below the tendon of
the obturator internus.
All these muscles are inserting onto the greater trochanter.
So the gemellus superior actually originates near the spine, the ischial spine and it inserts
obviously on the greater trochanter, but also along the border of the superior aspect of
the obturator internus tendon.
So the gemellus inferior inserts along the inferior aspect of the obturator internus
and tendon and also at the greater trochanter.
These three muscles, the obturator internus together with the gemellus superior and inferior
inserts together on the greater trochanter.
What these muscles do is they laterally rotate the femur and they can also abduct.
So the most inferior muscle is this muscle here, this quadrangular shape.
So it's called the quadratus femoris muscle.
This muscle originates on the lateral aspect of the ischium just anterior to the ischial
tuberosity and then it inserts on the femur between the greater and the lesser trochanter.
So this muscle purely laterally rotates the femur.
So you've got the piriformis at the top and then you've got the gemellus superior, obturator
internus and gemellus inferior, which insert together at the greater trochanter.
You've got the gemellus superior and inferior inserting on the top and bottom of the obturator
internus tendon.
And then you've got the most inferior muscle of the deep group, the quadratus femoris,
which originates anterior to the ischial tuberosity and inserts between the greater and the lesser
trochanter.
So I've just switched back to the 3D muscle and I'll talk you through those muscles here.
These muscles are actually out of place, so I'm going to get rid of them to make things
a bit more accurate.
I'll get rid of the tensor fasciae latae and the iliotibial tract.
So the piriformis muscle which you saw on that diagram was the most superior muscle.
That originated on the anterolateral aspect of the sacrum between the anterior sacral
foramina and it inserted onto the greater trochanter.
So it ran along from here and inserted onto the greater trochanter.
So this muscle ran through the greater sciatic foramen.
So the greater sciatic foramen is this foramen here.
It's not shown on this model, but you've got a ligament between the sacrum and this ischial
spine.
So the ischial spine is this little bump here and there's a ligament connecting the ischial
spine to the sacrum.
So this is the sacrospinus ligament and you've got the sacrotuberous ligament.
So the sacrotuberous ligament attaches to the sacrum and to the ischial tuberosity.
It runs more vertically like this.
And then you've got this little space enclosed by these two ligaments.
This is the greater sciatic foramen.
This little notch here is the greater sciatic notch.
So the greater sciatic foramen is formed by the greater sciatic notch and the borders
of the sacrospinous and the sacrotuberous ligament.
So the piriformis actually runs through the greater sciatic foramen to insert onto the
greater trochanter of the femur.
So I've just switched back to this diagram.
We're looking at the same view I just showed you.
This ligament here is the sacrospinous ligament.
And then you could see these two gaps.
So this is greater sciatic foramen with the piriformis passing through it.
You've got two little gaps, above and below and different vessels and nerves pass above
and below it.
So the sciatic nerve passes below the piriformis muscle and the greater sciatic foramen and
you've got the superior gluteal nerves and vessels, which passes above the piriformis
and the greater sciatic foramen.
So it's important to know about the relationship between the piriformis and the greater sciatic
foramen and that the sciatic nerve passes below the piriformis and the greater sciatic
foramen.
So I also mentioned the sacrotuberous ligament.
This is that vertically oriented ligament which runs posteriorly to the sacrospinous
ligament.
This runs from the ischial tuberosity and connects to the sacrum, so 'sacrotuberous
ligament' and you've got the sacrospinous ligament.
So the piriformis muscle is innervated by branches from S1 and S2.
It laterally rotates and extends the femur.
So just below, we've got the gemellus superior.
Remember this ligament attaching to the ischial spine?
This is where the origin of the gemellus superior is.
I'll just show you that.
So here, just looking at this model, this is the ischial spine and this is where the
gemellus superior would originate.
It inserts on the greater trochanter.
So the piriformis muscle lies above it and it originates on the anterolateral aspect
of the sacrum and it passes through the greater sciatic foramen separating it into two bits.
So it runs through here and inserts on the greater trochanter.
The obturator internus lies below the gemellus superior.
So the gemellus superior, you know where that is because it lies on the ischial spine here.
So the obturator internus lies just below that.
And the obturator internus, the tendon lies just below the gemellus superior (along here),
but the muscle originates on the medial aspect of the obturator membrane.
So the obturator foramen is this foramen in the pelvic bone here and it's actually covered
by a membrane.
So I'm just showing you this diagram.
We're looking anteriorly at the pelvis and the obturator foramen.
You could see this membrane which partially covers the obturator foramen.
You've got this little opening above the obturator canal, which isn't covered by the obturator
membrane where vessels and nerves pass through.
But this is the obturator membrane.
You've got the obturator externus, which attaches to this on the external surface.
But the obturator internus originates on the medial side of the obturator membrane.
So just looking back at this model, you can see that the obturator membrane would lie
here.
I'm rotating it posteriorly, so we're looking at the posterior surface of the obturator
membrane and that's where the obturator internus sits.
So it sits internally on the medial side of the obturator membrane.
So the muscle belly lies here and the tendon passes up between the ischial spine and the
ischial tuberosity.
So it runs along here and it passes so it bends around 90° the obturator internus tendon.
So the muscle originates here on the medial side of the obturator membrane and the adjacent
bone and the tendon runs below the gemellus superior and above the gemellus inferior (in
this space here) and it bends 90°.
You can see how it would bend around and it inserts onto the greater trochanter.
So that's the obturator internus muscle.
So both the gemellus superior and obturator internus are innervated by the nerve to the
obturator internus, which comes from L5 and S1.
These muscles will actually rotate and abduct the femur.
So below, we've just go the gemellus inferior.
This originates on the upper aspect of the ischial tuberosity.
Back to this model again, you've got the ischial tuberosity here -- ischial spine, you've got
this space where the obturator internus tendon runs and below that, you've got the origin
of the gemellus inferior muscle.
So it arises from the upper aspect of the ischial tuberosity here.
And again, it inserts onto the greater trochanter.
So this muscle also externally rotates and abducts the femur.
So the final muscle of the deep group is the quadratus femoris.
The quadratus femoris is the most inferior muscle and this originates just anterior to
the ischial tuberosity, so just here.
It's rectangular in shape, hence the name 'quadratus' and it inserts between the greater
and lesser trochanters on the femur, so on the quadrate tubercle on the intertrochanteric
crest.
This muscle laterally rotates the femur.
So both the gemellus inferior and the quadratus femoris are innervated by the nerve to quadratus
femoris.
This comes from L5 and S1.
You can just see this muscle again here, this rectangular-shaped muscle.
So those are the muscles of the deep layer of the gluteal region.
Just to go over those again.
You've got the piriformis superiorly, the gemellus superior, obturator internus, gemellus
inferior and the quadratus femoris most inferior.
I'm sorry that it was a very long tutorial, but I was trying to make that clear about
where these muscles originate and how they act.
So I hope that was useful.
One last thing which you might be wondering about is the obturator externus muscle.
This muscle isn't actually considered part of the gluteal region.
It's often thought of as being a part of the medial compartment of the thigh.
This muscle lies on the lateral surface of the obturator membrane.
So if you remember the obturator internus, it originated on the medial surface of the
obturator membrane, so that's why it gets the name 'obturator internus' because it's
on the internal surface of the obturator membrane.
So the obturator externus lies externally on the lateral surface of the obturator membrane
and it winds around behind the hip joint.
It originates here and it winds around behind the hip joint to insert on the trochanteric
fossa.
This muscle laterally rotates the femur, but it's often considered with the medial compartment
of the thigh rather than the gluteal muscles.