Hello all this is Dr Alsup and in this video we will be working through how to identify the
structures located in the posterior, or the last of the three, compartments of the thigh that
we are going to discuss. So when discussing the posterior compartment of the thigh we are talking
hamstring muscles that's often what you hear them referred to as. These all share a proximal
attachment on the ischial tuberosity which will be deep under kind of like in this region here.
And there are three hamstring muscles or three muscles of this posterior compartment of the thigh.
Two are going to be more medially placed and one is more laterally placed so this is medial
and this is lateral and I can tell this is lateral because I see the gluteus maximus
up here and I can see it attaching to the iliotibial band or IT tract right here and this IT
band is always going to be laterally placed. So the lateral hamstring muscle is going to be the
biceps femoris, I kept trying to say biceps brachii in my head and that is
we're way off there! So no this is the biceps femoris it will actually extend more proximally
here but you can't see it quite well in that in this part of the image. And as its name would
suggest there are two heads of the biceps femoris muscle but the short head is located deeper so
we're looking at the long head here you'd have to do a deeper dissection to see the short head.
So this is the more lateral hamstring muscle and the biceps femoris will extend and distally attach
on the head of the fibula. There are two medial hamstrings, you're going to have the semitendinosus
which is in this general region right here. And the semitendinosus is going to be more superficially
placed or more posteriorly placed than the deeper semimembranosus which you can see here-ish.
Look what you have going on right here you have that gracilis that is always that most medial
muscle when we're talking about the thigh. So I always sometimes even when i'm in the posterior
compartment sometimes I try to find that gracilis muscle because it is just so typically placed.
Okay so that semitendinosus muscle again is going to be sitting kind of on top of
the semimembranosus if you're looking at this view, and its tendon is often much more rope
like than the kind of flatter tendon that you see of the semimembranosus. In fact for
the semitendinosus oftentimes this tendon is visible for a little bit more of its length
than you have here on this individual but as always variation is key right in anatomy. So
biceps femoris is going to or femoris is going to be more lateral
semitendinosus is going to be superficial to the semimembranosus in its most typical patterns.
These muscles are innervated by the tibial division of the sciatic nerve for the most part
except for that tricky short head of the biceps femoris. But it's important to note that in most
individuals it is still the sciatic nerve in the thigh so in other words it is still wrapped up as
one nerve in the thigh region. So say this is a cross section of the sciatic nerve.
You have the nerve fibers of the tibial division kind of all over the place
here, and then you have the common fibular and its nerve fibers all over the place here, but they're
still all wrapped up together in one nerve called the sciatic nerve. So within the thigh it is still
just that one nerve wrapped together. It's not until you get to the popliteal fossa which is
in this which is this posterior knee region what we're looking at right here, that you get the
sciatic nerve splitting into its terminal branches, so where you can actually see this occur grossly.
So the tibial nerve will be the larger one and it kind of looks like it's heading more medially in
this particular view and then the common fibular or peroneal nerve is the smaller division and it's
going to be moving a bit more laterally in this particular position. So it is this tibial nerve or
tibial division of the sciatic nerve that's going to supply those hamstring muscles. All right most
excellent thank you for your time and attention here and have an excellent rest of your day