Hello anatomy friends this is Dr Alsup and we will be discussing the muscles of the anterior
compartment of the thigh. And this anterior compartment is the largest
compartment of the thigh mainly due to the quadriceps femoris muscle but there
are other muscles as well and some of them are actually pretty powerful
and so we will discuss this and all the typical players such as innervation
attachments actions and as always some clinical considerations we have one we want to discuss.
So as mentioned the dominant muscle in this compartment and really in the thigh overall
is the quadriceps femoris muscle which is in this general region right here and it extends
approximately as well and as its name would suggest it has four quad parts and these parts
are often considered as four separate muscles even though they all have a common distal tendon.
But one of these four the rectus femoris muscle is going to actually span a longer distance
than the others it's going to cross both the hip and the knee joint so it's going to run
right down the middle right straight down the middle of the anterior thigh that's where it
gets its name so that's the rectus femoris. And the other three parts are the vasti muscles
you'll have the vastus lateralis which is actually the largest the vastus medialis so they're exactly
where you would think one's more lateral ones more medial and the vastus intermedius which you can
see here up on this BlueLink image is going to be deep to the rectus femoris so the rectus femoris
had to be removed in order to clearly see that again. When looking at the anterior compartment
of the thigh it is the quadriceps femoris muscle which is dominant and takes up almost all of the
view there are other muscles though and in the case of the iliopsoas muscle that's actually a
very powerful muscle in terms of being able to flex the thigh it is a combination muscle which
means that it kind of has two major parts that come together as a distal tendon you have the
psoas major muscle which we talked a little bit about when we were talking about
the lumbar plexus and then you also have the iliacus muscle which is sitting right on the iliac
crest portion or the the body of the ilium. And so those two come together and have a common tendon
which is located in the superolateral portion of the anterior compartment but it's often
blocked from view that distal portion is blocked from view because of these other larger muscles
is also the sartorius muscle one of my favorites. It is the most superficial of the muscles of
the anterior compartment so I'm going to kind of trace the sartorius right here so it's one
of the most superficial muscles and it also has the distinction of being the longest muscle in
the body so it's extending all the way up here from the hip all the way down here towards the
knee we kind of lose it but it's going to be right around this region. In terms of its insertion
so we will be identifying sartorius and the iliopsoas in addition to the quadriceps femoris
we are not going to focus on the pectineus muscle which is located in the superior medial thigh
a deep portion as well but it is in this region.
Almost all of these muscles are innervated by the femoral nerve so when you are making your chart of
which nerve innervates which compartment go ahead and jot down femoral nerve for the anterior thigh
compartment this is a branch of the lumbar plexus which is unique other than the medial compartment
of the thigh and the gluteal region it is not those are the only compartments that are
not innervated by branches of the sciatic nerve which is the predominant supply of the lower limb.
So again anterior compartment of the thigh as well as the gluteal region and medial compartment of
the thigh are the exceptions to the rules everything else is sciatic nerve branches.
Okay let's talk a few distal attachments we're not going to go into every single one of them but
there are a few I want you to know starting with the iliopsoas muscle. Recall you have those two
muscles combining you have the psoas major here and the iliacus and they will come together
and they will share a distal tendon which is going to attach on the lesser not the greater
the lesser trochanter of the femur so when this muscle contracts it will pull the femur
anteriorly creating powerful flexion oh that's a squiggly line but it's moving it more anteriorly
and again this is going to be your most powerful flexor of the hip joint. I do want to note but
not get into the weeds here that the iliopsoas based on its more proximal attachments up here
will actually also allow this muscle to move the trunk so not only will it affect the hip joint
quite powerfully it can affect the trunk as well additionally you can also see that the iliopsoas
muscle does not reach the knee so in terms of the lower limb it can only affect the hip joint
moving to the quadriceps femoris muscle those four muscle parts will have a common tendon which
is dominant. It plays a very important role in the protection of the anterior knee joint
so you can see that right here and this is going to be called the quadriceps tendon
so this portion right here is called the quadriceps tendon.
Now a sesamoid bone will actually form within the quadriceps tendon called the patella
often colloquially referred to as the kneecap and this bone provides a bony surface in the
anterior knee region it helps to withstand compression in this region and provide protection
during movements of the knee joint. And again and we'll get into this when we get into the
knee joint the anterior part of the capsule of the knee joint isn't particularly strong so you have
all of this region here to add that protection the portion of the quadriceps tendon from the patella
to the tibial tuberosity of the of the tibia which is the distal most attachment
is often referred to as the patellar ligament sometimes you hear it referred to it's called
ligament sometimes because it's going from bone the patella to the tibial tuberosity but you
often hear it referred to as the patellar tendon as well because it is an extension of that tendon.
So let's talk actions and we can divide these into muscles that cross the hip joint
and those that cross the knee joint the prominent movement of us the prominent movement associated
with this compartment and the hip joint is flexion of the hip joint and you can see the hip being
flexed on this patient on the left side here so moving anteriorly and as mentioned this
is primarily the iliopsoas muscle but the rectus femoris portion of the quadriceps can play a role
that pectineus can play a role in sartorius too. So the sartorius muscle is a very clearly
observable muscle it's going to be one of the first things you see because it's so superficial
but it's not a particularly powerful muscle it plays synergistic roles and actions that allows
an individual to kind of sit in a cross-legged position.
By far the most prominent movement of the knee joint and for this compartment will be extension
of the knee joint which is facilitated by all components of the quadriceps femoris muscle
so this illustration here is showing the knee an extension such as what you have in standing
but think of other times extension is used so if you're rising from a sitting or squatting position
you're going to extend the knees if you're climbing you're walking upstairs to name a
few those are all examples of where extension is going to play a role.
Lastly I want to touch on one clinical consideration in this area which is
the patellar tendon ligament either way you'll hear both reflex and this test involves tapping
with a firm stroke the patellar ligament with a reflex hammer as you can see happening here and
hopefully this is going to elicit kind of a jerky extension of the knee which you can see happening
right there so eliciting a patellar reflex or knee jerk and tapping right here at that or at the
ligament tendon region is going to activate muscle spindles in the quadriceps femoris muscle sending
afferent impulses from the spindles through the femoral nerve to the L2 through L4 segments of the
spinal cord and from there efferent impulses are transmitted via motor fibers in the femoral nerve
to the quadriceps which is what is going to result in that jerky extension movement of the knee.
So don't worry about breaking down you don't have to memorize these specific numbers here of this
illustration it's just here to kind of show you this set here focus more on what we have over
here in the text so really this patellar reflex is testing the integrity of the L2 through L4 spinal
cord segments because that you know obviously is directly associated with the femoral nerve as well.
So it can test whether there are issues there so a pretty common test during routine physical exams
and I am sure your clinical friends will will show you how to to do this most appropriately.
Excellent we have reached the summary slide and I thank you very very much for your time and
attention here. If after this review you have any questions please feel free to reach out
to me or any of my anatomy colleagues, we always love to talk anatomy. Have a great rest of your day