Hello all this is Dr Alsup and in this video we will be discussing
how to identify the muscles of the anterior compartment of the forearm.
Now recall that there are three layers of muscles in this anterior compartment.
And these muscles are located more medially so we're looking mainly in this region right here,
because the brachioradialis which you can see right here
is taking up the majority of the lateral space in this anterior compartment.
The brachioradialis is the odd one when discussing the forearm. It's located a bit more anteriorly and
it also flexes the elbow joint but it's discussed with the posterior compartment because it is
innervated by the radial nerve. But enough about the brachioradialis we will come back to that
one when we talk about the posterior compartment
we're going to focus on this superficial layer
that and there are actually four muscles but we're only going to identify
these three today. The most medial and more proximally oriented is the pronator
teres which is identified right around here, and you lose sorry you lose some of that some of the
muscle because it is deep so you can only see a small portion of the pronator teres right here.
When I'm trying to get my bearings in this area I always try to locate the pronator teres first
as it forms part of this inferior medial border of the cubital fossa so it's easy to locate this
one because it seems like it's almost the start basically of this superficial layer.
Then we get to muscles that have longer tendons at least reaching the wrist region or further
and when we're talking about the superficial compartment it's really or the superficial
layer it's really only reaching around the wrist. And so the first one that we see is going to be
the flexor carpi radialis so right here and you can see it's tendon right here
it's going to be the flexor carpi radialis so radialis is more on the radial or lateral side
we know this is lateral because this is the first digit so this is going to be the medial side.
So again flexor carpi radialis is going to be more laterally located. It is going to start
with this muscle belly here and then you see a fairly prominent tendon right there. This skinny
neighboring tendon is going to be the tendon of the palmaris longus.
This is the muscle of the superficial layer that we are not you're not responsible for identifying.
The reason for that it's not very robust or a very strong muscle and in fact some individuals
don't have a palmaris longus at all but if you do see a very skinny long tendon that's what that is.
The last muscle of this superficial portion of this compartment is the flexor carpi ulnaris.
It is so medially placed that seeing that its muscle belly is actually quite difficult well
we often will see it better in a posterior view so when we talk about those muscles we'll
talk about or identify the belly there. But one thing that you can see quite well
is the tendon of the flexor carpi ulnaris and it as again as you might imagine it's on the
more medial side and so you can see the tendon heading towards right around this region here. If
you look up in this region you can see the muscle bellies basically kind of they look like one big
muscle and that's because these muscles share a proximal tendon right around here which is
the common flexor tendon that attaches to the medial epicondyle so we're on the medial side
that medial epicondyle will be just deep to that and that's where that common flexor tendon is.
Moving to the intermediate layer and this is considerably less complex as there's only one
muscle here, but this muscle does have four long tendons that will traverse the carpal
tunnel and you can see that right around this region here so here's the carpal tunnel
you can see some of the tendons some of them are going to be a little bit deeper but you can see
some of the tendons that will traverse this region. And they will distally attach so the tendons
of the flexor digitorum superficialis will distally attach to the middle phalanges.
When you're looking at that superficial anterior view so this image here is the
same image as the one we just talked about you can see a bit of the muscle belly kind of peeking out
between the tendons, those tendons and that superficial layer. Sometimes you
actually hear you have this layer kind of bulked in with the superficial layer
but really it is located deeper you can see here with the superficial layer removed how
wide this muscle is, and again those four tendons will traverse the carpal tunnel.
The flexor digitorum superficialis also has one of its proximal attachments on that medial
epicondyle with the muscles of the superficial layer as well. But it also has different proximal
attachments as it's such a large muscle. In a deeper dissection you can see two more muscles:
the flexor digitorum profundus and the flexor pollicis longus. The flexor digitorum profundus
is similar to the flexor digitorum superficialis and that it also has four long tendons
that will traverse the carpal tunnel. So you can see right here the cut tendons of the flexor
digitorum superficialis and then you see all over the place here these four tendons of the flexor
digitorum profundus so these will be located deep to the flexor digitorum superficialis.
The FDP so this is often abbreviated FDP
is going to distally attach on the distal phalanges of 2-5 making it the only
muscle that can flex the distal interphalangeal or DIP joints. Laterally enabling the flexor
digitorum profundus muscle is the flexor pollicis longus muscle and if you see pollicis or policus
longus or any policus you know that we're talking about a muscle that will affect the first
digit or the thumb. And so you can see here that it's going to have this lateral most tendon here,
I'm outlining the tendon, and it actually that tendon will actually also traverse the carpal
tunnel. So traversing the carpal tunnel you'll have the long tendons of flexor digitorum superficialis,
flexor digitorum profundus, and the flexor pollicis longus. Now in order to see this last muscle of
the deep layer you have to do an even deeper dissection, so you could almost really split this
anterior compartment into four layers but usually this pronator quadratus is lumped in with the deep
layer. And it looks to me I think this is a very distinctive muscle it almost looks like a bandage
that is covering the distal portions of the radius and the ulna, so this is the pronator quadratus.
If you can get to the correct depth there's little
chance of misidentifying this muscle it's quite distinctive in terms of its shape
and it is this muscle that is typically the prime mover in pronation of the radial ulnar joints.
Excellent those are the muscles in the anterior compartment of the forearm. My best advice is that
when you are getting confused with muscle bellies as it is not uncommon, sometimes
the muscle bellies are hard to differentiate, look at the tendons and where they are going.
These are typically more illustrative than the muscle bellies particularly the long tendons.
Please take time to review and always feel free to reach out to me or any of
my anatomy colleagues with any questions. Thank you for your time and attention