Video: Metacarpal muscles

Hello everyone! This is Joao from Kenhub. Welcome to another tutorial where, this time, I’m going to be talking about the metacarpal muscles.

Before I tell you what a metacarpal muscle is, I want to show you something: this image here of the palmar view of your hand if we were to strip all tissues except muscle, ligaments, and bone. Now, we’re left here with some of the muscles that we already talked about, some of the groups that we already covered here at Kenhub, but the other groups that or the other group that I’m going to be talking about on this tutorial specifically.

I’m going to be talking about intrinsic muscles of the hand. Now, intrinsic muscles of the hand means that these muscles have their attachment points within the bones of the hand. So within these bones right here that are covered in ligaments, the carpal bones, the metacarpals right about here, and then the bones of your finger, the phalanges.

Now, you can see also two groups of muscles that we already covered on different tutorials and also training units, and if you already guessed, you’re way ahead of me. This group right here found on the lateral side of your hand and in line with your thumb, if you guessed, these are the thenar muscles. And here, on the medial side, you’ll find another smaller group here on or in line with your small finger and found medially. These are the hypothenar muscles.

Now, we’re going to talk about another group of intrinsic muscles of the hand known as the metacarpal muscles, because these muscles have their attachment points on either the metacarpals or their bellies are running alongside with these bones. Mainly, that’s why we call them metacarpal muscles.

Now there are three groups, three distinct groups that we need to cover. And then within these groups, of course, there are smaller muscles that we need to distinguish, and of course, talk about their origins, insertions, and innervation. That’s what we’re going to do here on this tutorial.

Now, the first group that we’re going to look at is known as the palmar interossei, second group of metacarpal muscles are known as the dorsal interossei, and the final group that we’re going to look at is known as the lumbricals—so three group of muscles that belong to a larger group known as the metacarpal muscles.

Let’s start off with the very first group here on our list, the palmar interossei muscles, and these are seen here, highlighted in green, on both of these images. This is a group of three muscles that are located on the metacarpus or the metacarpal bones right between your wrist, right here or the carpal bones, and the bones of the fingers, also known as the phalanges. Now, they arise from the metacarpal bones of the index finger right here, also the ring finger, and the little finger.

We’re going to look, now, at each individual palmar interosseous muscles, and more specifically about… talking about their origin points, and we’re going to start, like I promised, with the first palmar interosseous muscle seen here, highlighted in green. And you’ll notice here that, as I mentioned, this muscle is in the direction of the index finger, also known as the second digit. Now, of course, we call it second or first, second, third, fourth, and fifth digits so we can locate ourselves, and we can call this metacarpal bone right here, the second metacarpal bone which will serve as an origin point, more specifically on the ulnar side of the second metacarpal bone. This is where the first palmar interosseous muscle will originate from.

Now, let’s look at the second palmar interosseous muscle seen here, also highlighted in green. And as I’ve mentioned before, this muscle is found on the ring finger or the fourth finger, and of course, this is the fourth metacarpal. And on the radial side of the fourth metacarpal, we’re going to see the origin point of the second palmar interrosseous muscle.
Moving on to the last palmar interosseous muscle, the third palmar interosseous muscle seen also here, highlighted in green. Notice that it’s originating from the fifth metacarpal bone, more specifically on the radial side of the fifth metacarpal bone.

Now, that we’ve just completed talking about the origin points of the palmar interossei muscles, it’s time for us to move logically and talk about the insertion points of the palmar interossei muscles. We’re going to start off with the same order as before, as the first palmar interosseous muscle seen here, highlighted in green. And you can see here one insertion point right about here, but I need to remember that all three palmar interossei muscles will have two insertion points.

The first one is the dorsal aponeurosis of the hand, so more specifically here on the second finger for the first palmar interosseous muscle. And then the insertion point, a bony insertion point will be the base of the proximal phalanx of the second finger right about here as you can see.

Now, the second palmar interosseous muscle will also have two insertion points like I mentioned before. The first one will also be the dorsal aponeurosis, but this time of the fourth finger as it is located within the same direction of the fourth finger or the ring finger. And a bony insertion point will be the base of the proximal phalanx of the fourth finger as you can see right about here.

Now, let’s talk about the insertion points of the third palmar interosseous muscle seen also here, highlighted in green, and as I mentioned before, this one will also have two insertion points. One is, as well, the dorsal aponeurosis of the fifth finger, and the other one, also the base of the proximal phalanx, but this time of the fifth finger, right about here.

Now that we covered the origin points, the insertion points, it makes sense to move on and talk about the innervation of the palmar interossei muscles. And as you see here, all three palmar interossei will have a nerve supply coming from the deep branch of the ulnar nerve C8-Th1.

Now, I want to add something, an important note here, that for you never to forget that your middle finger and the thumb do not have their own palmar interossei as you can see here. Thumb and middle finger are free of any palmar interossei.
So this is it for the palmar interossei muscles. It is time for us to move to the second group of muscles on our list: the dorsal interossei muscles seen here, highlighted in green on both of these images.

Now, the dorsal interossei muscles are four short muscles of the metacarpus, as you can see here—so one, two, three, and four. The first one right here is the largest and strongest among the four of the four dorsal interossei, and you can easily feel it on your hand and feel it between the web between the thumb and the index finger. Nevertheless, it is possible to palpate the remaining three between the metacarpal bones and the tendon of the extensor digitorum muscle.

Now, like we did with the palmar interossei muscles, I want to talk about the origin points for the dorsal interossei, and I’m going to do it in the same manner as I did with the other muscles starting off with the first dorsal interosseous, the strongest of them all. And this one is originating from two metacarpal bones, so the first metacarpal bone right about here and the second metacarpal bone right about here—so two origin points found on the metacarpal bones for this first dorsal interosseous muscle. And this is a pattern that you will see as well for the other three, and let’s see.

For the second dorsal interosseous, you can see that it is originating from the second metacarpal bone as well as the third metacarpal bone. The third dorsal interosseous muscle will follow, as well, the same pattern originating from the third metacarpal as well as the fourth metacarpal. And so on for the fourth dorsal interosseous muscle that will originate from the fourth metacarpal bone and the fifth metacarpal bone.

We just talked about the origin points for the dorsal interossei muscles. It is time for us to move on and talk about, then, the insertion points of the dorsal interossei, starting off with the first dorsal interosseous muscle which will have two insertion points. One is the dorsal aponeurosis of the second finger and the second proximal phalanx, on the radial side of the index finger, as you can see here. So this is the bony insertion point for the first dorsal interosseous muscle. But as you can see, and as you saw for the palmar interossei muscles, the dorsal interossei will also insert on the dorsal aponeurosis.

Now, let’s look at the insertion point for the second dorsal interosseous muscle, and this will also have an insertion point on the dorsal aponeurosis, but this time, of the third finger. And another insertion point or a bony insertion point that you can find right about here on the third proximal phalanx on the radial side. Notice here the radial side of the middle finger.

I cannot stress enough how tricky the next muscle might seem because we just talked about the second dorsal interosseous. Now, we’re going to look out for the insertion points for the third dorsal interosseous, which might look very similar to those we’ve seen on the second dorsal interosseous.

So we start off with the dorsal aponeurosis for the third finger where the third dorsal interosseous will be inserting on and also the third proximal phalanx as you can see here. This bony point will serve as attachment point for the third dorsal interosseous muscle. The only difference from this muscle here, the second dorsal interosseous muscle is that, this time, the third dorsal interosseous will be inserting on the ulnar side—very important, and write this down for your test so you won’t make a mistake here. This is the major difference on the insertion. When you write it down, you have to make sure that you tell your teacher that this is inserting on the ulnar side of the third proximal phalanx.

We’re going to move on to the fourth dorsal interosseous muscle. The insertion point for this muscle here is also a dorsal aponeurosis of the fourth finger this time. And the bony point will be the fourth
proximal phalanx right about here as you can see—so on the ulnar side of the ring finger.

And it wouldn’t be fair to conclude the dorsal interossei without talking about their innervation, and all you need to know is that the four muscles, the four dorsal interossei are supplied by none other than the deep branch of the ulnar nerve.

With that in mind, we’re going to move on to the last topic on our list, the last group of muscles, the lumbricals seen here, highlighted in green. These are four muscles, four short hand muscles that are located in the metacarpus deep to the palmar fascia. And as the name indicates, lumbricals means “lumbricidae” in Latin or earthworm because the muscles are so small, and they do resemble, somehow, to an earthworm, and that’s why anatomists associated the two things.

Now that we’re done covering a little bit of muscle trivia, it is time for us to go and talk about the origin points of the lumbricals, and one important feature that I need to mention about these muscles is that they originate from tendons instead of bony structures—as we’ve seen in most of the muscles that we learned in school—making their origin surfaces quite movable.

Usually, they arise from the radial side of the tendons of the flexor digitorum profundus as you can see here. So this is the tendon of the flexor digitorum profundus, which will split into four and will serve as origin points for the lumbricals. And in addition, the third and fourth lumbrical muscles have a second head attached to the ulnar side of the adjacent tendon.

Let’s move on and talk about, now, the insertion points for the lumbricals, and we’re going to cover them separately as we did for the others. So the first lumbrical is inserting on the dorsal aponeurosis of the second finger or the index finger. The second lumbrical, as you see here, is inserting on the dorsal aponeurosis of the third finger or the middle finger. Notice here that this may seem that the muscles are, in fact, attaching to a bony point, but it is and should be mentioned here that the dorsal aponeurosis of the hand is what is actually serving as an insertion point for these muscles, the lumbricals.

Let’s move on to the third lumbrical, and as you here, the insertion point will be the dorsal aponeurosis of the fourth finger or the ring finger. The fourth lumbrical will have, as an insertion point, the dorsal aponeurosis of the fifth finger or your little finger.

In terms of innervation of the lumbricals, things change a little bit, because on the previous muscle groups, we’ve seen that there is only one innervation for all muscles, but here, we have to split the lumbricals. So the lumbricals, the first and second lumbricals will be supplied by the median nerve, while the third and fourth lumbricals will be supplied by the ulnar nerve.