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Metacarpal bones and related bony landmarks.
Hello everyone! This is Joao from Kenhub, and today, I’m going to do a tutorial dedicated to another set of bones that you find on your hand, and these are the metacarpals. And as you can see here, the metacarpals are located between these bones here, this group of bones that we talked about, the carpal bones or the bones of the wrist. And on a distal portion, you can see that the metacarpals are articulating with the phalanges, more specifically, the proximal phalanges.
Now, knowing that, I want to clarify something before we go and move on to more detail on the metacarpals. Now, you’re looking at the hand on the palmar or also known as the volar surface. So this image here is a palmar surface, and you notice here a little bit of the radius, which is located laterally, and a little bit of the ulna that you know is located medially. So for that reason, you know that this direction here, going toward the thumb, and then if we start moving medially, you have the index finger, the middle finger, the annular, also known as the ring finger, and on the most medial part of the hand, then, you have the little finger.
But if we look at the dorsal side or the back of the hand, you still see here the radius. Now, let me highlight the metacarpals here. And you notice here, the radius, still located on the lateral side, the ulna, located on the medial side. So here on this perspective, it changes the positions, the lateral and medial. So here, you’ll have the lateral, and here, you’re going to have the medial side, and the thumb going all the way to the little finger. So now that we have this cleared out, because it’s usually a bit confusing to me, so I wanted to clear it out for you as well, so we can talk about these bones in a little bit more detail.
Now, as you notice already, there are five metacarpals. And each metacarpal is divided into three main structures. So let’s look at the middle finger here where you can see this metacarpal seems to be a little bit larger. And there are three structures that you need to know. The first one is located on the proximal side, and this is known as the base of the metacarpal. If you go all the way down to the middle portion of the metacarpal, this is known as the shaft, because as you can see, the metacarpals are little bit like a long bone, but they’re not as long as, say, the humerus or femur. But they’re still long bones, and for that matter, you can clearly see a body or a shaft for this bone. On the tip, you’re going to see this structure here that is known as the head of the metacarpals.
Now, in terms of surfaces, if we’re looking at the palmar side, you notice that this palmar surface is slightly concave. Now, if we look at the back or the dorsal portion, then you notice that the dorsal surface is slightly convex. And if you notice here, especially on the middle finger metacarpal, you notice that the dorsal surface has a slightly triangular shape if you go all the way down to the head.
Now, I want to give you a few words on each individual metacarpal, and we’re going to start with the first metacarpal here highlighted in yellow. And the first metacarpal is located laterally and in the direction of the thumb. And in terms of articulation, you notice that the first metacarpal is articulating with this carpal bone known as the trapezium. And both of their surfaces have what is known as a saddle-shaped surface or articulating surface. Now, if you go to a distal portion, you see that the first metacarpal is, then, articulating with the proximal phalanx here of the thumb.
Now, let’s talk about the second metacarpal here found in the direction of the index finger. And in terms of articulation, you notice that the notch-sized or notch-shaped articulating surface found on the base of the second metacarpal is, then, articulating with two carpal bones: the trapezoid here and the trapezium. Now, if we move on a little bit more medially, you see that the base of the second metacarpal is articulating slightly here with the base of the third metacarpal. Now, if we go to the distal portion, you have here an articulation with the head of the second metacarpal and also the second proximal phalanx.
Moving on to the third metacarpal in the direction of the middle finger, and you notice that this third metacarpal on the proximal side is articulating with one carpal bone as well. This large one known as the capitate. And on the lateral side, still on the proximal lateral side, then it’s articulating with the base of the second metacarpal. Moving on a little bit more medially, you notice that the third metacarpal is, then, articulating with the base of the fourth metacarpal. If we move on then distally, you’re going to notice also an articulation between the head of the third metacarpal and then the third proximal phalanx.
Now, let’s move on to the fourth metacarpal here. And the fourth metacarpal is in the direction of the annular or also known as the ring finger. And in terms of articulations, if we look at the proximal view, here, you can see that there is an articulation happening with one carpal bone, this carpal bone that has a hook—remember the hamate? So the hamate is articulating here with the base of the fourth metacarpal. But this fourth metacarpal is also articulating with other two metacarpals on the lateral side. You notice that it’s articulating with the third metacarpal. And on a medial side, it’s articulating with the fifth metacarpal. If we go to a more distal portion, you notice that the head of the fourth metacarpal is, then, articulating with the corresponding fourth proximal phalanx.
Now, on the last part of this tutorial, let’s have a quick view on the fifth metacarpal. And the fifth metacarpal, as you see here, is the most medial of all metacarpals, and it’s in the same direction as the little finger. And in terms of articulations, notice here on the proximal side, the fifth metacarpal is articulating here with this carpal bone that we talked about that has a hook, then it’s articulating with the hamate. Also on the proximal side on the lateral portion of the base of the fifth metacarpal, you notice that there is an articulation here with the fourth metacarpal. Now, going to the distal portion that you also notice that the head is articulating with, then, the corresponding fifth proximal phalanx.