The eight bones of the wrist, known as the carpal bones, and related bony landmarks.
Hello everyone! This is Joao from Kenhub, and today, I’m going to do a tutorial where I’m going to go into a little bit more detail on the carpal bones, here, these bones highlighted in green.
Now, as I probably mentioned before, these bones are eight bones—so eight bones in your wrist. And before we go and talk about them in a little bit more detail, each and every individual bone here, I need to clarify something that is usually a bit confusing to me as well, and this is the orientation or direction of these bones, where they’re exactly found.
Now, on this image here, you can see that this is the palmar side of the hand, and you see here a little bit of the radius that is located laterally and a little bit of the ulna that is located medially. Knowing that, you can see that the thumb is usually found or is found on the same direction: on the lateral side, in the same direction of the radius. And if we move in medially, then we find the index finger, the middle finger, the annular or ring finger, and on the most medial side, then, we find the little finger.
Now, knowing that, what I’m going to do is I’m going to zoom in—so the same direction, but now, a little bit more zoomed in so we can see these bones in a little bit more clarity. Now, keep in mind that this is still the lateral side of course, and this is the medial side, and the radius, ulna, and of course, these are the other set of bones that are found more distally, the metacarpals.
Now, let’s start the actual tutorial where I’m going to talk about the carpal bones. And it’s important to say that they’re divided into two rows: a proximal row that you see here highlighted in yellow and a distal row here, highlighted in red. Now, each row has four bones as you can see here, so each, the proximal row and the distal row, they have, each, four bones.
Now, let’s look at the bones that you find on the proximal row, and keep in mind that, for any exam, you usually rely on mnemonics to save you. So I’m going to also use one that I carry with me for every exam, for everywhere that I need to remember the carpal bones, and this is the “She Likes To Play. Try To Catch Her.” And the first four words represent the proximal row, and these are for the scaphoid, highlighted here in green now, then you have the lunate, the triquetrum, and on top of the triquetrum, you see the pisiform, which is, as the name indicates, it’s a pea-shaped bone, a small bone on top of the triquetrum.
Now, let’s look at the bones that you find on the distal row, and this is then the last part of the mnemonics, the “Try To Catch Her.” For that matter, you have… you start on the lateral side with the trapezium, then the trapezoid here, a little bit more medially, then move in and you’ll find the capitate, and finally, on the most medial side, you’ll find the hamate.
Now, let’s start talking about the largest bone on the proximal row, and this is the scaphoid. And the scaphoid on the palmar surface, as we’re looking at it right, it does resemble the shape of a tubercle, which then, you can actually feel it through palpation.
Now, let’s talk about articulations of the scaphoid. On the proximal side, right here, the scaphoid is articulating with the radius. On the distal portion here, it’s articulating with two bones, the trapezium and the trapezoid here. Now, on the medial side, it’s also articulating with two other bones, and these are the capitate here, and of course, the lunate right here.
Now, the next bone that we’re going to talk about is also known as the moon-shaped bone or the lunate, and you cannot see here on this image clearly, but if you look at the lunate, it does have a similar shape to a moon.
Now, in terms of articulations, proximally, you can see that it can articulate here with the radius. And on this space here, this wide space, you can find or usually find an articulate disk that actually prevents the lunate from entirely being involved in the wrist joint. Now, if you look at it laterally, this bone or the lunate is articulating here with the scaphoid. On the medial side, is with the triquetrum. And on a most distal part of it, it’s articulating with two bones, the capitate here and the hamate.
Now, the next bone on the proximal row that we’re going to talk about is the triquetrum as you can see here. And the triquetrum has a pyramidal shape, and the tip of the pyramid should be around here on the medial side.
In terms of articulation, you can see here on the lateral side, the triquetrum is articulating with this bone that we talked about, the lunate. And also, you should find here, on the proximal side, the articular disk, and this articular disk is articulating here with the proximal side of the triquetrum. You can see and notice here a little bit of the articulation that you find on the distal portion of the triquetrum, and this is the… or with the hamate right here. Also, notice here the pisiform that I talked about that I said that is lying on top of the triquetrum. And for that matter, the triquetrum needs to have an articular surface on its palmar side, which will then allow the pisiform to articulate with this surface.
Now, let’s talk about the last bone that you find on the proximal row, and this is the pisiform. And the pisiform is the smallest carpal bone and has the shape of a pea. And even here on this drawing, I decided to highlight it in green to make a little bit more obvious.
Now, on the dorsal side or the back part that we cannot see here but that’s say this is the dorsal side of the pisiform, you could find an articular surface that will allow articulation with this bone here, the triquetrum. Like I mentioned before, the triquetrum has also an articular surface on its palmar side that, then, allows these two bones to articulate with one another.
Now, keep in mind, and just for a curious note, that if you turn your wrist to the palmar side, and if you look to the medial portion of your wrist, you can actually palpate and feel the pisiform.
Now, let’s start talking about the bones that you find on the distal row. There are other four like I mentioned. And the one that you find on the most lateral part is, then, the trapezium, and the trapezium, as you can see here, is articulating on its distal portion with the first metacarpal bone. And notice that the surfaces of both the trapezium and also the first metacarpal bone have a saddle-shaped articular surface. Now, medially, as you notice here, this is articulating, or the trapezium is articulating with the trapezoid bone.
Also, between the medial and the distal articular facets, you notice here that the trapezium is articulating with a very small portion of the second metacarpal bone. Now, if you look here on the proximal side, the trapezium is articulating with this bone here, the scaphoid.
The next bone on the distal row, found a little bit more medial to the trapezium, it’s going to be one that has a similar name, the trapezoid, right here, highlighted in green. And keep in mind that on the dorsal side is a little bit wider. So here, on the palmar side that we’re looking at, this bone shows to be a little bit thinner. It looks a little bit thinner.
Now, in terms of articulation, proximally, so on this area right here, it is articulating with the scaphoid. On the distal portion, you can notice that it’s clearly articulating with the second metacarpal bone. On the lateral portion here, then, it’s articulating with its brother, I would say, the trapezium. And then on the most medial side, then it’s articulating with this large bone here, the capitate.
The next bone on the distal row is the capitate, and this is clearly the largest one of the carpal bones. And I usually think of captain every time I think about capitate, and for that reason, that’s why I associate its size and know that it’s the largest of the bunch.
Now, in terms of articulations, you can see that proximally, right here, it’s articulating with the scaphoid and also a little bit here on the lunate—so two bones articulating proximally with the capitate. Now, on the lateral portion, you see that it’s articulating here with the trapezoid. And on the medial portion, here, you see that it’s articulating with this bone that we’re going to talk about next, and this is the hamate.
Now, on the distal portion, you can see that it’s articulating here with the third metacarpal bone, and just a little bit, it sometimes can articulate with the second metacarpal around here and also a little bit with the fourth metacarpal bone.
Now, let’s talk about the last carpal bone of the list of eight that we discussed here on this tutorial, and this is the hamate, also found on the distal row. And the hamate has a structure here that is palpable, that you can feel just under your skin, and this is known as the hamulus, and the hamulus is what is known as the hook. So there is a hook-shaped structure on the hamate that actually gives a name to the bone. And also, this structure is quite important because it is associated with a muscle, the flexor digitiminimi, and also a ligament, the pisohamate ligament.
Now, in terms of articulations, let’s look at every side and every angle to know that on the distal portion, here, there are two articulations with two metacarpals, the first one here laterally, and this is the fourth metacarpal. And on the most medial side, you find an articulation with the fifth metacarpal.
On the lateral side, you can see here that the hamate is articulating here with the big capitate or the big captain, and the hook of the hamate and the captain here laterally, we can even go and talk about the Peter Pan story where there is a Captain Hook, but I will not go there. Anyway, jokes aside, the lateral side of the hamate is articulating with the capitate.
On the proximal side, there are other two bones articulating with the hamate. One on the medial portion, and this is the triquetrum. It’s articulating on the proximal medial side of the hamate. On the proximal lateral side, you see here this other bone, the moon-shaped bone, and this is definitely the lunate articulating with the hamate.