Hey, in this video we're going to take a look at the anatomy of the wrist and the hand. It turns out the wrist and hand are incredibly complex. There's lots of bones, lots of ligaments holding all those bones together, and our hands and wrists can make lots of complex movements, meaning there's a lot of different muscles that are there to cause those different movements. So we're going to break this down piece by piece. We'll start by looking at every bone in the hand, then all the joints in the hand and the wrist.
Then we'll focus specifically on the wrist joint or the radiocarpal joint. We'll look at the main ligaments that are giving structure to that joint. as well as the muscles that are causing the different movements of the wrist. And I'll have blank diagrams for you to practice and really learn this well, so stick around to the end of the video and you know the stuff like the back of your hand. I couldn't resist.
All right, let's jump to the whiteboard and get started. So I've got my diagram broken up into an anterior or front side and a posterior or back side of the hand. So the bones of the forearm, we have the radius and the ulna.
The radius you can remember is always on the thumb side. the ulna is always going to be on the pinky side. And when you're standing in anatomical position, you can remember that the ulna will always be medial. It'll be closer to the midline of the body and the radius will always be on the lateral side.
Also, this diagram will be a diagram of the right hand technically. So radius and ulna are the bones of the forearm. arm.
Next, we're going to go to the carpal bones. These are going to be the tiny bones in the wrist, and we've got eight of them. And here's the mnemonic that I use to remember these.
So long to pinky, here comes the thumb. And we'll start kind of on the thumb side. We'll go toward the pinky.
So long to pinky. to pinky, here comes the thumb. Alright so in our mnemonic is going to be the scaphoid bone. Here's how I remember the scaphoid bone. Sometimes whenever I trip and I'm starting to fall and I try to catch myself, I end up scraping this part of my wrist where I catch myself and I get a scab there and of course this is the scaphoid bone.
So just remember scab and scaphoid bone right here. All right, so long. So we have the lunate bone. And somebody, whenever they saw this, they said it looked like the moon.
So they named it lunate. And looking at it, you can kind of, no, it's a bit of a stretch. I'm not seeing the moon shape there. Up next, we have the third bone in the proximal row of carpals. And another word for three is tri.
So we have the triquetrum. The triquetrum is going to be the third bone. And these three bones are going to be the bones that articulate with the radius and this joint right here, the radiocarpal joint.
It's mainly the scaphoid and the lunate, but the triquetrum is involved in that as well. So long to, we have pinky, and this is going to be the pisiform. Pisiform and pinky, they just kind of sound the same. Both start with P.
And the pisiform is a little bit more anterior than the other bones. You can see it's kind of in front of the triquetrum right here. It's also an easy one to find on your wrist.
If you go to the pinky side of your wrist. you can really feel it pretty prominently right there on your wrist. So the proximal row, we've got scaphoid, lunate, triquetrum, and then pisiform. So along the pinky, here comes the thumb. We're going to start with here, which is going to be hamate.
Now the hamate bone, here's my kind of way to remember this. This is a bit ridiculous, but the hamate bone has a hook on it. You can see the hook outlined in gray right here. And I picture a meat locker where they've got a bunch of slabs of ham hanging up from a hook. And those are the hooks of ham.
Therefore the hook of hamate. mate. All right, here comes, so we have the capitate.
Now capitate is referring to head. And if you look at the location of this, it's right in the middle and it's at the top. Just like your head is, your head is right in the middle of your body.
It's at the top. So that's the capitate. Here comes the and thumb. We've got two bones that start with T.
We've got the trapezoid and we've got the trapezium. And these are really easy to get confused. So here's how I remember which is which.
The trapezium rhymes with thumb. So here comes the thumb. trapezium.
So just remember the one that goes with thumb in our mnemonic ends with um, trapezium. And then I just remember that trapezoid is the other one. And of course, I guess they just named this after their favorite geometric shape, which is sort of trapezoid shaped a little bit, if you use your imagination, I guess.
So long to pinky, here comes the thumb, scaphoid, lunate, triquetrum, pisiform, hamate, capitate, trapezoid, trapezium. So those are my memory devices for learning those, but it just takes some time to practice those to really learn them. A little bit later, we'll have a blank. diagram where you can get that practice in. And if you want to take your learning a step farther, I've got note sheets that go along with all of the different diagrams that are in this video.
I also have all these slides in high resolution with all the blank diagrams and everything. All that's available on my Patreon. There's a link down below. It's patreon.com slash seabirdscience.
So if you want to support the channel and take your learning a little bit farther with this, check that out. All right, let's add these to our other side. We've got the scaphoid, the lunate.
triquetrum. The pisiform is not going to show up on our posterior. Whenever you're looking at a posterior diagram, you often won't see the pisiform.
It's going to be blocked by the tricletrum because the pisiform is on the anterior side. We have the hamate, the capitate, the trapezoid, and the trapezium. All right, let's take a look at those carpal bones on the model here. So long to pinky, scaphoid, lunate, tricletrum, pisiform. So coming back the other way, here comes the thumb.
We've got the hamate. This is the hook of hamate right there, kind of sticking up. We have the capitate, which is this tall bone in the middle. We have the smaller trapezoid and then the trapezium.
And in any video about the wrist, I've got to talk at least a little bit about carpal tunnel and what is the carpal tunnel. I'm making a separate video about the carpal tunnel, but just as a basic intro, if you take a look at these carpal bones, you can see the hook of hamate, the pisiform bone, the trapezium and the scaphoid, those both kind of stick up anteriorly and there's this path right here. between those.
There's a ligament that goes across called the flexor retinaculum. And there's a bunch of stuff that goes in between there. There's some tendons that are going to help move the fingers.
And there's a nerve that runs through there called the median nerve. So over time, when you have wear and tear on the wrist, and you start getting inflammation in that carpal tunnel area, it'll start to pinch the median nerve. So the pain that people feel whenever they have carpal tunnel syndrome is going to be the inflammation in that carpal tunnel region right there, pinching on the median nerve and causing that pain.
So those are the carpal bones, the bones of the wrist. Up next, we have the metacarpals. The metacarpals are going to be the bones of the hand. So you can feel your metacarpals on the back of your hand here, and there's the thumb one right there as well.
Just looking at a skeletal diagram, it's easy to think these might be the beginning of the... fingers, but we're still in the hand right here. The fingers are going to be more up in this area. To distinguish between them, we don't have separate names.
We just number them one through five, starting with the thumb. So thumb is going to be metacarpal number one, index finger number two, middle finger number three, ring finger number four, and the pinky or little finger will be number five. Digit number one, your thumb is also referred to as the pollux. Later on, we'll look at a muscle called the abductor pollicis longus. If you see pollicis, it's referring to the thumb.
So it's a good term to know because a lot of the muscles are named after that as well. well. Alright let's add those to the other side and of course we're gonna start with the thumb label them one two three four and five.
You can see where they articulate with these different carpals. Some of them line up like the pollux and the trapezium or the second digit and the trapezoid. Some are gonna kind of articulate with multiple such as the fourth metacarpal will articulate the hamate and the capitate.
Up next we have the bones of the fingers and these are gonna be the phalanges. Our first of those is gonna be the proximal phalanx of the pollux or the thumb and phalanx is just the singular form of phalanges. So we have the proximal phalanx of the thumb and then the distal phalanx of the thumb. So if you look closely at the thumb, this would be the metacarpal, this would be the proximal phalanx, and then the distal phalanx. Now the thumb has proximal and distal, but the rest of the fingers are going to have a proximal, middle, and distal.
So here we have the proximal phalanx. Here we have the middle phalanges. and then finally we'll have the distal phalanges which make the tip of the fingers so on the hand we have the metacarpals then the proximal middle and distal phalanges add those to our posterior diagram so those are all the bones of the hand and the wrist joint now let's take a look at all of the joints that are involved in the hand and the wrist so you can see based on our diagram there's a lot of different surfaces where bones are articulating with each other we've got a surface right here between the carpals between the carpals and metacarpals metacarpals and phalanges between the different phalanges so there's a lot of different joints in involved here.
All right, let's start with the radiocarpal joint. The radiocarpal joint is going to be between the radius and the scaphoid lunate and triquetrum right here. The radiocarpal joint is an example of a condyloid joint, and it's going to allow two different degrees of motion.
We can flex and extend the wrist, so flexion and extension. We can also abduct and adduct the wrist, so this will be adduction and this abduction. Standing in anatomical position, that abduction is going to take their hand away from the rest of the body, and adduction will add that hand back into the body. Also I've got a separate video explaining movement terms.
Check that out if you need help with flexion, extension, abduction, adduction, and other movement terms. Now this is an example of a synovial joint. Synovial joints have a lot of movement in the body.
They are also always going to have articular cartilage. So right here at the distal end of the radius this is going to be covered in smooth articular cartilage. The lunate and the scaphoid are also going to be covered in that articular cartilage. And really any place here where multiple bones are touching each other.
Those are going to be covered in articular cartilage and that cartilage of course is going to reduce the friction between the bones so that we have nice and easy joint movements. When that cartilage breaks down we have something called osteoarthritis which can cause pain and inflammation in the joints. As a synovial joint there's also synovial fluid in these joints which acts further as a lubricant to reduce the friction and these are all going to be covered by joint capsules as well that keep that fluid in and provide a little bit of stability to each of the joints. Also not drawn into this diagram there's an articular disc which is going to extend out.
out from the articular cartilage of the radius and it's going to cover the ulna. So it kind of fills in some of this space here in this gap between the ulna and the pisiform and triquetrum. That articular disc is just going to be some more supportive cartilage right there.
So that's the radiocarpal joint, a condyloid joint with two degrees of motion, which is going to be flexion and extension, adduction and abduction. Now between the carpals and the metacarpals, we have the carpometacarpal joint. I take that back. We have five carpometacarpal joints. We're going to have one between the trapezium and the first metacarpal, and then one between these carpal bones and each of the other metacarpals.
Some of them have a lot of movement. Some of them don't. The first carpometacarpal, the one labeled right here, also sometimes called the trapeziometacarpal joint, is going to have the most movement.
This is a saddle joint, and it's located right here in the hand. It's not this knuckle. It's down here at the base, and you can actually have quite a bit of movement. You can do flexion and extension.
You can adduct or abduct the thumb. You can do circumduction and then opposition of the thumb whenever you're touching like this or grabbing something. So the trapeziocarpal joint or the first carpometacarpal joint has lots of motion, which allows us to have kind of of opposable thumbs and do a lot with our thumb.
Moving on to digits two through five, the carpal metacarpal joints in those digits are going to be condyloid joints and they're going to have varying degrees of motion. Digits two and three are going to have almost no motion right there. You can feel a little bit of a sliding motion, but you can't really get any flexion or extension to happen in those carpal metacarpal joints right there. But as you move toward the pinky and you get to the fifth carpal metacarpal joint, you can actually feel some flexion and extension happening down here. And that's going to be helpful again in thumb opposition when you you need to bring your your pinky or your ring finger down to your thumb that flexion right there is going to help with that so the carpometacarpal joints we've got a saddle joint in the thumb which has lots of range of motion the first and second carpometacarpal joints have almost no motion as you move toward the pinky and the fifth carpometacarpal joint you have a little bit of flexion and extension that can happen which will help in grasping things you can also see in the diagram where those line up the first metacarpal will articulate with the trapezium the second will articulate mostly with the trapezoid but also with the capitate and the trapezium the third third mostly articulates with the capitate, the fourth with the capitate and the hamate, and the fifth articulates just with the hamate.
All right, moving distally, we have the joint between the phalanges and the metacarpals. So we're going to call that the metacarpal phalangeal joints. And these are going to allow for several degrees of motion.
These are going to be the joints of the knuckle right here. And not only do they do flexion and extension, but they're also going to be able to move like this, like when you're spreading out your fingers. So they're not hinge joints because hinge joints just have one degree of motion, but they're going to be condyloid joints that can move.
like this and like this. So the first MCP or metacarpophalangeal joint will be this knuckle of the thumb and then the second through fifth metacarpophalangeal joints will be right there. And then finally we're going to have the interphalangeal joints. So first we have the proximal interphalangeal joint and in this case these are hinge joints.
They only have one degree of motion so you can see here I can bend my finger like this but I can't do a side to side motion or any other degree of motion for the joints of these knuckles right here. So it's just a hinge joint. It can just do that and that's about it.
So that's the proximal phalangeal joint. And then we're going to have the distal phalangeal joint. That's going to be right here.
And so that would be like this motion. So proximal phalangeal joint, distal phalangeal joint. Both of those are hinge joints, just allowing one degree of motion.
The thumb, however, only has one interphalangeal joint. So we don't call it the proximal or distal. We just call it the interphalangeal joint of the first digit or the interphalangeal joint of the thumb. All right, so we've covered a lot of information so far. If you're trying to learn all this stuff really well, I want to give you a chance to practice it on your own.
That's the only way to learn this stuff. So here's a blank diagram. Pause the video, see if you can name all of the bones as well as all of the joints between the bones and the wrist.
in the hand. All right, here's all that back on the diagram. We've got the radius and the ulna and the forearm.
So along the pinky here comes the thumb. We have the scaphoid, lunate, triquetrum, pisiform, hamate, capitate, trapezoid, trapezium. We've got metacarpals one through five, the bones of the hand here.
We've got the phalanges, the proximal and distal, and the proximal, middle, and distal phalanges of the fingers. We've got the radiocarpal joint, the carpometacarpal joints, the metacarpophalangeal joints, and then the interphalangeal joints between the phalanges. Now, any joint in the body is is going to need ligaments to help keep those bones together and provide stability as they're moving around with each other. It turns out the wrist and hand has a ridiculous number of ligaments, way too many to include in this video.
I've got a separate video that's going to go through all of the different ligaments, especially of these carpal bones right here. So check that out if you want to learn all of these ligaments. Right now we're going to focus on four main ligaments that's going to provide stability to the radiocarpal joint, which is the main joint of the wrist.
So the four main ligaments we're going to look at, we're going to have two ligaments on each side called collateral ligaments. Those ligaments are going to prevent over adduction and over abduction of the wrist and we'll have ligaments on the anterior and posterior side which is going to prevent over flexion and over extension of the wrist let's start with the radial collateral ligament the radial collateral ligament is going to connect the styloid process of the radius with the tubercle of the scaphoid bone this little protrusion right there is called the tubercle of the scaphoid and that little ligament is going to prevent the hand from moving too far in that direction that direction is going to be adduction so that radial collateral ligament is right in here if you try to over adduct the hand that's going to pull taut and prevent your hand from going too far that way up next we're going to have the ulnar collateral ligament so it's one ligament it's kind of got two parts to it and it's going to connect the end of the ulna with the pisiform as well as the triquetrum it's a ligament on the ulnar side so that's going to prevent the hand from over abducting so If you try to abduct the hand too much, this is going to pull taut and prevent your hand from going any farther that way. So the collateral ligaments preventing overabduction and abduction.
Now we're going to have ligaments that prevent overextension and overflexion. We're going to start here with the palmar radiocarpal ligament. break that down.
It's on the palm side. So it's palmar. It's radiocarpal, meaning it's going to connect the radius to some carpal bones and it's a ligament holding bones to bones.
The palmar radiocarpal ligament is really a series of about four ligaments. So I'm going to go through each of those, but if you just need to know the basics here, just know that it's the palmar radiocarpo ligament. The first one we're going to look at is the radioscaphocapitate. What a name for a ligament, right?
But if you break it down, it's just naming the bones that it connects to. It goes from the radius up to the scaphoid, and then on to the capitate. So radioscaphocapitate ligament. Next, we have the radioscapholunate.
And so it's going to connect from the radius to the scaphoid, as well as to the lunate. So radioscapholunate. Then we're going to have two radiolunate ligaments.
We're going to have the long radiolunate. And so it's going to connect from the radius here. I'm going to take this long path to the lunate. And then we'll have a short radiolunate ligament. So radius to the lunate, but it's a shorter path right there.
So all four of those ligaments, their powers combine to form the palmar radiocarpal ligament, which is going to prevent the hand from overextending. So if you try to move your hand back like this, extension, those ligaments are going to pull taut right here and prevent your hand from going back any farther. So we've got the palmar radiocarpal ligament.
And last, we must have something to prevent overflexion. So we need a dorsal radiocarpal ligament. carpal ligament. The dorsal radial carpal ligament is just one of those. It's going to connect the radius up to the triquetrum, and that's going to prevent over flexion of the wrist.
When you flex your wrist as far as you can, that ligament's pulled taut, preventing you from flexing it anymore. All right, in the spirit of learning this stuff really well, here's a blank diagram. Pause the video, see if you can name all of the ligaments involved here, as well as identifying what they prevent, over flexion, over extension, and so forth. All right, we have the radial collateral ligament, which is going to prevent over flexion.
over abduction. We have the ulnar collateral ligament, which is going to prevent over abduction. The palmar radiocarpal ligament, which is going to prevent over extension.
And then the dorsal radiocarpal ligament, which is going to prevent over flexion. Finally, let's move on to the muscles of the radiocarpal joint. There's tons of muscles involved with the wrist and the hand and all of that, but I'm going to break this down into four muscles, or really four categories, but most of the categories just contain one muscle.
And we're going to look at four different types of movement. We're going to have flexion and extension. abduction and abduction and there's going to be two muscles that go with each of these different movements it's not going to give us eight muscles though it's really going to be four groups of muscles because they'll pair together for each of these different movements so i've got this diagram that's going to help us break it down if you can think about it in these terms these would be a lot easier to remember so i've got a little diagram here that includes flexors and extensors obviously flexors do flexion extensors do extension all these muscles are going to have carpi because it's going to be connected to the carpals and then it's either going to be ulnaris or for radialis.
Ulnaris muscles are going to be for adduction and radialis muscles are going to be for abduction. That's going to give us four different combinations. So first we have flexor carpi ulnaris.
This muscle is going to do flexion as well as adduction. We're going to have the flexor carpi radialis. The flexor carpi radialis is going to do flexion as well as abduction. We have the extensor carpi ulnaris.
The extensor carpi ulnaris is going to do extension as well as adduction. And then finally we have the extensor car by radialis. That's going to do extension.
as well as abduction. And that last one, extensor carpi radialis, is going to include a longus muscle and a brevis muscle. So there's two muscles that are extensor carpi radialis muscles.
So anytime you see flexor, it's going to do flexion. Anytime you see extensor, it's going to do extension. And then anytime you see ulnaris, it's going to do abduction.
And anytime you see radialis, it's going to do abduction. If you can remember those, you're going to remember the functions of these muscles really quickly and easily. So let's go back to our diagram of our hands here and add in some muscles and talk about their functions. All right, first let's look at the flexor carpi ulnaris muscle. The flexor carpi ulnaris muscle is going to have an insertion in two spots.
It's going to connect to the hook of handmate right here. It's also going to connect to the anterior side of the proximal base of the fifth metacarpal. That'll be right about in there on the hand. So if you have a muscle that attaches right there and it's pulling, it's going to cause flexion.
It could also pull and cause adduction like this. That's the insertion. So where's the origin? Where's the spot where... it's pulling from so the origin is going to be on the medial epicondyle of the humerus so you've got the humerus here it's going to start here it's going to have the body of the muscle somewhere right here and then it's going to connect right there at the hook of handmate and the fifth metacarpal now technically in my diagram i don't have a muscle labeled here this is going to be the tendon of the flexor carpi ulnaris the actual body of the muscle or belly of the muscle is going to be down further towards the bottom here so that's the flexor carpi ulnaris up next we have the flexor carpi radialis The flexor carpi radialis muscle is also going to have an origin on the medial epicondyle of the humerus.
There's actually a lot of muscles that have an origin right there. And then the muscle itself will be in the forearm. And then it's going to go all the way up and have an insertion. And the anterior side of... the proximal base of the second and the third metacarpals.
So that insertion is gonna be somewhere over here. It's on the radius side, hence radialis. It's a flexor, so whenever you pull on this, it's gonna cause flexion, but it's also on the radius side, so it's gonna cause abduction. So when you abduction, actually do flexion of the wrist, you're going to contract both the flexor carpi ulnaris and the flexor carpi radialis. If you contract both those muscles, those will pull down and flex the wrist.
All of these movements we've been talking about, they're going to take at least two muscles to do. So in this case, the two flexor muscles cause that flexion. Also, before I get corrected too much in the comments, some of these muscles do have additional origins, like the flexor carpi ulnaris also has an origin on the olecranon of the ulna, but I'm not getting into every detail of every muscle here.
Up next, we have the extensor carpi ulnaris muscle. muscle. The extensor carpet ulnaris muscle is going to be on the posterior or back side.
Instead of having origin on the medial epicondyle, it's going to run from the lateral epicondyle. It's going to have the body of the muscle here in the posterior side of the forearm. And then it's going to come up here and connect on the posterior side of the fifth metacarpal. That's going to be on the ulna side, hence ulnaris here.
And it's on the posterior side, so it's an extensor. So now on our diagram, we have both of the ulnaris muscles. And if you think about contracting both ulnaris muscles, the one right here and the one back there, if you contract... both of those at the same time, it's going to pull the hand like this, causing adduction of the hand.
So the flexor carpi ulnaris and the extensor carpi ulnaris, they work together to cause that adduction of the hand. And last but not least, we need the extensor carpi radialis muscles. So first we're going to have the extensor carpi radialis brevis. Just like the ulnaris, it's going to have an origin on the lateral epicondyle of the humerus.
It's going to extend up the forearm, and this one's going to connect or have an insertion at the base of the third metacarpal on the posterior. side. Brevis means short, and it's still kind of a long muscle, but it's a little bit shorter than the longest muscle that we'll see next.
Up next, we have the extensor carpi radialis longus. This one's going to insert on the second metacarpal right here. So brevis inserts here, longus inserts here. Okay, how is that actually longer than the brevis muscle?
Well, it doesn't have an origin on the lateral epicondyle. It's got an origin just superior to the lateral epicondyle, still on the humerus. So it's going to actually be a little bit longer than the brevis is. I've got one more muscle I'm going to add on here. that I didn't talk about yet and that's going to be called the abductor pollicis longus.
I'm adding this one because this one also helps with extension of the wrist joint. Pollicis is referring to the thumb and so the abductor pollicis longus based on the name is going to cause abduction of the thumb or movement of the thumb away from the hand. So because that muscle goes from the ulna and the radius all the way up to the base of the first metacarpal of the thumb, whenever you contract that, that's going to cause extension of the wrist joint.
That'll also cause abduction of the thumb as well but as a muscle of the radiocarpal joint we're focused on the extension there so all three of these muscles the extensor carpi radialis brevis longest and the abductor pollicis longest those are all going to cause extension of the wrist joint so these extensor radialis muscles together with the extensor carpi ulnaris when you contract all those together that's going to cause the extension if you put these radialis muscles together with the flexor carpi radialis all those muscles on the radius side that's going to cause abduction of the wrist so to summarize if you can track the flexor carpi radialis flexor muscles together, you'll get flexion. If you contract the extensor muscles together, you'll get extension. If you contract all the radialis muscles together, you'll get abduction. And if you contract all the ulnaris muscles together, you'll get abduction. All right, that was a lot.
Here's another blank diagram. Take a moment, pause the video, see if you can identify all of these different muscles that we talked about, as well as the action or movement of each of these different muscles. And there's those muscles back on the diagram so you can check how well you did.
All right, so we covered a lot of stuff in this video. We looked at all of the bones of the wrist and the hand. We took a look at all the different joints between the bones and the wrist and the hand, all the way from the radiocarpal up to the distal interphalangeal joints. We studied the ligaments of the radiocarpal joint, both of the collateral ligaments as well as the radial and palmar radiocarpal ligaments.
And then finally, we took a look at the muscles of the radiocarpal joint, including the flexors, extensors, adductors, and abductors of the radiocarpal joint. Special thanks to these awesome supporters on Patreon. Also, here are the timestamps for each of those blank diagrams so you can go back and practice now if you'd like to.
I'm going to be making several other videos about the ligaments, the muscles, a little bit more in-depth on the joints of the hand. Some more great anatomy content coming up. Thank you all for your support and for being here, and I'll catch you in the next video.