Video: Bones of the wrist and hand
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You already know that you use your hands for a lot of different activities like writing, cooking, and, of course, dissecting. Hopefully, you won't be using your hands for the last two at the same t... Read more
You already know that you use your hands for a lot of different activities like writing, cooking, and, of course, dissecting. Hopefully, you won't be using your hands for the last two at the same time. That would just be weird – don't do it. If you’ve been using our website, you may even be familiar with the muscles, nerves, and arteries that are involved in helping you perform each of these actions. But for this tutorial, we’re going to be diving a little deeper – as deep as you can go, in fact!
Join me as we venture past all the muscles and neurovasculature as we explore the bones of the wrist and hand.
Our first stop on our journey through the 27 bones of the hand will be this proximal cluster of eight small bones called the carpal bones, also sometimes referred to as the wrist bones. Next, we’ll move a little more distally and explore the five metacarpal bones which help form the bulk of the structure of the palm of your hand. This will then take us to our last stop, the 14 phalanges, which form the fingers. To make learning these bones a little easier, we’ll divide them up into proximal, middle, and distal groups. We’ll then look between these various bones to name some important articulations that are found in the hand. At the end of the video, we’ll use what we learn and apply it to a relevant clinical scenario that relates to the bones of the wrist and hand.
We’ll begin our journey with the bones of the wrist called the carpal bones.
To avoid any confusion, let’s first get oriented. Here we have an anterior or palmar view of the wrist and hand. That means that this side – the pinky side – is medial and the thumb side is lateral. You’ll also see this respectively described as the ulnar and radial aspects of the hand. Keep this in mind as we move forward. The last thing you want on this journey is to get disoriented.
Now that we know what we’re looking at, we can delve into the bones themselves. As we mentioned earlier, the carpals are a group of eight bones located at the proximal aspect of the hand. This cluster of small bones can be delineated into two rows – one proximal and the other distal. Grouping them off like this may make it easier to study them.
Let’s run through the carpal bones of the proximal row, moving from lateral to medial.
The most lateral bone of the proximal row is the scaphoid bone. It is named after the Latin word for boat which makes sense because if you squint your eyes and tilt your head, it sort of looks like a small boat. The scaphoid bone has just one prominent landmark – the tubercle of the scaphoid bone – which is found on the palmar side of the bone. This tubercle can be felt through palpation, so why don't you try it out for yourself?
The scaphoid is the largest bone of the proximal row and it lies beneath this region which is known as the anatomical snuffbox. The scaphoid bone is surrounded by several other bones. From a palmar view, it is surrounded on the proximal side by the radius, on the distolateral side by the trapezium bone, and on the distomedial side by the trapezoid bone. Superomedially, it articulates with the lunate bone and inferomedially with the capitate bone. I know, it's a lot of new names, but don't worry. We'll go through all of these bones in just a moment.
As we already identified, medial to the scaphoid is the crescent-shaped lunate bone. Its name is derived from luna, referring to its crescent moon-like shape. The lunate bone has a large proximal articular surface which relates to the radius and also an articular disc that is located in this empty space here between the ulna and carpal bones. It sits medial to the scaphoid bone, superior to the capitate bone, and lateral to the triquetral bone. It may also sometimes come into contact with the hamate bone at its inferomedial angle.
Medial to the lunate is the triquetrum or triquetral bone. The name is a bit funny and maybe hard to say, but it refers to this bone’s three corners, giving it a somewhat triangular or pyramidal appearance. The triquetrum sits upon the hamate bone which is in the distal row of carpal bones and its base faces laterally and communicates with the lunate bone.
The fourth and final carpal bone of the proximal row all the way on the medial side is the pisiform bone. I guess some anatomists long ago thought this little round bone looked like a pea since the word pisiform literally means pea-shaped. The pisiform is a sesamoid bone, meaning it forms within a tendon of the muscle – in this case, the flexor carpi ulnaris muscle. The dorsal surface, or the back of the pisiform, is faceted, meaning it has an articular surface that allows it to articulate with the ventral surface of the triquetrum. Despite being the smallest carpal bone, the pisiform is actually palpable on the medial side of the palmar surface of the wrist.
Now that you’re a master of the proximal row of carpals, we’re ready to move on to the remaining four carpal bones found in the distal row.
Moving back to the lateral aspect of the carpals, we’ll first find the trapezium bone situated in between the scaphoid and the thumb. It has a quadrilateral appearance, meaning it has four sides. To remember this bone and its location, you can think of the thumb swinging on the trapezium like a trapeze artist. On the palmar aspect of the trapezium, there is a palpable tubercle and on its medial side runs a groove that holds the tendon of the flexor carpi radialis.
The trapezium bone is bordered medially by the trapezoid bone and superiorly by the scaphoid bone. Inferolaterally, its main articulation is with the first metacarpal bone via a saddle-shaped facet. Inferomedially, sometimes it also articulates with the second metacarpal bone.
Next is the shorter trapezoid bone, which is the smallest member of the distal carpal row. It is named after its – you guessed it – trapezoid shape. The trapezoid bone may look very small in comparison to the other bones from a palmar aspect, however, keep in mind that it is wider on its dorsal side. It communicates via its proximal facet with the scaphoid bone, laterally with the trapezium bone, medially with the capitate bone, and its distal facet allows it to articulate with the second metacarpal bone.
It can be easy to mix up the trapezium and trapezoid bones as they sound quite similar and are located right beside each other. To remember which is which, try memorizing the phrase “The trapezium is beside the thumb.”
Medial to the trapezoid and smack dab in the middle of the wrist joint is the largest of all the carpal bones – the capitate bone. Capitate comes from the Latin word caput which means head, so you can think of the largest carpal bone as being head of the carpal family. The capitate bone is surrounded by the lunate bone proximally, the third metacarpal bone distally, the trapezoid bone laterally, and the hamate bone medially.
The eighth and final carpal bone is the hamate bone. It has a wedge-shaped appearance and beyond being the most distal and medially located carpal bone, you can identify this bone by its trademark feature – the hook of the hamate. Sometimes, however, this hook is not fused with the rest of the hamate bone and is then referred to as the os hamuli proprium.
The hook of the hamate is also palpable under the skin. This structure is quite important because it is associated with a muscle – the flexor digiti minimi muscle – and also a ligament – the pisohamate ligament. The hamate bone is surrounded from a proximolateral direction by the lunate bone and a proximomedial direction by the triquetral bone. Laterally, it communicates with the capitate bone, and distally, it articulates with both the fourth and fifth metacarpal bones.
Don’t forget – all of these carpal bones can also be seen from the posterior view as well. If you remember their order from the anterior view, then all you have to do is flip it round and you’re good to go. See if you can work your way through it before I reveal the answers.
How did you do? I’m sure you did great. It’s understandable if recalling the eight carpal bones is a little difficult since some of their names are hard to pronounce. Fortunately, you can use a simple mnemonic to help you remember their name and their order. The mnemonic is Sam Likes To Push The Toy Car Hard. Hopefully, remembering this simple sentence can help you remember the names of all eight carpal bones.
Moving distal to the carpals will take us to this group of five bones called the metacarpal bones. Fortunately, you won’t have to learn any Latin when studying their names since they’re simply numbered one to five with the first metacarpal bone being the most lateral on the thumb side. These long bones form the bulk of your hand as they span between the wrist and fingers. Anatomists like to fancifully refer to this region as the hand proper.
The metacarpal bones themselves have a few bony features that are worth mentioning to. The first of which is the base of the metacarpal bones, which is found at the most proximal end of each metacarpal bone. This is the most variable part of this group of bones, meaning the base of each metacarpal bone looks different from the next. We’ll see later on that this bony feature plays an important role in articulating with the carpal bones.
Extending distally from the base are the bodies, or shafts, of the metacarpal bones. This is the long slender part of the metacarpal that gives its characteristic long bone appearance. Its palmar surface tends to be concave longitudinally.
The third and final bony feature of the metacarpals that we’ll look at are the heads of the metacarpal bones. Located all the way at the most distal end of the bone, the head of the metacarpal is responsible for articulating with the fingers, or digits, forming an important joint that we’ll look at in just a minute. The shape of the metacarpal head produces the noticeable prominence on the dorsal surface of the hand known as the knuckle.
Now let's talk a little bit about each individual metacarpal.
The first metacarpal bone is the most lateral, thickest, and shortest metacarpal bone. It is located at the root of the thumb. Its long axis is medially rotated in comparison to the other metacarpals which is a bit more noticeable in this image here. The head of this bone is flatter than the other metacarpals and it features a saddle-shaped articular surface on its base via which it articulates with the trapezium.
The second metacarpal bone is located at the base of the index finger. It has the largest base and the longest shaft. Its base shows several areas for the articulations with the surrounding bones. There is a groove in the coronal plane via which it articulates with the trapezoid bone. Medially to this groove is a ridge for the articulation with the capitate bone while laterally there is a quadrangular surface for the joint with the trapezium bone. There is also an elongated facet on its medial surface for the articulation with the third metacarpal bone.
The third metacarpal bone is located at the base of the middle finger. It differs from the others by a styloid process that projects proximally from the laterodorsal edge of its base, as you can see here in this posterior view. This process participates in the joint with the capitate bone. The lateral surface of the base articulates with the second metacarpal while the medial surface articulates with the fourth metacarpal via two oval articular surfaces.
The fourth metacarpal bone is located at the base of the annular or ring finger. It shows a few specificities of its base. It has two oval facets on the lateral surface via which it articulates with the base of the third metacarpal. The fourth metacarpal bone features a single elongated facet on the medial surface for the articulation with the base of the fifth metacarpal, and finally, the base also has a proximal surface which is quadrangular and serves for the articulation with the hamate bone.
And the last metacarpal, the fifth metacarpal bone, is the smallest and most medial of all five metacarpals. It is located at the base of the little finger. In this posterior view, we can see that the base slightly differs from the other metacarpals as its lateral part is non-articular and instead features a tubercle for the attachment of the extensor carpi ulnaris muscle.
So now we're finished with the metacarpals.
Now we can move on to our final group of bones found in the hand which are the phalanges. These 14 bones are what give structure to your digits or fingers, and despite their small size, they are still technically considered as long bones as each contains a proximal base, body or shaft, and distal head, but more on that in just a moment.
To make learning these little guys a little easier, we can divide them into three groups. Located most proximally are the appropriately named proximal phalanges. As you can see, there are five of these bones, one for each digit. These are the largest and longest of the phalanges. The proximal phalanx of the thumb is an exception because it is shorter and more stout compared to the rest.
If we move a little bit further down the finger, the next bone we come across are the middle phalanges. Notice how there are only four middle phalanges with the thumb lacking in this case. And, finally, our journey ends all the way at the tips of the fingers with the distal phalanges. The thumb rejoins the group so that all five fingers contain a distal phalanx bone. These are the smallest and shortest of the phalanges.
Similar to what we saw with the metacarpals, each proximal, middle, and distal phalanx also have a base at its proximal end. Immediately distal to that, we see the base tapers into a slender body or shaft, although you’ll notice that the body of the phalanges is much shorter than what we saw with the body of the metacarpals. Lastly, located most distally, at the end of each phalanx is the head of the phalanx. In the case of the distal phalanges, this is also known as the tuft or tuberosity of the distal phalanx.
We can identify an individual phalanx according to the number of each finger. So the phalanges of the thumb are the first; the ones found on the index finger, the second; those found on the middle finger, the third; the ones on the ring finger, the fourth; and finally, the ones on the little finger, the fifth phalanges. So, for example, if we wanted to talk about the proximal phalanx of the index finger, we say it is the second proximal phalanx.
Okay, great! Now that we’ve identified each bone of the hand and some of their bony features, let’s identify a few important joints that we find between these bones.
The first joint that we’ll look at is the radiocarpal joint. Even though you could probably already guess which bones form this joint based on its name, let’s zoom in a little and look at this articulation in a little more detail. Now we can clearly see that this joint is formed by the distal end of the radius with the carpal bones; specifically, the scaphoid and lunate bones. This joint permits abduction and adduction at the wrist joint, also known as radial and ulnar flexion or deviation as well as flexion and extension at the wrist joint.
As for the carpal bones, there are several small joints formed between adjacent bones; however, these are collectively referred to as intercarpal joints. Most important of these is the midcarpal joint. As the name suggests, this joint is found right in the middle of the carpal bones between the proximal and distal rows that we looked at earlier. Also occurring at this joint are the flexion, extension, adduction, and abduction movements that we saw earlier with the radiocarpal joint.
Each of the five bases of the metacarpals that we talked about earlier articulate with the carpal bones to form five individual carpometacarpal joints. Like the metacarpal bones themselves, these joints are simply numbered one to five, with the first carpometacarpal joint found laterally on the thumb side. Along with the other two joints that we’ve looked at so far, the carpometacarpal joints also permit flexion and extension at the wrist.
Let me just give you a bit more information about the first carpometacarpal joint – the carpometacarpal joint of the thumb – which is the most specialized and flexible of this group of joints. It is a synovial saddle joint between the trapezium and the base of the first metacarpal bone. It is multi-axial allowing movements in three degrees of freedom – flexion and extension, abduction and adduction, as well as axial rotation. When flexion, abduction, and axial rotation are combined together, they result in a complex movement called opposition. Opposition is the movement by which the tip of the thumb is brought in contact with the tip of any other of the remaining four digits. Thanks to this joint, you can write or grab things.
Moving distally takes us to this next set of joints called the metacarpophalangeal joints. As you can see, these joints are formed by the heads of the metacarpal bones and the bases of the proximal phalanges. This joint allows you to flex and extend your fingers as if you are waving bye-bye to your friends after a long study session.
We’ll find the last joint all the way at the fingers. These are the interphalangeal joints and they are found between the proximal, middle, and distal phalanges that we looked at earlier. Specifically, between the proximal and middle phalanges are the proximal interphalangeal joints while between the middle and distal phalanges is where you would find the distal interphalangeal joints. The thumb, meanwhile, only has one interphalangeal joint since it only has the two phalanges. Collectively, these interphalangeal joints allow your fingers to flex and extend, as if you are making and releasing a fist.
All right, with the bones and joints of the hand being covered, we’re ready to move on and look at some of this anatomy in a clinical context.
Although each and every bone that we learned about today could potentially sustain an injury, we’re going to zero in on the very first bone that we talked about – the scaphoid. In particular, we’ll investigate the clinical considerations of a fracture to this bone.
The scaphoid is the most vulnerable during what’s called a FOOSH injury. FOOSH is simply an acronym for falling on an outstretched hand which describes the mechanism of injury, which is exactly what’s about to happen to our friend here. By reaching out his hand to break his fall, he’ll be directing all of the force of his body weight right onto his wrist, specifically, his scaphoid bone. Ouch!
The most common symptoms of a scaphoid fracture are pain, swelling, and bruising over the wrist and thumb. This makes it kind of difficult to diagnose initially since it’s hard to distinguish a scaphoid fracture from just a badly sprained wrist. If a physician suspects a scaphoid fracture, they will likely order an x-ray to confirm the diagnosis. Can you use your anatomical intellect to identify the fractured scaphoid bone? Remember that the scaphoid is the proximal row of carpal bones and located laterally. If you are able to pinpoint the fractured scaphoid here, then nice work! You’re well on your way to being a successful radiologist.
Treatment for a scaphoid fracture depends on how severe it is. Most mild fractures can be treated by immobilizing the wrist with the use of a cast. More severe fractures may require a surgical intervention to repair the fracture with the use of pins or screws. Repairing the fracture in a timely manner is critical. This is because a fracture to the scaphoid could also damage the small artery that supplies it. If the blood supply to the fractured bone is compromised, this could lead to avascular necrosis or tissue death. This causes a whole other list of problems that you certainly would rather avoid.
And on that happy note, we’re done! Go ahead and give yourself a hand. You’ve made it through the bones of the hand tutorial.
Before we call it a day, let’s take a minute to review what we learned today.
We started off by identifying the carpal bones. Remember that this group of short bones can be separated into proximal and distal rows. Next, we looked at the five metacarpal bones, which are the long bones that are located in the palm of the hand. Remember that these bones don’t have unusual Latin names like the carpals; they’re just simply numbered one to five, from lateral to medial.
In studying these bones, we learned that they have a base located most proximally which tapers and elongates into the body and ends distally as the head. We then moved on to the bones of the fingers called the phalanges. We saw that there are 14 in total including five proximal phalanges, and just distal to the proximal phalanges are the four middle phalanges. Remember that the first digit, or the thumb, does not have a middle phalanx. And, finally, we reached the fingertips which are comprised of the five distal phalanges.
After learning about the bones themselves, we studied the articulations that can be found between them starting with the radiocarpal joint, which is the articulation between the distal end of the radius with the scaphoid and lunate bones. Then we moved a little distally and saw the midcarpal joint, found between the proximal and distal row of carpal bones.
The carpometacarpal joint was next, which is the joint formed by the distal row of carpal bones with the bases of the five metacarpals. The heads of the metacarpals, meanwhile, articulate with the proximal phalanges to form the metacarpophalangeal joints.
And finally, between all the individual phalanges, we studied the interphalangeal joints which we broke up into proximal interphalangeal joints occurring between the proximal and middle phalanges and distal interphalangeal joints which are found between the middle and distal phalanges. Remember that since the first digit only has two phalanges, it only has one interphalangeal joint.
And finally, we examined the clinical implications of the scaphoid fracture. This included looking at the FOOSH mechanism of injury and pain and swelling as the key symptoms. We identified what this injury looks like on an x-ray and discussed immobilization and surgery as potential treatment options to help heal the fracture and prevent avascular necrosis.
And there you have it! I hope you’ve enjoyed your tour through the bones of the hand. Happy studying and see you next time!