Bones of the Hand and Wrist

This is a tutorial on the bones of the hand.  In the hand, you’ve got carpal bones, eight carpal bones. You’ve got metacarpals, which are these bones here. And then you’ve got phalanges, which are the bones in the fingers, so these bones here. So you’ve got carpals, metacarpals and phalanges.

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Carpal Bones

The carpal bones are these bones in the wrist. The word ‘carpus’ in Latin means ‘wrist’.  The wrist joint is this articulation with the carpal bones and the radius.  It’s not shown that well on this model, but the radius bone articulates with these two carpal bones, these two proximal carpal bones, the scaphoid and the lunate. The distal end of the radius has articular surfaces for these two bones, the scaphoid and the lunate.

On this diagram, the positioning is shown a bit more accurately.  You’ve got the radius bone here laterally (because it’s thumb side) and you’ve got the ulnar bone here and you’ve got the scaphoid and the lunate bone articulating with the radius. This joint here is the wrist joint.

This joint is a condyloid synovial joint. It’s the articulation between the radius, the scaphoid and the lunate.

As you can see here in this 3D model, the scaphoid and the lunate are slightly more medial than they should be. They should be shifted over more laterally towards the thumb side, so that they articulate with the radius.

Proximal Carpal Bones

When you think of these eight carpal bones, you think of them in two rows. You’ve got a proximal row and a distal row.  In the proximal row, there are four bones.  Again, remembering these should be shifted slightly over laterally, these two bones would be in the proximal row.  The most radial (the thumb side), we’ve got the scaphoid (that’s lateral), then we’ve got the lunate here (just adjacent to the scaphoid bone) and you’ve got these two bones here, the triquetral bone and sitting on top of the triquetral bone, you’ve got this bone here called the pisiform bone.

These are the four bones that make up the proximal row.  You’ve got the scaphoid laterally, lunate, triquetral and pisiform.

Distal Carpal Bones

The distal row of carpal bones on the lateral side, you’ve got the trapezium. Then you’ve got the trapezoid one, the capitate and the hamate.

There’s a mnemonic for remembering these carpal bones and it’s ‘she looks too pretty, try to catch her’. It’s going lateral to medial on the proximal row, then lateral to medial on the distal row.

She (scaphoid), looks (lunate), too (triquetral), pretty (pisiform). And then going back laterally, try (trapezium), to (trapezoid), catch (capitate), her (hamate). So ‘she looks too pretty, try to catch her’.

Often a point of confusion is remembering which one is the trapezium and the trapezoid. The way I remembering it is that trapezium is on the thumb side.  It ends with –um just like ‘thumb’. So trapezium is thumb side. And then you’ve got the trapezoid bone in between the capitate and the trapezium.

The capitate bone is called the ‘capitate’ because the word ‘capitate’ comes from the Latin ‘head’ and it’s got this kind of head here which sits between the scaphoid and lunate bones.  That’s why the capitate is called that.

And I also remember capitate is like the head. It’s like the central, the head bone. It’s the biggest bone in the hand, the capitate.

And the hamate bone is called the ‘hamate’ because the word ‘hamulus’ or ‘hamus’ in Latin is hook.  It’s got this hook-like process on its volar surface. So that’s why the hamate is called the ‘hamate’. And you might remember the bone of the skull, the little process called the hamulus, that’s that hook-like process.

So that’s a way of remembering the carpal bones, ‘she looks too pretty, try to catch her’. And then trapezium, thumb side, capitate has the head and it’s the head bone, so it’s the biggest central bone and the hamate has this little hook because the word ‘hamus’ in Latin means hook.

Metacarpal Bones

Just after the carpal bones, you’ve got the metacarpal bones.  The prefix meta- is Greek. It means ‘after’, ‘around’, ‘beyond’, ‘adjacent’, that sort of meaning. They are after the carpal bones; they’re around the carpal bones, so they’re metacarpals. And these sit in the palm of the hands. I’ll just show you.

If you look at the skin, you can see the position they lie just before the fingers. These are the metacarpal bones and they’re referred to as metacarpal 1-5. The thumb side is the first metacarpal. You’ve got two, three, four, five.  When you’re referring to the metacarpals, you refer to them as the first, second, third, fourth, fifth metacarpal.

Phalanges

And then these articulate with the phalanges. The bones of the fingers are called phalanges.  The singular term is ‘phalanx’ and plural is ‘phalanges’.  In the thumb, you’ve only got two phalanges. You’ve got a proximal and a distal phalanx. In the four fingers, you’ve got proximal, middle and distal phalanges. And again, this is first, second, third, fourth, fifth phalanges.

Often, actually, you’ll hear them referred to as the phalanges of the thumb, index, middle, ring and little finger.  That avoids confusion because sometimes you might think, “Is it the first one, the little one or the thumb?”  To avoid confusion in clinical medicine, you’ll often hear people referring to fractures of the phalanges as the ‘proximal phalanx of the thumb’ or the ‘proximal phalanx of the index/middle/ring/little finger’ because that avoids confusion about which finger you’re talking about.

Joints

You’ve got some joints in the hand that you need to be aware of. The joint between the metacarpals and the carpal bones are called carpometacarpal joints because they join the carpus and the metacarpal.  Carpometacarpal joints between the carpal bones and the metacarpals. And then you’ve got the joints between the metacarpals and the phalanges. These are called metacarpophalangeal joints because they join the metacarpals and the phalanges, so these joints here. So these are the knuckle joints.

And you’ve got this mobile thumb joint. It’s a saddle joint between the first metacarpal and the proximal phalanx of the thumb.

And then you’ve got joints in the phalanges.  On the thumb, you’ve only got a proximal and distal phalanx. You only have one joint. This is the intermediate phalangeal joint. In the fingers, in the forefingers, you have these joints between the proximal and the middle phalanges. And then you’ve got these joint between the middle and the distal phalanges.

The first one is called the proximal interphalangeal joint and the distal joint is the distal interphalangeal joint.  They’re referred to as PIP’s and DIP’s for short and the metacarpophalangeal joints are referred to as the MCP joints.

Clinical Points

In rheumatoid arthritis, you get problems at the metacarpophalangeal and proximal interphalangeal joints. Whereas with osteoarthritis, you get problems at the distal interphalangeal joints, so the DIP’s.

You’ve got the carpometacarpal joints, the MCP joints at the knuckles. You get intermediate phalangeal joint of the thumb and the proximal interphalangeal joints (the PIP joints) and the DIP (distal interphalangeal joints).

One last point to bear in mind, which I forgot to mention before is that the scaphoid bone, its blood supply enters it distally.  A fall on the outstretched hand often fractures the scaphoid bone. This is something to bear in mind. Because it receives its blood supply distally, if it’s fractured, the proximal fragment can die in a process called avascular necrosis.  It’s important to be aware of that point.

So those are the bones of the hand.