To begin looking at the bones and joints of the hand, let's see what they’re called.
Here are the eight carpal bones, and here are the five metacarpals. Each finger has a proximal phalanx, a middle phalanx, and a distal phalanx. The thumb just has two phalanges, a proximal phalanx and a distal phalanx.
The joints of the hand have long names. The joints between the carpus and the metacarpals are the carpometacarpal joints. The joints between the metacarpals and the proximal phalanges are the metacarpo-phalangeal joints.
The joints between the phalanges are the interphalangeal joints - proximal and distal. We’ll often refer to these joints as CMC joints, MP joints, and IP joints, for short.
To look in some detail at the bones and joints of the hand, we’ll look first at the carpus, then at the four fingers with their metacarpals, then at the thumb with its metacarpal.
We saw the individual names of the carpal bones in the previous section. Let’s look at their overall shape. There are two bony projections on each side. On the ulnar side, the pisiform bone and this part of the hamate called the hook. On the radial side, the tubercle of the scaphoid and the crest of the trapezium. With these projections the bones of the carpus form the base and side walls of a space called the carpal tunnel.
Here’s how the carpus looks in the living body. The radiocarpal, and mid-carpal joints are hidden by their heavy capsular ligaments. Here are those four projections again, the tubercle of the scaphoid, the crest of the trapezium, the pisiform, and the hook of the hamate. And here’s the carpal tunnel, still without its roof.
Now let’s move on to look at the metacarpals of the four fingers, and at their CMC joints. Here are the carpometacarpal joints. The bases of the four finger metacarpals, tightly packed together, articulate here, with the distal row of carpal bones. The base of the first metacarpal, the one for the thumb, articulates separately here, with the trapezium.
These four carpometacarpal joints only allow a small amount of movement. The fifth metacarpal is the most mobile, the fourth is less so, the third hardly moves at all, and neither does the second. When the CMC joints are flexed, the metacarpal heads lie in a curve.
This strong ligament is the deep transverse metacarpal ligament. It keeps the metacarpal heads of the four fingers from spreading apart. As it crosses each MP joint, the ligament is continuous with a structure that we’ll meet shortly, the palmar plate. Since it doesn’t connect to the first metacarpal, the ligament doesn’t prevent movement of the thumb away from the hand.