Hello everyone! This is Joao from Kenhub. Today, I’m going to do a tutorial on a continuation of the bones of the hand, and this time, we’re going to talk, specifically, in a little bit more detail on the bones of your fingers, the phalanges. And keep in mind that “phalanges” is plural for “phalanx.” So the singular form is phalanx, and a phalanx is one of these bones that you see here, and combined, they are known as phalanges.
Now, keep in mind in terms of direction, we’re looking at the palmar, also known as the volar side of the hand, and for that matter, notice that you have here the radius, located laterally, and the ulna that is located medially. And for that matter, you notice that the radius is located in the same direction as the thumb going all the way to the medial portion where you see the middle finger… the little finger (sorry) located medially.
Now, the phalanges then are the actual bones that define your fingers, going from your thumb, your index finger, your middle finger, annular or ring finger, and your little finger. Now, keep in mind that all your fingers have one, two, three phalanges except your thumb. Notice that your thumb only has one, two phalanges. And for a regular finger other than the thumb, you would say that there is a proximal phalanx, a middle phalanx, and a distal phalanx. Now, on the thumb, because you only have two, then you would say that you have a proximal phalanx and a distal phalanx.
In the clinical setting when you have to report fractures of phalanges or also in an educational setting where you have to just talk about a specific type of phalanx, what you do is you number them according to the position of the fingers. So you will number the phalanges that are found on the thumb, the first; the ones found on the index finger, the second; then the ones found on the middle finger, the third; the ones on the ring finger, then, will be the fourth, and finally, the ones on the little finger would be, then, the fifth phalanges. Now, after that, what you would say is that, if you’re looking at this one here, the proximal phalanx of the index finger, then you would say this is the second proximal phalanx.
Now, let’s start by looking at the proximal phalanges. And as you can see, all the fingers have one proximal phalanx. And what you need to know is that, on the palmar view, you see that the palmar surface of the phalanges is slightly flat or flattened. Now, if you look at the dorsal or the back portion of the proximal phalanges, then you see that it’s slightly convex. Let’s go back to the palmar’s side where I'm going to also show you here that the borders or the sides of these bones are slightly sharp. You know why they’re sharp? Because, here, these are actually sites for attachment, are very important structures or known as the fibrous tendon sheaths of the flexor muscles—very, very important muscles that allow flexing of the fingers.
Now, in terms of structure, there is three main structures that we need to talk about on the phalanges. If we look here at this proximal phalanx of the middle finger, there are three structures. The first one here on the proximal view is known as, then, the base. And the base has an oval socket that allows articulation with the head of the metacarpal. Now, this long structure here is known, then, as the shaft, and at the most distal portion, this is known as the head of the phalanx, or you can also call it trochlea.
Now, moving on to the middle phalanges, and as you can see, there are only four on each hand because the thumb doesn’t have a middle phalanx. And what you need to know about the middle phalanges is that they are also divided into three main structures. If you notice here, a base that is articulating with the proximal phalanx, then there is a shaft, and on the most distal portion, you find also a head that is, then, articulating with the distal phalanx.
Now, let’s finish this tutorial by talking briefly about the distal phalanges. And as you notice here, every finger has one distal phalanx including the thumb. Now, in terms of structure, you notice that the distal phalanges have a base that is articulating with, then, the middle phalanx. And also, you notice that on the distal portion, there is a site for insertion of the tendon of the flexor digitorum profundus—very, very important structure. Now, also on the very tip of the distal phalanges, you see this mushroom cap-shaped structure or known as the tuberosity. So these phalanges, these distal phalanges have, at the very tip, this structure that is known as the tuberosity of the distal phalanges.