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Radius and Ulna

Overview of the bones that define the forearm - radius and ulna.

Show transcript

Hello everyone! This is Joao from Kenhub, and I’m bringing you another anatomy lecture where I’m going to talk about the forearm, the bones that you find on the forearm—and using the amazing illustrations provided by Kenhub. And the two bones that you find on your forearm are the ulna, which is found medially, this bone right here, and on the lateral side, you’re going to find another bone known as the radius.

Now, an important thing to know—and you can see here on the posterior view. Keep in mind that this one is the anterior view, and this one is the posterior view—and you can clearly see here that the ulna is a little bit longer than the radius.

Now, knowing that, we’re going to continue on the anterior view where I’m going to tell you that there are three main parts on the radius that we need to discuss. The first one is located proximally, and this is known as, then, the proximal extremity of the radius. And there are a few structures here that we need to look at. Then we’re going to look at the shaft, and finally, we’re going to look at the distal extremity of the radius.

Now, we’re going to start talking about the proximal extremity of the radius, which is the one away from the hand and closest to the shoulder or the center of your body. Now, what you can see here is the head of the radius. And on a posterior view… because this one here that you’re looking at right now, this is the anterior view of the radius. Now, if I show you the posterior view, you see another structure known as the articular facet which continues into another structure that you can see both on the posterior and also on the anterior view. And this one is the one that I'm showing you right now. It’s highlighted in red, and this is this is the articular circumference. Now, you can also see that the radius has a neck, so this is the neck and is located a little bit more distally. And between the neck and the shaft, you will find a radial tuberosity medially.

Now, we’re going to start talking about the shaft of the radius. And you can see here that on the anterior view, as well as the posterior view, you find a lot of twists and turns, and for that matter, we need to define a few surfaces and also the borders that outline them or that separate them. Now, the first one that we’re looking at here on the anterior view, this is known as the interosseous... this is the border that exists between the two bones, the radius and the ulna, then you also find one surface here, this is known as the anterior surface. And then you’ll find a border which is known as the anterior border.

Now, moving on to the posterior view, you also find the lateral surface outlined in green. You find the posterior border which is this outline in blue. And finally, you will find another surface known as the posterior surface of the shaft of the radius.

Now, we’re going to start talking about the distal extremity of the radius. And I have a posterior view of the radius and also the other structures. And what you see here is that the distal view is closer to the hand and a little bit more distance from your shoulder. Now, the first structure that you see here highlighted in green. This is known as the styloid process and is found along the suprastyloid crest.

Now, moving on to a different view, still on the distal extremity of the radius, but now, we’re looking at it on the anterior view. In here, you find another structure highlighted in red. This is known as the carpal articular surface and is found directly at the distal portion of the radius and articulating with the carpal bones.

Now, the next structure that we’re going to look at is still on the anterior view. And here, you find this structure highlighted in blue. And this is known as the ulnar notch, which is found medially to the styloid process and is articulating with the head of the ulna.

We are still talking about the distal extremity of the radius. And now, we have a posterior view where you can see here a few clearly developed grooves where the tendons of the long extensor muscle should pass through. Now, the first groove known as the first groove is found right on the styloid process, and this is where the tendons of the abductor pollicis longus and extensor pollicis brevis muscles pass through. Then the second groove, this is where the tendons of the extensor carpi radialis longus and brevis muscles pass through. Then you have a third groove, and it is an oblique line where the tendon of the extensor pollicis longus muscle should pass through. Now the fourth groove, here is where the tendons of the extensor digitorum and extensor indicis muscles pass through.

Now, I want to still show here, you can see an elevation here. This is known as the dorsal tubercle. And this is a bone ridge found by the third groove and is usually palpable. So you can actually feel this bony element.

Now, we’re going to talk about the second bone that we’re suppose to discuss on this tutorial, and this is known as the ulna. And the ulna is located medially as you can see here. This is an anterior view of the bone. And what you see here is three structures or three areas where we’re going to discuss. The first one is the proximal extremity. You also have a shaft, and we’re going to see other structures here on the distal extremity of the ulna.

Let’s start by talking about the radial notch, highlighted in red, and this is where the radial head will articulate with. And as you can, see it’s located laterally.

Now, let’s move on to, still, an anterior or another anterior view of the ulna, and here, you see other structures. The first one highlighted also in red. This is known as the trochlear notch, which goes all the way to another structure highlighted in green, and this is known as the coronoid process. Now, the other structure that you can still see here on this image is known as the ulnar tuberosity, and this is located right where the shaft originates.

Now, let’s go to the posterior view of the ulna to show you another structure that is highlighted in blue. And this is known as the olecranon. And as you can see, it has a hook shape, and is a bit curved process, and also has a rough surface.

One structure that we find on the shaft of the ulna is highlighted here in green, and it’s known as the nutrient foramen. It is found around the middle of the anterior surface of the ulna.

Now, let’s start talking about the distal extremity of the ulna. And here, you find one main, one main structure known as the head, and the head has two other structures that we need to talk about. The first one is known as the articular circumference, highlighted in yellow, and it’s clearly more evident or seen anteriorly. That’s why we have an anterior view of the ulna.

Now, it’s important to notice here that the ulna does not or is not involved in the wrist joint because there is an articular disc interrupting any joint, any articulation from happening between the joint, between the ulna (sorry) and the wrist bones. But keep in mind that the radius is involved in the wrist joint, and it articulates with the scaphoid and the lunate bones.

Now, another structure that you still see on the head of the ulna, and anteriorly, you can just see a little bit highlighted in red, and this is because this is a process that is projected distally. That’s why you can still see a little bit here on the anterior view, but I'm going to change here to a posterior view where you can clearly see this process. And this process highlighted in red is known as the styloid process of the ulna.

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