In this anatomy lesson, I’m going to cover the anatomy of the two forearm bones, the radius and ulna. These bones are classified as long bones, and they make up part of the appendicular skeleton.
Many people get these two bones confused, so let me begin by giving you a couple of memory tricks to help you keep them straight.
- When you position your arm as if you’re going to shake someone’s hand, the ulna is always “under” the radius. In addition, the large bony part of the elbow’s end is the olecranon process of the ulna (at the proximal end). So if you trace your elbow down, you’ll be feeling your ulna bone.
- When you hold your arms in the anatomical position, the radius is radiating out and away from the body (lateral to the ulna). You’ll also notice that the thumb is always going to be on the same side as the radial bone. In fact, if you watched Nurse Sarah’s video on checking the radial pulse, a common pulse point assessed, she used my thumb as a landmark while locating the radial artery.
When you look at the two forearm bones, you’ll notice that they have a web-looking connective tissue keeping them together. It kind of looks like these two bones just got in a fight with Spider-Man, and Spider-Man won.
This is called the interosseous membrane. The prefix “inter” means between, and “osseous” refers to the bones. Therefore, the name literally means “the membrane between the bones.”
This fibrous connective tissue consists of five ligaments, which not only help support and strengthen the forearm bones, but they also provide attachment points for some of the forearm muscles. This tissue runs along the border of the radius and ulna.
Ulna Bone Anatomy (also called Ulnar Bone)
Looking at the right forearm bones from the anterior (front) view, let’s examine the ulna first, which in the Latin means “elbow.” The good news is that you’ll see some of the same names that you saw when we looked at the humerus anatomy, because some of these parts fit together.
- Olecranon Process – The word olecranon comes from a Greek word that means “elbow head.” This bony prominence forms the elbow at the proximal end of the ulna and allows for the attachment of the triceps brachii muscle. If you watched my video on the humerus anatomy, you’ll know that the olecranon process of the ulna fits into the olecranon fossa of the humerus when the forearm is extended. The word “process” means a pointy growth or projection.
- Coronoid Process – The coronoid process is another bony prominence that is received into the coronoid fossa of the humerus during forearm flexion. It allows for the attachment of the brachialis muscle. Together with the olecranon process, it makes a sort of “C” shape when viewed from the side.
- Trochlear Notch – The trochlear notch is a large depression between the olecranon process and coronoid process that articulates (forms a joint) with the trochlea of the humerus bone, forming a hinge joint.
- Radial Notch – The radial notch is a depression on the ulna that accommodates the medial head of the radius and forms the proximal radioulnar joint. This is the big thing you’ve got to remember about the ulnar notch and the radial notch: They’re names are backwards. The ulnar notch is on the radius, and the radial notch is on the ulna. Don’t get those confused!
- Head of Ulna – Unlike the radius, the head of the ulna is located at the distal end. It articulates (forms a joint) with the radius at the ulnar notch but does not articulate directly with the wrist bones.
- Styloid Process of Ulna – There is a small pointy projection that comes off the head of the ulna, called the styloid process of the ulna. This projection provides an attachment point for the ulnar collateral ligament of the wrist.
Radius Bone Anatomy (also called Radial Bone)
Now let’s look at the radius bone anatomy, which is a Latin word that means “staff” or “spoke.”
- Head – the proximal end (or top) of the radius has a rounded cap looking area. This is the head, and it has a depression at the top that forms a joint with the capitulum of the humerus bone.
- Proximal Radioulnar Joint – The joint between the medial side of the radial head and the radial notch of the ulna is called the proximal radioulnar joint. This is a pivot joint that allows you to rotate your forearm and hand up (supination) or down (pronation).
- Neck – Below any head, you’re going to have a neck. This is the narrower part of the radius just distal to the head.
- Radial Tuberosity – The radial tuberosity is a rounded projection that provides an attachment point for the biceps brachii muscle.
- Styloid Process of Radius – This pointy projection at the distal end of the radius provides attachment of muscles from the forearm and hand, as well attachment of the radial collateral ligament, which articulates with the wrist bones.
- Ulnar Notch – The ulnar notch is a depression that accommodates the head of the ulna and forms the distal radioulnar joint.
- Distal Radioulnar Joint – The distal radioulnar joint is also a pivot joint that allows rotation of the forearm up (supination) and down (pronation).
Free Quiz and More Anatomy Videos
Ready to test your knowledge? Take our free (and quick!) radius and ulna anatomy quiz. Also, you might want to watch more of our anatomy and physiology lectures on YouTube, or check our anatomy and physiology notes.