I think most people have the location of their elbows mapped accurately, so I wanted to take a look at the shapes involved in this everyday mover. The image below is of the inside of a right elbow joint in anatomical position. It’s how it looks when you let your arm hang down at your side with your palm facing forward. The top bone is the humerus (upper arm bone), the bone on the left is the radius and the bone on the right is the ulna.

Look at how the radius joins the humerus. It articulates with the ball bearing looking part of the bone (capitulum) to bend and the radial notch of the ulna to rotate. It’s an absolutely genius design. This allows us to seamlessly rotate our forearms and put our hands in all kinds of positions while the sturdy and reliable olecranon process of the ulna articulates with the humerus at the olecranon fossa.

The radius bone is named primarily after its function. Radius, radial, rotate. Get it? See it?

See how the peak of the coronoid process of the ulna fits nicely into the trochlea of the humerus? It helps keep the elbow stable and in line when we bend it.

Take a few moments to let this image sink in. It is a truly remarkable design and single handedly separates us biomechanically from all other species. Next we are going map and refine this joints function in order to keep our elbows bending and forearms rotating smoothly.