The purpose of this section is to orientate yourself with the bony anatomy, allowing you to better understand the articulations and relations of the bones in later objectives and so each bone will be discussed separately. It is important to remember that we are only discussing the features relevant to the radioulnar joints and are not covering the full extent of the anatomy of the bones of the upper limb, information which you may feel free to supplement your learning with using a standard anatomy textbook such as those listed in the references section.
1.1 - Which bones and bony features are involved in the radioulnar joints?
Before we begin, it should be pointed out that the lack of images on this page is not a mistake. It is preferable, for the next few minutes while you read, that you have a picture in your head of what the humerus, radius and ulna look like and that you try to apply the information you are reading to the anatomical knowledge that you already have. In exercise 1.1 you will have the opportunity to label diagrams of the bones based on what you are about to read so full attention please!
As you are already aware, the humerus is the only bone in the arm forming part of the elbow joint at its distal end by articulating with the radius and the ulna. The most lateral of its articular surfaces is called the capitulum which is a hemispheric area on the anteroinferior surface for articulation with the discoid head of the radius. Medially is the trochlea which is a grooved articular surface for a more snug articulation with the trochlear notch of the ulna.
The radius is the more lateral of the two bones in the forearm. The head can be found at the most proximal end and is a thick disc of which the superior surface is concave, almost like a shallow cup, for articulation with the capitulum and the outer articular surface (part of the proximal radioulnar joint) is flattened. It is actually oval in shape if looked at from a superior view. Immediately inferiorly, the neck slopes medially and continues as the shaft which takes on a lateral convexity in the lower three-quarters. The interosseous border, for attachment of the interosseous membrane, can be found extending almost the full length of the medial aspect of the shaft. At the larger, distal end of the radius, the ulnar notch (part of the distal radioulnar joint) can be found on the medial surface. The inferior articular surface has two concavities for articulation with the scaphoid and lunate carpal bones.
Medial to the radius in the forearm, the ulna has a larger proximal end. Here the articular surface of the elbow joint, the trochlear notch, can be found formed from the olecranon process posteriorly and the coronoid process anteriorly. This articular surface is continuous with that of one on the lateral side of the coronoid process, the radial notch (part of the proximal radioulnar joint). The interosseous membrane attaches to the interosseous border which can be found on the lateral aspect of the shaft. Like the radius, the shaft has slight curvatures. Distally, the bone narrows to form a neck which then expands to become the ulnar head which is small and round. Projecting downwards from the posteromedial aspect of the head is the styloid process which is important in the attachment of certain soft tissue structures of the distal radioulnar joint. The inferior surface is flattened and articulates with the articular disc which can be found between it and the triquetrum and the anterolateral aspect has a smooth articular surface (part of the distal radioulnar joint).
Understood? Now click next and complete exercise 1.1!
Exercise 1.1 - Labelling diagrams of the bones
Now that you have read about the bones of the upper limb, you should have an idea of where to locate the bony features which are relevant to the radioulnar joints. Try to complete the following exercise from memory but you may return to the previous page if necessary - just click the back arrow at the top right corner of this page.
Please label the images below* with where you think the following features are located:
On the ulna
- head of the ulna
- trochlear notch
- olecranon process
- coronoid process
- radial notch
- interosseous border
- styloid process
- articular surface for the distal radioulnar joint
On the radius
- head of the radius - superior surface and outer articular surface of the proximal radioulnar joint
- interosseous border
- ulnar notch
- inferior articular surface
On the distal humerus
Once completed, click 'next' to view the answers.
*Diagrams can either be redrawn by yourself or printed out - simply right click to save the image to your computer before printing.
Exercise 1.1 - Answers
Did you label the diagrams correctly? Here are the answers:
Exercise 1.2 - quiz!!
Saying as it's the first quiz, let's make it a fairly simple one! Match the parts of the sentences below to create the correct full statements concerning the features and configuration of the bones involved in the radioulnar joints.
The radial notch can be found on thelateral aspect of the distal ulna.
The ulnar notch can be found on themedial aspect of the proximal radius.
Of the two bones of the forearm, the radius is the mostlateral.
Of the two bones in the forearm, the ulna is the mostmedial.
The capitulum articulates withthe superior surface of the head of the radius.
Distally, the inferior articular surface of the radius articulates withthe scaphoid and lunate carpal bones.
Distally, the inferior articular surface of the ulna articulates withthe articular disc.
A bone which does not articulate with either the radius or the ulna isthe triquetrum.
Of the two ends of the radius, the proximal end issmaller.
Of the two ends of the ulna, the proximal end islarger.
The head of the radius can be described asa thick disc.
The head of the ulna can be described assmall and round.