Functional Anatomy of the Radioulnar Joints

The radioulnar joints can be found in the forearm, one proximally and one distally, functioning as a pair. They serve to rotate the forearm and hand with assistance from the interosseous membrane which also has an important role in the transmission of forces throughout the upper limb. 

This online learning course is designed to aid your understanding of the anatomy of the radioulnar joints in conjunction with how they function. On the next page you will find the objectives of the course, breaking the topic down into subsections. Work through achieving these objectives in order by clicking on them, reading the information and completing the exercises as they are presented to you. Each of the information sections within the objectives are titled as a question which you should be able to answer to yourself after having read the content. Some exercises are activities designed to use skills such as problem solving, and others are quizzes of varying styles but each will come with their own instructions. These will allow you to test your knowledge more definitively as you get instant feedback. Active participation is required throughout the course which may involve you having to draw, print out a worksheet or perform some simple arm movements so all you should need is a pen and some paper (a printer isn't completely necessary, the worksheets are visible onscreen and fairly simple to reproduce). At each stage you will be directed to exactly where to find the answers but do try to work through the exercises to the best of your ability before checking as this will boost your knowledge and memory of the topic. 

You can take a break at any point by clicking 'take a break' in the top right corner, returning to complete the course at a later time but try to cover each section at some stage as this will provide you with the fullest understanding of the functional anatomy of the radioulnar joints. 

Once you have begun working through an objective, you can navigate through the pages by clicking next at the bottom of each page or by using the arrows in the top right corner which will also allow you to return to a previous page. If you wish to return to the list of objectives whilst in the middle of working through an objective, simply click the house icon in the top left corner.

Check your progress in the top right corner of the home page (where the list of objectives are) and only once you have reached 100% click 'submit results'. Important: only do this once you are sure you are finished otherwise you will lose your progress. 

If you are ready to begin, click 'Start Course' above and enjoy!!

1 - Develop an understanding of the bony anatomy relevant to the radioulnar joints

Introduction

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!

The Humerus

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

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.

The Ulna

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
  • neck
  • interosseous border
  • ulnar notch
  • inferior articular surface

On the distal humerus

  • capitulum
  • trochlea

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 the
    lateral aspect of the distal ulna.
  • The ulnar notch can be found on the
    medial aspect of the proximal radius.
  • Of the two bones of the forearm, the radius is the most
    lateral.
  • Of the two bones in the forearm, the ulna is the most
    medial.
  • The capitulum articulates with
    the superior surface of the head of the radius.
  • Distally, the inferior articular surface of the radius articulates with
    the scaphoid and lunate carpal bones.
  • Distally, the inferior articular surface of the ulna articulates with
    the articular disc.
  • A bone which does not articulate with either the radius or the ulna is
    the triquetrum.
  • Of the two ends of the radius, the proximal end is
    smaller.
  • Of the two ends of the ulna, the proximal end is
    larger.
  • The head of the radius can be described as
    a thick disc.
  • The head of the ulna can be described as
    small and round.

2 - To develop a general understanding of the radioulnar joints

Introducing the radioulnar joints

There are two radioulnar joints in each forearm in the human body. The lateral aspect of each end of the ulna articulates with the radius at individual synovial pivot joints termed the proximal and distal radioulnar joints (Fig. 2.1)
Figure 2.1. The red circles outline the location of the proximal (right) and distal (left) radioulnar joints.

Exercise 2.1. Draw a schematic diagram of the basic and fundamental components of a synovial joint. At the end of this page click next to see an example and check that you have included all the components.

Pivot joint – a synovial joint in which the movement occurs about a single axis with the convex articular surface of one bone parallel to the longitudinal axis of that bone. 

There is also a fibrous sheet between the shafts of the two bones, the interosseous membrane, which is sometimes considered as the middle radioulnar joint. 

Exercise 2.2. Answer the following questions:

  1. Can you think of the specific name for a fibrous joint found between two long bones?

  2. What is the main difference between this type of fibrous joint and a suture of the skull in the fully developed adult?
    Answers on the following page.

As will be explained more fully in later objectives, the structure of the bones and these joints allows the radius to rotate around the ulna producing the actions of pronation and supination of the forearm. Functionally they act as a unit and disruption of one results in a loss of these movements as well as disruption of the transferring of loads from the hand to the rest of the upper limb. However, firstly we will examine these joints in more detail in isolation so as to develop an understanding of their configuration which we can apply to allow a deeper understanding of their function altogether. 

 

Answers

Exercise 2.1.

This is an example of a schematic diagram of a synovial joint. Don’t worry if yours is not identical, what matters is that you have labelled each of the components in a logical place, similar to the image above. 

Exercise 2.2.

 Question 1 – Can you think of the specific name for a fibrous joint found between two long bones?

A syndesmosis

Question 2 – What is the main difference between this type of fibrous joint and a suture of the skull in the fully developed adult?

Unlike the sutures of the skull, syndemoses are moveable.

Quiz

The radioulnar joints are synovial  ¬≠¬≠joints of which there is/are  at the both the proximal and distal ends of the forearm bones. These articulations are between the  aspect of the ulna and the  aspect of the radius and their configuration allows a  movement of the forearm to occur. The interosseous membrane creates a  between the radius and the ulna which permits controlled movement. 

3 - To understand in greater detail the features of the proximal radioulnar joint relevant to its function

Introduction

The proximal radioulnar joint (PRUJ), also known as the superior radioulnar joint, can be found just distal to the elbow joint between the proximal ends of the radius and the ulna. The pages in this objective will take you through the features of the PRUJ which are important mainly to its function and stability.

Figure 3.1. The proximal radioulnar joint in an articulated skeleton.

 

What is the basic anatomy of the annular ligament?

Before explaining the joint in more detail, it is important to note the presence of a vital structure, the annular ligament (Fig. 3.2). This is a strong and flexible band which attaches to the anterior margin and a ridge at or just behind the posterior margin of the radial notch, encircling the radial head and neck. The majority of the proximal border blends with the elbow joint capsule (except posteriorly) and from the distal border a few fibres attach loosely to the radial neck. Externally, the surface blends with the radial collateral ligament. Nonetheless, the band is still well-defined. 

Figure 3.2. The annular ligament from a superior (left) and anterior (right) view.

 

What are the articular surfaces of the proximal radioulnar joint?

There are 3 components to the articular surfaces of the radioulnar joints (Fig. 3.3):

The head of the radius: the hyaline cartilage which covers the superior surface continues onto the circumference of the radial head making it a smooth articular surface for articulation with the fibro-osseous ring. 

Radial notch: is covered in hyaline cartilage and forms one-fifth of the fibro-osseous ring.

Annular ligament: the interior surface is lined with fibrocartilage on its upper part, continuous with the hyaline cartilage of the radial notch and so forms the remaining four-fifths of the fibro-osseous ring. 

Figure 3.3. Exposed articular surfaces of the radial head (left) and annular ligament and ulna (right) of the proximal radioulnar joint coloured blue.  

 

What is the basic anatomy of the joint capsule and synovial membrane at the proximal radioulnar joint?

Fibrous Capsule

The joint capsule of the PRUJ is continuous with that of the elbow joint. Of note is the fact that while distally the capsule attaches to the margins of the trochlear notch of the ulna, laterally it attaches to the annular ligament and not directly to the radius so as not to impede movement at the PRUJ. Posteriorly, the capsule passes underneath the annular ligament to attach to the posterior and inferior margins of the radial notch. 

Synovial Membrane

The synovial membrane is also continuous with that of the elbow joint meaning that the two joints share a synovial cavity. This membrane is attached to the articular margins, lining the capsule and the lower part of the annular ligament. A redundant fold of synovium hangs below the annular ligament (Fig. 3.3) and attaches to the neck of the radius. The lack of capsule enclosing the joint inferiorly at the radius is compensated for by the loose fibres of the annular ligament attaching to the radius which help to support this outpouching of synovial membrane. The quadrate ligament (see next page) functions in a similar manner to prevent herniation of the synovium between the anterior and posterior free edges of the lower border of the annular ligament (Fig. 3.4). 

Fig 3.4. Diagrammatic representation of a coronal section through the elbow and proximal radioulnar joints.

Bonus information: The deepest fibres of the supinator muscle have been found to attach to the synovial membrane fold and it is thought that these help to prevent its compression during pronation (Bozkurt et al., 2005).

What are the stabilising features of the proximal radioulnar joint?

Overall, the joint has limited stability in exchange for a reasonable range of motion, however there are several structures which aid in providing it with support. The primary stabiliser of the PRUJ is the annular ligament, holding the head of the radius securely against the radial notch. Its inferior diameter is narrower than the superior creating a cup-like structure which prevents downward displacement of the radial head. However, due to the oval shape of the radial head, the annular ligament needs to change shape with rotation of the radial head (Outcome 6) and so it may stretch over time (Fig. 3.5). Therefore other stabilising structures are required and these include:

  • The quadrate ligament (Fig. 3.6)– attaching between the radial neck and the inferior surface of the radial notch, not only does it support the synovial membrane on its superior surface but its criss-cross fibres means it is taut in any position
  • The interosseous membrane (Outcome 5)– prevents separation of the radius and ulna

Figure 3.5. Superior view of the oval-shaped radial head stretching the annular ligament as the major (short dotted line) and minor (long dotted line) axes change position with rotation

Figure 3.6. Position of the quadrate ligament between the radius and ulna

 

Quiz - Question 1

  • Anteriorly, the annular ligament attaches to the radial tuberosity
  • The annular ligaments is a well defined band
  • Externally, the annular ligament blends with the radial collateral ligament
  • The annular ligament encircles the radial head and neck
Regarding the annular ligament, select which statements are true and which are false.

Quiz - Question 2

Answer the following question: What are the articular surfaces of the proximal radioulnar joint? (hint: there are 3)

Quiz - Question 3

  • The annular ligament
  • The quadrate ligament
  • The radial tuberosity
  • The elbow joint capsule

Select the correct answer to the following question:

Which structure prevents herniation of the synovial membrane between the anterior and posterior free edges of the lower border of the annular ligament?

Quiz - Question 4

  • the annular ligament
  • joint surfaces
  • the quadrate ligament
  • the interosseous membrane
  • the joint capsule
  • the tendon of biceps brachii
Select from the list below the 3 main stabilising features of the proximal radioulnar joint

4 - To understand in greater detail the features of the distal radioulnar joint relevant to its function

Introduction

The distal radioulnar joint (DRUJ)(Fig. 4.1), also known as the inferior radioulnar joint, can be found between the distal ends of the radius and ulna. The pages in this objective will take you through the features of the DRUJ which are important mainly to its function and stability.

Fig 4.1. The proximal radioulnar joint in an articulated skeleton

 

What is the basic anatomy of the articular disc?

Like with the PRUJ and the annular ligament, it is important to ensure there is an awareness of the articular disc (Fig. 4.2) as an important structure at the DRUJ. It is a fibrocartilaginous structure which is triangular in shape. The apex attaches to the lateral side of the root of the ulnar styloid process and the base to the inferior edge of the ulnar notch, therefore intervening and preventing articulation between the ulna and the carpus. It is part of a collection of structures known as the triangular fibrocartilaginous complex (TFCC) which also consists of the ulnar collateral ligament and the radioulnar ligaments. We will only cover elements of the TFCC in minimal detail in this course but if you would like to read more then Soucacos and Darlis (2009) explains its structure and function in more detail.  

Figure 4.2. Anterior (left) and inferior (right) view of the articular disc at the distal radioulnar joint.

 

What are the articulating surfaces of the distal radioulnar joint?

At the DRUJ the convex head of the ulna articulates with the concave ulnar notch of the radius (Fig. 4.3). The ulnar head is covered in hyaline cartilage anteriorly and laterally which is continuous with that on the distal end where it articulates with the articular disc. The ulnar notch faces medially and is also lined with hyaline cartilage. 

Figure 4.3. exposed articular surfaces of the distal radioulnar joint

 

What is the basic anatomy of the joint capsule and synovial membrane at the distal radioulnar joint?

Fibrous capsule

The fibrous capsule of the DRUJ (Fig. 4.4) is weak and loose, permitting movement between the radius and ulna. Transverse bands of fibres, thickened by the radioulnar ligaments (Soucacos and Darlis, 2009), attach to the anterior margins of the radial notch and to corresponding regions on the ulna. Inferiorly they blend with the margins of the articular disc but superiorly they remain separated. 

Synovial membrane

Quite simply, the synovial membrane of the DRUJ lines the capsule, projecting proximally in front of the anterior surface of the interosseous membrane as the sacciform recess (Fig 4.4). Therefore, the synovial membrane is large in relation to the size of the joint. 

Figure 4.4. Anterior view of the distal radioulnar joint showing the joint capsule and sacciform recess anterior to the interosseous membrane

 

What are the stabilising features of the distal radioulnar joint?

Even though the joint capsule is loose, the DRUJ is a very stable joint. This is mainly due to the articular disc uniting the distal ends of the bones but is also as a result of the presence of the interosseous membrane and the pronator quadratus muscle (Fig 4.5).

Figure 4.5. Anterior view of the location of pronator quadratus

For a more in depth understanding of the stability of the DRUJ, Hagert and Hagert (2010) discuss the role of features such as the radioulnar ligaments as well as the concept of tensegrity – a balance of compression and tension forces – in maintaining stability of the joint.

Quiz - Question 1

What are the attachments of the articular disc at the distal radioulnar joint?

Quiz - Question 2

  • The inferior surface of the ulna
  • The ulnar notch
  • The radial notch
  • The inferior surface of the radius
  • The anterior and lateral aspects of the head of the ulna
Select from the list below the articular surfaces of the distal radioulnar joint

Quiz - Question 3

  • The synovial membrane is large in relation to the size of the joint
  • The synovial membrane is small in relation to the size of the joint
  • The fibrous capsule is weak and loose
  • The radiocarpal ligaments blend with the joint capsule
  • The capsule is closed superiorly
Regarding the joint capsule and synovial membrane of the distal radioulnar joint, decide if the following statements are true or false

Quiz - Question 4

  • Pronator quadratus
  • Pronator tertius
  • Biceps brachii
  • Quadratus femoris

Answer the following question:

What is the name of the muscle which definitely acts as a stabiliser of the distal radioulnar joint?

5 - To understand the basic anatomy of the interosseous membrane and its functional importance as part of the upper limb

Introduction

The interosseous membrane(Fig 5.1) is sometimes referred to as the middle radioulnar joint and it plays an essential role in allowing the proximal and distal joints to function as a pair

Figure 5.1. Location of the interosseous membrane as represented by the red hatchings
 

 

What is the basic anatomy of the interosseous membrane?

The basic anatomy of the interosseous membrane(Fig. 5.2) relevant to this course is as follows:

  • It is a strong, fibrous sheet
  • It attaches between the interosseous borders of the radius and ulna
  • Superior border attaches 2-3cm below the radial tuberosity and slightly lower on the ulna – it is deficient superiorly
  • Predominantly, its fibres pass downward and medially from the ulna to the radius

Fig 5.2. Anterior view of the interosseous membrane

 

What is the function of the interosseous membrane?

As well as providing a surface for muscle attachment and preventing migration of the forearm bones, the interosseous membrane is implicated in the transferring of forces in the upper limb.

At the radiocarpal joint, the radius has a large area of articulation with the scaphoid and lunate through which forces from the hand can be transferred to the forearm. However, at the elbow, the ulna has a far more effective articulation with the humerus in comparison with the radius. It makes sense, therefore, that these forces are transferred from the radius to the ulna before reaching the elbow, so to speak, before they are transferred to the humerus. How do you think this happens?

Thought of an answer? Click next to see if you were correct.

 

Answer

The oblique orientation of the fibres of the interosseous membrane passing downward and medially form the radius to the ulna transfers the forces from one bone to the other. This is most effective when the hand is in the midprone position. In fact, Birkbeck et al. (1997) proved this by demonstrating that when force was applied at the wrist, the radius carried 68% of the load and the ulna 32% whereas at the proximal ends of the bones the radius carried 51% and the ulna 41%. When the interosseous membrane was then sectioned, the forces at each end of the bones were equal thus proving the role of the interosseous membrane in transferring loads from one bone to the other.

6 - To be able to apply the information from the previous objectives in developing an understanding of how the radioulnar joints produce movement in the forearm

Introduction

As has probably become clear by now, the PRUJ and DRUJ are fairly specialised to produce very specific movements. In this section we will cover how the components of the joints each play their part in carrying out these movements and how rotation of the forearm and hand looks overall. 

What is pronation and supination? (Part 1)

In the anatomical position, with the palms facing anteriorly, the forearm is supinated. If you turn your palm in the direction of your body so that it faces posteriorly your forearm is pronatedTry these movements for yourself now.

This holds true when you flex the elbow joint to 90degrees so that palm first faces towards the ceiling (supination) and then the floor (pronation). However, if you stop the movement halfway so that the palm of the hand is vertical, i.e. parallel to the wall, then the forearm and hand are in the midprone position. Try these movements for yourself now.

In fact, pronation and supination are possible with the upper limb in any position when the hand is free to move in space. Try this for yourself now.

You can check to see if you carried out the correct movements by clicking next. 

What is pronation and supination? (Part 2)

Above:  superior view of the forearm and hand in the midprone (left), pronated (middle) and supinated (right) positions when positioned on a flat surface

Below: anterior view of the forearm and hand in the midprone (left), pronated (middle) and supinated (right) positions when the elbow is flexed to 90degrees

 

What is the range of movement for rotation of the forearm?

As demonstrated in the pictures on the previous page, it is possible to pronate the forearm through 180degrees from full supination, any further movement is prevented by passive resistance of the opposing muscles but, when the elbow is fully extended, if the humerus is medially rotated then the hand can be turned through 360degrees. However, the quoted ranges of motion do vary between texts. Also, it is interesting to note that most activities of daily living do not require the full range of motion, as demonstrated by Morrey et al. (1981).

The hand is carried with this rotation meaning it has another axis of movement at the wrist, increasing the variety of positions of which the hand can be placed and improving its stability for intricate tasks.

Which muscles are involved in pronation and supination?

Before reading on, with your knowledge of where muscles in the upper limb attach, first have a think for yourself which muscles might be involved in producing pronation and supination.

Pronationpronators teres and quadratus are involved in producing this movement with pronator teres being the more powerful. However, there is some debate as to whether flexor carpi radialis is also involved – anatomical texts (Palastanga and Soames, 2012) say it is but studies  such as Basmajian (1969 as cited in Nordin and Frankil, 1989) would disagree.

Supination – when the elbow is fully extended, only supinator produces this action. However, when the elbow is flexed the tendon of biceps brachii is no longer parallel to the shaft of the radius allowing it to also act as a supinator.

Supination is the more powerful of the two movements.

Exercise 6.1 - Answer the following questions then click next to reveal the answers.

  1. Can you think of some activities that require pronation and supination in everyday life?
  2. Which position of the upper limb do you think these movements are most powerful in?

Answers

Question 1 – Can you think of some activities that require pronation and supination in everyday life?

Activities include: using a screwdriver, opening a door, carrying food to the mouth, acts of personal hygiene, drinking from a cup, turning the pages of a newspaper, turning the steering wheel of a car, etc. etc. etc. Pretend to be doing some of these activities just now if you are not sure and make a conscious effort to notice when you use pronation and supination to manoeuvre your hand throughout the day.

Question 2 – Which position of the upper limb do you think these movements are most powerful in?

When the elbow is flexed to 90degrees.

How are the bones moving throughout pronation and supination and what is the axis of movement?

Movements of the radius and ulna

Considering the movements during pronation

  • At the PRUJmainly, the radial head rotates medially within the fibro-osseous ring. The fact that the joint capsule and annular ligament, except for its few loose distal fibres, do not attach to the radius and the flexibility of the annular ligament allow for the freedom of rotation but tension in the quadrate ligament may limit the movement. Unlike at the DRUJ, the radius remains lateral to the ulna.
    A number of related movements also occur at the radial head; the concave superior surface glides against the capitulum, the bevelled ridge glides in the capitulotrochlear groove, it is laterally displaced as its major axis comes to lie transversely and the plane tilts laterally and inferiorly as the radius moves obliquely around the ulna (Fig. 6.1)
  • At the DRUJ - the distal end of the radius, along with the articular disc, swings around the head of the ulna. As this happens, the head of the ulna is displaced posteriorly and laterally to due to an amplification of the slight extension and medial displacement of the trochlear notch at the elbow brought about by anconeus. However, the head of the ulna does not rotate during this process, demonstrated by the fact that its styloid process remains posteromedial throughout (Fig. 6.2)
  • At the interosseous membranespirals with the movements of the bones, maintaining their proximity throughout.

Ultimately, the result is the radius crossing the ulna anteriorly and obliquely (Fig. 6.3), a position which is further enabled by the curvature of the shafts of the bones and features such as the hollowing of the ulna to accommodate the radial tuberosity throughout rotation.

The reverse of these movements is supination which brings the bones back to their parallel alignment (Fig. 6.4). 

Figure 6.1. Diagrammatic representation of the anterior view of the position of the radius head in relation to the ulna during supination (left) and pronation (right)

Figure 6.2. Movements of the radius and ulna during pronation at the distal radioulnar joint

Figure 6.3. Superior view of the forearm of an articulated skeleton laid on a flat surface in the pronated position

Figure 6.4. Superior view of the forearm of an articulated skeleton laid on a flat surface in the supinated position

Axis of movement

The axis of movement of pronation and supination is classically described as a line, oblique to the longitudinal axis of the bones, passing from the centre of the radial head and through the ulnar head at the base of the styloid process. However, this axis is not stationary due to the fact that, as described above, the ulnar head moves posterolaterally during pronation and anteromedially during supination. Therefore, the axis of movement is also displaced laterally or medially.

This is a slightly simplified explanation. For more detail about how the axis of movement can change depending on which finger rotation is occurring about, see Palastanga and Soames (2012).

Supplementary information

Effect of elbow flexion/extension on pronation and supination:

Shaaban et al (2008) found that pronation was more possible with the elbow extended and that supination was greater when the elbow was flexed. This has a functional advantage if we think about the actions of bringing the hand to the mouth (flexion and supination) or typing on a keyboard at a distance (extension and pronation).

Another method to demonstrate the extent of the movements of the radius and ulna:

Adapting and simplifying a study by Russell et al. (2009) we can use markings on the skin to demonstrate the extensive movement of the radius in comparison to the relatively stationary ulna when performing pronation and supination. Grab a friend to help you and carry out the following:

  1. Ask your friend to lie flat on the ground
  2. Abduct their arm to approx. 90degrees
  3. Flex their elbow to approx. 90degrees so that their fingers are pointing to the ceiling
  4. Position their wrist in the midprone position i.e. palm facing the direction of their feet
  5. Now, with their permision, use a pen to draw 6 circles on the forearm of around 2cm diameter as perfectly as you can. The positions of the circles should be just distal to the elbow, mid-forearm and just proximal to the wrist on both the radial and ulnar sides
  6. Now ask your friend, with their arm in the same position as before, to pronate and supinate their forearm and hand
  7. Observe how the circles you have drawn distort to a more ellipsoidal shape on the radial side than on the ulnar side

This demonstration of a greater change in skin tension on the radial than the ulnar side of the forearm during pronation and supination further demonstrates how much more the radius moves during rotation of the forearm than the ulna does.

Further details of both of these studies can be found in Lees (2013). 

Quiz - Question 1

Drag and drop the labels which correspond to the position of the forearm and hand in each picture. Note: the arm is positioned on a flat surface.
  • supinated
  • midprone
  • pronated

Quiz - Question 2

Drag and drop the labels which correspond to the position of the forearm and hand in each picture. Note: This is an anterior view with the elbow flexed to 90degrees.
  • pronated
  • supinated
  • midprone

Quiz - Question 3

  • Tension in the quadrate ligament may limit rotation at the proximal radioulnar joint
  • The head of the ulna rotates in the fibro-osseous ring
  • It is not possible to pronate and supinate the forearm when the elbow is fully extended
  • The head of the ulna does not rotate throughout pronation
  • The interosseous membrane is spiraled in supination
  • The radius and ulna are in parallel alignment in supination
  • The distal end of the radius and the articular disc swing around the head of the ulna during pronation
  • Using a screwdriver requires pronation and supination
  • Pronation is more powerful than supination
  • Biceps brachii acts as a supinator in all positions of the upper limb
  • Pronator teres is the more powerful of the two main muscles producing pronation
Regarding the movements of the radioulnar joints, decide whether the following statements are true or false.

7 - Expand on knowledge by exploring topic in more detail through own research

Building on what you have learnt...

Just because you have completed this course it doesn't mean your learning has to stop here! There is plenty more information to be uncovered about the radioulnar joints so why not do some of your own research? If any particular aspect of what has been covered has caught your interest, see if you can find some scientific papers to add depth to your understanding in that area.

Also, this course is not an all-inclusive guide to the radioulnar joints.  Think about the knowledge you have regarding anatomy already and try to apply it to these joints or use textbooks to complete the picture. Areas to consider include:

  • blood supply
  • innervation
  • muscle attachments
  • relations

References

References

Birkbeck, D.P., Failla, J.M., Hoshaw, S.J., Fyhrie, D.P. and Schaffler, M. (1997) The Interosseous Membrane Affects Load Distribution in the Forearm. Journal of Hand Surgery – American Volume, 22A(6), pp. 975-980.

Bozkurt, M., Acar, H.I., Apaydin, N., Leblebicioglu, G., Elhan, A., Tekdemir, I. and Tonuk, E. (2005) The Annular Ligament: An Anatomical Study. American Journal of Sports Medicine, 33(1), pp. 114-118.

Hagert, E. and Hagert, C. (2010) Understanding Stability of the Distal Radioulnar Joint through an Understanding of its Anatomy. Hand Clinics, 26(4), pp. 459-466.

Lees, V.C. (2013) Function Anatomy of the Distal Radioulnar Joint in Health and Disease. Annals of the Royal College of Surgeons of England, 95(3), pp. 163-170.

Morrey, B.F., Askew, L.J., An, K.N. and Chao, E.Y. (1981) A Biomechanical Study of Normal Functional Elbow Motion. Journal of Bone and Joint Surgery – American Volume, 63(6), pp. 872-877.

Nordin, M. and Frankel, V.H. (1989) Basic Biomechanics of the Musculoskeletal System. 2nd ed. Philadelphia: Lea & Febiger.

Palastanga, N. and Soames, R. (2012) Anatomy and Human Movement. 6th ed. Edinburgh: Churchill Livingstone.

Russell, C.J.H., Bush, J.A., Russell, G.W.P., Thorlby, A., McGrouther, D.A. and Lees, V.C. (2009) Dynamic Skin Tension in the Forearm: Effects of Pronation and Supination. Journal of Hand Surgery – American Volume, 34A(3), pp. 423-431.

Shaaban, H., Pereira, C., Williams, R. and Lees, V.C. (2008) The Effect of Elbow Position on the Range of Supination and Pronation of the Forearm. Journal of Hand Surgery – European Volume, 33(1), pp. 3-8.

Soucacos, P.N. and Darlis, N.A. (2009) The Distal Radio-Ulnar Joint Function Anatomy, Biomechanics, Instability and Management. European Instructional Lectures, 9, pp. 115-124.