Radio-ulnar Joints

Question 1

Classification of both proximal and distal joints

Answer 1

Synovial pivots

Question 2

What is the predominent movement of the joints

Answer 2

Rotation of the radius round the ulna

Question 3

Articular surfaces of the proximal/ superior radioulnar joint (PRUJ)

Answer 3

Head of the radius which rotates within the fibro-osseous ring of the radial notch of the ulna and the annular ligament

Question 4

Describe the annular ligament

Answer 4

Strong, flexible and well defined, attached to the anterior and posterior margins of the radial notch of the ulna, cups the radial head

Question 5

What is the function of the radioulnar joints

Answer 5

Allows positioning of the hand in space to perform delicate tasks and when the combination of pronation and supination of the forearm is combined with movements at the wrist means that the hand is united to the arm by a universal joint

Question 6

Describe the joint capsule of the PRUJ

Answer 6

Continuous with that of the elbow

Question 7

What other ligaments support the pruj

Answer 7

Aside from the annular ligament which is not itself enough:
Quadrate ligament
Interosseous membrane

Question 8

Describe the quadrate ligament

Answer 8

Runs from lower border of radial notch of ulna to adjacent medial surface of neck of radius
Is always under some tension due to criss-cross arrangement of fibres

Question 9

How stable is the pruj

Answer 9

Has good inherent stability due to annular ligament

Question 10

What group are susceptible to radial head dislocation and what is the mechanism of injury

Answer 10

Children
Radial head is pulled out of the annular ligament, is a form of traction dislocation, often due to a sharp tug on the arm

Question 11

What is the main movement at the pruj

Answer 11

Rotation of the radial head within the annular ligament and radial notch

Question 12

Articular surfaces of the distal/ inferior radioulnar joint (DRUJ)

Answer 12

The head of the ulna and the ulnar notch on the lower end of the radius, united by the presence of a triangular fibrocartilagenous intra-articular disc

Question 13

Describe the articular disc of the druj

Answer 13

Attaches via its apex to the lateral side of the ulnar styloid process then by its base to the inferior edge of the ulnar notch of the radius
Is rarely perforated
Inferiorly participates in the radiocarpal joint

See pp. 145 Palastanga for picture

Question 14

Describe the joint capsule of the druj

Answer 14

Relatively loose and weak, inferior margins of the anterior and posterior fibres blend with the anterior and posterior edges of the articular disc

Question 15

How stable is the druj and why

Answer 15

Is very stable and rarely dislocated due to the intra-articular disc and despite the loose joint capsule

Question 16

What is the main movement at the druj

Answer 16

Rotation of the distal end of the radius around the head of the ulna (pronation and supination)

Question 17

During everyday activities radial rotation at the druj is accompanied by what movement and why

Answer 17

Due to the axis of pronation and supination running through the middle finger of the hand (axis of the hand) radial rotation is accompanied by movement of the head of the ulna as it is relatively displaced

The head of the ulna DOES NOT rotate but remains parallel to itself throughout

Question 18

What allows the relative displacement of the ulnar head seen at the druj

Answer 18

Small side to side movement of the trochlea of the humerus and the trochlear notch of the ulna which is mechanically amplified to a considerable movement of the ulna at the druj

Question 19

Describe the interosseous membrane

Answer 19

Runs predominantly obliquely downward and medially

Question 20

What is the function of the interosseous membrane

Answer 20

Allows transmission of forces from the wrist through the radius to the ulna and there to the elbow and humerus
Also site of muscle attachment

Question 21

Describe pronation of the forearm

Answer 21

The movement that causes the bones of the forearm to cross eachother and the palm to be face down

Question 22

Muscles producing pronation

Answer 22

Pronator teres (strongest) and quadratus 
(acting on both superior and inferior radioulnar joints as cannot be functionally separated)

Question 23

Describe supination of the forearm

Answer 23

The movement causing the bones of the forearm to lie parallel to eachother and the palm to be face up

Question 24

Muscles producing supination

Answer 24

Supinator and biceps brachii (strongest)

Question 25

Which movement is more powerful - pronation or supination

Answer 25

Supination

Question 26

In which position are pronation and supination most powerful

Answer 26

With the elbow flexed to 90d

biceps brachii cannot act to supinate when the elbow is extended

Question 27

Where does the axis of pronation/ supination lie

Answer 27

Varies depending on which finger the movement is occurring about but is always through the head of the radius at the PRUJ
At wrist can pass through any point between the 2 styloid processes

Question 28

Range of pronation/ supination

Answer 28

Almost a full 180d

must not involve humeral rotation

Question 29

What restrains pronation/ supination

Answer 29

Predominantly passive resistance of the opposing muscles