RADIOULNAR JOINTSLearning outcome:

Name the radioulnar joints. Specify the type of each joint. Describe the type, articular surfaces, fibrous capsule, synovial membrane,

ligaments & neurovascular supply of superior radioulnar joint. Explain the factors responsible for its stability & their clinical significance Describe the type, articular surfaces, fibrous capsule, synovial membrane,

ligaments & neurovascular supply of inferior radioulnar joint.

RADIOULNAR JOINT The two bones of forearm i.e. radius & ulna are articulated to each other at

two sites making the proximal or superior & distal or inferior radioulnar joints. The two bones are also connected by the Interosseous membrane. The description of these two joints is as under:

1. PROXIMAL (SUPERIOR) RADIOULNAR JOINT: ARTICULAR SURFACES:

The joint is formed by articulation between the circumference of the head of the radius and the anular ligament and the radial notch on the ulna.

TYPE Synovial pivot joint

CAPSULE• The capsule encloses the joint and is continuous with that of the elbow joint

LIGAMENTS• The anular ligament is attached to the anterior and posterior margins of the

radial notch on ulna and forms a collar around the head of the radius. It is continuous above with the capsule of the elbow joint. It is not attached to the radius.

• The small quadrate ligament extends between the neck of the radius and ulna, just below the radial notch.

SYNOVIAL MEMBRANE • This is continuous above with that of the elbow joint. Below, it is attached to

the inferior margin of the articular surface of the radius and the lower margin of the radial notch of ulna.

NERVE SUPPLY• Branches of median, ulnar, musculocutaneous and radial nerves

BLOOD SUPPLY :• The articular arteries supplying the proximal radioulnar joint are derived from

the anastomoses around the elbow region, whereas those supplying the distal radioulnar joint are derived from the anterior and posterior interosseous. arteries.

MOVEMENTS • Pronation and supination of the forearm.

IMPORTANT RELATIONS• ANTERIORLY

Supinator muscle and the radial nerve.• POSTERIORLY

Supinator muscle and the common extensor tendon.2. DISTAL (INFERIOR) RADIOULNAR JOINT:

ARTICULATION The joint is formed by articulation between the rounded head

of the ulna and the ulnar notch on the radius.TYPE

Synovial pivot joint.CAPSULE

The capsule encloses the joint but is deficient superiorlyLIGAMENTS

Weak anterior and posterior ligaments strength the capsule.ARTICULAR DISC

This is triangular and composed of fibrocartilage.It is attatched by its apex to the lateral side of the base of the styloid process of the ulna and by its base to the lower border of the ulnar notch of the radius. It shuts off the distal radioulnar joint from the wrist and strongly unites the radius to the ulna.

SYNOVIAL MEMBRANE This lines the capsule passing from the edge of one articular

surface to that of the other.NERVE SUPPLY

Anterior interosseous nerve and the deep branch of the radial nerve.

BLOOD SUPPLY Branches from radial and ulnar arteries.

MOVEMENTS• The movements of pronation and supination of the forearm involve a rotary

movement around a vertical axis at the proximal and distal radioulnar joints.• The axis passes through the head of the radius above and the attachment of the

apex of the triangular disc below.• In the movement of pronation, the head of the radius rotates within the anular

ligament, whereas the distal end of the radius with the hand moves bodily forward, the ulnar notch of the radius moving around the circumference of the head of the ulna.

• In addition, the distal end of the ulna moves laterally so that the hand remains in line with the upper limb and is not displaced medially. This movement of the ulna is important when using an instrument such as a screwdriver because it prevents side to side movement of the hand during the repetitive movements of supination and pronation.

• Pronation is performed by the pronator teres and the pronator quadratus. • Supination is performed by biceps brachii and the supinator. Supination is the

more powerful of the two movements because of the strength of the biceps muscle.

IMPORTANT RELATIONS• Anteriorly: The tendons of flexor digitorum profundus.• Posteriorly: The tendon of extensor digiti minimi.