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The radius and ulna articulate with each other at three levels:
Superior (proximal) radioulnar joint
Middle radioulnar joint (via interosseous membrane)
Inferior (distal) radioulnar joint
➡ Together, they allow the rotatory movements of forearm — supination and pronation.
Pivot-type synovial joint.
Head of radius: Cylindrical, articulates medially.
Radial notch of ulna: Concave surface on lateral side of coronoid process.
Annular ligament: Encircles radial head and holds it in place.
Annular ligament:
Strong band attached to anterior and posterior margins of radial notch of ulna.
Forms 4/5 of a ring for head of radius.
Inner surface lined by synovial membrane.
Quadrate ligament:
Between radial notch of ulna and neck of radius.
Limits rotation of head of radius.
Musculocutaneous, Median, and Radial nerves (Hilton’s law).
Rotation of radius around ulna (in supination–pronation).
Interosseous membrane and oblique cord joining radius and ulna.
Connects interosseous borders of radius and ulna.
Fibres run downward and medially from radius to ulna.
Provides firm union between radius and ulna.
Serves as muscle attachment (for FDP, FPL, APL, etc.).
Transmits forces from radius → ulna → humerus.
Maintains relative position during rotation.
Upper aperture: For passage of posterior interosseous vessels.
Lower aperture: For anterior interosseous vessels.
Fibrous band running opposite to main fibres, from ulna (below tuberosity) → radius (below radial tuberosity).
Function: Prevents downward displacement of radius.
Pivot-type synovial joint.
Head of ulna → Convex.
Ulnar notch of radius → Concave.
Articular disc (triangular fibrocartilage complex, TFCC) → between ulna and carpus; strengthens joint inferiorly.
Anterior and posterior radioulnar ligaments → reinforce capsule.
Continuous with cavity of inferior radioulnar joint but separate from wrist joint cavity.
Radius rotates around fixed ulna → supination & pronation.
Passes through head of radius (above) and head of ulna (below).
The radius rotates over ulna.
Supination: Palm faces upward (anatomical position).
Pronation: Palm faces downward.
| Movement | Muscles | Nerve Supply |
|---|---|---|
| Supination | Supinator (in extension), Biceps brachii (in flexion) | Radial nerve (supinator), Musculocutaneous nerve (biceps) |
| Pronation | Pronator teres (rapid movement), Pronator quadratus (slow, steady) | Median nerve |
Allows rotation of hand without movement at shoulder.
Essential for writing, typing, eating, and screwing actions.
Each: ~80–90°.
Complete rotation (supination to pronation): ~180°.
Ask patient to pronate and supinate forearm with elbow flexed 90°.
Observe restriction (may indicate nerve/muscle lesion or joint pathology).
Supinate forearm and make a longitudinal incision along midline.
Expose biceps tendon, brachialis, and supinator around proximal joint.
Identify annular ligament around radial head.
Reflect flexor and extensor groups partially to expose interosseous membrane.
Note its direction of fibres and the oblique cord.
Identify apertures for interosseous arteries.
Trace posterior interosseous nerve between supinator and APL.
Distally, clean the inferior radioulnar joint, identify articular disc, and open capsule to view surfaces.
Demonstrate pronation and supination movements by rotating radius around ulna.
Common in children.
Sudden jerk on pronated forearm → head of radius slips out of annular ligament.
Symptoms: Pain, forearm held semiflexed and pronated.
Treatment: Supination and flexion to relocate.
Restricts pronation/supination due to disruption of radioulnar mechanics.
Fracture of ulna + dislocation of head of radius at superior radioulnar joint.
Fracture of radius + dislocation of distal radioulnar joint.
May cause longitudinal instability and abnormal load transmission from radius to ulna.
Entrapment of posterior interosseous nerve in the supinator → weakness of finger extension.
Seen in median nerve injury → loss of pronators → hand remains supinated.
Due to biceps tendon rupture, posterior interosseous nerve palsy, or post-fracture stiffness.
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