Ulna

Function

The forearm's stable hinge bone. Its olecranon lever is what the triceps pulls on to straighten the elbow, and its firm interosseous bond to the radius transfers hand forces upward.

Landmarks

• Olecranon
• Coronoid process
• Trochlear notch
• Radial notch
• Supinator crest
• Interosseous border
• Styloid process

Articulations (joints)

• Humerus (elbow — the true hinge)
• Radius (radioulnar joints)
• Triquetrum via articular disc (wrist)

Clinical relevance

Olecranon fractures from a direct elbow fall may need wiring of the avulsed fragment; 'pulled elbow' in toddlers is a slipped radial head under the annular ligament beside the ulna.