CorpusHuman Anatomy
SkeletalBone

Ulna

Ulna

Also known as: olecranon, coronoid process, ulnar styloid

The medial bone of the forearm (on the little-finger side), large proximally where it forms the main hinge of the elbow with the humerus, and small distally where its head is separated from the carpus by an articular disc.

Show on body map Muscles — Posterior View

Overview

Proximal end: the large hook-shaped olecranon (point of the elbow; insertion of triceps) and the anterior coronoid process together form the jaws of the trochlear notch, which grips the trochlea of the humerus in a hinge joint. On the lateral side of the coronoid process the radial notch articulates with the head of the radius (proximal radioulnar joint), and below the coronoid the ulnar tuberosity receives brachialis. The supinator crest below the radial notch gives origin to supinator.

Shaft: triangular in section, with a sharp lateral interosseous border; its posterior border is subcutaneous along its whole length (palpable from olecranon to wrist). Distal end: the small head of the ulna articulates with the ulnar notch of the radius (distal radioulnar joint) but is separated from the carpal bones by the articular disc of the triangular fibrocartilage complex (TFCC). The short, conical ulnar styloid process projects from its posteromedial side, with a groove for extensor carpi ulnaris between head and styloid.

Location

Medial forearm, from the elbow (olecranon) to the little-finger side of the wrist.

Parts & subdivisions

  1. Olecranon
    Insertion of triceps brachii; point of the elbow.
  2. Coronoid process
    Anterior lip of the trochlear notch; brachialis below on the ulnar tuberosity.
  3. Trochlear notch
    Articulates with the trochlea of the humerus.
  4. Radial notch
    Articulates with the radial head; annular ligament attaches to its margins.
  5. Interosseous border
    Attachment of the interosseous membrane.
  6. Head
    Distal; articulates with the radius; separated from the carpus by the TFCC.
  7. Styloid process
    Distal medial projection; attachment of the TFCC and ulnar collateral ligament of the wrist.

Anatomy

Articulations

Humerus (humero-ulnar joint), radius (proximal and distal radioulnar joints); indirectly with the triquetrum via the articular disc.

Ossification

Primary centre ≈week 8. Distal epiphysis appears ≈5–6 years and fuses ≈17–19 years (growing end); olecranon centre ≈9–11 years, fusing ≈15–16 years.

Function

  • Forms the stable hinge of the elbow with the humerus
  • Acts as the fixed axis around which the radius rotates
  • Attachment for triceps, brachialis, supinator and forearm flexors/extensors

Clinical significance

Monteggia fracture–dislocation

Fracture of the proximal third of the ulnar shaft with anterior dislocation of the radial head; the posterior interosseous nerve may be injured.

Olecranon fracture

From a direct fall on the point of the elbow; the triceps pulls the fragment proximally, so displaced fractures usually need tension-band wiring.

Nightstick fracture

Isolated ulnar shaft fracture from a direct blow when the forearm is raised to protect the face.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.