Ulna

Original Editor

Top Contributors - Abbey Wright, Kim Jackson, Chrysolite Jyothi Kommu, Rishika Babburu and Joao Costa

Ulna in the anatomical position

Description

The ulna is one of two bones that make up the forearm, the other being the radius. It forms the elbow joint with the humerus and also articulates with the radius both proximally and distally. It is located in the medial forearm when the arm is in the anatomical position. It is the larger of the two forearm bones.

Structure

The ulna is a long bone larger proximally than distally.

Lateral view of ulna. Ulna and radius annotated

Proximal ulna

The proximal ulna is hook-like in form which articulates with the trochlea of the humerus to create the hinge joint of the elbow.

The articulation is formed of the olecranon and the coronoid process.

Olecranon

This is a large, curved bony prominence which is accepted into the olecranon fossa, located on the humerus, during elbow extension.

The olecranon forms the upper part of the semi-lunar notch which is a smooth, large depression and articulates with the humeral trochlea during elbow flexion and extension.

Coronoid process

The coronoid process is a horizontal, bony projection which attaches directly onto the ulnar shaft. It is received into the coronoid fossa of the humerus in elbow flexion. The coronoid process also forms the lower part of the semi-lunar notch.

On the lateral side of the coronoid process is the radial notch where the head of the radius sits.

Head of the ulna

The lateral, distal end of the ulna is the head of the ulna. It articulates with the ulnar notch on the radius and with the triangular articular disc in the wrist joint.

Styloid process

Is a medial eminence of bone that provides a surface for the ulnar carpel medial collateral ligament.

Function

Articulations

Elbow

The ulna articulates with the humerus at its most proximal point forming the elbow in a hinge joint. It is the trochlea of the humerus which sits in the semi-lunar notch of the ulna to form this joint.

Radio-ulnar joints

The ulna articulates with the radius proximally and distally to produce pronation (from the proximal joint) and supination (from the distal joint) of the forearm.

The ulna also articulates with the radius in a syndesmosis joint via its interosseous membrane. Which runs the length of the shaft of the ulna from the radial notch proximally to the head of the ulna. This also acts to compartmentalise dorsal and volar sides of the forearm.

Muscle attachments

Olecranon process

Triceps - inserts onto the posterior of the olecranon process.

Anconeus - inserts onto lateral aspect

Flexor carpi ulnaris - origin:posterior, also shares an origin from humeral medial epicondyle

Coronoid process

Brachialis - inserts to anterior, inferior coronoid process

Pronator teres - originates medial surface, also from humeral medial epicondyle

Flexor digitorum superficialis - originates medial surface, also from humeral medial epicondyle

Shaft of ulna

All of the following arise from the shaft of the ulna:

Flexor digitorum profundus

Pronator quadratus

Extensor carpi ulnaris - also shared with lateral epicondyle of humerus

Abductor pollicis longus - also originates from interosseous membrane

Extensor pollicis longus - also originates from interosseous membrane

Extensor indicis - also originates from interosseous membrane

Clinical relevance

Monteggia fracture - common from a fall on an outstretched hand (FOOSH) is the fracture of the proximal 1/3 of the ulnar shaft accompanied by the dislocation of the radial head.

Hume fracture - fracture of the olecranon accompanied by anterior dislocation of the radial head.