Olecranon: The bony tip of the elbow. The olecranon is the near end of the ulna, the bone in the forearm, and it forms the pointed portion of the elbow. The triceps muscle tendon of the back of the arm attaches to the olecranon. Disease can affect the olecranon. For example, inflammation of the tiny fluid-filled sac (bursa) at the tip of the elbow can occur; this is referred to as olecranon bursitis. A firm nodule can form at the tip of the elbow; it is referred to as an olecranon nodule and is sometimes found in gout or rheumatoid arthritis. Also known as the olecranon process of the ulna.
Structure of Ulna
The ulna is a long bone larger proximally than distally.
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.[2]
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.
Functions of Ulna
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:
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
Like any other joint in the body the ulna can be affected by osteoarthritis in the elbow joint.
Ulnar fractures
Typically occur as a result of fragility and normally following a fall such as a fall on an outstretched hand (FOOSH)
- Monteggia fracture - 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.
- Galezzi's fracture-fracture to the distal radius accompanied by ulnar head dislocation at distal radio-ulna joint.
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