Learning Objectives
By the end of this section, you should be able to:
- Describe the anatomical position and function of the ulna
- Identify the major bony landmarks of the proximal, shaft, and distal ulna
- Explain the articulations of the ulna at the elbow and wrist
- Recognize common clinical fractures involving the ulna and their complications
The ulna is a long bone of the forearm that lies medially and runs parallel to the radius. It acts as the stabilizing bone, while the radius rotates around it during pronation and supination.
- Proximally, the ulna articulates with the humerus at the elbow joint.
- Distally, it articulates with the radius, forming the distal radioulnar joint.
Proximal Ulna: Osteology and Articulation
The proximal end of the ulna is specially shaped to allow hinge-type movement at the elbow and to provide attachment for powerful muscles.
Key Landmarks
Olecranon
A large posterior projection forms the tip of the elbow.
- Part of the trochlear notch
- Attachment for triceps brachii
Coronoid process
An anterior projection forming the lower part of the trochlear notch.
Trochlear notch
A C-shaped surface formed by the olecranon and coronoid process.
- Articulates with the trochlea of the humerus
Radial notch
Located laterally; articulates with the head of the radius.
Ulnar tuberosity
A rough area just distal to the coronoid process.
- Attachment for brachialis
Shaft of the Ulna
The shaft is triangular in cross-section and tapers distally.
Surfaces
-
Anterior – attachment for pronator quadratus (distally)
-
Posterior – attachment for several extensor muscles
-
Medial – largely smooth
Borders
- Posterior border – palpable along the forearm
- Interosseous border – attachment for the interosseous membrane
- Anterior border – unremarkable
Distal Ulna
The distal ulna is narrow and ends in:
- Head of ulna – articulates with the ulnar notch of the radius
- Styloid process – pointed projection on the posteromedial side
This forms the distal radioulnar joint, which allows for pronation and supination.
Clinical Relevance: Common Ulna Fractures
Isolated Ulnar Shaft Fracture
- Usually caused by a direct blow
- The proximal fragment is pulled posteriorly by muscle tone
Olecranon Fracture
- Occurs after a fall on a flexed elbow
- The triceps pull the fragment proximally
Paired Forearm Injuries
Because the ulna and radius are joined by the interosseous membrane, force is transmitted between them.
Monteggia Fracture
- Fracture of the proximal ulna
- Anterior dislocation of the radial head
Galeazzi Fracture
- Fracture of the distal radius
- Dislocation of the ulna head at the wrist
