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M01.03.014 Ulna
The ulna, a vital long forearm bone, plays a key role in stabilization and movement. Positioned medially and parallel to the radius, it forms essential articulations at the elbow and wrist joints. This guide covers the anatomy of the ulna, including its bony landmarks, muscle attachments, and clinical relevance.
Overview
- Position: Medial and parallel to the radius.
- Function: Stabilizing bone; allows movement through articulation with the humerus and radius.
- Key Articulations:
- Proximal: Elbow joint (with the humerus).
- Distal: Distal radio-ulnar joint (with the radius).
Proximal Osteology and Articulations
The proximal ulna is specialized for movement at the elbow joint, featuring prominent bony landmarks.
Key Landmarks
| Landmark | Description | Muscle Attachments |
|---|---|---|
| Olecranon | Large projection forms part of the trochlear notch, which is palpable as the ‘tip’ of the elbow. | Triceps brachii (superior surface). |
| Coronoid Process | Anterior ridge forming part of the trochlear notch. | – |
| Trochlear Notch | Wrench-shaped structure articulating with the trochlea of the humerus. | – |
| Radial Notch | Lateral surface articulating with the head of the radius. | – |
| Tuberosity of Ulna | Roughened area distal to the coronoid process. | Brachialis muscle. |
Shaft of the Ulna
The ulnar shaft is triangular, tapering distally, with three surfaces and three borders.
Surfaces
- Anterior: Attachment site for pronator quadratus muscle.
- Posterior: Attachment for various muscles.
- Medial: Smooth and unremarkable.
Borders
| Border | Features |
|---|---|
| Posterior | Palpable along the entire posterior forearm. |
| Interosseous | Attachment site for the interosseous membrane, connecting the ulna and radius. |
| Anterior | Unremarkable. |
Distal Osteology and Articulations
The distal ulna is slender and terminates in:
- Head: Articulates with the ulnar notch of the radius at the distal radio-ulnar joint.
- Ulnar Styloid Process: A small distal projection.
Clinical Relevance: Common Fractures of the Ulna
Fractures of the ulna often occur from trauma. Muscle tone and interosseous membrane connections influence fracture patterns.
Common Fractures
- Isolated Ulna Fracture:
- Cause: Direct trauma.
- Site: Shaft of the ulna.
- Features: Proximal ulna may be pulled posteriorly by muscle tone.
- Olecranon Fracture:
- Cause: Fall on a flexed elbow.
- Features: Triceps brachii can displace the fractured fragment Proximally.
- Combined Ulna and Radius Fractures:
- Cause: Force transmitted via the interosseous membrane.
- Types:
- Monteggia’s Fracture: Proximal ulnar fracture with anterior radial head dislocation.
- Galeazzi’s Fracture: Distal radial fracture with dislocation of the ulnar head at the distal radio-ulnar joint.
Key Points to Remember
- Articulations: The ulna forms the elbow joint proximally and the distal radio-ulnar joint distally.
- Muscle Attachments: Specific landmarks serve as attachment points for key muscles like triceps brachii and brachialis.
- Fractures: Monteggia’s and Galeazzi’s fractures highlight the interdependence of forearm bones.
- Clinical Examination: Palpation of the posterior border and olecranon assists in the diagnosis of injuries.