Ulna

 The ulna

The ulna is a long bone in the forearm. It lies medially and parallel to the radius, the second of the forearm bones. The ulna acts as the stabilising bone, with the radius pivoting to produce movement.

Proximally, the ulna articulates with the humerus at the elbow joint. Distally, the ulna articulates with the radius, forming the distal radio-ulnar joint.


Proximal Osteology and Articulation

The proximal end of the ulna articulates with the trochlea of the humerus. To enable movement at the elbow joint, the ulna has a specialised structure, with bony prominences for muscle attachment.

Important landmarks of the proximal ulna are the olecranon, coronoid process, trochlear notch, radial notch and the tuberosity of ulna:

1. Olecranon – a large projection of bone that extends proximally, forming part of trochlear notch. It can be palpated as the ‘tip’ of the elbow. The triceps brachii muscle attaches to its superior surface.

2. Coronoid process – this ridge of bone projects outwards anteriorly, forming part of the trochlear notch.

3. Trochlear notch – formed by the olecranon and coronoid process. It is wrench shaped, and articulates with the trochlea of the humerus.

4. Radial notch – located on the lateral surface of the trochlear notch, this area articulates with the head of the radius.

5. Tuberosity of ulna – a roughening immediately distal to the coronoid process. It is where the brachialis muscle attaches.

Shaft of the Ulna

The ulnar shaft is triangular in shape, with three borders and three surfaces. As it moves distally, it decreases in width.

The three surfaces:

• Anterior – site of attachment for the pronator quadratus muscle distally.

• Posterior – site of attachment for many muscles.

• Medial – unremarkable.

The three borders:

• Posterior – palpable along the entire length of the forearm posteriorly

• Interosseous – site of attachment for the interosseous membrane, which spans the distance between the two forearm bones.

• Anterior – unremarkable.

Distal Osteology and Articulations

The distal end of the ulna is much smaller in diameter than the proximal end. It is mostly unremarkable, terminating in a rounded head, with distal proje

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