Introduction
The ulna is a longbone located medially in the forearm which extends from the elbow to the wrist joint. It runs parallel to the radius, which is the other longe bone in the forearm located laterally.
The ulnar is usually slightly longer than the radius. The ulna is is involved in the wrist and the elbow joint, with the following articulations:
- Humeroulnar
- Proximal radioulnar joint
- Distal radioulnar joint
Proximal Ulna
Conisists of the olecranon, trochlear notch, coronoid process, radial notch and ulnar tuberosity.
- Olecranon: bony projection extending proximally. The triceps brachii muscle inserts here.
- Trochlear notch: forms the humeroulnar articulation with the trochlear of the humerus
- Coronoid process: anterior projection from the proximal ulnar, forming the anterior part of the trochlear notch
- Ulnar tuberosity – roughening distal to the coronoid process which provides attachment for the brachialis muscle
- Radial notch: articulates with the radial head – in pronation and supination, the radial head is able to rotate via this notch, causing the shaft of the radius to swing over the ulnar shaft, which remains relatively fixed in position.
Shaft
The ulna shaft is broad superiorly and narrow distally. It is approximately triangular in cross section, with 3 borders and 3 surfaces
Borders:
- Anterior (volar) – smooth and round.
- Posterior (dorsal) – sharp and palpable
- Interosseus – sharp and palpable
Surfaces:
- Anterior (volar) – attachment for pronator quadratus
- Posterior (dorsal) – several muscle attachments
- Medial
Distal Ulna
Consists of the head and styloid process.
- Head: articulates with the radius at the distal radio-ulnar joint via the ulnar notch. The head is covered by the triangular articular disc which forms part of the triangular fibrocartilage complex.
- Styloid process: extends distally, provides attachment for the ulnar collateral ligament