Overview
The radius is, with the ulna, one of the two bones of the forearm. It is the main weight-bearing bone: it receives the load of the humerus at the elbow and passes it to the carpus. In the cat the radius and ulna are joined by an interosseous membrane and loose ligaments, and the radius can rotate around the ulna with a range of pronation and supination much greater than in the dog.
Key features
- Head of the radius (caput radii): the proximal end, with a concave fovea that articulates with the capitulum of the humerus and an articular circumference that turns in the radial notch of the ulna.
- Radial tuberosity: on the medial surface, distal to the neck, insertion of the biceps brachii.
- Body: slightly curved cranially; the extensor muscles of the carpus and digits cover it cranially.
- Trochlea of the radius: distal articular surface for the radial carpal bone.
- Styloid process (processus styloideus radii): medial distal projection, palpable.
- Ulnar notch: on the lateral edge of the distal end, articulates with the head of the ulna.
Clinical relevance
- Radius and ulna fractures: common after road accidents and falls. They are repaired with plates or external fixators; intramedullary pins are not suitable for the radius.
- Osteosarcoma: can affect the radius, although in the cat it is less common than in the pelvic limb.
- Examination: forearm rotation is assessed by holding the elbow and turning the paw; its loss suggests joint injury or fracture.