Overview
The radius (radius) is the weight-bearing bone of the forearm. In the horse it is long and straight, and the much reduced ulna fuses with it distally, so the forearm cannot pronate or supinate. Proximally it articulates with the humerus and distally with the proximal row of the carpus. Its medial surface is subcutaneous and can be palpated along its whole length.
Key features
- Proximal end: the head forms most of the articular surface of the elbow. On the craniomedial side, the radial tuberosity receives the tendon of the biceps brachii.
- Interosseous space of the forearm: small, between radius and ulna in the proximal part; distal to it the two bones are fused.
- Shaft: slightly bowed cranially; its caudal surface is flat.
- Distal end: the trochlea of the radius articulates with the carpus. On each side there is a styloid process: the medial one belongs to the radius and the lateral one is actually the fused distal end of the ulna.
- Distal physis: remains open for much of growth and provides most of the lengthening of the forearm.
- Chestnut (castanea): a horny plate of the skin on the medial forearm, proximal to the carpus.
Clinical relevance
- Angular limb deformities: in foals, carpal valgus (carpus deviated medially and hoof laterally) usually arises at the distal radial physis. Many correct themselves; those that do not are treated by slowing or stimulating growth on one side of the physis.
- Physitis: painful enlargement of the distal physis in fast-growing foals, linked to nutrition and exercise.
- Kick fractures: the subcutaneous medial surface takes many kicks from other horses; incomplete fractures can become complete if the horse is not protected.