Overview
The ulna (ulna) is much reduced in the horse. Its proximal part is robust and forms the point of the elbow, but the shaft thins quickly and fuses with the caudolateral surface of the radius; the distal end is incorporated into the radius as its lateral styloid process. As a result it bears no weight and there is no movement between the two forearm bones.
Key features
- Olecranon (olecranon): a long lever projecting caudal to the elbow; its tuberosity receives the triceps brachii, the main extensor of the elbow.
- Anconeal process (processus anconeus): the cranial beak of the olecranon, which fits into the olecranon fossa of the humerus when the elbow is extended.
- Trochlear notch (incisura trochlearis): a concave articular surface that grips the trochlea of the humerus.
- Shaft: slender and triangular, it tapers distally and is joined to the radius by fibrous tissue that eventually ossifies.
- Interosseous space: small, between ulna and radius, below the elbow.
Clinical relevance
- Olecranon fractures: common from kicks or falls. The triceps pulls the proximal fragment and the horse cannot lock the elbow: it adopts a dropped elbow posture, with the carpus flexed. Displaced fractures are repaired with a tension band plate on the caudal surface.
- Physeal fractures of the olecranon: in foals, through the physis of the tuberosity.
- Olecranon bursitis ("capped elbow", "shoe boil"): an acquired bursa over the point of the elbow, caused mainly by the heel of the shoe rubbing when the horse lies with its limbs folded.