Overview
The ulna is the caudal bone of the forearm. It is longer than the radius, because its proximal end projects behind the elbow as the olecranon. In the cat it keeps a complete, well-developed body down to the carpus, around which the radius turns in pronation and supination.
Key features
- Olecranon and olecranon tuberosity: the lever of the elbow, where the triceps brachii and anconeus insert. It forms the palpable point of the elbow.
- Trochlear notch (incisura trochlearis): half-moon articular surface that grips the humeral trochlea.
- Anconeal process: the proximal end of the trochlear notch, which fits into the olecranon fossa of the humerus when the elbow is extended.
- Medial and lateral coronoid processes: the distal ends of the trochlear notch, which also support the humerus.
- Radial notch: articulates with the articular circumference of the head of the radius.
- Head of the ulna and styloid process: at the lateral distal end; they articulate with the radius and with the ulnar and accessory carpal bones.
Clinical relevance
- Olecranon fractures: the pull of the triceps distracts the fragments; they are repaired with pins and a tension-band wire.
- Radius and ulna fractures after trauma.
- Elbow osteoarthritis: very common in older cats; osteophytes form on the anconeal process and the margins of the trochlear notch.