Overview
The ulna is the longest bone of the forearm, although it bears less weight than the radius. Its proximal end is bulky and forms most of the elbow joint; distally the shaft narrows progressively and ends in the lateral styloid process, which articulates with the ulnar carpal bone.
Key features
- Olecranon (olecranon): proximal prominence, the "point of the elbow", where the triceps brachii inserts. It works as the lever arm for elbow extension.
- Anconeal process (processus anconeus): sits in the olecranon fossa of the humerus when the elbow is extended.
- Trochlear notch (incisura trochlearis): semilunar notch that embraces the humeral trochlea.
- Medial and lateral coronoid processes: the medial one is larger and shares load with the head of the radius.
- Radial notch: articular surface for the articular circumference of the radial head.
Clinical relevance
The ulna hosts the components of elbow dysplasia: fragmented medial coronoid process, ununited anconeal process (typical of the German Shepherd) and joint incongruity. Olecranon fractures need tension-band fixation because of the pull of the triceps. Premature closure of the distal ulnar physis (which provides most of the growth in length) bows the radius ("radius curvus").