["Around the head of the ulna": injury pattern and classification].

The ulnar head represents a keystone for normal forearm function. A complex system of soft tissues stabilizes the radius and the ulnocarpal joint against the ulnar head which is an essential part of the distal radioulnar joint as well as the ulnocarpal joint. Injuries around the ulnar head can destabilize these joints leading to loss of congruity and secondary arthrosis. The different injury patterns can result in axial or transverse instability. Axial instability primarily affects ulnocarpal function, transverse instability the function of the distal radioulnar joint. The injury pattern determines the degree of bony and soft tissue lesions that will clinically present in a variety ranging from acute dislocation to chronic instability of the ulnar head. An early and exact diagnosis of the injured structures with their anatomical reconstruction is necessary to avoid secondary arthrosis that will result in functional impairment of the distal radioulnar and ulnocarpal joints.