Distal radius fracture and the distal radioulnar joint--anatomical considerations.

The ulna represents the non-rotating, stable and weightbearing part of the forearm around which the radius rotates in pronation and supination. The distal radioulnar joint is the distal half of an articulation, the proximal half of which is the proximal radioulnar joint. In spite of the distance between the two, the distal and proximal radioulnar joints together form a bi-condylar joint, the "forearm joint", with the axis of rotation running from the centre of the radial head out distally into the interosseous space towards the centre of the ulnar head. The end of the radius together with the hand and what is held in the hand will rest against the stable, immobile ulnar head, which acts as the keystone of the wrist. Mobility and stability of the distal radioulnar joint is accomplished by the combined action between fully congruent articulating surfaces and intact radioulnar ligaments. Following a distal radius fracture, the semilunar notch of the radius will no longer be congruent to the ulnar head due to the displacement of the distal fracture fragment of the radius into either dorsal angulation, radial angulation, or both. The stabilizing ligaments will tear. Any posttraumatic disabling dysfunction of the distal radioulnar joint should accordingly be treated by a corrective osteotomy of the radius at the fracture site in order to achieve full congruity between the semilunar notch and the ulnar head. Resection of the ulnar head deprives the wrist its keystone and should therefore be avoided.