Anatomical studies on the geometry and stability of the distal radio ulnar joint.

In fresh-frozen amputated- and cadaver arm specimens the anatomy and stability of the distal radio ulnar joint were investigated. The articulating surface of the sigmoid notch of the radius and the corresponding surface of the ulnar head facing the sigmoid notch were studied in transverse cryo sections. In each specimen the radius of the curvature of the sigmoid notch was 4-7 mm larger than that of the ulnar head and consequently pronation and supination are combined rotation-sliding movement in the distal radio ulnar joint. The radio ulnar ligament consists of a dorsal and a volar fibrous part, broadly attached to the distal rim of the sigmoid notch and converging towards the fovea of the ulnar head. The cartilaginous disc is centrally located between these fibrous strands. In neutral position the articulating surface of the sigmoid notch is optimally covering the articulating surface of the ulnar head. This contact area is gradually diminished during pronation-supination until only a marginal contact remains at the end of each movement. The distal radius is kept stable in pronation by the volar part and in supination by the dorsal part of the radio ulnar ligament.