[Triquetro-lunar instability. The role of the radio-styloidian index].

Based on a series of 13 isolated triquetro-lunar instabilities, the authors underline the excess of the radio styloidian index measured radiologically. They found a significant difference (p < 0.001) when comparing this series with a group of 100 normal wrists. A similar comparative study of 13 triquetro-lunar instabilities secondary to perilunar dislocations and of a series of 16 hyperlax wrists did not reveal any significant difference. The same applies to a similar parallel study of the ulnar variance index measurements when comparing the various groups with the control group. After reviewing the mechanism of lesions, and disorders of the wrist's axial forces, caused by changes in the ulnar lengths, ulnar styloid overshooting is designated as a risk factor for isolated triquetro-lunar instabilities. Finally, the authors insist on the necessity of proper reduction of radial low end fractures and detachments, and on the shortening of the long ulna, as a "complementary" procedure when treating isolated triquetro-lunar instabilities.