The radioulnar ratio: a new method of quantifying distal radioulnar joint subluxation.

Computed tomography was used to image the distal radioulnar joint (DRUJ) for instability. Four methods were used to quantify subluxation of the DRUJ: the Mino criteria, the epicenter method, the congruency method, and a new method called the radioulnar ratio (RUR). Validity of the various methods was evaluated in clinical and laboratory situations. Rheumatoid patients with symptomatic DRUJ pathology had significantly more abnormal RUR values (100% vs 73% [epicenter method] and 88% [Mino criteria]). The RUR detected instability sooner in a progressive laboratory-induced instability model. The intraobserver and interobserver reliability of the RUR was high, with intraclass correlation coefficients of 0.89 and 0.87, respectively. The RUR demonstrated superior performance in the diagnosis of DRUJ subluxation.