Background: Several techniques have been proposed to measure translation of the distal radioulnar joint on computed tomography scans, but the criteria for diagnosing abnormal subluxation have not been standardized. The aims of this study were to evaluate the reliability of the current methods and to derive normal population values with these methods.
Methods: Computed tomography scans of forty-five asymptomatic wrists were performed with the hand in supination, neutral, and pronation. Four methods for diagnosing subluxation of the distal radioulnar joint were used: the radioulnar line method; the epicenter method; the radioulnar ratio method; and the subluxation ratio method, which is a modification of the radioulnar line method that involves use of a line perpendicular to the sigmoid notch. Three observers measured all of the scans independently and repeated the measurements three months later to determine the interobserver and intraobserver reliability. All of the measurements for each subject were averaged, and the average was considered to be the normal value for that subject.
Results: Interobserver reliability was best (substantial to almost perfect) with use of the subluxation ratio method. The intraclass correlation coefficients showed substantial to almost perfect reliability of the radioulnar line method, substantial reliability of the radioulnar ratio method, and moderate to substantial reliability of the epicenter method. The intraobserver reliability of all methods was almost perfect. The radioulnar line and subluxation ratio methods always showed the ulnar head to be located outside of the dorsal line in pronation and outside of the volar line in supination. The normal epicenter values indicated that the center of rotation of the distal radioulnar joint fell in the middle half of the sigmoid notch in all positions. The normal ranges derived with the radioulnar ratio method demonstrated larger variation than originally reported.
Conclusions: This study suggests that the subluxation ratio method is the most useful technique for measuring translation of the distal radioulnar joint as a result of its reliability and simplicity. Substantial variations in normal values derived with the current methods should be considered in a computed tomography evaluation of the distal radioulnar joint in symptomatic patients.