Relationship between radial inclination angle and ulnar deviation of the fingers.

Fifty wrists (thirty-two patients) with rheumatoid arthritis and ulnar drift of the fingers were examined radiologically and compared to fifty normal wrists radiographs. Statistically significant differences were found for measurements of radial inclination angle, carpal-radial distance, third metacarpal-phalangeal angle, and carpal height ratio. Third metacarpal-phalangeal angle of ten degrees or greater on standard posteroanterior radiograph appears to accurately represent digital ulnar drift. Elevated radial inclination angle was highly correlated with digital ulnar drift (p much less than 0.001). Radial inclination angle greater than twenty-two degrees is associated with the development of digital ulnar drift through two mechanisms, radial carpal rotation, and ulnar carpal translocation.