The distal extent of the radius and ulna (ulnar variance) was compared
on roentgenograms of normal wrists in randomly selected black and white
patients and of fifteen affected wrists in patients with Kienbock's
disease. The results establish a statistically significant association
between negative ulnar variance and Kienbock's disease. Blacks have more
positive ulnar variance and the disease is less likely to develop in them
than in whites.