Rotary subluxation of the scaphoid is not an "all or nothing" phenomenon, but a spectrum of instability including constant displacement of the scaphoid apparent on plain non-stress radiographs (the previously defined static type), subluxation seen only on loading X-rays or other special studies ("dynamic"), and instability demonstrable on physical examination but not by radiographic studies ("predynamic"). A clinical study of 1,000 random individuals was carried out to determine the incidence of unilateral hypermobility of the scaphoid. 21% of the subjects were found to have an abnormal difference in mobility between their scaphoids. The incidence of significant symptoms and physical findings associated with this hypermobility was determined.