Carpal ligamentous disruptions and negative ulnar variance.

Negative ulnar variance is a condition in which the ulna is relatively shorter than the radius at the carpus. It was found in 21% of 203 normal wrists. We have observed an increased incidence (49%) of this anomaly in patients with carpal ligamentous instabilities (dorsiflexion instability, palmar flexion instability, scapholunate dissociation with rotary luxation of the scaphoid, and lunate and perilunate dislocations). While the reasons for this association have yet to be adequately delineated, the presence of a negative ulnar variant may serve as an impartial clue to the presence of ligamentous instability. Many carpal instabilities present with subtle radiographic findings requiring careful evaluation of radiographs. Patients with negative ulnar variance and histories suggestive of ligamentous instability should undergo careful radiologic evaluation to assure early diagnosis of carpal disruption.