In vivo changes in lengths of the ligaments stabilizing the distal radioulnar joint.

PURPOSE: To investigate changes in lengths of the ligaments stabilizing the distal radioulnar joint during forearm pronation and supination in vivo.

METHODS: We studied in vivo kinematics of the distal radioulnar joint by measuring the length changes of the ligaments of the distal radioulnar joint in 6 wrists of normal volunteers. Using serial computed tomography scans and volume registration techniques, the distal radioulnar joints were examined at 7 positions from 90 degrees pronation to 90 degrees supination in 30 degrees increments. The 3-dimensional structures of the joint were reconstructed with customized software. The paths of palmar and dorsal superficial and deep fibers of the radioulnar ligaments were modeled, and changes in their lengths were computed and analyzed statistically.

RESULTS: The lengths of the palmar superficial radioulnar ligaments decreased significantly during forearm pronation from 90 degrees to 30 degrees compared with those at the other positions. During pronation from 90 degrees to neutral rotation, lengths of the dorsal deep radioulnar ligaments decreased significantly. The lengths of the dorsal superficial radioulnar ligament decreased significantly during forearm supination from neutral rotation to 90 degrees , as did the lengths of the palmar deep radioulnar ligaments. The palmar and dorsal superficial radioulnar ligaments showed greater length changes than did the palmar and dorsal deep radioulnar ligaments during forearm pronation-supination. The dorsal superficial radioulnar ligament had the greatest length changes during pronation-supination among the studied ligaments.

CONCLUSIONS: These in vivo measurements validate that in forearm pronation, the dorsal superficial radioulnar ligament and palmar deep radioulnar ligament tighten, serving as restraints for the distal radioulnar joint instability. In forearm supination, the palmar superficial radioulnar ligament and dorsal deep radioulnar ligament tighten, maintaining stability of the distal radioulnar joint.