In Vivo Gliding and Contact Characteristics of the Sigmoid Notch and the Ulna in Forearm Rotation

PurposeTo investigate shifting of the contact center over the surfaces of 2 opposing bones of the distal radioulnar joint during forearm rotation.MethodsWe recruited 8 volunteers and used their right wrists. Serial computed tomography scans were obtained with the forearm at neutral position and 6 other positions of forearm rotation. We reconstructed 3-dimensional images and mapped contact regions of both the sigmoid notch and ulnar head by calculating the shortest distance between the 2 opposing bones. The center of contact was also defined and plotted against the distal radioulnar joint rotation to determine the sliding distance over the surfaces of the 2 bones.ResultsDuring forearm rotation, the maximal sliding of the sigmoid notch over the ulnar head was 7.4 mm in forearm pronation and 9.2 mm in forearm supination, which occurred in volar-dorsal direction primarily. Sliding of the ulnar head over the sigmoid notch was more limited, measuring 4.7 mm during pronation and 2.3 mm during supination. Most of the motion occurred between 30° pronation and 60° supination. In the proximal-distal direction, the contact site of the sigmoid notch with the ulnar head translated distally 1.6 mm during pronation and proximally 0.7 mm during supination.ConclusionsDuring forearm rotation, the sigmoid notch slides substantially against the ulnar head at each part of the forearm rotation arc. The sliding of the ulnar head over the sigmoid notch is smaller, most of which is at the range from moderate forearm pronation to slight supination. The contact site of the sigmoid notch with the ulnar head moves slightly distally during forearm pronation and proximally during supination.Clinical relevanceThe in vivo findings provide more detailed information and insight into distal radioulnar joint motion kinematics.