Changes in Contact Site of the Radiocarpal Joint and Lengths of the Carpal Ligaments in Forearm Rotation: An In Vivo Study

PurposeTo examine the contact site of the radiocarpal joint and lengths of carpal ligaments at different forearm rotations in vivo. Rotation of the forearm could exert noteworthy influence on mechanics of the wrist, and understanding how forearm rotation influences wrist mechanics may help treat carpal disorders because wrist position closely relates to forearm rotation.MethodsWe obtained computed tomography scans of the wrists of 8 volunteers at the following 7 positions of forearm rotation: neutral; 30°, 60°, and 90° of pronation; and 30°, 60°, and 90° of supination. Three-dimensional images of the carpals and distal radius and ulna were reconstructed with software. Subsequently, the contact site of the scaphoid and lunate on the radial articular surface and the lengths of 8 carpal ligaments between their respective origin and insertion points were measured and compared among different positions of forearm rotation.ResultsWe found that the contact site of the scaphoid on the distal radius moved between 0.2 and 2.0 mm during forearm rotation. The lengths of the 3 ulnar carpal ligaments (ie, ulnocapitate [UC], ulnolunate [UL], and ulnotriquetral [UT] ligaments) showed the greatest and significant change. From neutral position to pronation, the UC, UL, and UT ligaments shortened significantly. From neutral position to supination, the UT ligament lengthened significantly, but the radioscaphocapitate, UC, UL, and dorsal intercarpal ligaments decreased significantly.ConclusionsDuring forearm rotation, the contact site of the scaphoid and the lunate on the distal radial articular surface changed minimally. The lengths of 3 ulnar carpal ligaments (UC, UL, and UT ligaments) changed substantially.Clinical relevanceOur findings will help elucidate carpal biomechanics during forearm rotation. The findings may inform decisions about how to reduce the load to these carpal ligaments when treating the carpal disorders.