Carpal bone kinematics in combined wrist joint motions may differ from the bone kinematics during simple wrist motions

Present in-vivo carpal kinematic studies have been limited to flexion-extension and radio-ulnar deviation. However these simple motions do not represent the full range of wrist motion employed during activities of daily living. In this study, we investigated combined carpal bone motions for one normal subject. A healthy left wrist from a 48 year old female was CT scanned in three positions: the clinical neutral position of the forearm, the pronated and maximum extended wrist posture, and the supinated and maximum flexed wrist posture. The scans were obtained using a GE8800 scanner at 120 kV and 40 mA. The voxel size was 0.234 mm X0.234 mm X1.0 mm. Principal axes registration methods were used to quantify the carpal bone kinematics. The movement of the carpal bones were described by the means of helical axis parameters. Our subject's carpal bone kinematics in the complex motions differed from the previously studied simple motions. For example, published studies have found that the primary motion of the capitate follows the global motion of the wrist during simple wrist flexion-extension. However, for the complex pronation and extension motion, the capitate rotated ulnarly out of the plane of motion. The only previous study of pisiform motion has shown that during flexion-extension the pisiform moves in the plane of motion. However during pronation and extension, the pisiform rotated ulnarly; while in flexion, the rotation was a combination of flexion and supination.