CARPAL KINEMATICS DURING RADIAL ULNAR DEVIATION

This study investigates carpal kinematics during a wrist Radial/Ulnar deviation motion using high speed video data acquisition. A cadaver forearm was stabilized allowing unconstrained excursion of the wrist for passive range of motion. Capitate/radius and 3rd metacarpal/radius angles were calculated to determine which measurement would be best for determining global wrist angle. The average difference in angle between the capitate and third metacarpal was 1.3 ± 1.3 degrees with a maximum difference of 5.0 degrees. Hence, the capitate-third metacarpal joint can be considered ridged. The proximal wrist joint (R/L angle) contributed 15.1 degrees to global wrist radial ulnar deviation and the midcarpal joint (C/L angle) contributed 20.6 degrees to global wrist radial ulnar deviation (43.0% and 55.8%, respectively, of the 36.4° total wrist ROM). Radio-scaphoid angles averaged 16.8 degrees (46.5% of the 36.4° total wrist ROM). The radio-lunate joint and the capito-lunate joint contribute equally to global wrist radial ulnar deviation. This new combination of motion analysis and 3D reconstructions of CT images affords a high speed, dynamic analysis of kinematics. It shows that normal carpal kinematics, during wrist radial/ulnar deviation, does not have an instantaneous screw axis (ISA) fixed in or limited to the capitate. In addition, the ISA data provides evidence that translational motion is a real and measurable component of normal carpal motion. This would change the understanding of carpal kinematics from previous studies, which suggested that the center of rotation was fixed in the capitate.