AbstractThe objectives of this study were (a) to describe the three‐dimensional in vivo kinematic behavior of wrists affected by rheumatoid arthritis, (b) to correlate kinematic parameters and two radiographic indices of carpal disease, and (c) to describe the in vivo kinematic behavior of the Swanson Silastic wrist implant. Fifteen normal wrists, 17 rheumatoid wrists, and 7 wrists with Silastic wrist implants were tested using a three‐dimensional sonic digitizing system. The motion of the hand segment relative to the forearm segment, corresponding to the positions exhibited during flexion‐extension motion (FEM) and radial‐ulnar deviation (RUD), was described using the equivalent screw displacement (ESD) concept. The mean magnitudes of ESD rotation for both FEM and RUD were statistically different (p0.05) among the normal, rheumatoid, and implant groups. The two radiographic indices (carpal collapse and carpal translation) did not correlate with the magnitude of rotation or with any other ESD pa
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