Ideal scaphoid angle for intercarpal arthrodesis

This experimental study was conducted to determine the best scaphoid position, measured as the radioscaphoid (RS) angle for optimum wrist motion after scapho-trapezio-trapezoid (STT) and scaphocapitate (SC) fusion and to assess the implications of radial styloidectomy on motion after STT fusion. STT and SC fusions were simulated in six fresh cadaver hands with the scaphoid in horizontal, neutral, and vertical positions with respect to the long axis of the radius seen on lateral x-rays. RS angle and wrist motion were measured on x-ray films before and after each simulated arthrodesis. Radial deviation and wrist extension increased as the RS angle increased (i.e., increased as the scaphoid became more nearly vertical). Ulnar deviation and flexion decreased as the scaphoid became more nearly horizontal. We found no statistically significant differences in RS angle between SST and SC fusions with respect to ulnar deviation, flexion, or extension. However, radial deviation was more sensitive to RS angle after STT fusion than after SC fusion, but the differences were not statistically significant. The ideal radioscaphoid angle (range) for maximal wrist motion when STT fusion is performed is 41 to 60 degrees; when SC fusion is performed, it is 30 to 57 degrees. Motion is not improved by radial styloidectomy after simulated STT fusion.