Pisiform kinematics in vivo.

The purpose of this study was to quantify in vivo pisiform kinematics. Wrists of healthy volunteers were imaged by spiral computed tomography during ulnar-radial deviation (n = 11) and during flexion-extension (n = 5). Relative translations and rotations of the carpal bones were determined by using a 3-dimensional matching technique. The error of this registration procedure was less than 0.5 mm for translation and 0.4 degrees for rotation. With radial wrist deviation the pisiform flexes while the triquetrum extends; with ulnar deviation the triquetrum shows more ulnar deviation and extension. With wrist extension the pisiform translates over the distal part of the triquetrum while being pressed against it. With flexion the pisiform moves away from the triquetrum while translating proximally. These in vivo findings provide a further explanation for certain clinical entities, such as degenerative changes of the pisotriquetral joint, and may be used as a reference for normal kinematics of the pisiform.