A PHYSICAL MODEL OF THE WRIST DYNAMICS

Abstract

The wrist articulation represents one of the most complex mechanical system of the human body. It is composed of eight bones rolling and sliding along their surface and along the faces of the five metacarpals of the hand and the two bones of the arm. The wrist dynamics is however fundamental for the hand movement, but it is so complex that it still remains incompletely explored. This work is part of a new concept of Computer Assisted Surgery, which consists in developing computer models to perfect surgery acts by predicting their consequences. The physical wrist dynamics model is based first on the static model of its bones in three dimensions. Their 3D model is chosen to optimize the collision detection procedure, which is the necessary step to estimate the physical contact constraints. As many other possible computer vision models do not fit with enough precision to this problem, a new 3D model has been developed using the Median Axis of the digital distance map of the bones reconstructed volume. The collision detection procedure is then simplified for contacts were detected between spheres. With a good 3D model of the solids, the dynamics of the wrist can then be approached by integrating its fundamental differential equations, and thanks to a geometric model of the contact constraints. The experiments of this original 3D dynamic model has already produced computer animations. The wrist dynamic model must be however completed with ligament models to reach realistic animations, which would be then compared to radio-camera data.