A rigid body model of the forearm

In this article the forearm, with its complex, continuous motion of masses during pronation/supination, was approximated by a rigid body model consist ing of a radial segment rotating around an ulnar segment. The method used t o obtain the model parameters is based on three-dimensional voxel data that include velocity information. We propose a criterion that allows the voxel s to be attributed to either of the two segments. It is based on the notion that the rotational kinetic energy determined from the voxel data equals t he kinetic energy of the rigid body model. To obtain a three-dimensional sm oothing we further propose a parameterization of the shape of both segments . These shapes can then be used to determine the dynamic integrals of the s egments, i.e. mass, center of mass, and inertia. Using this approach we det ermined all model parameters for a human forearm from three series of MRI s cans in a supinated, a pronated, and an intermediate position. In the appen dix, a procedure is described that allows the dynamic quantities to be scal ed homogeneously without recalculation of the integrals. Thus, this article provides all essential parameters required for three-dimensional dynamic s imulations of general movements of the forearm. (C) 2000 Elsevier Science L td. All rights reserved.