A Method for Finding an Arbitrary Revolute From Three Dimensional Motion Data With Application to the Elbow

Many human joints such as those of the ankle (Inman, 1976, Singh et al, 1993), ulnohumeral (Weber and Weber 1836, London, 1980), and radioulnar (Hollister et al., 1994) have been postulated to rotate about single, fixed offset axes of rotation. These investigations are of the joint surface shape in the plane of motion and planar kinematic analyses in the motion plane. Arbitrary axes of rotation are not coincident with a reference coordinate axis. The motion of a body moving about an arbitrary axis includes X, Y, and Z displacements and yaw, pitch and roll rotations if the axis is not parallel to a reference plane. Rotations and displacements of a body moving about an arbitrary axis are determined by the axis’ α and β angles of offset from the reference frame, the θ angle of rotation about the arbitrary axis, the distance (d) from the point on the axis about which the body rotates to the reference origin and the distance (r) from the body to the axis. An algorithm was developed to determine an arbitrary axis’ location from X, Y, Z, yaw, pitch and roll data of one body relative to another. The algorithm was tested with kinematic data from a hinge and from 4 elbow specimens.