A bone fixation device has a housing on the exposed head of a screw mounted in a bone part from which it projects. A clamp for a fixation rod is mounted on a plate extending from each of opposite lateral sides of the housing in such a manner that allows the plate to rotate about a lateral axis relative to the housing. Each clamp is itself rotatable on its plate about an axis perpendicular to its respective lateral axis, and thereby provides universal movement relative to the housing. Mechanisms are provided for closing the clamps, for locking each plate against rotation about its lateral axis, and blocking each clamp against rotation about its perpendicular axis. In this way rods can be fixed in the clamps and relative to the device.
