Abstract: A polyaxial pedicle screw for use with rod implant apparatus includes a rod receiving body, a screw having a curvate head, a compression element, and a means for loosely and reversibly maintaining a coupled relationship between the compression element and the screw head during angulation thereof relative to the rod receiving body, while still permitting compressive locking of the assembly in a specific orientation by means of a compressive force applied by a rod onto the compression element and the head of the screw.

Abstract: A polyaxial pedicle screw device for use with rod implant apparatus, which utilizes a rod mounted ferrule, includes a screw having a curvate head and a rod receiving body. The body has a rod receiving channel and an axial bore into which the head of the screw is inserted. The interior surface of the bore is inwardly curvate at the lower end thereof to form a socket for polyaxially retaining the curvate head of the screw. In an initial position the screw head remains polyaxially free with respect to the body. The rod mounted ferrule seats into a small curvate recess in the upper portion of the screw head such that the rod may enter the body at a variety of angles while maintaining a secure seating against the head of the screw. The insertion of a top set screw compresses down on the ferrule, locking the rod in position, and onto the screw head, locking it and the body in position, thus completely securing the assembly.