SPINAL FIXATION SYSTEM

摘要

A spinal fixation system comprises an elongated fixation plate (13) having an elongated slot (21) with a number of concave depressions (28, 25) formed at the top and bottom surfaces (19, 17) of the plate. The system further includes a pedicle screw (40) and a nut (32) for load transmission between a vertebra and the plate. The pedicle screw includes a threaded nut engaging portion (42), a threaded bone engaging portion (44) and an intermediate portion (46) therebetween which has rigid upper and lower arcuate surfaces (47) that are complementary to the concave depressions in the plate. The nut also includes a rigid lower arcuate surface (36) which is complementary to the upper concave depressions of the plate. In one assembled configuration the plate is clamped between the upper arcuate surface of the pedicle screw and the nut. In an alternative embodiment of the pedicle screw (70), the intermediate portion has an upper and lower arcuate surface (79, 77) of different spherical radii of curvature.