Importance

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Abstract

The present invention is a polyaxial lateral mass locking screw plate assembly for immobilization of vertebral bones, via fixation to surfaces thereof. In one embodiment the invention includes a narrow elongate plate having a plurality of holes, which in one variation are threaded, into which holes coupling elements may be inserted, or correspondingly screwed. The coupling elements have a cylindrical exterior, and have an semi-spherical interior volume into which the semi-spherical head of a bone screw may be inserted, and therein polyaxially mounted. In one variation the coupling element is a 7/8ths ring including a single axial slot. In another variation the coupling element includes a plurality of slots in its lower portion. In either variation insertion of a coupling element into a corresponding hole causes the interior volume to be crush locked to the head of the screw. In a second embodiment, the present invention includes a similar plate, having holes which are, however, threaded part of the way through the plate. In this embodiment, the bottom portion of the holes of the plate, additionally, have a curved interior surface which forms an annular lip for supporting a semi-spherical head portion of a bone screw. The coupling element of this embodiment is a short threaded cylindrical piece, having a concave bottom which locks the screw into the hole. Variations of each embodiment have means associated with the holes and/or the coupling element for locking the angle of the screw to the plate.

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First Claim