Bone plate and bone screw locking system
A bone plating system includes a bone screw lock that includes a circular disc with a hole which is offset from the geometric center of the disc, and a tang which extends down from the disc into a circular slot on the bone plate.
1. A bone plate usable with at least two bone screws to be attached to bone, the plate comprising:
a plate having a top surface and a bottom surface;
two bone screw holes formed through the plate between the top and bottom surface, each bone screw hole having a center, the two bone screw holes defining a line between the two bone screw hole centers;
a plate hole configured and arranged to receive a bone screw lock system, the plate hole extending through the plate and positioned a distance Y from said line;
a semi-circular groove formed in the top surface of the plate and having two groove ends; and
a bone screw lock system including
a lock element having an upper surface, a lower surface, a geometric center, and a lock hole extending through the lock element between the upper and lower surfaces, the lock hole having a geometric center which is offset from the lock element geometric center by a non-zero distance X;
a tang extending from the lock element lower surface; and
a retainer holding the lock element to the plate at the lock hole, with the tang positioned in the semi-circular groove.
2. A bone plate according to claim 1 , wherein the groove is positioned between the two bone screw holes.
3. A bone plate according to claim 1 , wherein the distance Y, the distance X, and the lateral size of the locking element are together selected so that, when the tang is positioned against a first of said groove ends, the locking element does not overlie either of said two bone screw holes, and when the tang is positioned against a second of said groove ends, the locking element overlies both of said two bone screw holes.
4. A bone plate according to claim 1 , wherein the distance Y, the distance X, and the diameter of the circular disc are together selected so that, when the tang is positioned against a first of said groove ends, the locking element overlies only one of said two bone screw holes, and when the tang is positioned against a second of said groove ends, the locking element overlies both of said two bone screw holes.
5. A bone plate according to claim 1 , wherein the lock element has a shape selected from the group consisting of circular, a star-shape, a T-shape, an I-shape, a V-shape, a cross-shape, and an X-shape.