Bone plate and screw retaining mechanism

1. A bone plate assembly comprising: a base plate defining at least one elongated slot and a hole, the hole having an outer perimeter inside an outer perimeter of the elongated slot offset from a center of the elongated slot outer perimeter and extending through the base plate; and a screw retaining mechanism mounted within the elongated slot and slidably movable between locked and unlocked positions relative to the hole along a side surface of the base plate defining the outer perimeter of the slot, said screw retaining mechanism including a top portion and opposed side portions with a recess between the side portions, the screw retaining mechanism configured such that in the locked position, the screw retaining mechanism encircles a portion of a screw received within the hole.

2. The assembly according to claim 1 , wherein said screw retaining mechanism includes a tab for engaging at least one groove located along an outer edge of the elongated slot in a side surface of the base plate.

3. The assembly according to claim 1 , wherein said screw retaining mechanism does not block a portion of a screw disposed through said hole thereby defining said unlocked position.

4. The assembly according to claim 1 , wherein said screw retaining mechanism engages the screw in the locked position and prevents any movement thereof.

5. The assembly according to claim 1 , wherein said screw retaining mechanism allows the screw to pivot freely while said screw retaining mechanism is in said locked position.

6. The assembly according to claim 1 , wherein said screw retaining mechanism is removably mounted within the elongated slot of the base plate.

7. The assembly according to claim 1 , wherein said screw retaining mechanism maintains the screw below an upper surface of the base plate when in said locked position.

8. The assembly according to claim 1 , wherein said screw retaining mechanism is U-shaped.

9. The assembly according to claim 1 , wherein said screw retaining mechanism is compressible about said central axis.

10. The assembly according to claim 1 , wherein said screw retaining mechanism includes a bottom portion having a spherically-shaped recess.

11. The assembly according to claim 10 , wherein the recess forms a substantially U-shaped inner first surface.

12. The assembly according to claim 11 , wherein the recess further includes a second surface extending arcuately further radially outward relative to said first surface.

13. The assembly according to claim 1 , wherein each of said side portions includes an indentation which operatively engages protrusions on the base plate in a locked position.

14. An insert for placement into an aperture of a base plate comprising screw retaining means mountable and slidably movable on a plate between locked and unlocked positions relative to an aperture for preventing a bone screw from backing out from the base plate, wherein said screw retaining means includes a bottom portion, a top portion, and two side portions, said bottom portion having a spherically-shaped recess, said top portion having a first recess forming a substantially U-shaped inner surface and a second surface extending arcually further radially outward relative to said first surface such that the second surface defines a larger opening into the first recess, and said side portions having lip means radially extending therefrom for engaging an undercut situated within the aperture of the base plate.

15. The insert according to claim 14 , wherein said side portions further include an indentation that operatively engage over protrusions that extend into the aperture on the base plate.