US Patent 7220263 Cervical plate/screw system for immobilizing vertebral bodies

A plate/screw system for immobilizing adjacent vertebral bodies or an interbody device includes a plate having at least one spaced opening with an upper section of a width or diameter of d1 and a lower section having or diameter less than w1. The lower section defines a partial or completed helical track for receiving a screw. A bone screw for insertion into the threaded opening has a head section of d1, an adjacent neck section of d2 and a thread section of d3 where d2<d3<d1 whereby the relationship between d1 and w1 determines whether the screw can or cannot pivot relative to the plate.