US Patent 7699880 Bone fixation system and bone screws having anti-back out feature

The system includes a plate with a screw hole and a bone screw wherein the screw and plate cooperate such that the screw is inhibited from back out from the plate after inserted into bone. Described embodiments include a pawl, with and without ratchet, an interfering clip about the screw head, and a snap-fit engagement between the screw and screw hole. The screw hole is preferably provided with openings at at least one of two diametric sides which provide dynamic compression functionality and access under the screw for an instrument to facilitate screw release.