A bone fixation system includes a plate (10) with a screw hole (14) and a bone screw (12) in which the screw and plate cooperate such that the screw is inhibited from back out from the plate after inserted into bone. The system can include a pawl (56), with or without ratchet (60). The screw hole can be provided with openings (66,68) at at least one of two diametric sides which provide dynamic compression functionality and access under the screw head for an instrument to facilitate screw release. The pawl may be provided on a ring (382) which is mounted in a groove (344) in the screw head (330) and which expands into a groove (345) in the screw hole.
