Patent ID: 7942913

Claim:
A bone fixation apparatus comprising: a bone fixation plate having a fixation hole; a fastener shaft received in the fixation hole and including a first portion having an outer surface defining a first cam and a second bone-engaging portion; and an annular member received in the fixation hole and including an inner surface defining a second cam for cooperating with the first cam to selectively move the annular member in a radial direction between an unexpanded position permitting movement of the fastener shaft and annular member relative to the fixation hole and an expanded position restricting movement of the fastener shaft and annular member relative to the fixation hole, the annular member including at least one engagement formation operable to receive a tool to move the annular member between the expanded position and the unexpanded position by rotation of the annular member relative to the fastener shaft following insertion of the fastener shaft into a bone.