A bone fixation apparatus is provided and includes a bone fixation plate having a fixation hole, a fastener shaft having a bone-anchoring portion and an upper portion defining an outer cam, and a C-shaped annular member having an outer surface, an inner surface defining an inner cam, and a gap formed through the entire annular member. The inner cam cooperates with the outer cam of the fastener shaft to move the annular member between an unexpanded position and an expanded position independent from movement of the fastener shaft relative to the bone fixation plate.
