US Patent 6905500 Bone fixation apparatus

Disclosed is a bone fixation apparatus. This device comprises a bone screw having a head; a cap member placed on an upper part of the head of the bone screw; a receiver member having a bore in which the cap member and the head of the bone screw are respectively accommodated and held, and a U-shaped channel through which a support bar extends; and a compression member threadedly coupled into the receiver member to downwardly bias the support bar. A multitude of stepped portions are formed at a lower end and inner surface of the receiver member to be brought into linear contact with an outer surface of a lower part of the head so that the supporting force for the head of the bone screw is increased.