Patent ID: 8075590

Claim:
A spinal fixation system comprising: a bone anchor member for being secured to a vertebral bone of the spine and having an enlarged head at one end thereof; an elongate member for extending generally along the spine; a coupling device for securing the elongate member relative to the bone anchor member; a seat of the coupling device having a bore about which the seat extends and sized to allow the anchor member to extend through the bore in a plurality of orientations with the head engaged against the seat; a cam lock member of the coupling device having a cam surface which cooperates to push the elongate member downward with the cam lock member being fixed against translation during turning thereof for clamping the head of the anchor member against the seat to fix the anchor member in one of the orientations thereof with the elongate member secured between the cam lock member and the anchor member head, wherein the elongate member is a spinal rod having a convexly curved surface, the cam surface of the cam lock member is a bottom surface thereof that is formed by a concave surface portion and ramp surface portions on either side of the concave surface portion so that both the concave surface portion and the ramp surface portions face downwardly toward the spinal rod; and a saddle member of the coupling device including an upper cam surface and a lower concave surface with the upper cam surface configured to cammingly engage the cam lock member bottom surface to cooperate therewith upon turning of the cam lock member for driving the lower concave surface into tight fitting engagement on the rod surface.