POSTERIOR POLYAXIAL SYSTEM FOR THE SPINE

摘要

The invention provides a rod assembly for implantation into the spine which includes a bone anchor assembly providing two points of angulation for the connection between the point of fixation and the rod. Further, the distance of offset between the point of fixation and the rod can be varied. The invention uses a bone screw having a pronged cage with a recess that accommodates the head of a post member. The cage can be tightened around the head by the camming surfaces of a locking cap that is drawn down around the compressible cage as the head is screwed upward in the recess by the engagement of the threads of the post by a locking nut. Further, the locking cap has a slotted bushing that is positionable in the elongated slot of a rod connector member. The locking nut includes an external taper that expands the bushing outward to lock it into position in the slot. In a further embodiment, the head has an internal hollow that receives a spindle journaled in a cavity in the recess to limit the amount of play in the assembly prior to tightening. In a further embodiment, the connection between bone anchors is provided by a plate that has locking caps pre-assembled into the plate.