US Patent 8366753 Polyaxial bone screw assembly with fixed retaining structure

A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver and retained within the receiver by a retaining structure in the form of an open ring. The receiver has a U-shaped channel for receiving a spinal fixation rod. The shank upper portion is designed to directly frictionally engage the spinal fixation rod when a closure structure operably urges the rod toward the upper portion, fixing the bone screw shank body in a selected angular orientation with respect to the receiver.