POLYAXIAL BONE ANCHOR WITH NON-PIVOTABLE RETAINER AND POP-ON SHANK, SOME WITH FRICTION FIT

摘要

A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. The upper portion expands a retaining member in the receiver cavity to capture the shank upper portion in the receiver. In some embodiment either the retaining member or an insert provide for a friction fit of the shank upper portion in the receiver resulting in non-floppy placement of the shank with respect to the receiver. Some retainers and inserts have a lock- and-release feature. Final locking of the polyaxial mechanism is provided by frictional engagement between the shank upper portion and the retaining member. A pre-assembled receiver, retaining member and optional insert may be popped-on or snapped-on to the shank upper portion prior to or after implantation of the shank into a vertebra.