| abstract |
An open polyaxial bone anchor includes a pre-assembled receiver, retaining member and compression insert that may be popped-on or snapped-on to the shank upper portion prior to or after implantation of the shank into a vertebra. Cooperating closures have at least two helically wound forms thereon providing a multi-start closing mechanism for use between spaced arms of the bone anchor having mating helically wound structure thereon. |