Patent attributes
A pivotal bone anchor assembly includes a shank having a shank head with a partial spherical shape at a proximal end and an anchor portion opposite the shank head for fixation to the bone of a patient. The assembly also includes a receiver having an upper portion defining a channel for receiving an elongate rod and a base defining a cavity in communication with the channel and with a bottom surface of the receiver through a distal opening. The assembly further includes a retainer positionable into non-rotatable and non-pivotal engagement with an inner surface of the cavity prior to the shank head being received within the cavity, with the retainer having a central opening configured to receive and capture the shank head within the cavity while allowing for pivotal motion between the shank and the receiver in at least one plane, and with a lower portion of the retainer extending below the bottom surface of the receiver.
