Polyaxial bone screw with split retainer ring

In a polyaxial head bone screw assembly for surgical implantation and including a shank having a threaded body and a capture end and a head having an outward opening channel adapted to receive a rod within said channel, said head having a shank receiving bore formed therethrough and a seat, the improvement comprising:

• (a) said capture end of said shank having a top surface, and being received within said shank receiving bore of said head;
• (b) a retainer ring that is loaded separately from said shank into said head and being joined to said capture end of said shank within said head to retain said capture end within said head;
• said shank and retainer ring forming an assembled structure wherein the top surface of the capture end is located above the retainer ring when the shank and retainer ring are joined, and the assembly structure is rotatable in the head seat so as to enable angular positioning of said shank with respect to said head;
• said shank and retainer ring being joined such that said retainer ring rotates with said shank during the angular positioning of said shank relative to said head;
• and
• (c) a closure member operably engageable with said head and adapted to engage a rod within said channel so as to produce friction between said retainer ring and said head seat so as to secure said head from movement relative to such a rod and to secure said head from angular movement relative to said shank and said retainer ring structure, when in a locking configuration.

A polyaxial bone screw assembly, comprising:

• a) a head including a rod-receiving channel, an inner cavity communicating with the rod-receiving channel and having a seat therein, and lower opening joining the seat with an outer surface of the head;
• b) a resilient retainer ring received in the cavity and including an inner bore with an inner surface, and an outer seating surface;
• and
• c) a shank including a threaded body and a capture end extending upwardly therefrom, the capture end having a top surface, the threaded body being adapted for implantation into a bone, and the shank being sized and shaped to be received through the head lower opening and into the cavity;
• d) the retainer ring inner bore surface resiliently receiving and matingly engaging the shank capture structure such that the top surface of the capture structure is located above the retainer ring, when the shank is received through the lower opening and joined with the retainer ring, the retainer ring outer seating surface slidingly engaging the head seat, such that the shank polyaxially rotates relative to the head while in an adjustment configuration;
• and
• e) a closure member operably received in the head in such a manner as to capture a rod located within the rod-receiving channel.

A polyaxial bone screw assembly for surgical implantation comprising:

• a) a shank having a lower threaded body and an upper capture end;
• the shank capture end having an upper dome that is convex in shape and that has a first radius;
• b) a head having a channel for receiving a rod and a cavity for receiving the shank capture end, such that the shank dome extends into the channel;
• and
• c) a retainer that operably joins with and rotates with the shank in the head cavity such that the retainer is located below the upper dome;
• the retainer being sized and shaped to hold the shank capture end within the cavity and allow polyaxial movement of the shank relative to the head during angular positioning of the shank;
• the retainer having a second radius at the maximum width of the retainer that is larger than the first radius.