Spinal stabilization implant assemblies with interchangeable threaded closures

1. A polyaxial bone anchor implant assembly configured for surgical implantation into a bone of a patient, the polyaxial bone anchor implant assembly comprising:

an elongate rod;

a closure mechanism;

a shank; and

a head including a pair of upstanding arms each with a top surface and an outer surface portion extending toward a bottom of the head, the pair of upstanding arms forming a channel configured for receiving the elongate rod therein and configured for the closure mechanism to close the channel and lock the elongate rod between the pair of upstanding arms, the pair of upstanding arms having an internal surface with a discontinuous helically wound guide and advancement structure, the head configured to pivot relative to the shank,

the closure mechanism being configured as a one-part closure or a two-part closure, the closure mechanism comprising:

a plug body formed in a cylindrical shape and including a longitudinal axis, a top surface having a flat portion, a bottom surface, the bottom surface and the flat portion of the top surface defining an axial height therebetween, an external surface having a continuous helically wound guide and advancement structure portion formed thereon extending between the bottom surface and the flat portion of the top surface along the axial height, a first axial opening extending into the plug body from the top surface, and a lower implant engaging surface extending circumferentially with respect to the first axial opening, at least a portion of the first axial opening defining a closed perimeter around an entirety thereof, the closure mechanism configured to lock the implant assembly and the elongate rod positioned between the upstanding arms;

wherein, when the closure mechanism is configured as a two-part closure:

the plug body includes an outer plug body configured as a closed ring and the first axial opening is configured as at least a partial central bore extending between the top surface and a bottom surface of the outer plug body, at least a portion of the central bore being threaded, the outer plug body further comprises a drive structure that is non-threaded and axially extending, the drive structure is formed on an upper portion of the outer plug body and includes a lower surface for engaging a driving tool that does not communicate with the bottom surface of the outer plug body; and

the two-part closure further comprising an inner plug that is separate from the outer plug body and includes a longitudinal axis and an outer surface that is configured to be at least partially threadedly received in the central bore of the outer plug body, the inner plug including a solid lower portion with a bottom surface configured to engage and lock the elongate rod when positioned within the channel, the bottom surface including a substantially flat portion,

wherein the inner plug includes a central drive socket formed therein above the solid lower portion with a lower tool abutment surface and defining a second axial opening that is non-threaded, the central drive socket extending from a top surface of the inner plug to the lower tool abutment surface so as to not communicate with the bottom surface, the substantially flat portion of the bottom surface of the inner plug extending circumferentially with respect to the second axial opening,

wherein the inner plug is configured to be threadedly received in the outer plug body prior to the two-part closure being received in the channel formed between the pair of upstanding arms of the head, and

wherein the continuous helically wound guide and advancement structure portion of the plug body of the one-part closure and the two-part closure are configured to be interchangeable with each other for closing the channel and locking the assembly and the elongate rod between the pair of upstanding arms with the closure mechanism.

2. The bone anchor implant assembly of claim 1 , wherein the bottom surface of the inner plug comprises a central point.

3. The bone anchor implant assembly of claim 1 , wherein the top surface of the inner plug is flat.

4. The bone anchor implant assembly of claim 1 , wherein a thread on the outer surface of the inner plug is continuous from the top surface to the bottom surface of the inner plug.

5. The bone anchor implant assembly of claim 1 , wherein the drive structure of the outer plug body comprises a plurality of spaced apart non-threaded drive structures including a first radially located slot formed in the top surface of the outer plug body which extends from the external surface to the central bore and intersects the threaded central bore of the outer plug body.

6. The bone anchor implant assembly of claim 5 , wherein the plurality of spaced apart non-threaded drive structures of the outer plug body includes a second radially located slot formed in the top surface of the outer plug body diametrically opposed to the first slot which extends from the external surface to the central bore and intersects the central bore.

7. The bone anchor implant assembly of claim 1 , wherein the helically wound guide and advancement structure portion includes interlocking flanges.

8. The bone anchor implant assembly of claim 1 , wherein the first axial opening is centrally positioned with respect to the longitudinal axis of the plug body.

9. The bone anchor implant assembly of claim 1 , wherein the closure mechanism is configured as the one-part closure.

10. The bone anchor implant assembly of claim 1 , wherein the closure mechanism is configured as the two-part closure.

11. The bone anchor implant assembly of claim 1 , wherein the closure mechanism comprises one of the one-part closure and the two-part closure.

12. A method for locking the elongate rod within the polyaxial bone anchor implant assembly of claim 1 , the method comprising:

providing the polyaxial bone anchor implant assembly of claim 1 ;

receiving the elongate rod in the channel; and

closing the channel with the closure mechanism.

13. The method of claim 12 , wherein the bottom surface of the inner plug comprises a central point.

14. The method of claim 12 , wherein the top surface of the inner plug is flat.

15. The method of claim 12 , wherein a thread on the outer surface of the inner plug is continuous from the top surface to the bottom surface of the inner plug.

16. The method of claim 12 , wherein the drive structure of the outer plug body comprises a plurality of spaced apart non-threaded drive structures including a first radially located slot formed in the top surface of the outer plug body which extends from the external surface to the central bore and intersects the threaded central bore of the outer plug body.

17. The method of claim 16 , wherein the plurality of spaced apart non-threaded drive structures of the outer plug body includes a second radially located slot formed in the top surface of the outer plug body diametrically opposed to the first slot which extends from the external surface to the central bore and intersects the central bore.

18. The method of claim 12 , wherein the helically wound guide and advancement structure portion is a flange form.

19. The method of claim 12 , wherein the first axial opening is centrally positioned with respect to the longitudinal axis of the plug body.

20. The method of claim 12 , wherein the closure mechanism is configured as the one- part closure.

21. The method of claim 12 , wherein the closure mechanism is configured as the two- part closure.

22. The method of claim 12 , wherein the closure mechanism comprises one of the one-part closure and the two-part closure.