Polyaxial pedicle screw having a rotating locking element

1. An orthopedic rod implantation apparatus having screws and coupling elements, comprising:

at least one elongate rod; and

a plurality of screw and coupling element assemblies, wherein at least one of the assemblies comprises:

a screw that has a head and a shaft that extends from the head;

a coupling element that has a seat within which the head can be seated such that the shaft protrudes from the coupling element; and

a locking element that can be mated with the coupling element and that thereafter can be selectively moved through a plurality of positions including an unlocked position and a locked position; wherein:

when the locking element is in the unlocked position:

the locking element presents a rod-receiving channel, and

the head is movable in the seat such that the shaft can be directed in a plurality of angles relative to the coupling element; and

when the locking element is in the locked position:

the rod, if disposed within the rod-receiving channel, is fixed relative to the coupling element, and

the head is immovable in the seat such that the shaft is fixed at an angle relative to the coupling element;

wherein the selective movability of the locking element is provided by the locking element being selectively rotatable about the longitudinal axis of the rod through the plurality of positions.

2. The apparatus of claim 1 , wherein:

the head has engagement surface that can be engaged by a screwdriving tool; and

at least one of the coupling element and the locking element has a bore that permits use of the tool when the head is seated in the scat.

3. The apparatus of claim 2 , wherein:

one of the head and the tool has a polygonal recess; and

the other of the head and tool has an external structure that fits within the recess.

4. The apparatus of claim 1 , wherein:

the head has a curvate proximal portion from which the shaft extends;

the seat is defined by a bore in the coupling element and a socket defined by a curvate volume adjacent the bore;

the curvate volume corresponds to the curvate proximal portion such that the curvate proximal portion can be nested in the socket; and

when the curvate proximal portion is nested in the socket:

the shaft protrudes from the bore;

the curvate proximal portion cannot pass fully through the bore;

when the locking element is in the unlocked position the curvate proximal portion can rotate and angulate in the socket such that the shaft can be directed through a range of angles relative to the coupling element; and

when the locking element is in the locked position the curvate proximal portion is immovable in the socket such that the shaft is fixed at an angle relative to the coupling element.

5. The apparatus of claim 1 , wherein:

the head has a distal portion defined by a compression surface;

the locking element has a permissive surface that is presented to the compression surface when the locking element is in the unlocked position;

when presented with the permissive surface, the compression surface is unhindered such that the head is movable in the seat;

the locking element has a confrontational surface that is presented to the compression surface when the locking element is in the locked position,

the confrontational surface is defined by a recess that has a recessed surface corresponding to the compression surface; and

when the locking element is in the locked position:

the locking element is compressed within the coupling element,

the compression surface is compressed by the confrontational surface such that the curvate proximal portion is compressed toward a bore in the coupling element and the head is immovable in the seat, and

the compression surface seats in the recess and thereby is biased against retreat from the recess.

6. The apparatus of claim 5 , wherein:

the compression surface is a curvate surface;

the confrontational surface extends from an edge of the permissive surface and terminates in the recess; and

the confrontational surface is gradually presented to the compression surface as the locking element is moved from the unlocked position to the locked position.

7. The apparatus of claim 1 , wherein:

the rod-receiving channel is defined by substantially parallel walls; and

when the locking element is in the locked position the walls are compressed toward one another such that the rod is compressed within the channel and thereby fixed relative to the coupling element.

8. A screw and coupling element assembly for use with an orthopedic rod implantation apparatus, comprising:

a screw that has a head and a shaft that extends from the head, the head has a distal portion defined by a compression surface;

a coupling element that has a seat within which the head can be seated such that the shaft protrudes from the coupling element; and

a locking element that can be mated with the coupling element and that thereafter can be selectively moved through a plurality of positions including an unlocked position and a locked position, the locking element has a permissive surface that is presented to the compression surface when the locking element is in the unlocked position and when presented with the permissive surface, the compression surface is unhindered such that the head is movable in the seat, the locking element further has a confrontational surface that is presented to the compression surface when the locking element is in the locked position, the confrontational surface is defined by a recess that has a recessed surface corresponding to the compression surface; wherein:

when the locking element is in the unlocked position:

the locking element presents a rod-receiving channel, and

the head is movable in the seat such that the shaft can be directed in a plurality of angles relative to the coupling element; and

when the locking element is in the locked position:

a rod disposed within the rod-receiving channel is fixed relative to the coupling element,

the locking element is compressed within the coupling element,

the compression surface is compressed by the confrontational surface such that the curvate proximal portion of the head is compressed toward a bore in the coupling element and the head is immovable in the seat, and

the compression surface seats in the recess and thereby is biased against retreat from the recess, and

the head is immovable in the seat such that the shaft is fixed at an angle relative to the coupling element;

wherein the selective movability of the locking element is provided by the locking element being selectively rotatable about the longitudinal axis of the rod through the plurality of positions.

9. The assembly of claim 8 , wherein:

the head has an engagement surface that can be engaged by a screwdriving tool; and

at least one of the elements has a bore that permits use of the tool when the head is seated in the seat.

10. The assembly of claim 9 , wherein:

one of the head and the tool has a polygonal recess; and

the other of the head and the tool has an external structure that fits within the recess.

11. The assembly of claim 8 , wherein:

the shaft extends from the curvate proximal portion of the head

the seat is defined by the bore in the coupling element and a socket defined by a curvate volume adjacent the bore;

the curvate volume corresponds to the curvate proximal portion such that the curvate proximal portion can be nested in the socket; and

when the curvate proximal portion is nested in the socket:

the shaft protrudes from the bore;

the curvate proximal portion cannot pass fully through the bore;

when the locking element is in the unlocked position the curvate proximal portion can rotate and angulate in the socket such that the shaft can be directed through a range of angles relative to the coupling element; and

when the locking element is in the locked position the curvate proximal portion is immovable in the socket such that the shaft is fixed at an angle relative to the coupling element.

12. The assembly of claim 8 , wherein:

the compression surface is a curvate surface;

the confrontational surface extends from an edge of the permissive surface and terminates in the recess; and

the confrontational surface is gradually presented to the compression surface as the locking element is moved from the unlocked position to the locked position.

13. The assembly of claim 8 , wherein:

the rod-receiving channel is defined by substantially parallel walls; and

when the locking element is in the locked position the walls are compressed toward one another such that the rod is compressed within the channel and thereby fixed relative to the coupling element.

14. A locking assembly, comprising:

a securing element that has a head and a shaft that extends from the head;

a coupling element that has a seat within which the head can be seated such that the shaft protrudes from the coupling element, the seat is defined by a bore in the coupling element and a socket adjacent the bore wherein the head can be nested in the socket such that head cannot pass fully through the bore but the shaft protrudes from the bore; and

a locking element that can be mated with the coupling element and that thereafter can be selectively moved through a plurality of positions including an unlocked position and a locked position, the locking element has an increasingly confrontational surface terminating in a recess that has a recessed surface, the head has a compression surface corresponding to the recessed surface; wherein:

when the locking element is in the unlocked position:

the locking element presents a channel for receiving a rod, the channel is defined by walls of the locking element, and

the head is movable in the seal such that the shaft can be directed in a plurality of angles relative to the coupling element;

when the locking element is in the locked position:

the rod, if disposed within the channel, is fixed relative to the coupling element, and

the head is immovable in the seat such that shaft is fixed at an angle relative to the coupling element; and

when the locking element is moved from the unlocked position to the locked position:

the locking element is compressed within the coupling element;

the walls are compressed toward one another such that the rod, if disposed within the channel, is compressed within the channel and thereby fixed relative to the coupling element;

the compression surface is compressed by the confrontational surface such that the head is compressed toward the bore and rendered immovable in the socket; and

the compression surface seats in the recess and thereby is biased against retreat from the recess;

wherein the selective movability of the locking element is provided by the locking element being selectively rotatable about the longitudinal axis of the rod through the plurality of positions.

15. The assembly of claim 14 , wherein when the locking element is in the locked position:

the locking element is compression locked within the coupling element;

the head is compression locked within the seat; and

the rod, if disposed within the channel, is compression locked within the channel.

16. The assembly of claim 14 , wherein the locking element is provided with at least one engagement surface that can be engaged by a tool to move the locking element through the plurality of positions.

17. The assembly of claim 16 , wherein the tool has a corresponding surface that engages the engagement surface and the tool accommodates the rod as the tool is used to move the locking element through the plurality of positions.