Pedicle-screw assembly

1. A pedicle-screw assembly comprising:

a screw having a threaded shaft extending along a screw axis and having at an axially outer end of the shaft a ball head having a substantially spherical outer surface from which the threaded shaft extends and an equator lying in a plane perpendicular to the screw axis;

a tulip body extending along a body axis and formed with an inwardly open screw-head seat in which the ball head can fit, with two pin seats open radially inwardly of the body axis into the screw-head seat, and with an oppositely outwardly open rod seat adapted for holding a spine-stabilizing rod;

a retainer fitted in the screw-head seat and engaging around the spherical outer surface of the ball head mostly between the equator and the shaft; and

respective pins extending radially of the body axis and seated in the pin seats of the body and in the retainer for pivoting of the retainer in the screw-head seat about a retainer axis substantially perpendicular to the body axis between a position with the body axis coaxial with the screw axis and a position with the body axis forming an acute outwardly open angle with the screw axis, the ball head being swivelable in and relative to the retainer.

2. The pedicle-screw assembly defined in claim 1 , wherein the pins diametrally flank the screw head.

3. The pedicle-screw assembly defined in claim 1 , wherein the retainer is V-shaped and opens inward toward the screw shaft.

4. The pedicle-screw assembly defined in claim 1 , wherein the retainer has a substantially spherical inner surface complementary to the substantially spherical outer surface of the ball head, both surfaces being centered on a substantially common point about which the screw is swivelable polyaxially in the retainer.

5. The pedicle-screw assembly defined in claim 1 , wherein the body is formed at an axial inner end with an inwardly open cutout in which the screw shaft can fit in an end position.

6. The pedicle-screw assembly defined in claim 5 , wherein, when the screw shaft is deflected to fit into the cutout, an angle between the body axis and the screw axis is greater than when the screw shaft is deflected into axial contact with an axial inner end of the body outside the cutout.

7. The pedicle-screw assembly defined in claim 6 , wherein, when the screw shaft is engaged in the cutout, the angle is at most 61° and, when the screw shaft is engaged with a body edge outside the cutout, the angle is at most 45°.

8. The pedicle-screw assembly defined in claim 1 , wherein the pin seats open radially outwardly of the body axis.

9. The pedicle-screw assembly defined in claim 1 , further comprising:

a clamping piece located between the screw-head seat and the rod seat and defining faces of both of the screw-head and rod seats.

10. The pedicle-screw assembly defined in claim 9 , wherein the clamping piece has a throughgoing guide passage on the body axis and through which a tool can pass and the screw head is formed with a seat open axially along the screw axis, alignable with the guide passage, and shaped to complementarily receive the tool.

11. The pedicle-screw assembly defined in claim 1 , wherein the body is formed with at least one annular and radially outwardly open groove spaced outwardly of the retainer axis.

12. The pedicle-screw assembly defined in claim 1 , wherein the body tapers outward.

13. The pedicle-screw assembly defined in claim 1 , wherein an inner surface of the rod seat is formed at an outer end of the rod seat with a screwthread.