Bottom mounted pedical screw assembly
A bone screw, which can be a pedicle screw, is generally tulip-shaped. A bore in the bottom of the tulip permits a threaded shaft to be partially inserted into the open interior of the tulip. A seat is formed on the threaded shaft and receives the bottom of the tulip, and prevents the threaded shaft from being inserted too far into the tulip. A saddle is positioned in the interior of the tulip and receives the end of the threaded shaft on one end and can include a trough on its opposite face which can receive a rod that connects together two or more such assemblies. A retaining screw threads into the upper interior surface of the tulip to hold the subcomponents together.
1. A polyaxial bone screw assembly comprising:
a generally cup-shaped tulip having a top opening, a bottom bore, a semi-spherical inner bottom surface, and a semi-spherical outer bottom surface;
a saddle sized to be received in the tulip, the saddle having a semi-spherical outer bottom surface;
a bone screw having a distal end and a proximal end, a threaded shaft extending proximally from the distal end, a laterally extending platform positioned distal of the proximal end, and a post extending proximally of the platform, the platform including a semi-spherical proximal surface;
wherein the bone screw post and the saddle are both configured and arranged to form a snap fit connection, the snap fit connection including a recess in one of the bone screw post and the saddle and an enlargement on the other of the bone screw post and the saddle, the enlargement received in the recess.
2. The bone screw assembly according to claim 1 , further comprising a retaining screw having a thread, and wherein the tulip further comprises a thread configured and arranged to mate with the retaining element thread.
3. The bone screw assembly according to claim 2 , the retaining screw thread comprises an external thread, the tulip comprises a proximal inner surface, and the thread of the tulip is on the tulip proximal inner surface.
4. The bone screw assembly according to claim 3 , further comprising a bar extending laterally through the tulip between the retaining screw and the saddle.
5. The bone screw assembly according to claim 1 , wherein the saddle comprises said recess, and said recess comprises a blind bore.
6. The bone screw assembly according to claim 1 , wherein the saddle comprises said recess, and said recess comprises a throughbore.
7. The bone screw assembly according to claim 1 , wherein the recess is in the saddle and the enlargement is on the bone screw post.
8. The bone screw assembly according to claim 1 , wherein the recess is in the bone screw post and the enlargement is on the saddle.
9. The bone screw assembly according to claim 1 , wherein the bone screw platform is laterally larger than the tulip bottom bore.
10. The bone screw assembly according to claim 1 , wherein the tulip bottom bore and the bone screw post are mutually sized so that the tulip can pivot relative to the bone screw.
11. The bone screw assembly according to claim 1 , wherein the tulip bottom bore and the bone screw post are mutually sized so that the tulip can pivot relative to the bone screw up to about 15 degrees.