Polyaxial screwdriver for a pedicle screw system
View Patent ↗A polyaxial screwdriver for inserting a bone screw in a vertebra. A polyaxial bone screw assembly includes a coupling element. When a screw engaging end of the polyaxial screwdriver is lowered on the head of the bone screw, the complimentary surfaces of the screw engaging end of the screwdriver and the head of the screw self-align. A ratchet mechanism formed in the screwdriver provides progressive and automatic locking of the polyaxial screwdriver to the coupling element and prevents the accidental unthreading from the coupling element. In another embodiment of the polyaxial screwdriver, a collet slides over the outside surface of the upper end of the coupling element and locks on to the coupling element. In yet another embodiment of a polyaxial screwdriver, the outer sleeve of the polyaxial screwdriver has a split end that securely engages the coupling element.
1. A polyaxial screwdriver comprising:
a handle;
a shaft having a first end attached to the handle and a screw engaging end;
a cylindrical portion formed at the screw engaging end, the cylindrical portion having a first surface and a second surface alternatingly arranged at a periphery portion, the first surface and the second surface being adapted to engage a head of a polyaxial screw shaped to receive the screw engaging end; and
a sleeve being slidable over the shaft, the sleeve having a collet adapted to engage a tulip of the polyaxial screw;
a locking button mounted on the sleeve, the locking button being capable of automatically locking the shaft and thereby preventing the shaft from disengaging from the head of the polyaxial screw;
at least one projection formed on the collet, the projection being capable of engaging a depression on the surface of the tulip;
a nut mounted on the shaft, the nut having internal threads; and
external threads formed on the sleeve at the end that is close to the handle, the external threads being capable of engaging the internal threads.
2. The polyaxial screwdriver of claim 1 , wherein the first surface is substantially concave and the second surface is substantially convex.
3. The polyaxial screwdriver of claim 2 , wherein the first surface and the second surface are cylindrical, spherical or rectilinear.
4. The polyaxial screwdriver of claim 2 , wherein the leading edge of the convex surface is rounded such that the screwdriver is capable of self aligning with the head of the polyaxial screw.
5. The polyaxial screwdriver of claim 1 , further comprising:
a spline like structure formed around a periphery portion of the shaft, the spline like structure engaging a portion of the locking button to lock the shaft.
6. The polyaxial screwdriver of claim 5 , further comprising:
a spring mounted in the sleeve, the spring biasing the locking button towards the spline like structure, thereby continuously keeping the shaft in the locked position.
7. A polyaxial screwdriver comprising:
a handle;
a shaft having a first end attached to the handle and a screw engaging end;
a cylindrical portion formed at the screw engaging end, the cylindrical portion having a first surface and a second surface alternatingly arranged at a periphery portion, the first surface and the second surface being adapted to engage a head of a polyaxial screw shaped to receive the screw engaging end;
a sleeve slidable over the shaft, the sleeve having at least two arms adapted to engage a tulip of the polyaxial screw;
a locking button mounted on the sleeve, the locking button being capable of automatically locking the shaft and thereby preventing the shaft from disengaging from the head of the polyaxial screw; and
a ring, the ring being slidably engaged with the sleeve such that sliding the ring towards the handle will disengage the arms from the tulip.
8. The polyaxial screwdriver of claim 7 , further comprising:
a spline like structure formed around a periphery portion of the shaft, the spline like structure engaging a portion of the locking button to lock the shaft.
9. The polyaxial screwdriver of claim 8 , further comprising:
a spring mounted in the sleeve, the spring biasing the button towards the spline like structure, thereby continuously keeping the shaft in the locked position.
10. The polyaxial screwdriver of claim 9 , wherein the first surface is substantially concave and the second surface is substantially convex.
11. The polyaxial screwdriver of claim 10 , wherein the first surface and the second surface are cylindrical, spherical or rectilinear.
12. The polyaxial screwdriver of claim 10 , wherein the leading edge of the convex surface is rounded such that the screwdriver is capable of self aligning with the head of the polyaxial screw.