Bottom loaded pedicle screw
A pedicle screw includes a tulip head, a rod seat, a screw shank, and a retainer collar. The tulip head has an upper opening disposed in a top end of the tulip head and a lower opening disposed in a bottom end of the tulip head opposite the upper opening. The upper and lower openings form a single cavity extending through the tulip head from a top end to the bottom end. The rod seat is disposed within the cavity of the tulip head and engages a stop extending inwardly from an interior wall of the cavity. The screw shank has a thread disposed along a length of the screw shank and a connector positioned at an upper end. The retainer collar has a pass through aperture, an expansion slit, and is disposed about the connector of the screw shank. Other embodiments are described and claimed.
1. A pedicle screw comprising:
a tulip head having an upper opening disposed in a top end of the tulip head and a lower opening disposed in a bottom end of the tulip head opposite the upper opening, wherein:
the upper and lower openings form a single cavity extending through the tulip head from the top end to the bottom end, and
the cavity has an interior wall, internal threads disposed within the interior wall and adjacent to the upper opening, and a stop disposed between the lower opening and the upper opening, the stop extending substantially at right angles inwardly from the interior wall and separate from the internal threads;
a rod seat disposed within the cavity and engageable with the stop, the rod seat having a rod mating face, a shank mating face opposite the rod mating face, and a hole disposed through the rod mating face and shank mating face;
a screw shank having a thread disposed along a length of the screw shank and a connector positioned at an upper end of the screw shank;
a retainer collar having a collar body, a pass through aperture disposed through the collar body, an anti-rotation tab extending from the collar body, and a collar expansion split disposed within the collar body, wherein the retainer collar is disposed about the connector of the screw shank; and
wherein the cavity of the tulip head further includes an anti-rotation socket constructed to receive and engage the anti-rotation tab of the retainer collar.
2. The pedicle screw according to claim 1 , wherein:
the cavity of the tulip head has a retention groove disposed within the interior wall;
the stop is disposed between the retention groove and the upper opening; and
the retainer collar has a locking ring groove disposed within an outer surface of the collar body.
3. The pedicle screw according to claim 2 , further comprising a locking ring disposed within the retention groove and the locking ring groove.
4. The pedicle screw according to claim 3 , wherein the locking ring has a compression zone disposed therein such that when the compression zone is in its natural state it has an unloaded outer diameter (D O1 ) and an unloaded inner diameter (D I1 ), and wherein when the compression zone is reduced, the locking ring has a loaded outer diameter (D O2 ) and a loaded inner diameter (D I2 ).
5. The pedicle screw according to claim 3 , wherein the tulip head includes a retention groove inlet that is connected to the retention groove and extends to an exterior surface of the tulip head opposite the interior wall.
6. The pedicle screw according to claim 5 , wherein the locking ring is disposed in the retention groove inlet.
7. The pedicle screw according to claim 6 , wherein the locking ring is a wire fabricated from a material selected from a group consisting of metals, alloys, and composites.
8. The pedicle screw according to claim 1 , wherein the rod seat includes a retention ledge engageable with the stop.
9. The pedicle screw according to claim 1 , wherein:
the rod seat includes a pair of retention ledges; and
the tulip head includes a pair of arms defining a U-shaped channel transverse to the cavity, the pair of arms defining the stop of the cavity of the tulip head.
10. The pedicle screw according to claim 9 , wherein the retention ledges are engageable with the arms to thereby prevent rotation of the rod seat relative to the tulip head.
11. A pedicle screw comprising:
a tulip head having an upper opening disposed in a top end of the tulip head and a lower opening disposed in a bottom end of the tulip head opposite the upper opening, wherein:
the upper and lower openings form a single cavity extending through the tulip head from the top end to the bottom end, and
the cavity has an interior wall, internal threads disposed within the interior wall and adjacent to the upper opening, and a stop disposed between the lower opening and the upper opening, the stop extending inwardly from the interior wall and separate from the internal threads;
a rod seat disposed within the cavity and engageable with the stop, the rod seat having a rod mating face, a shank mating face opposite the rod mating face, and a hole disposed through the rod mating face and shank mating face;
a screw shank having a thread disposed along a length of the screw shank and a connector positioned at an upper end of the screw shank;
a retainer collar having a collar body, a pass through aperture disposed through the collar body, an anti-rotation tab extending from the collar body, and a collar expansion split disposed within the collar body, wherein the retainer collar is disposed about the connector of the screw shank; and
wherein the cavity of the tulip head further includes an anti-rotation socket constructed to receive and engage the anti-rotation tab of the retainer collar.
12. The pedicle screw according to claim 11 , wherein:
the cavity of the tulip head has a retention groove disposed within the interior wall;
the stop is disposed between the retention groove and the upper opening; and
the retainer collar has a locking ring groove disposed within an outer surface of the collar body.
13. The pedicle screw according to claim 12 , further comprising a locking ring disposed within the retention groove and the locking ring groove.
14. The pedicle screw according to claim 13 , wherein the locking ring has a compression zone disposed therein such that when the compression zone is in its natural state it has an unloaded outer diameter (D O1 ) and an unloaded inner diameter (D I1 ), and wherein when the compression zone is reduced, the locking ring has a loaded outer diameter (D O2 ) and a loaded inner diameter (D I2 ).
15. The pedicle screw according to claim 13 , wherein the tulip head includes a retention groove inlet that is connected to the retention groove and extends to an exterior surface of the tulip head opposite the interior wall.
16. The pedicle screw according to claim 15 , wherein the locking ring is disposed in the retention groove inlet.
17. The pedicle screw according to claim 16 , wherein the locking ring is a wire fabricated from a material selected from a group consisting of metals, alloys, and composites.
18. The pedicle screw according to claim 11 , wherein the rod seat includes a retention ledge engageable with the stop.
19. The pedicle screw according to claim 11 , wherein:
the rod seat includes a pair of retention ledges; and
the tulip head includes a pair of arms defining a U-shaped channel transverse to the cavity, the pair of arms defining the stop of the cavity of the tulip head.
20. The pedicle screw according to claim 19 , wherein the retention ledges are engageable with the arms to thereby prevent rotation of the rod seat relative to the tulip head.