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. Retention ledges of the rod seat engage opposing arms of the tulip head. 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, a lower opening disposed in a bottom end of the tulip head opposite the upper opening, and a pair of opposing arms, wherein:
the upper and lower openings form a single cavity extending through the tulip head from the top end to the bottom end,
the pair of opposing arms define a U-shaped channel transverse to the cavity, 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;
a rod seat disposed within the cavity, the rod seat having:
a rod mating face,
a shank mating face opposite the rod mating face,
a hole disposed through the rod mating face and shank mating face, and
a pair of retention ledges, wherein the pair of retention ledges are engageable with the stop of the cavity of the tulip head to prevent the rod seat from moving into the upper opening of the tulip head, and wherein the pair of retention ledges are engageable with the pair of opposing arms of the tulip head to prevent rotation of the rod seat relative to the tulip head;
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; and
a retainer collar having a collar body, a pass through aperture disposed through 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.
2. The pedicle screw of 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 of claim 2 , further comprising a locking ring disposed within the retention groove and the locking ring groove.
4. The pedicle screw of 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 of 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 of claim 5 , wherein the locking ring is disposed in the retention groove inlet.
7. The pedicle screw of 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 of claim 1 , wherein each retention ledge of the pair of retention ledges comprises a first retention surface engageable with the stop of the cavity of the tulip head and a second retention surface engageable with a different opposing arm of the pair of opposing arms of the tulip head, the second retention surface of each retention ledge extends in a direction transverse to the first retention surface.
9. The pedicle screw of claim 1 , wherein the retainer collar comprises an anti-rotation tab extending from the collar body; 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.
10. A pedicle screw comprising:
a tulip head having an upper opening disposed in a top end of the tulip head, a lower opening disposed in a bottom end of the tulip head opposite the upper opening, and a pair of opposing arms, wherein:
the upper and lower openings form a single cavity extending through the tulip head from the top end to the bottom end,
the pair of opposing arms define a U-shaped channel transverse to the cavity, and
the cavity has an interior wall and internal threads, wherein the internal threads are disposed within the interior wall adjacent to the upper opening;
a rod seat disposed within the cavity, the rod seat having:
a rod mating face,
a shank mating face opposite the rod mating face,
a hole disposed through the rod mating face and shank mating face, and
a pair of retention ledges engageable with the pair of opposing arms to prevent rotation of the rod seat relative to the tulip head;
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, and a collar expansion split disposed within the collar body, wherein the retainer collar is disposed about the connector of the screw shank.
11. The pedicle screw of claim 10 , wherein:
the cavity of the tulip head has a retention groove disposed within the interior wall; and
the retainer collar has a locking ring groove disposed within an outer surface of the collar body.
12. The pedicle screw of claim 11 , further comprising a locking ring disposed within the retention groove and the locking ring groove.
13. The pedicle screw of claim 12 , 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 ).
14. The pedicle screw of claim 12 , 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.
15. The pedicle screw of claim 14 , wherein the locking ring is disposed in the retention groove inlet.
16. The pedicle screw of claim 15 , wherein the locking ring is a wire fabricated from a material selected from a group consisting of metals, alloys, and composites.
17. The pedicle screw of claim 10 , wherein the cavity of the tulip head comprises a stop disposed between the lower opening and the upper opening; and
wherein the pair of retention ledges are engageable with the stop of the cavity of the tulip head to prevent the rod seat from moving into the upper opening of the tulip head.
18. The pedicle screw of claim 17 , wherein each retention ledge of the pair of retention ledges comprises a first retention surface engageable with the stop of the cavity of the tulip head and a second retention surface engageable with a different opposing arm of the pair of opposing arms of the tulip head, the second retention surface of each retention ledge extends in a direction transverse to the first retention surface.
19. The pedicle screw of claim 10 , wherein the retainer collar comprises a sharpened spherical connector mating edge, wherein the sharpened spherical connector mating edge depresses into the connector of the screw shank.
20. The pedicle screw of claim 10 , wherein the retainer collar comprises an anti-rotation tab extending from the collar body; 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.