Apparatus and methods for reduction of vertebral bodies in a spine
A system for reduction of vertebral bodies (or vertebrae) various embodiments includes a reducer, and extender, and a hollow tube. The reducer couples to the extender, which in turn couples to an elongated member, such as a rod, and to a bone fastener assembly. The reducer allows reduction of the vertebral body incrementally, and by a desired amount. The reducer may include or may be used in conjunction with a holding device or holder in order to hold or keep the amount of reduction constant or steady once the desired amount of reduction has been obtained. The reducer may use one of several embodiments, including embodiments that use threaded assemblies or members, inclining members or wedges, offset cams, scissor jacks, and/or levers.
1. A rod reducing apparatus, comprising:
a screw assembly comprising:
a threaded shaft with a controlling member at a proximal end thereof; and
a threaded body engaged with the threaded shaft;
a rod contacting member engaged at a distal end of the threaded body; and
a grasping element having a distal end, a proximal end and a longitudinal axis extending therebetween, the distal end configured to grasp and detachably couple to a bone fastener and the proximal end connected to the threaded shaft of the screw assembly;
wherein the rod contacting member defines a passage configured to slidably receive the grasping element; and
wherein rotation of the threaded shaft slides the rod contacting member along the longitudinal axis.
2. The apparatus of claim 1 , wherein turning the controlling member causes the rod contacting member and the grasping element to move relative to each other in opposite directions.
3. The apparatus of claim 1 , wherein the controlling member is a knob.
4. The apparatus of claim 3 , wherein:
turning the knob in a first direction causes the rod contacting member to extend; and
turning the knob in a second direction opposite the first direction causes the rod contacting member to retract.
5. The apparatus of claim 1 , further comprising at least a first locking member coupled to the threaded shaft of the screw assembly and configured to selectively engage the grasping element.
6. The apparatus of claim 5 , further comprising a second locking member coupled to the threaded shaft of the screw assembly and configured to selectively engage the grasping element, wherein the first and second locking members are disposed on opposing sides of the screw assembly.
7. A spinal reduction assembly comprising:
a bone fastener configured to be coupled to a vertebral body;
a collar configured to be coupled to the bone fastener, the collar including a slot for seating a rod; and
a reducer configured to be coupled to the collar to seat the rod in the slot, the reducer comprising:
a screw assembly comprising:
a threaded shaft with a controlling member at a proximal end thereof; and
a threaded body engaged with the threaded shaft;
a rod contacting member engaged at a distal end of the threaded body; and
a grasping element having a distal end, a proximal end and a longitudinal axis extending therebetween, the distal end configured to grasp and detachably couple to the collar and the proximal end connected to the threaded shaft of the screw assembly;
wherein the rod contacting member defines a passage configured to slidably receive the grasping element; and
wherein rotation of the threaded shaft slides the rod contacting member along the longitudinal axis.
8. The apparatus of claim 7 , wherein turning the controlling member causes the rod contacting member and the grasping element to move relative to each other in opposite directions.
9. The apparatus of claim 8 , wherein the controlling member is a knob located at a proximal end of the reducer, wherein:
turning the knob in a first direction causes the rod contacting member to extend; and
turning the knob in a second direction opposite the first direction causes the rod contacting member to retract.
10. The apparatus of claim 7 , further comprising at least a first spring-biased locking member coupled to the screw assembly and configured to selectively engage the grasping element.
11. The apparatus of claim 10 , further comprising a second spring-biased locking member coupled to the screw assembly and configured to selectively engage the grasping element, wherein the first and second spring-biased locking members are disposed on opposing sides of the screw assembly.
12. The apparatus of claim 5 , wherein:
the grasping element comprises an outer channel; and
the first locking member comprises a tab that is resiliently biased into the outer channel.
13. The apparatus of claim 12 , wherein the first locking member can be displaced via a button to overcome the resilient bias and linearly push the tab directly out of the channel to unlock the threaded shaft from the grasping member.
14. The apparatus of claim 12 , wherein the first locking member can be displaced via a lever to overcome the resilient bias and rotate the tab out of the channel to unlock the threaded shaft from the grasping member.
15. The apparatus of claim 12 , wherein the threaded shaft comprises a pocket to retain the first locking member and prevent axial displacement of the first locking member.
16. The apparatus of claim 15 , wherein the first locking member is rotatable within the pocket.
17. The apparatus of claim 10 , wherein the locking member comprises a button having a tab resiliently biased into the grasping element, wherein pushing of the button moves the tab out of engagement with the grasping element.
18. A rod reducer apparatus comprising:
a resiliently-biased attachment mechanism configured to selectively couple to an extender positioned within the resiliently-biased attachment mechanism, the resiliently-biased attachment mechanism comprising a button that is configured to be is resiliently-biased against the extender;
a rod-contacting tube configured to be positioned coaxially with the extender;
a reducing mechanism comprising:
a knob located at a proximal end of the rod reducer apparatus and coupled to the resiliently-biased attachment mechanism; and
a body threadedly engaged with the knob and engaged with the rod-contacting tube;
a shaft extending downward from the knob, the shaft comprising:
an outer surface having external threading; and
an internal surface;
internal threading located on the body to engage with the external threading;
a locking member adjustably extending from the resiliently-biased attachment mechanism; and
a spring to bias the locking member away from the internal surface and toward the extender when the extender is positioned within the resiliently-biased attachment mechanism.
19. The rod reducer apparatus of claim 18 , wherein the locking member comprises:
a tab extending from the button and configured to engage the extender when the extender is positioned within the resiliently-biased attachment mechanism;
wherein the spring biases the button such that the tab is biased into engagement with the extender when the extender is positioned within the resiliently-biased attachment mechanism.
20. The rod reducer apparatus of claim 18 , wherein the locking member comprises:
a first locking handle pivotably coupled to a housing of the resiliently-biased attachment mechanism; and
a first tab extending from the first locking handle and configured to engage the extender when the extender is positioned within the resiliently-biased attachment mechanism; and
wherein the spring biases the first locking handle such that the first tab is biased into engagement with the extender when the extender is positioned within the resiliently-biased attachment mechanism.
21. The rod reducer apparatus of claim 18 , wherein the button moves at least partially in a radial direction from an axis of the rod reducer apparatus.