Tethered restraint of vertebral bodies
Methods and devices for the tailored restraint of two separate bones, in which the bones are generally permitted to rotate relative to one another, or move toward each other, but are restrained from separating beyond a predetermined, fixed distance. In some embodiments, the restraint is provided by compressing a tether into a notched groove.
1. An apparatus for tethered connection between vertebrae, the apparatus comprising:
a bone screw having a shaft with threads and a head;
a portion of flexible tether having an uncompressed width; and
a tethering restraint member having a channel between opposing walls, the channel having an open top and a closed bottom, the open top extending from an entrance on a side of the tethering restraint member to an exit on a side of said tethering restraint member, the bottom including a region less wide than the uncompressed width of the tether, the region being adapted and configured for restraint of the tether within the channel, said member defining a through aperture sized to accept therethrough the shaft but not the head.
2. The apparatus of claim 1 , wherein at least one of the opposing walls includes a plurality of grooves that are angled and converge toward the bottom of the channel.
3. The apparatus of claim 1 , wherein the region of the channel compressing the tether is above the head of said screw.
4. The apparatus of claim 1 , wherein said member has a length between ends, and the channel has a V-shape that extends along the length from one end to the other end.
5. The apparatus of claim 4 , wherein said tethering restraint member includes an external bone contacting surface having at least one projection that extends toward the bone.
6. The apparatus of claim 1 , further comprising:
a cap having a threaded body and a driving pocket on a proximal end,
wherein said tethering restraint member includes threads within the surfaces of the walls to accept the threaded body.
7. The apparatus of claim 6 , wherein the tether is compressed between the bottom of the assembled cap and the surfaces of the channel.
8. The apparatus of claim 1 , wherein the head of said bone screw is contained within said tethering restraint member when said screw is within the aperture.
9. An apparatus for tethered connection between vertebrae, the apparatus comprising:
a tethering restraint member having a channel between opposing walls and extending from an entrance to an exit, the channel having a top and a bottom, the opposing walls converging toward each other, each opposing wall including at least one groove of a plurality of respective grooves, at least one groove of the plurality of respective grooves having a respective first end and a respective second end, the respective first end being located closer to the entrance of the channel than is the respective second end, the respective second end being located closer to the bottom of the channel than is the respective first end; and
means for attaching said tethering restraint member to a vertebra.
10. The apparatus of claim 9 , wherein each groove of each respective plurality of grooves has a respective corresponding first end and a respective corresponding second end, wherein each respective corresponding first end is located closer to the entrance of the channel than is the respective corresponding second end, and wherein each respective corresponding second end is located closer to the bottom of the channel than is the respective corresponding first end.
11. The apparatus of claim 10 , wherein the grooves of at least one of the respective pluralities of grooves are generally parallel to each other.
12. The apparatus of claim 11 , wherein said tethering restraint member has a longitudinal axis for the channel and the opposing ends of said member are open to permit passage therethrough of the tether.
13. The apparatus of claim 12 , wherein the top of the channel is open between the entrance and the exit.
14. The apparatus of claim 10 , wherein said tethering restraint member includes a bone contacting surface, and the grooves of the side walls converge toward the bottom of the channel and toward the bone contacting surface.
15. The apparatus of claim 14 , wherein the grooves on one wall are a mirror image of the grooves on the other wall.
16. The apparatus of claim 15 , wherein said attaching means is a threaded screw.
17. The apparatus of claim 10 , wherein the channel is a longitudinal oriented V-shaped channel, and said tethering restraint member includes a bone contacting surface generally proximate to the vertex of the V-shaped channel.
18. The apparatus of claim 9 , further comprising:
a cap having a threaded body, a driving pocket on a proximal end, and a smooth surface on a distal end,
wherein said tethering restraint member includes threads to accept the threaded body such that the smooth surface is directed toward the bottom of the channel.
19. An apparatus for tethered connection between vertebrae, the apparatus comprising:
a bone screw having a shaft with threads and an end with a concave driving feature;
a cap having a threaded body;
a portion of flexible tether having a width; and
a tethering restraint member having a longitudinal channel between opposing walls, said member defining a through aperture sized to accept therethrough the shaft, said tethering restraint member including a threaded portion within the channel to accept the threaded body, the channel including a region wherein the width of the channel is less than an uncompressed width of the tether, wherein the region is between the through aperture and the threaded portion.
20. The apparatus of claim 19 , wherein said screw includes an exterior shoulder, said body includes an interior shoulder surrounding a through aperture, and the interior shoulder is adapted and configured to prevent passage of the head through the aperture.
21. The apparatus of claim 20 , wherein the channel is a longitudinal oriented V-shaped channel, the through aperture extends generally perpendicularly to the channel, and said tethering restraint member includes a bone contacting surface generally parallel to one of the sides of the V-groove.
22. The apparatus of claim 20 , wherein the top of said cap is about flush with the top of said tethering restraint member when the cap is threaded into said member.
23. The apparatus of claim 20 , wherein said tethering restraint member includes a bone contacting surface generally opposite of the opening of the channel.
24. The apparatus of claim 20 , wherein the channel has an entrance and an exit, and the entrance and the exit are located on opposite sides of said tethering restraint member.