Bone anchor with offset rod connector
This disclosure describes example an surgical fixation anchor and methods for implanting the surgical fixation anchor on the spine as part of a spinal fixation construct. The surgical fixation anchor can be coupled to a spinal rod. The coupling between the spinal rod and the anchor can be offset from an axis of the anchor. The position and orientation of the coupling to the spinal rod can also be transnationally and rotationally adjusted relative to the anchor to facilitate the coupling and/or to optimize space usage adjacent to the fixation construct.
1. A spinal anchor, comprising:
a shank having a threaded region for anchoring in bone, and a spherical head; and
an offset connector for coupling the shank to a spinal rod offset from an axis of the shank, wherein the offset connector comprises:
a base, the base having a first end with a receptacle for forming a first lockable polyaxial joint with the spherical head of the shank, the base further including an arm that extends from the receptacle, the arm having a first length, a first height, and a first width; and
a tulip, the tulip forming a second lockable polyaxial joint translatable along a length of the base and having a rod channel for coupling the tulip to a spinal rod, the tulip further including a passage, the passage having a second length less than the first length, a second height greater than the first height, and a second width greater than the first width, the arm of the base extending through the passage such that the arm can rotate relative to the tulip while extending through the passage, the arm also extending through a compressible member situated within the passage, the compressible member comprising the second polyaxial joint.
2. The spinal anchor of claim 1 , wherein the receptacle includes a collet having an interior spherical pocket that receives the spherical head of the shank.
3. The spinal anchor of claim 2 , wherein the collet is advanced along a conical taper within the receptacle to collapse the collet around the spherical head of the shank and lock the first polyaxial joint.
4. The spinal anchor of claim 3 , wherein a locking cap threadingly engages the receptacle to advance the collet along the conical taper.
5. The bone anchor of claim 1 , wherein the compressible member includes a first compressible element having a spherical first upper side and a planar first under side and a second compressible element having a planar second upper side and a spherical second underside, and wherein the arm slidably engages the planar first under surface and the planar second upper surface such that the arm such that the tulip is translatable along the arm.
6. The spinal anchor of claim 5 , wherein the spherical first upper surface rests in a first spherical cavity within the tulip and the spherical second under surface rests in a second spherical cavity within the tulip, such that the tulip is rotatable about the compressible member and relative to the base.
7. The spinal anchor of claim 6 , wherein the first spherical cavity is formed by the lower surface of a load ring situated in the tulip, the load ring having an upper surface for seating the rod.
8. The spinal anchor of claim 7 , wherein forcing a rod against the load ring causes the load ring to load the compressible member and lock the second polyaxial joint.
9. The spinal anchor of claim 8 , wherein a locking cap engages with the tulip to force the rod against the load ring.
10. A spinal anchor, comprising:
a shank having a threaded region for anchoring in bone; and
an offset connector for coupling the shank to a spinal rod offset from an axis of the shank, wherein the offset connector comprises:
a base having a first end connectable to the shank and an arm that extends from the first end, the arm having a first length, a first height, and a first width; and
a tulip having a rod channel for receiving a spinal rod therein, a passage situated below the rod channel, and a compressible element situated in the passage and polyaxially rotatable therein, the passage having a second length less than the first length, a second height greater than the first height, and a second width greater than the first width, the arm of the base extending through the compressible member and the passage, such that the tulip is translatable along the arm and polyaxially rotatable relative to the base.
11. The spinal anchor of claim 10 , wherein the compressible member includes a first compressible element having a spherical first upper side and a planar first under side and a second compressible element having a planar second upper side and a spherical second underside, and wherein the arm slidably engages the planar first under surface and the planar second upper surface thereby permitting the translation of the tulip along the arm.
12. The spinal anchor of claim 11 , wherein the spherical first upper surface rests in a first spherical cavity within the tulip and the spherical second under surface rests in a second spherical cavity within the tulip.
13. The spinal anchor of claim 12 , wherein the first spherical cavity is formed by the lower surface of a load ring situated in the tulip, the load ring having an upper surface for seating the rod.
14. The spinal anchor of claim 13 , wherein forcing a rod against the load ring causes the load ring to load the compressible member thereby inhibiting further translation of the tulip along the arm and rotation of the tulip relative to the base.
15. The spinal anchor of claim 14 , wherein a locking cap engages with the tulip to force the rod against the load ring.
16. The spinal anchor of claim 10 , wherein the shank has a spherical head and the first end of the base includes a receptacle that receives the spherical head of the shank.
17. The spinal anchor of claim 16 , wherein the receptacle includes a collet having an interior spherical pocket that receives the spherical head of the shank such that the base is polyaxially rotatable relative to the shank, the receptacle defining a conical taper such that the collet collapses around the spherical head of the shank when the collet is forced down the conical taper thereby inhibiting further rotation of the base relative to the shank.
18. The spinal anchor of claim 17 , wherein a locking cap engages the receptacle to advance the collet down the conical taper.