Post-operatively adjustable angled rod
A jointed rod assembly for use in a spinal fixation construct involves a caudal rod portion connectable to an adjustment mechanism, and a cranial rod portion connectable to the adjustment mechanism. The adjustment mechanism is configured to rotate the caudal and cranial rod portions relative to one another about a joint axis that is generally perpendicular to the longitudinal axes of the caudal and cranial rod portions. The caudal and cranial rod portions may be dimensioned to be compatible with other pieces of hardware commonly used for spinal fixation, such as bone anchors (e.g., pedicle screws), occipital plates, reducers, and others. The caudal and cranial rod portions are composed of a strong, rigid, non-absorbable, biocompatible material. The jointed rod assembly may be advantageously used in spinal fixation systems and methods of spinal fixation.
1. A cervical fixation system for fixing the relative positions of a cervical vertebra and an occipital bone in a subject, the system comprising:
a jointed spinal rod assembly having a longitudinal length sufficient to extend from the vertebra to the occipital bone, and comprising a caudal rod portion, a cranial rod portion, and an adjustment mechanism connectable to the caudal rod portion and the cranial rod portion, and configured to rotate the caudal and cranial rod portions relative to one another about a joint axis that is generally perpendicular to the longitudinal axes of the caudal and cranial rod portions, said rotation occurring in response to a rotating magnetic field; and
a bone anchor having a bone fastener connected to a rod housing, said rod housing dimensioned to accept the caudal rod portion of the spinal rod assembly; and an occipital plate member having a fixation screw, and a rod receiver dimensioned to accept the cranial rod portion of the spinal rod assembly, wherein the adjustment mechanism comprises a magnetically-activated locking mechanism configured to prevent rotation of the caudal rod portion relative to the cranial rod portion when engaged, but to allow rotation of the caudal rod portion relative to the cranial rod portion when not engaged.
2. The cervical fixation system of claim 1 , comprising: a second spinal rod assembly; and a crossbar, said crossbar dimensioned to fit between two spinous processes of two adjacent cervical vertebra, and comprising: a first rod connector at a first end configured to connect the crossbar to the caudal rod portion, and a second rod connector at a second end configured to connect the crossbar to a rod portion of the second spinal rod assembly.
3. The cervical fixation system of claim 2 , wherein: the second spinal rod assembly is a second jointed rod assembly, and comprises a second caudal rod portion connected to a second adjustment mechanism, and a second cranial rod portion connected to the second adjustment mechanism, said second spinal rod assembly having a longitudinal length sufficient to extend from the vertebra to the occipital bone; the second adjustment mechanism is configured to rotate the second caudal and second cranial rod portions relative to one another about a second joint axis that is generally perpendicular to the longitudinal axes of the second caudal and second cranial rod portions; the cervical fixation system comprises a second bone anchor dimensioned to accept the second caudal rod portion; and the occipital plate member has a second rod receiver dimensioned to accept the second cranial rod portion.
4. The cervical fixation system of claim 1 , wherein the caudal rod portion is seated in the rod housing of the bone anchor, and the cranial rod portion is fastened to the rod receiver of the occipital plate.
5. The cervical fixation system of claim 1 , wherein the jointed spinal rod assembly, bone anchor, and occipital plate are at least partially composed of a non-absorbable biocompatible material.
6. The cervical fixation system of claim 1 , wherein the jointed spinal rod assembly, bone anchor, and occipital plate are at least partially composed of a non-absorbable biocompatible material selected from the group consisting of: titanium, alloys of titanium, steel, stainless steel, austenitic stainless steel, aluminum oxide, calcium oxide, calcium phosphate, hydroxyapatite, zirconium oxide, and polypropylene.
7. The cervical fixation system of claim 1 , wherein the caudal rod portion is connected to the adjustment mechanism.
8. The cervical fixation system of claim 1 , wherein the cranial rod portion is connected to the adjustment mechanism.
9. The cervical fixation system of claim 1 , wherein the caudal rod portion is connected to the adjustment mechanism and the cranial rod portion is connected to the adjustment mechanism.
10. The cervical fixation system of claim 1 , wherein the adjustment mechanism is configured to rotate the caudal and cranial rod portions relative to one another about exactly one joint axis.
11. The cervical fixation system of claim 1 , wherein the adjustment mechanism is operatively linked to a first magnet configured to rotate when exposed to a rotating magnetic field; and wherein the adjustment mechanism is configured to rotate the caudal rod portion relative to the cranial rod portion in response to the rotation of the first magnet.
12. The cervical fixation system of claim 11 , wherein the adjustment mechanism apart from the first magnet is composed of one or more non-magnetic or weakly magnetic materials.
13. The cervical fixation system of claim 11 , wherein the adjustment mechanism apart from the first magnet is composed of one or more non-magnetic or weakly magnetic materials selected from the group consisting of: titanium, aluminum oxide, calcium oxide, calcium phosphate, hydroxyapatite, zirconium oxide, polypropylene, and austenitic stainless steel.
14. The cervical fixation system of claim 11 , wherein the first magnet is a quadrupole magnet.
15. The cervical fixation system of claim 11 , comprising a gear train to translate the rotation of the first magnet into inclination of the caudal rod portion relative to the cranial rod portion.
16. The cervical fixation system of claim 15 , wherein the gear train comprises a rotatable worm that is driven by the first magnet, a worm wheel engaged to be driven by the worm, and a grooved surface on the cranial rod portion having a plurality of grooves engaged to the worm wheel.
17. The cervical fixation system of claim 15 , wherein the gear train comprises a rotatable worm that is driven by the first magnet, and a grooved surface on the cranial rod portion having a plurality of grooves engaged to the worm.
18. A cervical fixation system for fixing the relative positions of a cervical vertebra and an occipital bone in a subject, the system comprising: a jointed spinal rod assembly having a longitudinal length sufficient to extend from the vertebra to the occipital bone, and comprising a caudal rod portion, a cranial rod portion, and an adjustment mechanism connectable to the caudal rod portion and the cranial rod portion, and configured to rotate the caudal and cranial rod portions relative to one another about a joint axis that is generally perpendicular to the longitudinal axes of the caudal and cranial rod portions, said rotation occurring in response to a rotating magnetic field; a bone anchor having a bone fastener connected to a rod housing, said rod housing dimensioned to accept the caudal rod portion of the spinal rod assembly; and an occipital plate member having a fixation screw, and a rod receiver dimensioned to accept the cranial rod portion of the spinal rod assembly, wherein the adjustment mechanism is operatively linked to a first magnet configured to rotate when exposed to a rotating magnetic field; and wherein the adjustment mechanism is configured to rotate the caudal rod portion relative to the cranial rod portion in response to the rotation of the first magnet, and wherein the first magnet is mounted to the adjustment mechanism to allow said first magnet to rotate about a longitudinal axis of one of the caudal rod portion and the cranial rod portion.
19. A cervical fixation system for fixing the relative positions of a cervical vertebra and an occipital bone in a subject, the system comprising: a jointed spinal rod assembly having a longitudinal length sufficient to extend from the vertebra to the occipital bone, and comprising a caudal rod portion, a cranial rod portion, and an adjustment mechanism connectable to the caudal rod portion and the cranial rod portion, and configured to rotate the caudal and cranial rod portions relative to one another about a joint axis that is generally perpendicular to the longitudinal axes of the caudal and cranial rod portions, said rotation occurring in response to a rotating magnetic field; a bone anchor having a bone fastener connected to a rod housing, said rod housing dimensioned to accept the caudal rod portion of the spinal rod assembly; and an occipital plate member having a fixation screw, and a rod receiver dimensioned to accept the cranial rod portion of the spinal rod assembly, wherein the adjustment mechanism is operatively linked to a first magnet configured to rotate when exposed to a rotating magnetic field; and wherein the adjustment mechanism is configured to rotate the caudal rod portion relative to the cranial rod portion in response to the rotation of the first magnet, wherein the first magnet directly drives the adjustment mechanism.