Adjustable magnetic devices and methods of using same
A system includes a first pedicle screw, a second pedicle screw, and an adjustable rod having an outer housing coupled to one of the first pedicle screw and the second pedicle screw, the outer housing having a threaded shaft secured to one end thereof extending along an interior portion thereof. The system further includes a hollow magnetic assembly disposed within the outer housing and having a magnetic element disposed therein, the hollow magnetic assembly having an internal threaded surface engaged with the threaded shaft, the magnetic assembly being coupled to the other of the first pedicle screw and the second pedicle screw, wherein the hollow magnetic assembly rotates in response to an externally applied magnetic field to thereby lengthen or shorten the distance between the first pedicle screw and the second pedicle screw.
1. A system comprising:
a first pedicle screw having a shank and a head;
a second pedicle screw having a housing and a shank with a spherical head, the spherical head disposed within the housing;
a rod coupled to the head of the first pedicle screw and extending from the first pedicle screw to the second pedicle screw; wherein the rod is configured to be received within the housing of the second pedicle and directly contact the spherical head of the shank;
and
a magnetic actuator, including:
a threaded magnetic element disposed within an inner threaded surface of the housing of the second pedicle screw;
the threaded magnetic element rotationally coupled to a bushing configured to frictionally engage a surface of the rod; and
an external adjustment device configured to generate a rotating magnetic field;
wherein the threaded magnetic element is configured to rotate in response to the rotating magnetic field generated by the external adjustment device, and wherein rotation of the threaded magnetic element in a first direction frictionally engages the rod between the spherical head and the bushing to substantially fix the rod with respect to the housing, and wherein rotation of the threaded magnetic element in a second direction disengages the rod from the spherical head and the bushing.
2. The system of claim 1 , wherein the bushing includes a saddle-shaped surface configured to engage the rod.
3. The system of claim 1 wherein the threaded magnetic element comprises a radially-poled magnet.
4. The system of claim 3 , wherein the radially-poled magnet comprises a rare earth magnet.
5. The system of claim 1 , wherein the threaded magnetic element can rotate freely with respect to the bushing.
6. The system of claim 1 , wherein the spherical head of the second pedicle screw comprises a protrusion.
7. The system of claim 6 , wherein the protrusion has a contact surface configured to contact the rod.
8. The system of claim 1 , wherein the bushing comprises a cavity and the threaded magnetic element comprises a coupler which fits into the cavity such that rotation of the threaded magnetic element does not cause rotation of the bushing, and wherein the coupler transfers axial movement of the threaded magnetic element to axial movement of the bushing.
9. The system of claim 8 , wherein the coupler has a t-shaped cross-section that fits into the cavity.
10. The system of claim 1 , wherein an inner surface of the housing includes female threads and the threaded magnetic element includes male threads threadingly engaged with female threads.
11. The system of claim 1 , wherein the rod has an axis, and wherein the magnetic actuator actuates in a direction that is generally perpendicular to the axis of the rod.
12. The system of claim 1 , wherein the inner contents of the housing are protected by a seal.
13. The system of claim 12 , wherein the seal comprises an o-ring.
14. The system of claim 1 , wherein the spherical head directly contacts the rod in an engaged state.
15. The system of claim 1 , wherein the threaded magnetic element comprises a cup having a threaded outer surface and a hollow configured to hold a magnetic element substantially fixed with respect to the cup.
16. The system of claim 1 , further comprising a cap configured to cover an end of the housing over the rod.
17. The system of claim 16 , further comprising a male thread on an outer surface of the housing and a female thread on an inner surface of the cap, wherein the male thread on the outer surface of the housing and the female thread on the inner surface of the cap are configured to mate to hold the cap to the housing.