Disc therapy

1. Apparatus for treating an intervertebral disc of a subject, the apparatus comprising:

at least three intra-pulposus exposed electrode surfaces, which are configured to be implanted within a nucleus pulposus of the disc, at different respective locations;

one or more extra-pulposus exposed electrode surfaces, which are configured to be implanted outside the nucleus pulposus, in electrical communication with the disc; and

control circuitry, which is configured to:

configure the intra-pulposus exposed electrode surfaces to be cathodes at different respective negative potentials, and the one or more extra-pulposus exposed electrode surfaces to be one or more anodes, and

drive the intra-pulposus exposed electrode surfaces and the one or more extra-pulposus exposed electrode surfaces to electroosmotically drive fluid into the nucleus pulposus to increase pressure in the disc.

2. The apparatus according to claim 1 , wherein the apparatus comprises at least five intra-pulposus exposed electrode surfaces, which are configured to be implanted implanting within the nucleus pulposus, at different respective locations.

3. Apparatus for treating an intervertebral disc of a subject, the apparatus comprising:

at least three intra-pulposus exposed electrode surfaces, which are configured to be implanted within a nucleus pulposus of the disc, at different respective locations;

one or more extra-pulposus exposed electrode surfaces, which are configured to be implanted outside the nucleus pulposus, in electrical communication with the disc; and

control circuitry, which is configured to:

configure the intra-pulposus exposed electrode surfaces to be cathodes, and the one or more extra-pulposus exposed electrode surfaces to be one or more anodes, and

drive the intra-pulposus exposed electrode surfaces and the one or more extra-pulposus exposed electrode surfaces to electroosmotically drive fluid into the nucleus pulposus to increase pressure in the disc based on a circadian cycle of the subject.

4. The apparatus according to claim 1 , wherein the control circuitry is configured to:

drive the intra-pulposus exposed electrode surfaces and the one or more extra-pulposus exposed electrode surfaces to electroosmotically drive the fluid into the nucleus pulposus during a plurality of discrete activation periods alternating with non-activation periods, and

ramp a strength of currents applied between the intra-pulposus exposed electrode surfaces and the one or more extra-pulposus exposed electrode surfaces at a beginning of at least one of the activation periods such that the strength reaches a maximum value no earlier than 10 minutes after the beginning of the period.

5. The apparatus according to claim 4 , wherein the control circuitry is configured to set a length of at least one of the non-activation periods to be at least 30 minutes.

6. The apparatus according to claim 3 , wherein the control circuitry is configured to configure the cathodes to be at different respective negative potentials.

7. Apparatus for treating an intervertebral disc of a subject, the apparatus comprising:

at least three intra-pulposus exposed electrode surfaces, which are configured to be implanted within a nucleus pulposus of the disc, at different respective locations;

one or more extra-pulposus exposed electrode surfaces, which are configured to be implanted outside the nucleus pulposus, in electrical communication with the disc; and

control circuitry, which is configured to:

configure the intra-pulposus exposed electrode surfaces to be cathodes, and the one or more extra-pulposus exposed electrode surfaces to be one or more anodes, and

drive the intra-pulposus exposed electrode surfaces and the one or more extra-pulposus exposed electrode surfaces to electroosmotically drive fluid into the nucleus pulposus to increase pressure in the disc by applying:

(a) a first voltage between at least a first one of the intra-pulposus exposed electrode surfaces and at least one of the one or more extra-pulposus exposed electrode surfaces, and

(b) a second voltage between at least a second one of the intra-pulposus exposed electrode surfaces and at least one of the one or more extra-pulposus exposed electrode surfaces, the second voltage different from the first voltage.

8. The apparatus according to claim 7 , wherein the control circuitry is configured to drive the intra-pulposus exposed electrode surfaces and the one or more extra-pulposus exposed electrode surfaces to electroosmotically drive the fluid into the nucleus pulposus by applying a third voltage between at least a third one of the intra-pulposus exposed electrode surfaces and at least one of the one or more extra-pulposus exposed electrode surfaces, the third voltage different from at least one of the first and the second voltages.

9. The apparatus according to claim 8 , wherein the third voltage is different from both the first and the second voltages.

10. The apparatus according to claim 1 , wherein the apparatus comprises at least one intra-pulposus electrode, which comprises:

at least two of the intra-pulposus exposed electrode surfaces; and

a support structure along which the at least two of the intra-pulposus exposed electrode surfaces are disposed, wherein the support structure is configured to be shaped as a partial ring or a complete ring after implantation.

11. The apparatus according to claim 10 , wherein the support structure is configured to be shaped as the complete ring that surrounds an area of at least 1 cm2.

12. The apparatus according to claim 10 , wherein the support structure is configured to be shaped as the partial ring that surrounds an area of at least 1 cm2.

13. The apparatus according to claim 10 , wherein the at least one intra-pulposus electrode comprises a partially insulated wire, which serves as the support structure, and wherein non-insulated portions of the wire serve as respective ones of the intra-pulposus exposed electrode surfaces.

14. The apparatus according to claim 1 , wherein the apparatus comprises at least one intra-pulposus electrode, which comprises:

at least two of the intra-pulposus exposed electrode surfaces; and

a support structure along which the at least two of the intra-pulposus exposed electrode surfaces are disposed, wherein the support structure is configured to remain straight during and after implantation.

15. The apparatus according to claim 14 , wherein the at least one intra-pulposus electrode comprises a partially insulated wire, which serves as the support structure, and wherein non-insulated portions of the wire serve as respective ones of the intra-pulposus exposed electrode surfaces.

16. The apparatus according to claim 14 ,

wherein the at least two of the intra-pulposus exposed electrode surfaces comprise first, second, and third intra-pulposus exposed electrode surfaces disposed along the support structure, with the second longitudinally between the first and the third intra-pulposus exposed electrode surfaces, and

wherein the control circuitry is configured to configure the first, the second, and the third intra-pulposus exposed electrode surfaces to be at the respective different negative potentials, the negative potential at the second intra-pulposus exposed electrode surface (a) greater than the negative potential at the first intra-pulposus exposed electrode surface, and (b) greater than the negative potential at the third intra-pulposus exposed electrode surface.

17. The apparatus according to claim 1 , wherein the apparatus comprises at least one intra-pulposus electrode, which comprises:

at least two of the intra-pulposus exposed electrode surfaces; and

a support structure, which comprises a plurality of spines that respectively comprise one or more of the intra-pulposus exposed electrode surfaces.

18. The apparatus according to claim 17 , wherein the support structure further comprises a backbone, from which the spines extend.

19. The apparatus according to claim 17 , wherein the support structure comprises a partially insulated wire, and wherein non-insulated portions of the wire serve as respective ones of the intra-pulposus exposed electrode surfaces.