Spring cage spinal fixation systems

1. A spinal fixation system, comprising:

a connector body configured to be coupled with a spinal fixation rod;

an engagement member configured to be coupled with and received within the connector body, wherein the engagement member comprises a head wherein at least a portion of the head of the engagement member comprises an at least substantially spherical surface; and

a spring cage structure configured to be coupled with the connector body,

wherein the spring cage structure comprises a spring having a plurality of helical cuts extending between opposing surfaces of the spring cage structure, wherein a first helical cut extends from an opening in a bottom surface of the spring cage structure to an opening in a top surface of the spring cage structure, the spring configured to be positioned in a relaxed configuration, a flexed configuration, and a compressed configuration,

wherein the spring is configured to define an opening having a first size in the relaxed configuration,

wherein the spring is configured to expand such that the opening has a second size in the flexed configuration, wherein the second size is larger than the first size, and

wherein the opening is configured to receive and engage the head of the engagement member and at least substantially matches and mates with the shape of the at least a portion of the head, and

wherein the spring comprises an inner surface configured to extend below a midpoint of a curvature of a sphere coincident with the at least substantially spherical surface such that the spring can engage both an upper portion of the head of the engagement member and a lower portion of the head of the engagement member in the relaxed configuration.

2. The spinal fixation system of claim 1 , wherein the engagement member comprises a pedicle screw comprising a threaded section opposite from the head.

3. The spinal fixation system of claim 1 , wherein the head of the engagement member comprises a frusto-spherical surface.

4. The spinal fixation system of claim 1 , wherein the spring is further configured such that, in the flexed configuration, the inner surface is configured to engage the upper portion of the head without simultaneously engaging the lower portion of the head.

5. The spinal fixation system of claim 1 , further comprising a saddle positioned within the connector body, wherein the saddle is configured to engage the spinal fixation rod.

6. The spinal fixation system of claim 5 , wherein the saddle comprises an integral part of the spring cage structure.

7. The pedicle screw fixation system of claim 1 , wherein second and third helical cuts extend from respective openings in the bottom surface of the spring cage structure to respective terminal ends adjacent to the top surface of the spring cage structure.

8. The pedicle screw fixation system of claim 1 , wherein the top opening of the first helical cut comprises a gap.

9. A pedicle screw spinal fixation system, comprising:

a connector body configured to be coupled with a spinal fixation rod;

a pedicle screw configured to be coupled with and received within the connector body, wherein the pedicle screw comprises a head having an at least partially spherical surface;

a saddle configured to be positioned within the connector body and to engage the spinal fixation rod; and

a spring cage structure configured to be positioned within the connector body,

wherein the spring cage structure comprises a spring having a plurality of helical cuts extending between opposing surfaces of the spring cage structure, wherein a first helical cut extends from an opening in a bottom surface of the spring cage structure to an opening in a top surface of the spring cage structure, the spring configured to be positioned in a relaxed configuration, a flexed configuration, and a compressed configuration,

wherein the spring is configured to define an at least partially spherical inner surface for receiving the head of the pedicle screw, the at least partially spherical inner surface having a first radius in the relaxed configuration, and

wherein the spring is configured to expand such that the inner surface has a second radius in the flexed configuration, wherein the second radius is larger than the first radius

wherein the spring substantially matches and mates with the at least partially spherical surface of the head, and

wherein the at least partially spherical inner surface is configured to extend below a midpoint of a curvature of a sphere coincident with the at least partially spherical inner surface such that the spring can engage both an upper portion of the head of the engagement member and a lower portion of the head of the engagement member in the relaxed configuration.

10. The pedicle screw spinal fixation system of claim 9 , wherein the at least partially spherical surface comprises a frusto-spherical surface.

11. The pedicle screw spinal fixation system of claim 9 , wherein the saddle is an integral part of the spring cage structure, and wherein the saddle comprises an upper portion of the spring cage structure.

12. The pedicle screw spinal fixation system of claim 9 , wherein the saddle and the spring cage structure are distinct structures, and wherein the saddle is configured to be coupled with an upper portion of the spring cage structure.

13. The pedicle screw spinal fixation system of claim 12 , wherein the saddle comprises:

an upper portion configured to seat the spinal fixation rod;

a lower portion comprising a protruding rim, wherein the protruding rim is configured to fit within a flat portion of the at least partially spherical inner surface of the spring.

14. The pedicle screw spinal fixation system of claim 13 , wherein the protruding rim comprises an at least partially spherical surface configured to engage the at least partially spherical surface of the head.

15. The pedicle screw spinal fixation system of claim 13 , wherein the upper portion of the saddle is separated from the lower portion of the saddle by a flange extending about a periphery of the saddle, and wherein the flange is configured to engage a corresponding shelf formed within the spring cage structure.

16. The pedicle screw spinal fixation system of claim 9 , wherein the spring comprises three separate helical cuts.

17. The pedicle screw fixation system of claim 9 , wherein second and third helical cuts extend from respective openings in the bottom surface of the spring cage structure to respective terminal ends adjacent to the top surface of the spring cage structure.

18. The pedicle screw fixation system of claim 9 , wherein the top opening of the first helical cut comprises a gap.