Implant for bones or vertebrae with self-constrained flexibility
As implant for the stabilization of bones or vertebrae is provided, the implant being a solid body including a longitudinal axis that defines a longitudinal direction and including a flexible section that has a surface and has a length in the longitudinal direction, the flexible section including at least one cavity located near the surface and having a width in the longitudinal direction that is smaller than the length of the flexible section, the at least one cavity being connected to the surface through at least one slit, and a width of the slit in the longitudinal direction being smaller than the width of the cavity.
1. An implant for the stabilization of bones or vertebrae, the implant having a longitudinal axis that defines a longitudinal direction, the implant comprising a flexible section having a length in the longitudinal direction, wherein the flexible section comprises an outer surface, and at least one cavity located near the surface and having in a cross-section in a plane containing the longitudinal axis a width in the longitudinal direction that is less than the length of the flexible section, the at least one cavity extending in a helical shape around the longitudinal axis, wherein the at least one cavity is connected to the outer surface through at least one slit having in a cross-section in a plane containing the longitudinal axis a width in the longitudinal direction less than the width of the cavity in the longitudinal direction, and wherein the implant is configured to be elastically flexed by a load acting on the implant in a direction transverse to the longitudinal axis from an open position in which opposing sidewalls of the slit are spaced apart by the width of the slit to a closed position in which the opposing sidewalls abut one another such that the flexion of the implant is limited by the closure of the slit.
2. The implant of claim 1 , wherein a compression side of the implant is defined as a side of the implant that is compressed when the load acts on the implant in the direction transverse to the longitudinal axis, and a tension side of the implant is defined as a side of the implant where the load is applied, and wherein, when the load is applied to the tension side, the implant is configured such that the width of a slit of the at least one slit located on the compression side narrows and the width of a slit of the at least one slit located on the tension side widens.
3. The implant of claim 1 , wherein the implant has at least two stiffness zones in a load versus displacement curve, a stiffness of the implant in a second stiffness zone of the at least two stiffness zones in which the implant is in the closed position and the load continues to act on the implant being greater than a stiffness of the implant in a first stiffness zone of the at least two stiffness zones in which the implant is between the open position and the closed position.
4. The implant of claim 1 , wherein the at least one cavity is located closer to the surface than to a center of the implant in a direction transverse to the longitudinal direction.
5. The implant of claim 1 , wherein a cross-section of at least one section of the at least one cavity is substantially oval-shaped, substantially circular, or substantially inverted tear drop-shaped.
6. The implant of claim 1 , wherein the opposing sidewalls of the slit extend from the cavity to the surface in a substantially straight manner.
7. The implant of claim 1 , wherein the opposing sidewalls of the slit extend from the cavity to the surface in an interlocking manner.
8. The implant of claim 7 , wherein the opposing sidewalls of the slit extend from the cavity to the surface in a V-shape or a stepped shape.
9. The implant of claim 1 , wherein the slit extends in a helix-shape around the longitudinal axis.
10. The implant of claim 1 , wherein the implant is a bone anchor.
11. The implant of claim 10 , wherein the implant is a bone screw with a bone thread, and wherein the slit is arranged at a location corresponding to a root of the bone thread.
12. The implant of claim 1 , wherein the implant is a rod.
13. The implant of claim 1 , wherein a compression side of the implant is defined as a side of the implant that is compressed when the load acts on the implant in the direction transverse to the longitudinal axis, and a tension side of the implant is defined as a side of the implant where the load is applied, wherein a wall defining the at least one cavity and the at least one slit comprises at least one of first opposing wall portions located on the compression side and configured to move towards each other when the implant is flexed in the direction transverse to the longitudinal direction and form a first stop to limit the flexion and second opposing wall portions located on the tension side and configured to move towards each other when the implant is flexed in the direction transverse to the longitudinal direction and form a second stop to limit the flexion.
14. The implant of claim 13 , wherein the first opposing wall portions and the second opposing wall portions extend substantially transverse to the longitudinal axis.
15. The implant of claim 13 , wherein the cavity has in a cross-section in a plane containing the longitudinal axis a substantially S-shape or inverted S-shape, and wherein a bottom of the S-shape comprises the slit.
16. The implant of claim 1 , wherein the implant comprises a solid wall at a base of the at least one cavity.
17. The implant of claim 1 , wherein the implant is at least partially manufactured by an additive manufacturing process.
18. The implant of claim 13 , wherein the flexible section comprises third opposing wall portions located on the compression side and configured to move towards each other when the implant is flexed in the direction transverse to the longitudinal direction and form a third stop to limit the flexion.
19. A method of manufacturing an implant having a longitudinal axis that defines a longitudinal direction, the implant including a flexible section having a length in the longitudinal direction, the flexible section including an outer surface, at least one cavity located near the outer surface and having in a cross-section in a plane containing the longitudinal axis a width in the longitudinal direction that is less than the length of the flexible section, the at least one cavity extending in a helical shape around the longitudinal axis, the at least one cavity being connected to the outer surface through at least one slit having in a cross-section in a plane containing the longitudinal axis a width in the longitudinal direction less than the width of the cavity in the longitudinal direction, the implant being configured to be elastically flexed by a load acting on the implant in a direction transverse to the longitudinal axis from an open position in which opposing sidewalls of the slit are spaced apart by the width of the slit to a closed position in which the opposing sidewalls abut one another such that the flexion of the implant is limited by the closure of the slit, the method comprising:
using an additive manufacturing process to build up the implant in a layerwise manner including the at least one cavity and with the at least one slit being closed; and
subsequent to using the additive manufacturing process, cutting the at least one slit into the built-up implant.
20. The method of claim 19 , wherein the additive manufacturing process is Selective Laser Sintering.
21. The method of claim 19 , wherein cutting the at least one slit is performed by an electric discharge manufacturing process.