Expandable implant, instrument, and method
Embodiments of the invention include expandable, implantable devices and methods. Devices expand linearly to provide secure fixation between or among anatomical structures. In some embodiments, an implant replaces one or more vertebral bodies of the spine.
1. An expandable medical implant for supporting skeletal structures comprising:
a first tubular member with a first connection end and an opposite first skeletal interface end and a first longitudinal axis extending between the first connection end and the first skeletal interface;
a second tubular member with a second connection end configured to engage with the first connection end of the first tubular member, the second tubular member having an opposite second skeletal interface end and a second longitudinal axis extending between the second connection end and the second skeletal interface;
a key pin non-threadedly fixed to the first tubular member and positioned in a slot extending through the second tubular member from an outer surface to the an inner surface of the second tubular member and extending in a direction parallel to the second longitudinal axis, the slot defining a desired longitudinal path of translation between the first and second tubular members such that the key pin positioned in the slot guides translation between the first tubular member and the second tubular member along the desired path in a direction parallel to the first and second longitudinal axes without relative rotation of the first and second tubular members;
wherein the first tubular member includes a first set of adjacent protrusions that are spaced apart from one another by a first distance; and
wherein the second tubular member includes a second set of protrusions that are spaced apart from one another by a second distance that is greater than the first distance, wherein one or more of the second set of protrusions interdigitate with one or more of the first set of adjacent protrusions.
2. The expandable medical implant of claim 1 wherein the first tubular member fits within the second tubular member.
3. The expandable medical implant of claim 1 wherein the first tubular member includes a relief cut to facilitate portions of the first tubular member flexing away from the second tubular member to permit translation between the first and second tubular members.
4. The expandable medical implant of claim 1 wherein the first and second tubular members are generally cylindrical.
5. The expandable medical implant of claim 1 wherein the key pin contributes to torsional stability between the first tubular member and the second tubular member.
6. The expandable medical implant of claim 1 wherein the key pin is a stop for movement of the first tubular member relative to the second tubular member.
7. The expandable medical implant of claim 1 further comprising an insertion instrument for expanding the implant, wherein the implant progressively locks as expanded by motion of at least a portion of the insertion instrument in a first direction, and the locked implant releases by motion of the portion of the insertion instrument in a generally opposite direction.
8. The expandable medical implant of claim 7 wherein the locked implant is released by applying a force to the key pin.
9. An expandable medical implant for supporting one or more skeletal structures, comprising:
a first tubular member having a first body portion extending along a first axis, the first body portion having a first bone-engaging portion adjacent a first end and an opposing connection portion adjacent a second end, the connection portion comprising a plurality of external projections and at least one key pin non-threadedly fixed to the first body portion and extending radially outward from the first body portion perpendicular to the first axis; and
a second tubular member movably engaged with the first tubular member, the second tubular member having a second body portion extending along the first axis, the second body portion having a plurality of internal projections mating with the plurality of external projections of the first tubular member and at least one slot extending through a side of the second body portion and defining a desired path of movement between the first tubular and second tubular members, the at least one slot receiving the at least one key pin of the first tubular member such that the mechanical engagement of the at least one key pin and the at least one slot guides translational movement between the first tubular member and the second tubular member along the first axis;
wherein the first tubular member comprises at least one relief cut to facilitate portions of the first tubular member flexing away from the second tubular member to permit translational movement between the first and second tubular members without relative rotation between the first and second tubular members.
10. The expandable medical implant of claim 9 , wherein the first tubular member comprises a pair of key pins positioned substantially opposite one another and wherein the second tubular member comprises a pair of slots positioned substantially opposite one another and receiving the pair of key pins of the first tubular member.
11. The expandable implant of claim 9 , wherein the at least one slot extends in a generally linear direction.
12. The expandable implant of claim 11 , wherein the at least one slot extends in a direction parallel to the first axis.
13. The expandable implant of claim 9 , wherein engagement of the at least one key pin with a bottom portion of the at least one slot limits an expansion of the first and second tubular members.
14. The expandable implant of claim 13 , wherein engagement of the at least one key pin with an upper portion of the at least one slot limits a contraction of the first and second tubular members.
15. The expandable implant of claim 9 , wherein at least the connection portion of the first tubular member is sized and shaped to be disposed within the second tubular member.
16. An expandable medical implant comprising:
a first tubular member having a first body portion extending along a first axis, the first body portion having a connection portion comprising a plurality of external projections, a first key pin extending radially outward from the first body portion along a second axis substantially perpendicular to the first axis, and a second key pin extending radially outward from the first body portion along the second axis in a direction substantially opposite the first key pin; and
a second tubular member movably engaged with the first tubular member, the second tubular member having a second body portion extending along the first axis, the second body portion having a plurality of internal projections mating with the plurality of external projections of the first tubular member, the second body portion also having a first slot extending through a first side of the second body portion and generally along the first axis, the first slot bounded by a first upper surface and a first lower surface, the first slot receiving the first key pin of the first tubular member, the second body portion also having a second slot extending through a second side of the second body portion substantially opposite the first side, the second slot extending generally along the first axis and bounded by a second upper surface and a second lower surface, the second slot receiving the second key pin of the first tubular member, wherein the moving engagement of the first and second key pins with the first and second slots guides translational movement of the first and second tubular members with respect to one another along the first axis such that engagement of the first and second key pins with the first and second lower surfaces stops translation of the first and second tubular members away from one another and such that engagement of the first and second key pins with the first and second upper surfaces stops translation of the first and second tubular members towards one another; wherein the engagement of the first and second key pins with the first and second slots prevents rotational movement of the first and second tubular members with respect to one another.
17. The expandable medical implant of claim 16 , wherein the first and second key pins increase the torsional stability of the implant.
18. The expandable medical implant of claim 16 , wherein at least the connection portion of the first tubular member is sized and shaped to be disposed within the second tubular member.
19. The expandable medical implant of claim 16 , wherein the first tubular member is inwardly flexible to facilitate translation of the first tubular member relative to the second tubular member.
20. The expandable medical implant of claim 19 , wherein the first tubular member comprises a relief allowing the first tubular member to be inwardly flexible.
21. The expandable medical implant of claim 16 , wherein the plurality of external and internal projections are sized and shaped such that the first and second tubular members are progressively locked as expanded.
22. The expandable medical implant of claim 21 , wherein the first and second tubular members are configured to be inserted, expanded, and locked using a single instrument.