Devices for generating and applying compression within a body
This disclosure describes exemplary screw and intramedullary devices that are better able to bring bone fragments into close proximity with each other, generate a compressive load, and maintain that compressive load for a prolonged period of time while healing occurs. The devices are made of a shape memory material.
1. A compression screw system, comprising:
a compression screw made of a shape memory material such that a portion of a shaft of the compression screw is positionable in a bent condition, wherein the compression screw includes a central lumen having an annular shoulder; and
an internal retaining pin insertable into the compression screw and configured for moving the portion from the bent condition to a straightened and stretched condition, wherein the internal retaining pin extends into the central lumen, and the internal retaining pin is seated against the annular shoulder of the central lumen when the portion of the shaft is in the straightened and stretched condition.
2. The compression screw system as recited in claim 1 , wherein the internal retaining pin holds the portion of the shaft in the straightened and stretched condition while the compression screw is inserted into a bone, and wherein the internal retaining pin is configured for releasing the portion from the stretched and straightened condition back toward the bent condition after the compression screw has been inserted into the bone.
3. The compression screw system as recited in claim 1 , wherein the shape memory material is Nitinol.
4. The compression screw system as recited in claim 1 , wherein the shape memory material is PEEK.
5. The compression screw system as recited in claim 1 , comprising a first screw thread formed on the shaft at a distal location and a second screw thread formed on the shaft at a proximal location, wherein the portion of the shaft is disposed between the first and second screw threads.
6. The compression screw system as recited in claim 5 , wherein the first screw thread and the second screw thread include different thread pitches.
7. The compression screw system as recited in claim 1 , wherein the portion of the compression screw is bent at an angle of about 10° relative to a longitudinal axis of the compression screw when in the bent condition.
8. The compression screw system as recited in claim 1 , comprising a first drive feature on the compression screw and a second drive feature on the internal retaining pin, and wherein the first drive feature and the second drive feature are engageable to insert the compression screw into bone.
9. The compression screw system as recited in claim 8 , wherein the first drive feature of the compression screw is a thread.
10. The compression screw system as recited in claim 1 , wherein the annular shoulder is in a distal half of the compression screw, and a distal end of the internal retaining pin is seated against the annular shoulder.