Fastener retention system for spinal plates
A fastener retention system for retaining fasteners within apertures of an orthopedic plate includes a first pocket disposed between two of the apertures in the plate, a blocking member disposed between the two apertures and including a second pocket that forms a cavity with the first pocket, and a spring that expands from a compressed configuration within the first pocket to a decompressed configuration within the cavity.
1. An apparatus for fixation of two or more vertebrae, the apparatus comprising:
a plate configured to span at least from a first vertebra to a second vertebra, the plate having a depth extending from a top surface of the plate to a bottom surface of the plate;
first and second openings in the plate extending from the top surface to the bottom surface, the first and second openings configured to receive first and second bone screws, respectively;
a first pocket located on the top surface of the plate, the first pocket having a first length and positioned between the first and second openings, and the first pocket having a depth less than the depth of the plate;
a blocking member having a length sufficient to extend into both the first and second openings when the blocking member is centered between the two, the blocking member having a depth extending from a top surface of the blocking member to a bottom surface of the blocking member, the blocking member positioned over the first pocket, the bottom surface of the blocking member including a second pocket having a second length equal to the first length, and the second pocket having a depth that is less than the depth of the blocking member; and
a spring located in the first and second pockets;
wherein the spring operates to re-center the blocking member that is offset when a head of the first or second bone screw is advanced into the first or second opening; and
wherein the top surface of the blocking member does not include any openings.
2. The apparatus of claim 1 , wherein the first pocket is located in a channel extending between the first and second openings.
3. The apparatus of claim 1 , wherein the spring is configured to expand from a flattened configuration during assembly of the apparatus to a curved configuration.
4. The apparatus of claim 3 , wherein the flattened configuration is achieved when the spring is exposed to a temperature at or below a first temperature and the curved configuration is achieved when the spring is exposed to a temperature at or above a second temperature, the second temperature being greater than the first temperature.
5. The apparatus of claim 3 , wherein the spring in the curved configuration operates to re-center the blocking member.
6. The apparatus of claim 3 , wherein the spring comprises a shape-memory alloy.
7. The apparatus of claim 6 , wherein the spring comprises Nitinol or a nickel titanium alloy.
8. The apparatus of claim 3 , wherein the spring comprises a super elastic alloy.
9. The apparatus of claim 8 , wherein the spring comprises Nitinol or a nickel titanium alloy.
10. The apparatus of claim 3 , wherein the spring when in the flattened configuration has a depth that is less than the combined depth of the first and second pockets.
11. The apparatus of claim 10 , wherein the spring when in the curved configuration has a depth that is greater than the depth of the first pocket.
12. The apparatus of claim 3 , wherein the spring in the curved configuration has a length equal to the first length of the first pocket.
13. The apparatus of claim 1 , wherein the spring has a length equal to the first length of the first pocket.
14. An apparatus for fixation of two or more vertebrae, the apparatus comprising:
a plate configured to span at least from a first vertebra to a second vertebra, the plate having a depth extending from a top surface of the plate to a bottom surface of the plate;
first and second openings in the plate extending from the top surface to the bottom surface, the first and second openings configured to receive first and second bone screws, respectively;
a first pocket located on the top surface of the plate, the first pocket having a first length and positioned between the first and second openings, and the first pocket having a depth less than the depth of the plate;
a blocking member having a length sufficient to extend into both the first and second openings when the blocking member is centered between the two, the blocking member having a depth extending from a top surface of the blocking member to a bottom surface of the blocking member, the blocking member positioned over the first pocket, the bottom surface of the blocking member including a second pocket having a second length equal to the first length, the second pocket having a depth that is less than the depth of the blocking member, and the second pocket being accessible only from the bottom surface of the blocking member; and
a spring located in the first and second pockets;
wherein the spring operates to re-center the blocking member that is offset when a head of the first or second bone screw is advanced into the first or second opening.
15. The apparatus of claim 14 , wherein the spring is configured to expand from a flattened configuration during assembly of the apparatus to a curved configuration.
16. The apparatus of claim 15 , wherein the flattened configuration is achieved when the spring is exposed to a temperature at or below a first temperature and the curved configuration is achieved when the spring is exposed to a temperature at or above a second temperature, the second temperature being greater than the first temperature.
17. The apparatus of claim 15 , wherein the spring in the curved configuration operates to re-center the blocking member.
18. The apparatus of claim 15 , wherein the spring comprises a shape-memory alloy.
19. The apparatus of claim 18 , wherein the spring comprises Nitinol or a nickel titanium alloy.
20. The apparatus of claim 15 , wherein the spring comprises a super elastic alloy.