Multi-axial bone screw assembly

• US 6,053,917 A
• Filed: 03/09/1999
• Issued: 04/25/2000
• Est. Priority Date: 09/24/1996
• Status: Expired due to Term

• Current Assignee: SDGI Holdings Incorporated (Medtronic Plc)
• Original Assignee: SDGI Holdings Incorporated (Medtronic Plc)
• Inventors: Sherman, Michael C., Drewry, Troy
• Primary Examiner(s): Buiz, Michael
• Assistant Examiner(s): Woo, Julian W.
• Application Number:
  US09/265,265
• Time in Patent Office: 413 Days
• Field of Search: 606/61, 606/72, 606/73
• US Class Current: 606/270
• CPC Class Codes: A61B 17/7032 Screws or hooks with U-shaped head or back through which longitudinal rods pass
• CPC Class Codes: A61B 17/7037 wherein pivoting is blocked when the rod is clamped
• CPC Class Codes: A61B 2090/037 with a frangible part, e.g. by reduced diameter

Abstract

A multi-axial bone screw assembly includes a bone screw having a partially spherical head. The bone screw head is truncated at an upper surface in which a tool receiving recess is defined. The assembly includes a receiver member including a central bore that defines a tapered recess to receive a contracting collet carrying the head of the bone screw. The bore of the receiver member also defines a channel communicating with the recess and configured to receive a spinal rod therein. A portion of the channel is threaded to receive a set screw above the rod. The assembly also includes a contracting collet disposed between the rod and the head of the bone screw. The collet defines a partially spherical recess to receive the head of the bone screw, and includes deflectable fingers that substantially surround the screw head. As the set screw is tightened into the receiver member, the set screw compresses the rod against the collet, which presses the collet into the tapered recess of the receiver member, thereby deflecting the fingers of the collet against the bone screw head.

Claims

1. A spinal fixation assembly, comprising:

an elongated member configured for placement adjacent and along a length of the spine;

a bone engaging fastener, said fastener having a lower portion configured for engaging a vertebra and an enlarged head;

a collet defining a recess sized to receive at least a portion of said head of said fastener therein, said collet including a lower portion deflectable to substantially surround and engage said portion of said head of said fastener when said head is disposed within said recess, said collet further including an upper portion defining a substantially planar top surface;

a receiver member defining a bore therethrough from a top end to a bottom end, said bore including a lower recess for receiving said collet with said head of said fastener disposed within said recess, said lower recess having a lower opening at said bottom end of said receiver member through which said lower portion of said fastener extends, said receiver member also including a channel communicating with said lower recess said channel being configured to receive said elongated member therein adjacent said recess; and

a compression member engaged within said bore, said compression member operable to press said elongated member against said top surface of said collet, to thereby press said collet into said lower recess in said receiver member, whereby as said collet is pressed into said lower recess said deflectable portion of said collet is deflected by said lower recess against said head of said fastener to fix said head within said recess of said collet.

2. The spinal fixation assembly according to claim 1, wherein:

said bore includes an internally threaded portion adjacent said upper opening; and

said compression member is a set screw having threads for engagement with said internally threaded portion.

3. The spinal fixation assembly according to claim 1, wherein said head of said bone engaging fastener includes a truncated upper surface, and defines a tool receiving recess through said upper surface.

4. The spinal fixation assembly according to claim 1, wherein said collet includes a bore therethrough, said bore including said recess and a tool insertion bore configured to receive a driving tool to engage said head of said fastener through said bore of said collet.

5. The spinal fixation assembly according to claim 1, wherein said lower recess is tapered from a larger diameter to a smaller diameter at said bottom end.

6. The spinal fixation assembly according to claim 5, wherein said collet includes a conical outer surface configured for complementary engagement with said tapered recess of said receiver member.

7. The spinal fixation assembly according to claim 1, wherein said lower opening of said receiver member is tapered.

8. The spinal fixation assembly according to claim 1, wherein said deflectable portion of said collet includes a plurality of deflectable fingers.

9. The spinal fixation assembly according to claim 1, wherein said collet includes a recess opening at one end of said recess, said recess opening having a diameter smaller than a diameter of said enlarged head of said fastener, whereby said deflectable portion of said collet deflects to receive said fastener head within said recess.

10. The spinal fixation assembly according to claim 9, wherein said recess opening is tapered.

11. A spinal fixation assembly, comprising:

an elongated member configured for placement adjacent and along a length of the spine;

a bone engaging fastener, said fastener having a lower portion configured for engaging a vertebra and a head, said head being at least partially spherical in configuration;

a collet defining a partially spherical recess sized to receive at least a portion of said head of said fastener therein, said collet including a lower contractible portion to substantially surround said head of said fastener when said head is disposed within said spherical recess, and an upper portion having a substantially planar surface and a tapered aperture which communicates with said recess;

a receiver member defining a bore therethrough from a top end to a bottom end, said bore including a recess for receiving said collet with said head of said fastener disposed within said spherical recess, said recess having a lower opening at said bottom end of said receiver member through which said lower portion of said fastener extends, said member also including a channel communicating with said recess and having an upper opening at said top end of said receiver member, said channel being configured to receive said elongated member therein adjacent said recess; and

a compression member engaged within said bore at said upper opening, said compression member operable to press said elongated member against said collet, to thereby press said collet into said recess in said receiver member, whereby as said collet is pressed into said recess said contractible portion of said collet is contracted by said recess against said head of said fastener to fix said head within said spherical recess of said collet.

12. The spinal fixation assembly of claim 11, wherein said aperture in said collet is conical.

13. The spinal fixation assembly of claim 11, wherein said contractible portion includes a plurality of deflectable fingers.

14. The spinal fixation assembly of claim 13, wherein said receiver member includes an internally threaded portion adjacent said top end, and said compression member is a set screw having threads configured to engage said threaded portion.

15. The spinal fixation assembly of claim 14, wherein said set screw is a break-off set screw.

16. The spinal fixation assembly of claim 13, wherein said head and said spherical recess have a snap-fit relationship.

17. The spinal fixation assembly of claim 1, wherein said collet upper portion defines a continuous top surface.