Set Screw Having Variable Pitch Thread for Use With Spinal Implant Systems

• US 20110106179A1
• Filed: 10/30/2009
• Published: 05/05/2011
• Est. Priority Date: 10/30/2009
• Status: Abandoned Application

• Current Assignee: Warsaw Orthopedic Incorporated (Medtronic Plc)
• Original Assignee: Warsaw Orthopedic Incorporated (Medtronic Plc)
• Inventors: Mirda, James J., Prevost, Julien J.
• Application Number:
  US12/609,728
• Publication Number:
  US 20110106179A1
• Time in Patent Office: Days
• US Class Current: 606/308
• CPC Class Codes: A61B 17/7002 Longitudinal elements, e.g. rods
• 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

An improved set screw for use with spinal implants to attach an elongated member to a bone. The set screw has a body with a lower portion. An external thread is on the lower portion wherein at least a portion of the external thread has a variable pitch. The set screw will engage a receiver member by a predetermined longitudinal distance before encountering the variable pitch of the external thread on the set screw. A preselected torque value for seating the set screw is achieved at this predetermined longitudinal distance of thread engagement by the set screw into the receiver member. The variable pitch provides consistent clamping force even when excessive torque is applied to the set screw. An upper portion can be connected to the lower portion of the set screw through a frangible portion. The preselected torque value for seating the set screw is selected at a value less than the break-off or separation torque required to cause the frangible portion to separate the upper portion from the lower portion of the set screw.

Claims

1. A set screw for use with a receiver to secure an elongated member in a spinal implant system, the set screw comprising:

a body having a lower portion;

an external thread on the lower portion wherein at least a portion of the external thread has a variable pitch, and wherein the external thread of the set screw includes a thread start having a truncation cut.

2. The set screw according to claim 1, wherein the truncation cut begins at a location aligned with a reference datum on the set screw so that the set screw will engage the receiver member by a predetermined distance before encountering the variable pitch of the set screw.

3. The set screw according to claim 1, wherein the external thread includes at least a portion of the external thread having a standard pitch

4. The set screw according to claim 1, wherein the external thread is a single continuous thread.

5. The set screw according to claim 1, wherein the external thread is a reverse angle thread.

6. The set screw according to claim 1, wherein the lower portion includes a driving recess.

7. The set screw according to claim 6, wherein the driving recess is a recess having a shape selected from the group consisting of hexagon, hexalobular, clutch, fluted, frearson, slotted, star, Torx, reverse thread, Pozidriv, or Phillips.

8. A set screw for use with a receiver to secure an elongated member in a spinal implant system, the set screw comprising:

a body having an upper portion and a lower portion, the upper portion being connected to the lower portion through a frangible portion;

an external thread on the lower portion wherein at least a portion of the external thread has a variable pitch.

9. The set screw according to claim 8, wherein the external thread includes at least a portion of the external thread having a standard pitch and at least a portion having a variable pitch.

10. The set screw according to claim 8, further comprising at least a first and second crest of the external thread, and wherein the external thread has a variable pitch that starts after the second crest.

11. The set screw according to claim 8, wherein the external thread is a reverse angle thread.

12. The set screw according to claim 8, wherein the external thread includes a thread start having a truncation cut.

13. The set screw according to claim 12, further comprising a beginning of the truncation cut at an angle of greater than 120°

from an exit of the truncation cut.

14. The set screw according to claim 13, further comprising a reference datum on the upper portion, and wherein the truncation cut begins at a location aligned with the reference datum.

15. The set screw according to claim 8, wherein the external thread has a variable pitch along the entire length of the thread.

16. A spinal implant system comprising;

an elongated member having at least an outer surface; and

a set screw including an upper portion connected to a lower portion by a frangible portion, the lower portion separable from the upper portion by breaking at the frangible portion, the lower portion having an external thread with a variable pitch; and

a receiver member having a proximal end and a distal end, the distal end adapted to be affixed to the vertebral column of a patient, the proximal end having a threaded opening leading to a receptacle, wherein the threaded opening is configured to engage the external thread of the set screw; and

wherein the elongated member is capable of being secured within the receptacle of the receiver member by the set screw without causing detrimental deformation of the outer surface of the elongated member and wherein a break-off torque for separation of the frangible portion is greater than the amount of torque needed to secure the elongated member in the receptacle of the receiver member by the set screw.

17. The spinal implant system according to claim 16, further comprising a first extending arm and a second extending arm forming the receptacle and, wherein the first extending arm has a first proximal face and the second extending arm has a second proximal face, and the first proximal face has at least a partial thread formed therein to engage the exterior thread of the set screw.

18. The spinal implant system according to claim 17, wherein the second proximal face has wholly omitted any thread being formed therein to assure the external threads engage the first extending arm before engaging the second extending arm in order to avoid cross-threading of the exterior thread on the set screw.

19. The spinal implant system according to claim 18, wherein the external thread of the set screw includes at least a portion of the external thread having a standard pitch and at least another portion having a variable pitch.

20. The spinal implant system according to claim 19, wherein the external thread of the set screw includes a thread start having a truncation cut, and wherein the truncation cut begins at a location aligned with a reference datum on the upper portion of the set screw so that the set screw will engage the receiver member by a predetermined distance before encountering the variable pitch of the set screw.