Resorbable metal screw with increased torsional strength for osteopathy

Patent metadata

Field	Value
Publication number	US-9962210-B2
Application number	US-201615059571-A
Country	US
Kind code	B2
Filing date	Mar 3, 2016
Priority date	Mar 24, 2015
Publication date	May 8, 2018
Grant date	May 8, 2018

Abstract

A bone screw formed primarily of a magnesium alloy has a self-tapping thread, and is prestressed with a retained torsional stress oriented oppositely to the direction in which the screw is screwed into bone. The pre-stressing opposes the torsional stresses arising from screwing in the screw, thereby raising the effective strength of the screw and/or allowing for a reduction in its size/mass.

First claim

What is claimed is:

1. A bone screw:
a. formed primarily of a magnesium alloy,
b. having a screw length wherein at least a portion of the screw length bears a self-tapping thread, and
c. being pre-stressed with an inherent torsional stress oriented opposite the screw-in direction of the thread.

2. The bone screw of claim 1 wherein the inherent torsional stress is constant over at least the portion of the screw length bearing the self-tapping thread.

3. The bone screw of claim 1 wherein the bone screw is cannulated along at least a portion of the screw length.

4. The bone screw of claim 3 wherein the bone screw has:
a. an outer diameter in the range between 1.5 and 5 mm, and
b. an inner diameter in the range between 0.5 and 2.5 mm.

5. The bone screw of claim 3 wherein the bone screw has:
a. an outer diameter in the range between 2.5 and 3.5 mm, and
b. an inner diameter in the range between 0.8 and 1.3 mm.

6. The bone screw of claim 1 further including a surface coating on at least a portion of the thread, wherein the surface coating includes one or more of:
a. micro-abrasives, and
b. microcapsules containing at least one of:
(1) a lubricant, and
(2) a bioactive substance configured to promote bone growth,
wherein the microcapsules are configured to rupture as the thread penetrates bone.

7. The bone screw of claim 6 wherein the micro-abrasives include crystalline hydroxyapatite.

8. The bone screw of claim 6 wherein the micro-abrasives are needle-shaped.

9. A method for producing the bone screw of claim 1 , the method including the steps of:
a. providing a member formed primarily of a magnesium alloy;
b. forming a self-tapping thread in an outer wall of the member, whereby the threaded member defines the bone screw;
c. pre-stressing the member with an inherent torsional stress oriented opposite the screw-in direction of the thread.

10. The method of claim 9 wherein the step of pre-stressing the member occurs at least partially simultaneously with the step of forming the self-tapping thread.

11. The method of claim 9 wherein the step of forming the self-tapping thread includes urging the member through a die while rotating at least one of the member and the die.

12. The method of claim 11 wherein the step of forming the self-tapping thread further includes cutting and/or grinding the member.

13. The method of claim 12 wherein cutting and/or grinding the member removes less than 0.2 mm from the diameter of the member.

14. The method of claim 11 wherein the step of forming the self-tapping thread occurs at a temperature above 100° C.

15. The method of claim 11 wherein the step of forming the self-tapping thread occurs at a strain rate between 0.05 s −1 and 25 s −1 .

16. The method of claim 11 wherein the step of forming the self-tapping thread includes rotating the member with respect to the die by 1.0 to 8 revolutions per centimeter of advancement of the member through the die.

17. The method of claim 9 wherein the member is at least partially defined by a tube.

18. The method of claim 9 further including the steps of:
a. forming a surface coating on at least a portion of the thread; and
b. providing one or more of:
a. micro-abrasives, and
b. microcapsules containing at least one of:
(1) a lubricant, and
(2) a bioactive substance configured to promote bone growth, to the surface coating.

19. The method of claim 18 wherein the micro-abrasives and/or the microcapsules are provided to the surface coating prior to forming the surface coating on at least a portion of the thread.

20. A method for producing the bone screw of claim 1 , the method including the steps of:
a. providing a member formed primarily of a magnesium alloy;
b. forming a self-tapping thread in the member via rotary extrusion, whereby the threaded member defines the bone screw.

Assignees

• Biotronik Ag

Inventors

• Bayer Ullrich
• Anopuo Okechukwu
• Lootz Daniel

Classifications

• A61B2017/8655

  with special features for locking in the bone · CPC title

• A61L31/022

  Metals or alloys · CPC title

• A61B17/1655

  for tapping · CPC title

• A61B17/863

  with thread interrupted or changing its form along shank, other than constant taper · CPC title

• A61B2017/00526

  Methods of manufacturing · CPC title