Allograft bone fixation screw method and apparatus

• US 6,162,225 A
• Filed: 10/26/1998
• Issued: 12/19/2000
• Est. Priority Date: 10/26/1998
• Status: Expired due to Term

• Current Assignee: Musculoskeletal Transplant Foundation
• Original Assignee: Musculoskeletal Transplant Foundation
• Inventors: Gertzman, Arthur A., Haines, Timothy G.
• Primary Examiner(s): Thaler, Michael H.
• Assistant Examiner(s): HO, TAN-UYEN THI
• Application Number:
  US09/178,684
• Time in Patent Office: 785 Days
• Field of Search: 606/232, 606/73, 411/310, 411/500-510, 411/399, 411/401, 411/409, 411/400
• US Class Current: 606/309
• CPC Class Codes: A61B 17/861 specially shaped for gripping driver
• CPC Class Codes: A61B 17/8625 Shanks, i.e. parts contacting bone tissue
• CPC Class Codes: A61B 17/866 Material or manufacture
• CPC Class Codes: A61B 17/8877 characterised by the cross-section of the driver bit
• CPC Class Codes: A61F 2/0077 Special surfaces of prostheses, e.g. for improving ingrowth A61F2/30767 takes precedence
• CPC Class Codes: Y10S 606/909 Bone

Abstract

A combination driver and bone screw assembly comprising a screw shank with a uniform diameter threaded portion, an unthreaded portion with a outwardly tapered end and a driving end portion of substantially wedge shaped configuration which can be engagably seated in a wedge shaped notch seat of a driver member. The driver member comprises a body, a drive head defining a wedge shaped notch seat secured to the body forming a shoulder and a drive collar mounted around the drive head and seated on the shoulder.

In operation a bore is drilled in the patients bone with the top portion of the bore having a tapered geometry which widens from the diameter of the bore. The bone screw driving end portion is placed in the wedge shaped notch seat of a driver member and a drive collar is mounted around the driver drive head and engages the shoulder. The driver member is rotated driving the bone screw into the previously cut bore in the patients bone until the tapered surface of the bore engages the tapered undercut surface of the screw.

Claims

1. A bone screw comprising a shank with a threaded portion and an unthreaded portion which tapers outwardly adjacent an integrally formed drive head to form a tapered undercut for the drive head, said tapered undercut being funnel shaped and tapered at an angle ranging from 10°

to 45°

from the center axis of the shank and has its greatest diameter adjacent said drive head, said drive head being substantially wedge shaped.

2. A bone screw as claimed in claim 1 wherein the screw is constructed of a biomaterial.

4. A bone screw as claimed in claim 2 wherein said biomaterial is bioceramics.

5. A bone screw as claimed in claim 2 wherein said biomaterial is a biocompatible/bioresorbable polymeric material.

6. A bone screw as claimed in claim 1 wherein said screw is constructed of an inert metal.

7. A bone screw as claimed in claim 6 wherein said inert metal is stainless steel.

8. A bone screw as claimed in claim 6 wherein said inert metal is titanium.

9. A bone screw as claimed in claim 6 wherein said inert metal is a titanium alloy.

10. A bone screw as claimed in claim 6 wherein said inert metal is tantalum.

11. A bone screw as claimed in claim 6 wherein said inert metal is a tantalum alloy.

12. A bone screw as claimed in claim 6 wherein said inert metal is niobium.

13. A bone screw as claimed in claim 6 wherein said inert metal is a niobium alloy.

14. A bone screw as claimed in claim 6 wherein said inert metal is cobalt-chromium -molybdenum alloy.

15. A bone screw as claimed in claim 6 wherein said inert metal is HEDROCEL, a porous tantalum-carbon composite.

16. A bone screw as claimed in claim 6 wherein said tapered undercut when extended to intersect a longitudinal center axis of said shank forms an angle of about 20°

.

17. A bone screw as claimed in claim 6 wherein said tapered undercut when extended to intersect a longitudinal center axis of said shank forms an angle ranging from about 10°

to about 20°

.

18. A bone screw as claimed in claim 6 wherein said tapered undercut when extended to intersect a longitudinal center axis of said shank forms an angle ranging from about 20°

to about 30°

.

32. A bone screw as claimed in claim 1 wherein said wedge shaped driving head forms an angle on its distal end which allows disengagement from a driver assembly when a predetermined torque is applied.

3. A bone screw constructed of allograft bone comprising a shank with a threaded portion and an unthreaded portion which tapers outwardly adjacent an integrally formed drive head to form a tapered undercut for the drive head, said tapered undercut being funnel shaped and tapered at an angle ranging from 10°

to 45°

from the center axis of the shank and has its greatest diameter adjacent said drive head, said drive head being provided with at least two flat surfaces adapted to engage a driving tool and receive torque from said driving tool.

19. A bone screw as claimed in claim 3 wherein said bone screw has a torque shear of at least 0.10 Newton-meters.

20. A bone screw as claimed in claim 3 wherein said bone screw has a torque shear of at least 0.20 Newton-meters.

21. A bone screw as claimed in claim 3 wherein said bone screw has a torque shear ranging from about 0.214 Newton-meters to about 0.276 Newton-meters.

22. A bone screw as claimed in claim 3 wherein said bone screw has a pullout force ranging from 440-685 Newtons.

23. A bone screw constructed of allograft bone comprising:

a shank with a portion provided with a thread of a given pitch running along a portion of its length and terminating in a conical end;

an unthreaded portion of said shank is formed with an outwardly flaring section having a diameter which is greater than the diameter of said threaded portion, said outwardly flaring section being located adjacent to and integrally formed with a screw head having a wedge shape configuration with angular inclined planes.

24. A bone screw as claimed in claim 23 wherein said screw is threaded about 1/2 the length of the shank.

25. A bone screw as claimed in claim 23 wherein the wedge shaped drive head has a shear stress in relation to torque calculated by the formula T_max =1.57 r³ t_max.

26. A bone screw as claimed in claim 23 wherein said bone screw is constructed of cortical allograft bone.

27. A bone screw as claimed in claim 23 wherein said bone screw is constructed of cancellous allograft bone.

28. A bone screw as claimed in claim 23 wherein said angular inclined planes when intersected form an angle ranging between about 15°

and about 60°

.

29. A bone screw constructed of allograft bone comprising a shank with a substantially uniform diameter threaded portion having a distal pointed end and an unthreaded portion adjacent said threaded portion, said unthreaded portion defining an outwardly tapered end with a male wedge shaped driving head defining inclined planes, said bone screw having a shear stress in relation to torque calculated by the formula T_max =1.57 r³ t_max with said unthreaded outwardly tapered end forming a tapered undercut for said male wedge shaped driving head at an angle less than the angle formed by the inclined planes of said driving head.

30. A bone screw as claimed in claim 29 wherein said wedge shaped driving head forms an angle ranging from about 10°

to about 60°

.

31. A bone screw as claimed in claim 29 wherein said tapered undercut forms an angle with the center axis of the shank ranging from about 10°

to about 45°

.

33. A bone screw comprising a shank with a threaded portion and an unthreaded portion which tapers outwardly adjacent an integrally formed drive head to form a tapered undercut for the drive head, said screw being threaded about 1/2 the length of its shank and ranging in length from 1 to 1.25 inches, said drive head being substantially wedge shaped.

34. A bone screw constructed of allograft bone comprising a shank with a threaded portion and an unthreaded portion which tapers outwardly adjacent an integrally formed drive head to form a tapered undercut for the drive head, said drive head being substantially wedge shaped, said wedge shaped drive head having a shear stress in relation to torque determined by the formula T_max =1.57 r³ t_max.

35. A bone screw as claimed in claim 34 wherein said allograft bone is cortical bone.

36. A bone screw constructed of allograft bone comprising a shank with a threaded portion and an unthreaded portion which tapers outwardly adjacent an integrally formed drive head to form a tapered undercut for the drive head, said tapered undercut having a cross sectional area taken transverse a central axis of said screw across its distal end which is greater than a cross sectional area taken transverse to a central axis of said screw across the unthreaded portion of the shank, said tapered undercut when extended to intersect a longitudinal center axis of said shank forming an angle ranging from about 20°

to about 30°

, said drive head being provided with at least two flat surfaces adapted to receive torque from a driver.

37. A bone screw as claimed in claim 36 wherein said tapered undercut is funnel shaped and ends at one end of said drive head.

38. A bone screw as claimed in claim 36 wherein said screw is threaded about 1/2 the total length of the screw.