Bone stabilization system including multi-directional threaded fixation element

• US 20070088360A1
• Filed: 03/20/2006
• Published: 04/19/2007
• Est. Priority Date: 09/19/2005
• Status: Active Grant

• Current Assignee: Biomet Incorporated (Zimmer Biomet Holdings, Inc.)
• Original Assignee: Depuy Products Incorporated (Johnson & Johnson)
• Inventors: Mebarak, Edward, Sixto, Robert, Castaneda, Javier, Orbay, Jorge, Casteneda, Alfredo
• Granted Patent: US 7,905,909 B2
• Time in Patent Office: Days
• US Class Current: 606/287
• CPC Class Codes: A61B 17/8057 the interlocking form comprising a thread
• CPC Class Codes: A61B 17/8061 specially adapted for particular bones A61B17/70 and A61B17/74 take precedence
• CPC Class Codes: A61B 17/8605 Heads, i.e. proximal ends projecting from bone
• CPC Class Codes: A61B 17/863 with thread interrupted or changing its form along shank, other than constant taper
• CPC Class Codes: A61B 17/866 Material or manufacture
• CPC Class Codes: A61B 2017/8655 with special features for locking in the bone
• CPC Class Codes: A61B 2017/868 self-locking due to part of nut being deformed upon tightening

Abstract

A bone fixation system includes a plate and a set of fixation locking screws. The plate defines a set of locking screw holes each having an internal thread. Each respective locking screw has a head with an external structure that is adapted to self-tap into the internal thread of a given locking screw hole to secure the respective first-type fixation locking screw at an surgeon-directed angle relative to the plate. This angle is defined during forcible insertion and rotation of the respective locking screw into the given screw hole. The system may also include unidirectional locking screws. In a preferred embodiment the plate and first-type of screw are made of different metals, with the plate made of titanium alloy and the screw made of cobalt chrome alloy.

Claims

1. A bone fixation system, comprising:

a substantially rigid plate having a bone contacting surface and defining a set of screw holes with internal threads, with said internal threads of said screw holes defining respective screw hole axes; and

a set of a first-type of locking screws, each respective first-type of locking screws having a head with an external thread that is adapted to self-tap into the internal thread of a given locking screw hole at an oblique angle relative to said respective screw hole axis to secure said first-type of locking screws to said plate.

2. A bone fixation system according to claim 1, wherein:

said plate is made of a first metal having a first hardness, and

said first-type of locking screws are made of a different second metal having a second hardness substantially harder than said first hardness.

3. A bone fixation system according to claim 2, wherein:

said first metal is a titanium alloy, and said second metal is a cobalt chrome alloy.

4. A bone fixation system according to claim 1, wherein:

said external thread and said internal thread are wound in a same direction.

5. A bone fixation system according to claim 1, wherein:

for said first-type of locking screws, said external thread has an angle of thread of approximately 90°

.

6. A bone fixation system according to claim 1, wherein:

for said first-type of locking screws, said head is tapered by approximately 8°

.

7. A bone fixation system according to claim 1, wherein:

for said first-type of locking screws, said head is provided with two-start threads.

8. A bone fixation system according to claim 1, wherein:

said first-type of locking screws each include a shaft, a portion of said shaft spaced apart from said head and an opposite end of said screw is reduced in diameter.

9. A bone fixation system according to claim 8, wherein:

said shaft is provided with bone-engagable distal threads, and said portion reduced in diameter is located between said head and said distal threads.

10. A bone fixation system according to claim 1, further comprising:

a set of second-type of fixation locking screw, each respective second-type of fixation locking screw having a head with an external thread that is adapted to threadably engage the internal thread of a given screw hole to secure the respective second-type of fixation locking screw at a fixed angle relative to said plate in alignment with the respective screw hole axis.

11. A bone fixation system according to claim 10, wherein:

said plate is made of a first metal having a first hardness,

said first-type of locking screws are made of a different second metal having a second hardness substantially harder than said first hardness, and

said second-type of fixation locking screws are made of said first metal.

12. A bone fixation system according to claim 11, wherein:

said first-type and second-type of fixation locking screws each have driver slots, said driver slots of said first-type having a larger cross-sectional area than said driver slots of said second-type.

13. A bone fixation system according to claim 1, wherein:

at least two of said screw hole axes are oblique relative to each other.

14. A bone fixation system according to claim 13, wherein:

at least two of said screw hole axes are oblique in two dimensions relative to each other.

15. A fixation screw for a bone plate having at least one threaded hole for a threaded locking screw, said fixation screw comprising:

a cobalt chrome screw having a head and a shaft, said head being tapered and including external two-start threads starting 180°

apart, said shaft includes a reduced diameter portion that is spaced apart from both said head and an opposite end of said screw.

16. A fixation screw according to claim 15, wherein:

an angle of taper of said head is approximately 8°

.

17. A fixation screw according to claim 15, wherein:

said thread on said head having an angle of thread of approximately 90°

.

18. A fixation screw according to claim 15, wherein:

said shaft is provided with distal threads, and said reduced diameter portion reduced is located between said head and said threads.