Bone fastening device

• US 5,336,225 A
• Filed: 09/17/1992
• Issued: 08/09/1994
• Est. Priority Date: 05/24/1991
• Status: Expired due to Term

• Current Assignee: Orthopaedic Biosystems Ltd. Inc. (Smith & Nephew PLC)
• Original Assignee: Orthopaedic Biosystems Ltd. Inc. (Smith & Nephew PLC)
• Inventors: Zang, Kerry
• Primary Examiner(s): DeMille, Danton D.
• Assistant Examiner(s): Kenealy, David
• Application Number:
  US07/946,815
• Time in Patent Office: 691 Days
• Field of Search: 128/69, 606/60, 606/61, 606/62, 606/64, 606/68-73, 606/53, 411/378, 411/398, 411/402, 411/388, 411/389, 411/396, 411/397, 411/401, 411/411
• US Class Current: 606/304
• CPC Class Codes: A61B 17/8605 Heads, i.e. proximal ends projecting from bone

Abstract

A surgical bone screw having a head which has asymmetrical radii relative to the central axis of the screw. The cross-section of the head is configured as a lobular shape having a constant radii along one hemisphere of the head, and smaller radii along the opposing hemisphere of the head, with the smallest radius existing approximately perpendicular to the midline of the head member. The asymmetry of the head minimizes surface area of the screw protruding above the bone surface.

Claims

1. A bone screw, comprising a shaft portion and a head portion, said shaft portion being threaded on at least a section thereof, and said head portion having a first portion with a circular cross-section taken perpendicular to a longitudinal axis of said head portion and a second portion having a generally ellipsoidal cross-section, taken perpendicular to a longitudinal axis of said head portion, said second portion being generally outwardly convex about its perimeter relative to a central axis of said bone screw, wherein said first portion begins and ends in continuation with said second portion.

2. The bone screw of claim 1, wherein said head portion further comprises a generally lobular cross-sectional shape.

3. The bone screw of claim 1, wherein said head portion further comprises a generally cam-shaped cross-sectional shape.

4. The bone screw of claim 1, wherein said circular cross-section of said first portion further comprises substantially uniform radii relative to said central axis of said bone screw and said generally ellipsoidal cross-section of said second portion further comprises smaller radii relative to said central axis than said radii of said circular cross section.

5. The bone screw of claim 4, wherein said hemielliptical cross-sectional portion further comprisses gradually smaller radii relative to said central axix of said bone screw, wherein a smallest radius is present at a point on the circumference of the head portion corresponding to a smallest diameter of said head portion.

6. The bone screw of claim 1, further comprising a longitudinal cannula extending an entire longitudinal aspect of said bone screw.

7. A device for reducing fractures, comprising a screw having a threaded surface formed on at least an end of said screw adapted in use to engage bone tissue;

said screw further comprising a head having an asymmetrical lobular cross-sectional shape taken perpendicular to a longitudinal axis of said head and defining a generally ellipsoidal side aspect and a generally circular side aspect of said head, said ellipsoidal side aspect being generally outwardly convex about its perimeter and forming a truncation of the circular shape of said circular side aspect, beginning and ending in continuation with said generally circular side aspect, and having a regular ellipsoidal surface substantially without protuberances and depressions therein and means for engaging a tool for driving said screw into bone tissue.

8. The device for reducing fractures according to claim 7, wherein said circular side aspect comprises substantially uniform radii relative to a central axis of said bone screw and said elliposidal side aspect comprises smaller radii relative to said central axis than said radii of said circular side aspect.

9. The device for reducing fractures according to claim 7, further comprising a longitudinal cannula extending an entire longitudinal aspect of said bone screw.

14. The device for reducing fractures according to claim 8, wherein said ellipsoidal side aspect further comprises gradually smaller radii relative to said central axis of said bone screw, wherein a smallest radius is present at a point on a circumference of the head portion corresponding to a smallest diameter of said head portion.

10. A method for reducing a fracture, comprising the steps of:

A. joining the fractured bones in physiologically correct alignment;

B. drilling a guide hole through the fractured bones at an angle of incidence sufficient to anchor and compress a fixation device in the fractured bones;

C. inserting a fixation device into said drilled guide hole, said fixation device comprising a head having an ellipsoidal side portion with an ellipsoidal cross-section perpendicular to a longitudinal axis of said fixation device, wherein said head of said fixation device is substantially co-planar with the surface of the bone being reduced; and

D. compressing the fracture by torquing said fixation device, counter-sinking said fixation device in said guide hole and orienting said ellipsoidal side portion substantially coplanar with the surface of the bone being reduced.

11. The method according to claim 10 wherein said step of inserting a fixation device further comprises the step of selecting a fixation device having a head comprising a first circular cross-sectional portion taken a long a longitudinal axis of the fixation device having substantially uniform radii relative to a central axis of said bone screw and a second ellipsoidal cross-sectional portion having smaller radii relative to said central axis than said radii of said first circular cross-sectional portion.

12. The method according to claim 11, wherein said step of inserting a fixation device further comprises the step of selecting said fixation device such that said second hemielliptical cross-sectional portion further comprises gradually smaller radii relative to said central axis of said bone screw, wherein a smallest radius is present at a point on the circumference of the head portion corresponding to a smallest diamter of said head portion.

13. A method for reducing a fracture, comprising the steps of:

A. joining the fractured bones in physiologically correct alignment;

B. drilling a guide hole through the fractured bones at an angle of incidence sufficient to anchor and compress a fixation device in the fractured bones; and

C. inserting and compressing a fixation device, said fixation device comprising a head having a side portion thereof, said side portion having a generally ellipsoidal cross-section taken perpendicular to a longitudinal axis of said fixation device and without substantial protuberances and depressions, said generally ellipsoidal side portion being outwardly convex about its perimeter relative to a central axis of said fixation devices, such that when the fixation device is counter-sunk in the guide hole and said head of said fixation device is at an acute angel relative to the longitudinal axis of the bone, said ellipsoidal side portion of said head is substantially co-planar with and does not project substantially from the surface of the bone being reduced.