Variable angle bone fixation device

1. A system for bone fixation, comprising:

a bone fixation plate including an opening extending therethrough, the opening extending through the bone fixation plate from a first surface which, when the plate is in an operative position faces away from a bone, to a second surface which, in the operative position, contacts the bone, the bone fixation plate having a first hardness;

an elongated bone implant including a shaft configured to be inserted through the opening of the bone fixation plate, and a threaded head at a proximal end of the shaft, an exterior surface of the bone implant being one of carburized and nitrided to have a second hardness that is greater than the first hardness; and

a first groove extending into an outer surface of the head along a path interrupting the threading and extending along an angle counter to a direction of the threading, wherein the outer surface of the head includes a thread that is sloped in a distal direction as it extends clockwise about the outer surface with respect to a view in a distal direction and the path of the first groove is sloped counterclockwise as it extends in the distal direction with respect to the view in the distal direction.

2. The system of claim 1 , wherein the second hardness is in the range of 67-74 HRC.

3. The system of claim 1 , wherein the first hardness is in the range of 74 HRB-44 HRC.

4. The system of claim 1 , wherein the bone implant is a bone screw having the threaded head.

5. The system of claim 1 , wherein the opening is a variable angle hole.

6. The system of claim 1 , wherein the bone implant is formed of one of stainless steel and CCM.

7. The system of claim 1 , wherein the bone fixation plate is formed of one or more of commercially pure Titanium grades 1, 2, 3 and 4, Ti-6Al-7Nb, Ti-6Al-4V, Ti-6Al-4V ELI, Ti-15Mo, CCM (Co-28Cr-6Mo Alloy) and stainless steel.

8. A bone fixation device, comprising:

an elongated shaft extending along a longitudinal axis from a proximal end to a distal end, the elongated shaft configured to be inserted through an opening of a bone implant; and

a threaded head at the proximal end of the elongated shaft, the threaded head being one of carburized and nitrided to increase a surface hardness thereof, wherein the surface hardness is in the range of 67-74 HRC.

9. The device of claim 8 , further comprising a first groove extending into an outer surface of the head along a path interrupting the threading and extending along an angle counter to a direction of the threading.

10. The device of claim 9 , wherein the outer surface of the head carries a thread that is sloped in a distal direction as it extends clockwise about the outer surface with respect to a view in a distal direction and the path of the first groove is sloped counterclockwise as it extends in the distal direction with respect to the view in the distal direction.

11. The device of claim 9 , wherein the first groove extends along a groove axis perpendicular to the longitudinal axis of the elongated shaft.

12. The device of claim 8 , wherein the surface hardness of the threaded head is selected to be harder than a material of the bone implant through which the bone fixation device is inserted.

13. The device of claim 8 , wherein the head comprises five grooves.

14. The device of claim 8 , wherein the head comprises eight grooves.

15. The device of claim 8 , wherein the shaft is threaded along a length thereof.

16. The device of claim 15 , wherein a pitch of a threading of the shaft is the same as a pitch of the threading of the head.

17. The device of claim 15 , wherein the threading of the shaft includes multiple leads.

18. The device of claim 8 , further comprising a notch formed adjacent the distal end of the shaft.

19. The device of claim 18 , further comprising a recess in a proximal end of the head, the recess configured to engage a driving mechanism.

20. The device of claim 8 , wherein the head is substantially spherical.