Self-holding screw head

1. A bone fastener comprising:

a threaded shaft extending from a leading end to a trailing end, the threaded shaft having a central longitudinal axis therethrough; and

a head extending from the trailing end of the threaded shaft, the head having a threaded surface including a helical root,

wherein the helical root continuously becomes closer to the central longitudinal axis moving away from the threaded shaft to a free end of the head.

2. The bone fastener of claim 1 , wherein the helical root extends from a first end proximal to the trailing end of the threaded shaft to a second end proximal to the free end of the head.

3. The bone fastener of claim 1 , wherein at least a portion of the helical root becomes closer to the central axis at a constant rate moving away from the threaded shaft toward the free end of the head.

4. The bone fastener of claim 1 , wherein the threaded shaft includes a tapered tip, the tapered tip being threaded.

5. The bone fastener of claim 1 , wherein the threaded shaft further comprises a threaded surface from a first location on the threaded shaft to the leading end of the threaded shaft, and a distance from the first location to the trailing end of the threaded shaft is less than a dimension of the head along the central longitudinal axis.

6. The bone fastener of claim 1 , wherein the threaded shaft further comprises a trailing portion including a circumferential concave surface abutting the head.

7. A bone fastener insertion system including:

the bone fastener of claim 1 ; and

a bone fastener holder including an internal bore configured to receive the head of the bone fastener.

8. A bone fastener comprising:

a threaded shaft extending from a leading end to a trailing end, the threaded shaft having a central longitudinal axis therethrough; and

a head extending from the trailing end of the threaded shaft, the head having a threaded surface including a crest portion having a width bounded by a first root portion of the threaded surface on a first side of the crest portion and a second root portion on a second side of the crest portion opposite the first side, a surface of the crest portion at a first circumferential location on the head tapering toward the central longitudinal axis across the width of the crest portion between the first root portion and the second root portion.

9. The bone fastener of claim 8 , wherein a linear axis is coincident with a surface extending across the width of the tapering crest portion at the first circumferential location, the linear axis and the central longitudinal axis defining a first plane.

10. The bone fastener of claim 8 , wherein the crest portion is part of a crest on the threaded surface, the crest extending from a first end of the head proximal to the trailing end of the threaded shaft to a second end of the head opposite the first end.

11. The bone fastener of claim 10 , wherein the head further comprises a circumferential surface parallel to the central longitudinal axis at the first end of the head.

12. The bone fastener of claim 10 , wherein the threaded shaft further comprises a trailing portion abutting the head, the trailing portion including a concave circumferential surface.

13. The bone fastener of claim 12 , wherein a length of the threaded shaft from the trailing end to the leading end is defined by the trailing portion and a threaded portion, the trailing portion being shorter than the head and the threaded portion being threaded throughout.

14. A bone fastener insertion system including:

the bone fastener of claim 8 ; and

a bone fastener holder including an internal bore configured to receive the head of the bone fastener.

15. A bone fastener comprising:

a shaft; and

a threaded head extending from the shaft such that a first end of the threaded head abuts the shaft and a second end of the threaded head is opposite the first end, a maximum diameter of the bone fastener being at the first end,

wherein the threaded head has a threaded outer surface extending from a first location at the first end of the threaded head to a second location proximal to the second end of the threaded head.

16. The bone fastener of claim 15 , wherein the threaded outer surface includes a crest and a root from the first location to the second location, the root having a constant rate of taper over at least part of a distance between the first location and the second location.

17. The bone fastener of claim 15 , wherein the screw has a central longitudinal axis therethrough and a diameter of the screw decreases in both opposite directions moving away from the first end of the threaded head along the central longitudinal axis.

18. The bone fastener of claim 17 , wherein the shaft further comprises a trailing portion abutting the first end of the threaded head, the trailing portion including a concave circumferential surface.

19. The bone fastener of claim 18 , wherein the shaft has a length defined by the trailing portion and a threaded portion, the trailing portion being shorter than the threaded head and the threaded portion being threaded throughout.

20. A bone fastener insertion system including:

the bone fastener of claim 15 ; and

a bone fastener holder including an internal bore configured to receive the threaded head of the bone fastener.