Locking screw

1 . A locking screw comprising:

a screw head;

a screw shaft having an external thread, and a diameter d,

wherein one end of the screw shaft is connected to the screw head, and the other end of the screw shaft being a free end,

wherein a center line, defined as the line connecting the centers of gravity of the axially sequential, orthogonal cross-sectional surfaces of the locking screw, having a first end point at the screw head and a second end point at a free end of the screw shaft, is not a continuously straight line, and

wherein the center line coincides with a point of inflection.

2 . A locking screw according to claim 1 , wherein the locking screw does not have a rotational axis of symmetry.

3 . A locking screw according to claim 1 , wherein the center line lies in a plane.

4 . A locking screw according to claim 1 , wherein the center line lies in more than one plane.

5 . A locking screw according to claim 1 , wherein the center line is formed from several mutually transposed straight lines.

6 . A locking screw according to claim 1 , wherein a straight connecting line passing through the two end points of the center line is at a distance x from the center line at least at one point between the two end points, and

wherein x>0.01 mm and more preferably x>0.10 mm.

7 . A locking screw according claim 6 , wherein the distance x fulfills the condition 0.01 d<x<0.30 d and more preferably the condition 0.05 d<x<0.20 d, where d is the diameter of the screw shaft.

8 . A locking screw according to claim 1 ,

wherein the length of the center line between the two end points is L,

wherein the center line is divided between the two end points into three sections A, B and C, such that section A extends a distance between 0.10 L and 0.25 L from the first end point towards the second end point, section B extends a distance between 0.10 to 0.25 L from the second end point towards the first end point, and section C, being disposed between the two sections A and B, having a length C=(L−A−B), and

wherein the center line in sections A and B being essentially linear and extending coaxially to one another.

9 . A locking screw according to claim 8 , wherein the center line is curved S-shaped or is eccentric only in section C.

10 . A locking screw according to claim 8 , wherein the center line has a point of inflection preferably only in section C.

11 . A locking screw according to claim 8 , wherein center line has at least two points of inflection preferably only in section C at a distance y from one another.

12 . A locking screw according to claim 1 , wherein the diameter “d” of the screw shaft is substantially constant.

13 . A method of installing at least one locking screw into a medullary pin, said method comprising the steps of:

inserting the locking screw into the borehole of the medullary pin 10 , wherein the transverse borehole has a cross-sectional profile with a maximum extent “a” measured in the direction of center line and a maximum extent “b” measured perpendicularly to “a”, such that a>b and a>d<b; and

turning the locking screw in a standard fashion through the transverse borehole, wherein relatively thin and soft corticalis yields as the locking screw is screwed through it, so that there is no strain over the thickness of the corticalis,

wherein in the region of the medullary pin 10 , the locking screw is stretched because of a reaction of the wall of the transverse borehole and an increased force is required for screwing in the locking screw, resulting in a higher holding force results.

14 . A method according to claim 13 , wherein the cross-sectional profile is circular with a=b and a condition of 0.70 b<d<0.95 b and more preferably a condition of 0.8 b<d<0.9 b applies.

15 . A method according to claim 13 , wherein a distance “x” fulfills a condition of x<(b−d+1 mm), where “b” is the diameter of the transverse borehole in mm, “d” is the diameter of the screw shaft in mm, and “x” is a distance between a connecting straight line and a center line.

16 . A method according to claim 15 , wherein the distance “x” fulfills a condition of 0.05 (b−d)<x<0.35 (b−d) and more preferably a condition of 1.5 (b−d)<x<2.2 (b−d), where “d” is the diameter of the screw shaft in mm.

17 . A method according to claim 13 , a distance “y” between two adjacent points of inflection substantially fulfills a condition of D=ny, where “n” is an odd number and “D” the diameter of the medullary pin.