Variable angle bone screw fixation arrangement
A fixation apparatus comprises a holder and a tension sleeve receiving a bone screw, wherein the bone screw has a shaft with a front thread and a head at the rear end, and the holder has a through borehole with a receiving seat, in which the tension sleeve is mounted and able to swivel, while the shaft has a thickening in a rear region, to the front of the head, whose width increases toward the head, and the width of the tension sleeve is larger than the width of the shaft immediately before the thickening and smaller than the greatest width of the thickening. When screwed in, the thickening widens the tension sleeve so that it is pressed by its envelope against the wall of the receiving seat. In this way, an angle-stable pressing is achieved for any given orientation of the bone screw.
1. A fixation apparatus comprising:
a bone screw;
a holder; and
a tension sleeve configured to receive the bone screw,
wherein the bone screw comprises a shaft with a front thread, a thickened region with a secondary thread, and a head comprising a sidewall without a threaded region,
wherein the holder comprises a through borehole with a receiving seat, in which the tension sleeve is mounted and able to swivel, and
wherein the thickened region is forward of the head, and a width of the thickened region increases toward the head, wherein the secondary thread has a lead that is 0.4 to 0.6 times the lead of the front thread on the shaft and wherein a width of the tension sleeve is larger than a width of the shaft immediately before the thickened region and smaller than a width of the head.
2. The fixation apparatus of claim 1 , wherein the thickened region has a cone angle of at most 15 degrees.
3. The fixation apparatus of claim 1 , wherein the thickened region has a cone angle of at most 15 degrees and a greater length than a length of the tension sleeve.
4. The fixation apparatus of claim 1 , wherein the thickened region has a conical front segment and an envelope surface on which the secondary thread is formed.
5. The fixation apparatus of claim 4 , wherein the thickened region has a front flange.
6. The fixation apparatus of claim 1 , wherein the thickened region is combined with the head.
7. The fixation apparatus of claim 1 , wherein a boundary surface between the tension sleeve and the receiving seat is ball-shaped, an outer envelope of the tension sleeve being spherical.
8. The fixation apparatus of claim 1 , wherein a cylindrical inner wall of the tension sleeve has an encircling, inwardly facing shoulder, the fixation apparatus further comprising an inner thread arranged on the inwardly facing shoulder.
9. A fixation apparatus of claim 1 , wherein a width of the tension sleeve is larger than a width of the shaft immediately before the thickened region and smaller than a greatest width of the thickened region.
10. The fixation apparatus of claim 1 , wherein the thickened region has a greater length than a length of the tension sleeve.
11. The fixation apparatus of claim 1 , wherein the thickened region has a length that is at least two and a half times a length of the tension sleeve.
12. The fixation apparatus of claim 1 , wherein the head broadens conically toward a rear end.
13. The fixation apparatus of claim 1 , wherein the receiving seat is open to a rear end and forms a mouth, and wherein a width of the mouth is smaller than a width of a middle region of the receiving seat.
14. The fixation apparatus of claim 1 , wherein the tension sleeve comprises a continuous opening comprising: a cylindrical segment and a conical segment and a transition between the cylindrical segment and the conical segment,
wherein a radial strip at the transition is arranged with a short internal thread.
15. A fixation apparatus comprising:
a bone screw;
a holder; and
a tension sleeve configured to receive the bone screw,
wherein the bone screw comprises a shaft with a front thread, a thickened region with a secondary thread, and a head comprising a sidewall without a threaded region,
wherein the holder comprises a through borehole with a receiving seat, in which the tension sleeve is mounted and able to swivel, and
wherein the thickened region is forward of the head, and a width of the thickened region increases toward the head, wherein the secondary thread has a smaller lead than the front thread on the shaft and wherein a width of the tension sleeve is larger than a width of the shaft immediately before the thickened region and smaller than a width of the head, and
wherein a cylindrical inner wall of the tension sleeve has an encircling, inwardly facing shoulder and an inner thread is arranged on the inwardly facing shoulder.
16. The fixation apparatus of claim 15 , wherein the thickened region has a cone angle of at most 15 degrees.
17. The fixation apparatus of claim 15 , wherein the lead of the secondary thread is 0.4 to 0.6 times the lead of the front thread on the shaft.
18. The fixation apparatus of claim 15 , wherein a boundary surface between the tension sleeve and the receiving seat is ball-shaped, an outer envelope of the tension sleeve being spherical.
19. The fixation apparatus of claim 15 , wherein the receiving seat is open to a rear end and forms a mouth.
20. The fixation apparatus of claim 15 , wherein the tension sleeve is slotted.
21. The fixation apparatus of claim 20 , further comprising a continuous slot running an entire length of the tension sleeve.
22. The fixation apparatus of claim 20 , wherein the tension sleeve comprises a plurality of one-ended slots.
23. The fixation apparatus of claim 20 , wherein the tension sleeve comprises a plurality of one-ended slots that are open toward a front end.
24. The fixation apparatus of claim 15 , wherein the tension sleeve comprises a continuous opening comprising: a cylindrical segment and a conical segment.
25. The fixation apparatus of claim 15 , wherein the holder is fashioned as a multiple holder with at least two receiving seats for tension sleeves.
26. The fixation apparatus of claim 15 , wherein a width of the tension sleeve is larger than a width of the shaft immediately before the thickened region and smaller than a greatest width of the thickened region.
27. The fixation apparatus of claim 15 , wherein the head broadens conically toward a rear end.
28. The fixation apparatus of claim 15 , wherein the receiving seat is open to a rear end and forms a mouth, and wherein a width of the mouth is smaller than a width of a middle region of the receiving seat.
29. A fixation apparatus comprising:
a bone screw;
a holder; and
a tension sleeve configured to receive the bone screw,
wherein the bone screw comprises a shaft with a front thread, a thickened region with a secondary thread, and a head comprising a sidewall without a threaded region,
wherein the holder comprises a through borehole with a receiving seat, in which the tension sleeve is mounted and able to swivel, and
wherein the thickened region is forward of the head, and a width of the thickened region increases toward the head, wherein the secondary thread has a smaller lead than the front thread on the shaft and wherein a width of the tension sleeve is larger than a width of the shaft immediately before the thickened region and smaller than a width of the head, and
wherein the head broadens conically toward a rear end.
30. The fixation apparatus of claim 29 , wherein the thickened region has a cone angle of at most 15 degrees.
31. The fixation apparatus of claim 29 , wherein the thickened region has a cone angle of at most 15 degrees and a greater length than a length of the tension sleeve.
32. The fixation apparatus of claim 29 , wherein the thickened region has a conical front segment and an envelope surface on which the secondary thread is formed.
33. The fixation apparatus of claim 32 , wherein the thickened region has a front flange.
34. The fixation apparatus of claim 29 , wherein the lead of the secondary thread is 0.4 to 0.6 times the lead of the front thread on the shaft.
35. The fixation apparatus of claim 29 , wherein the thickened region is combined with the head.
36. The fixation apparatus of claim 29 , wherein a boundary surface between the tension sleeve and the receiving seat is ball-shaped, in particular, an outer envelope of the tension sleeve being spherical.
37. The fixation apparatus of claim 29 , wherein a cylindrical inner wall of the tension sleeve has an encircling, inwardly facing shoulder, the fixation apparatus further comprising an inner thread arranged on the inwardly facing shoulder.
38. The fixation apparatus of claim 29 , wherein a width of the tension sleeve is larger than a width of the shaft immediately before the thickened region and smaller than a greatest width of the thickened region.
39. The fixation apparatus of claim 29 , wherein the thickened region has a greater length than a length of the tension sleeve.
40. The fixation apparatus of claim 29 , wherein the thickened region has a length that is at least two and a half times a length of the tension sleeve.
41. The fixation apparatus of claim 29 , wherein the receiving seat is open to a rear end and forms a mouth, and wherein a width of the mouth is smaller than a width of a middle region of the receiving seat.
42. The fixation apparatus of claim 29 , wherein the tension sleeve comprises a continuous opening comprising: a cylindrical segment and a conical segment and a transition between the cylindrical segment and the conical segment,
wherein a radial strip at the transition is arranged with a short internal thread.