The invention concerns a bone screw having a distal end and a proximal end, which has the distinguishing features a shaft with a core diameter “k” and having an external thread with an external diameter “d”. The external diameter “d” of the thread or the core diameter “k” of the shaft tapers in a middle region of the shaft from a larger dimension “d 2 ” or “k 2 ” respectively towards the proximal end to a smaller dimension “d 1 ” or “k 1 ”, respectively, where “d 1 ” and “k 1 ” do not equal zero. Further, the shaft is provided with a concentrically disposed, radially expandable sleeve, and the sleeve being positioned on the part of the shaft which has the smaller external diameter “d 1 ”. The bone screw may be introduced into a transverse borehole of a medullary pin. The medullary pin is provided with a continuous cannulation, which extends coaxially with the longitudinal axis of the medullary pin and has an external diameter D N and a wall thickness W N . The transverse borehole may have a diameter D B , which is larger than d 2 as well as larger than d B-L5 . In one embodiment, diameter D B may be approximately 90% of the diameter d B-L3 of the sleeve. The sleeve may be inserted completely into the transverse borehole and, with the flange, is in contact with the wall of a facet of the transverse borehole.
1. A bone screw having a distal end and a proximal end comprising:
a shaft with a core diameter “k” and having an external thread with an external diameter “d”, the shaft comprising:
a first elongated part extending from a first end to a second end of the bone screw, the first part having a first length and a uniform external diameter “d 2 ” and uniform core diameter “k 2 ”;
a second elongated part extending from a third end to a distal end of the bone screw, the second elongated part having a second length and a uniform external diameter“d 1 ” and uniform core diameter “k 1 ”;
a tapered part extending from the second end to the third end of the bone screw, the tapered part tapering from the larger dimensions “d 2 ” and “k 2 ” respectively towards the smaller dimensions “d 1 ” and “k 1 ”, respectively, where “d 1 ” and “k 1 ” do not equal zero,
wherein the shaft is provided with a concentrically disposed, radially expandable sleeve, and
wherein the sleeve is positioned on the part of the shaft which has the smaller external diameter “d 1 ”.
2. A bone screw according to claim 1 , wherein the thread has a constant depth.
3. A bone screw according to claim 1 , wherein the sleeve has an internal thread.
4. A bone screw according to claim 1 , wherein the sleeve has at least one longitudinal slot.
5. A bone screw according to claim 4 , wherein the at least one longitudinal slot extends over the whole length of the sleeve.
6. A bone screw according to claim 4 , wherein the at least one longitudinal slot extends over a portion of the length of the sleeve.
7. A bone screw according to claim 1 , wherein the sleeve has several longitudinal slots, the longitudinal slots extending over a portion of the length of the sleeve and openings of the longitudinal slots are positioned alternatingly at the top and bottom of the sleeve.
8. A bone screw according to claim 1 , wherein the sleeve having a diameter D H has a peripheral, encircling flange with an enlarged diameter D F , where D F is greater than D H at one of its ends.
9. A bone screw according to claim 1 , wherein the sleeve consists of a non-absorbable plastic.
10. A bone screw according to claim 1 , wherein the sleeve consists of a metallic material.
11. A bone screw according to claim 1 , wherein the sleeve consists of a bio-absorbable plastic.
12. A bone screw according to claim 1 , further comprising a third elongated part extending from a proximal end of the bone screw to the first end, the third part having a third length and a uniform external diameter “d 3 ” such that d 3 >d 2 .
13. A bone screw according to claim 12 , wherein the third elongated part has an external thread.