| 摘要 |
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<SUB>2</SUB>" or "k<SUB>2</SUB>" respectively towards the proximal end to a smaller dimension "d<SUB>1</SUB>" or "k<SUB>1</SUB>", respectively, where "d<SUB>1</SUB>" and "k<SUB>1</SUB>" 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<SUB>1</SUB>". 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<SUB>N </SUB>and a wall thickness W<SUB>N</SUB>. The transverse borehole may have a diameter D<SUB>B</SUB>, which is larger than d<SUB>2 </SUB>as well as larger than d<SUB>B-L5</SUB>. In one embodiment, diameter D<SUB>B </SUB>may be approximately 90% of the diameter d<SUB>B-L3 </SUB>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.
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