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 “d2” or “k2” respectively towards the proximal end to a smaller dimension “d1” or “k1”, respectively, where “d1” and “k1” 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 “d1”. 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 DN and a wall thickness WN. The transverse borehole may have a diameter DB, which is larger than d2 as well as larger than dB-L5. In one embodiment, diameter DB may be approximately 90% of the diameter dB-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.