The bone screw (1) comprises shaft (3) carrying a thread (2), a front end (4) and a rear end (5), the external diameter "d" of the thread (2) or the core diameter "k" of the shaft (3) tapering in a middle region (L4) of the shaft (3) from a larger dimension "d2" or "k2" respectively towards the front end (4) to a smaller dimension "d1" or "k1" respectively, "d1" and "k1" not being equal to zero. The shaft (3) is provided with a concentrically disposed, radially expandable sleeve (10), the sleeve (10) being positioned on that part of the shaft (3), which has the smaller external diameter "d1".
