Abstract: For anchoring a prosthesis within a bone by means of a bone cement (32), prothesis shaft has a surface which is formed by the surfaces of a plurality of spheres (23 . . . 25) partially penetrating each other and having radii which decrease from the proximal towards the distal shaft end. The transitional zones between adjacent spheres (23 . . . 25) are concavely rounded. This shape is especially suited for use with a glass ionomer-type bone cement, because the shaft exerts substantially only compressive forces on the cement, whereas tensile and notch stresses, with respect to which this kind of cement exhibits little resistance, are largely avoided.