An elongated sleeve is insertable into a passage provided in a fractured bone, so as to bridge the fracture thereof. The front end of the sleeve carries an expansion anchor sleeve which is longitudinally slotted so that its circumferential wall is composed of strips which are connected only at the leading and trailing ends. The strips are buckled in radially outward direction by inserting a rod through the sleeve and connecting it with the leading end of the expansion anchor sleeve so as to exert a rearwardly directed tensile force upon the same, causing its buckling.