Abstract: In a screw made of biodegradable material for bone surgery purposes, the outer surface of the screw body is provided with a coaxial external thread. A coaxial channel of sawtoothed star-shaped transverse cross-sectional profile is provided in the screw body, which channel is open at the proximal end in order to receive the complementarily shaped shaft of a screwdriver, and extends into the area of the distal end. The channel wall is radially symmetrical about the longitudinal axis in regular rotary steps and defines an axial channel area and a plurality of lobe areas arranged uniformly around the channel area. In each lobe area the channel wall has a pair of flanks which extend into the vicinity of an end of the lobe area remote from the channel area. In a cross-section of the screw body, each lobe area is formed asymmetrical in respect of a diametrical plane.