Abstract: An endoprosthesis (10) is composed of a stem (12) tapering to the distal end thereof and a screw spindle (38) having a broadflanged helical flank (42). The stem is provided with a helical slot (36) guiding flank (42) of spindle (38) during assembling of the prosthesis. The flank (42) projects outwards from both broad side faces (14) of the stem and forms a plurality of broad flanged thin supporting ribs in the proximal portion of the prosthesis (10), the ribs cutting not only into the cancellous bone structure but also into the cortex. The prosthesis (10) provides for a load transmission exclusively into the proximal femur portion, while the distal portion is free of axial loads.