Abstract: A bone nail for the treatment of upper arm fractures comprises a hollow shank adapted to be introduced into the medullary canal and slotted at the distal end, and an expansion screw adapted to be advanced into the shank through rotation of the screw so as to radially expand the slotted end of the shank. An inner thread is formed on the inner wall of the shank outside the slotted region for cooperation with the expansion screw. At least in the slotted region, the cross sectional profile of the shank is provided with alternating elevations and depressions on the inner surface of the wall of the hollow shank.