A bone cement plug for fitting into the intramedullary canal within a bone to restrict flow of bone cement during surgery comprises a sleeve (2) whose wall is circumferentially continuous and has an outer surface (10) for contacting the wall (32) of the canal. The sleeve (2) is formed from a deformable material so that it can be expanded transversely to contact the surface (32) of the canal. The plug includes an expander which can be drawn through the cavity (12) in a direction generally along the axis of the sleeve (2), to cause the sleeve (2) to expand transversely to contact the surface (32) of the canal. The inner surfaces of the wall converge towards the end (16) of the sleeve (2) towards which the expander is drawn to cause the sleeve (2) to expand to contact the surface (32) of the canal.