A prosthetic cup member, in particular for use in the hip joint, has a hollow outer shell which is adapted to be affixed to the bone. The cup has an inner shell having a recess for accommodating a bearing element. The inner shell and the outer shell are spaced radially from each other at a predetermined distance to define an intermediate space therebetween. The outer surface of the outer shell has coaxial threads interrupted by grooves extending transversely to the thread. The threads are self-tapping threads and are formed to permit the threaded outer shell to be screwed into the bone. The outer shell has a plurality of elongated openings or slots connected to the intermediate space to permit loose spongious material such as cancellous bone, to be introduced into and held in the intermediate space during surgical emplacement of the cup member. This enhances the growth of new bone tissue into the intermediate space. The elongated openings extend over almost the entire axial length of the outer shell.