Provided are acetabular cup implant assemblies that can be used in hip replacement surgery. Example assemblies comprise a shell and a liner. The liner can be positioned within a shell. Optionally, the liner can be rotated relative to the shell until the liner is seated in the shell in a position where the liner and shell can be secured to one another. Waveform-shaped features of the shell and liner can guide the relative rotation of the liner and shell. Also provided are methods of seating a liner in shell of an acetabular cup implant assembly.