We examined 25 different threaded cups using a specific biomechanical procedure. Great differences between the tested cups concerning their biomechanical parameters could be found. There is some evidence that the design of several cups might be inappropriate for stable acetabular fixation, and this may be the reason for early loosening. The new procedure is the first to allow biomechanical assessment of threaded cups by using quantified data, which correspond to long-term stability of the cup.