Review of the evolution of the cementless acetabular cup.

First-generation porous coated acetabular cups have achieved durable biologic fixation, although liner dissociation and wear were common failure mechanisms. Second-generation modular acetabular cups retained the successful ingrowth surfaces used in earlier cup designs and incorporated congruent contact between the liner and shell. However, impingement-related fractures of highly cross-linked ultra-high-molecular-weight-polyethylene (UHMWPE) used in second-generation cup designs have occurred. Third-generation cup designs that eliminate UHMWPE protruding above the metal rim and minimize sharp corners at the liner-locking mechanism would be expected to reduce the risk of liner fracture in modular acetabular cups used with highly crosslinked UHMWPE.