Late shedding of uncemented cup-Retrieval analysis and postulate the mechanism of failure

Uncemented modular acetabulum components demonstrate a lower rate of radiographic loosening. However, most of late failure was caused by the osteolysis, inducing bone destruction and loss of fixation. Loosening of the well-fixed cup caused by late shedding of the ingrowth surface of uncemented cup is a rare complication. We report of three cases, and through retrieval analysis of the cup we postulate the possible mechanism of late shedding of well-fixed cup. We found that improper position of the cup and eccentric polyethylene (PE) wear may cause impingement of the cup by neck and increase tensile and shear forces which may cause late shedding of good bone-ingrowth cup. Early revision of the eccentric wear PE is indicated for prevention of this complication.