The Measurement of Creep in Ultrahigh Molecular Weight Polyethylene

Quantification of creep of highly cross-linked polyethylene would enable separation of creep from wear when evaluating femoral head penetration into polyethylene. We compared creep magnitude of a highly cross-linked versus conventional polyethylene in the laboratory. Twelve acetabular liners of each material were tested, 6 of which had a 32-mm inner diameter (ID) and 6 had 28-mm ID. Creep was measured using coordinate measuring machines during loading at 2 Hz without motion to 4 million cycles. Penetration into 32-mm ID conventional liners reached 97 μm versus 107 μm for highly cross-linked material, not significant. Penetration into 28-mm conventional liners was 132 μm versus 155 μm for highly cross-linked material (P = .017). Ninety percent of the creep had occurred by 2.5 million cycles.