FATIGUE PERFORMANCE OF ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE - EFFECT OF GAMMA-RADIATION STERILIZATION

Ultra-high-molecular-weight polyethylene (UHMWPE) failure presents a s ignificant materials concern in the orthopaedic community. Clinical fa ilure following joint arthroplasty can result from the biological resp onse to wear debris as well as structural failure owing to UHMWPE fati gue. In this study, cantilever rotating beam fatigue testing was condu cted on GUR 415 UHMWPE in both the unsterilized and gamma radiation st erilized conditions. Calculations of flexural fatigue stresses were ba sed on extreme fibre stresses and assumed negligible plastic deformati on. Both material conditions exhibited similar fatigue strengths at 25 0,000 cycles (approximately 41 MPa) and at one million cycles (approxi mately 36 MPa), but a large difference developed after two million cyc les. At ten million cycles, the unsterilized condition exhibited a fat igue strength of approximately 31 MPa, while the gamma-sterilized cond ition exhibited a reduced fatigue strength of approximately 18 MPa, an approximate decrease of 42%. High-cycle fatigue testing was necessary to fully characterize this behaviour owing to the pronounced differen ce in fatigue behaviour beyond two million cycles. These results sugge st that gamma radiation sterilization of UHMWPE medical implants reduc es their resistance to cyclic loading and, subsequently, may contribut e to the associated fatigue-related failures which have been reported clinically. (C) 1966 Elsevier Science Limited.