DISTINGUISHING WEAR AND CREEP IN CLINICALLY RETRIEVED POLYETHYLENE INSERTS

There is an increasing awareness of the clinical problems associated w ith ultra-high-molecular-weight polyethylene (UHMWPE) wear and failure in orthopedics. To better understand the reasons for wear and failure , methods were developed using polarized light microscopic analysis an d backscattered electron (BSE) imaging with correlated elemental analy sis to distinguish the contributions of wear, creep, and third-body pa rticulate. This study determined that microscopic metal particles (<10 mu m) previously not observed with the stereomicroscope could be easi ly observed with the BSE technique. BSE imaging identified embedded me tal in 5/5 of the tibial and 2/4 of the acetabular inserts, which were thought to be free of metal debris after stereoscopic examination. Co rrelated elemental analysis showed that the microscopic particles coul d be traced to the elements known to be present in the porous coatings of the retrieved uncemented implants. Creep was distinguished from we ar in the total hip and total knee inserts by using polarized light mi croscopic techniques. Continued development of polarized light microsc opic techniques applied in this investigation should assist biomateria ls experts in the future to better distinguish wear and creep in retri eved clinical inserts. The correlated BSE and elemental analysis will assist in determining the roll of microscopic third-body particular in wear and osteolysis in total joint replacement. (C) 1995 John Wiley a nd Sons, Inc.