Acetabular metal backed fatigue due to severe wear before revision

Abstract

The polymer UHMWPE is widely applied as bearing element at acetabular side in total hip arthroplasty. In some designs, a metal backed is placed between the polymer and bone. Today, wear of the polymer is the major cause of revisions. In some extreme cases, the metallic cephalic component and the metal backed experience contact wear promoting wear debris, which has catastrophic consequences. In this paper, it was analyzed a retrieved acetabular component of total hip arthroplasty re-revised due to metal backed rupture after gross metal wear. Failure analysis shown fatigue of the metal backed. To simulate the stress distribution over the metal backed and polymer liner, a finite element analysis was performed taking account metal backed wall reduction due to wear. It was observed that the decrease in the metal backed thickness increase stresses at the metal/polymer interface and the stresses which enhance polymer wear. It was also observed that wear produces a change of the location of maximum stress, from the contact periphery to the middle section of the hemispherical wall. This change promotes failure due to bending of the metal backed. Revision of metal backed shall be always made when metal backed wear is observed, even when it is well fixed in the bone.