POLYETHYLENE WEAR DEBRIS AND TISSUE-REACTIONS IN KNEE AS COMPARED TO HIP-REPLACEMENT PROSTHESES

Differences in bearing surface conformity and wear mechanisms suggest that the polyethylene (PE) wear debris generated by total knee replace ment (TKR) prostheses should be different than that in total hip repla cement prostheses (THR). To address this issue, PE near debris and the cellular response in periprosthetic tissues from 19 failed TKRs was c ompared to that from 24 failed THRs using polarized light microscopy a nd a semiquantitative grading system. The foreign-body inflammatory re action in the THR cases was characterized by plump macrophages with a diffuse cytoplasmic birefringence when examined under polarized light, indicating the presence of multiple submicron particles of PE. The ma jority of the PE particles were <1 mu m in size and only a small fract ion of the total were >10 mu m. The foreign-body inflammatory reaction in the TKR eases was characterized by giant cells with fewer macropha ges. In the TKR specimens, the size range of PE particles was broader than in the hips. PE particles between 2 and 20 pm were frequent in TK R specimens; particles. <1 mu m in length were less common than in the THR specimens. Diffuse cytoplasmic birefringence was not a characteri stic of the TKR cases. These histologic differences were so consistent ly distinct that the source of the specimen (i.e., from a THR or TKR) could be blindly determined by light microscopy. The size distribution of the PE wear particles in these cases indicate that THRs generate a higher number of submicron PE particles and relatively few large part icles while TKRs generate a broader range of particles that includes f ewer submicron particles. The observed differences in the cellular res ponses is likely a direct result of the differences in the spectrum of PE wear particles. These differences mag in part account far differen ces in periprosthetic bone resorption and loosening in TKRs as compare d to THRs. (C) 1994 John Wiley & Sons, Inc.