Histological characterization of periprosthetic tissue responses for metal-on-metal hip replacement.

The histology of periprosthetic tissue from metal-on-metal (MOM) hip devices has been characterized using a variety of methods. The purpose of this study was to compare and evaluate the suitability of two previously developed aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL) scoring systems for periprosthetic hip tissue responses retrieved from MOM total hip replacement (THR) systems revised for loosening. Two ALVAL scoring systems (Campbell and Oxford) were used to perform histological analyses of soft tissues from 17 failed MOM THRs. The predominant reactions for this patient cohort were macrophage infiltration and necrosis, with less than half of the patients (41%) showing a significant lymphocytic response or a high ALVAL reaction (6%). Other morphological changes varied among patients and included hemosiderin accumulation, cartilage formation, and heterotopic ossification. Both scoring systems are useful for correlating macrophage and lymphocyte responses and for comparison with the other; however, given the diversity and variability of the current responses, the Oxford-ALVAL system is more suitable for scoring tissues from MOM THR patients revised for loosening. It is important that standardized methods of scoring MOM tissue responses be used consistently so multiple study results can be compared and a consensus can be generated.