An assessment of the histological criteria used to diagnose infection in hip revision arthroplasty tissues

Aim-To characterise the number and nature of the inflammatory cells seen in cases of septic or aseptic loosening of hip arthroplasty, and to establish reliable histological criteria to distinguish between these two conditions . Methods-Histological examination of paraffin sections of periprosthetic tis sues (pseudocapsule, femoral and acetabular pseudomembranes) of 523 cases o f aseptic loosening and 79 cases of microbiology culture proven septic loos ening. The cellular composition of the inflammatory cell infiltrate was det ermined semiquantitatively. Results-The finding of a 2+ or greater neutrophil polymorph infiltrate tone or more cells per high power field (x 400) on average after examination of 10 fields) in arthroplasty tissues correlated strongly with the microbiolo gical diagnosis of septic loosening: diagnostic sensitivity 100%, specifici ty 97%, accuracy 99%, positive predictive value 92%, negative predictive va lue 100%. The finding of a 3+ neutrophil polymorph infiltrate (five or more cells on average per high power field) had a diagnostic sensitivity of 72% , specificity 100%, accuracy 98%, positive predictive value 100%, and negat ive predictive value 97%. In some cases of septic loosening the finding of a heavy lymphocytic and plasma cell infiltrate was of low diagnostic sensit ivity. A neutrophil polymorph infiltrate (generally less than one cell per 10 high power fields) was also seen in cases of aseptic loosening. Conclusions-The presence of 2+ or more (more than one neutrophil polymorph per high power field (x 400) on average after examination of at least 10 hi gh power fields) in periprosthetic tissues provides the most sensitive and accurate histopathological criterion for distinguishing between septic and aseptic loosening of hip arthroplasty.