Use of chloroacetate esterase staining for the histological diagnosis of prosthetic joint infection.

A heavy neutrophil polymorph infiltrate [>5 per high-power field (HPF) after examination of at least 5 HPF by Musculoskeletal Infection Society (MSIS) criteria] is characteristically seen in peri-implant tissues of infected prosthetic hip and knee joints. We determined whether chloroacetate esterase (CAE) staining facilitated the identification of neutrophil polymorphs in peri-implant tissues in cases of hip and knee arthroplasty infection and reassessed MSIS criteria in the light of our findings. Frozen and paraffin sections of peri-prosthetic tissues of 76 cases of failed hip and knee arthroplasties classified as septic or aseptic loosening microbiologically were analysed histologically by both haematoxylin-eosin and CAE staining. The extent of the neutrophil polymorph infiltrate was determined semiquantitatively and correlated with the microbiological and clinical diagnosis. CAE staining facilitated identification of neutrophil polymorphs in arthroplasty tissues. All cases of aseptic loosening contained fewer than two neutrophil polymorphs per HPF. CAE staining showed that in some cases of septic loosening, fewer than five neutrophil polymorphs per HPF (on average) are present in peri-prosthetic tissues. The histological criterion of more than two neutrophil polymorphs per HPF showed increased sensitivity and accuracy for the diagnosis of septic loosening. CAE is a useful stain that facilitates the identification of neutrophil polymorphs in both frozen and paraffin sections of peri-implant tissues. CAE staining shows that some microbiologically confirmed cases of septic loosening contain relatively few neutrophil polymorphs, indicating that the MSIS histological criterion of more than five neutrophil polymorphs per HPF is too high an index figure for the diagnosis of all cases of hip and knee arthroplasty infection.