STUDY OF POLYMORPHONUCLEAR LEUKOCYTES IN INFECTIONS OF HIP AND KNEE PROSTHESES

Abstract

Introduction and purpose: To assess the validity of determining polymorphonuclear leukocytes in frozen intraoperative samples for diagnosing infections in hip and knee prosthetic revision surgery.

Materials and methods: We reviewed the 146 revisions (83 hips and 63 knees) carried out between 1996 and 2002. We analysed the polymorphonuclear leukocytes per high-magnification field in frozen intraoperative sections (diagnostic test) and periprosthetic tissue culture (gold standard). We evaluated sensitivity (S), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV), Youden index, positive likelihood ratio (PLR) and negative likelihood ratio (NLR). We compared the intraoperative results with the analysis of the same samples embedded in paraffin in the knee group.

Results: In the knee group we found S=66.7% (CI 95%); Sp=89.7% (CI 95%); PPV=81% (CI 95%); NPV=81.4% (CI 95%); Youden index=0.56; PLR=6,5 (CI 95%); and NLR=0.4 (CI 95%). In the analysis of the same samples in paraffin (postoperative) we found S=91% (CI 95%); Sp=87% (CI 95%); PPV=81% (CI 95%); NPV=94% (CI 95%); PLR=7 (CI 95%); NLR=8.7 (CI 95%) (significant differences between the two analyses with p< 0.05). In the hip group we found S=50%; Sp=100% (CI 95%); PPV=100%% (CI 95%); NPV=94.9% (CI 95%); Youden index=0.5; and NLR=0.5 (CI 95%).

Conclusions: The analysis of the validity of the test showed that the presence of polymorphonuclear leukocytes is related to infection, but negative results of the test do not rule out infection. It is a quick, low-cost test that we recommend for inclusion in the diagnostic protocol for hip revision surgery.