[FDG PET as an early nuclear medical diagnostic tool for aseptic wear-induced loosening of hip joint endoprostheses--a report of two cases]

Endoglin (CD105) expression differentiates between aseptic loosening and periprosthetic joint infection after total joint arthroplasty

The differentiation between aseptic loosening and periprosthetic joint infection (PJI) after total joint arthroplasty is essential for successful therapy. A better understanding of pathogenesis of aseptic loosening and PJI may help to prevent or treat these complications. Previous investigations revealed an increased vascularization in the periprosthetic membrane in cases of PJI via PET signals. Based on these findings our hypothesis was that PJI is associated with an increased neovascularization in the periprosthetic membrane.

Tissue samples from periprosthetic membranes of the bone-implant interface were investigated histologically for inflammation, wear particles, vascularization and fibrosis. To identify vascular structures antibodies against CD 31, CD 34, factor VIII and CD 105 (endoglin) were applied for immunohistochemical investigations. According to a consensus classification of Morawietz the tissue samples were divided into four types: type I (wear particle induced type, n = 11), type II (infectious type, n = 7), type III (combined type, n = 7) and type IV (indeterminate type, n = 7).

Patients with PJI (type II) showed a pronounced infiltration of neutrophil granulocytes in the periprosthetic membrane and an enhanced neovascularization indicated by positive immunoreaction with antibodies against CD 105 (endoglin). Tissue samples classified as type I, type III and type IV showed significantly less immune reaction for CD 105.

In cases of aseptic loosening and PJI vascularization is found in different expression in periprosthetic membranes. However, in aseptic loosening, there is nearly no neovascularization with CD 105-positive immune reaction. Therefore, endoglin (CD 105) expression allows for differentiation between aseptic loosening and PJI.

Use of 18F-FDG-PET in the diagnosis of endoprosthetic loosening of knee and hip implants

INTRODUCTION

To diagnose septic and aseptic loosening 18-fluorodeoxyglucose positron emission tomography ((18)F-FDG-PET) has been described with good results for hip arthroplasties. The purpose of the present study was to examine whether there is a difference of feasibility in detecting loosening of hip versus knee prostheses by use of (18)F-FDG-PET.

PATIENTS

Thirty-two patients with lower limb arthroplasty complaints (74 components) were studied preoperatively with (18)F-FDG-PET. The interpretation of (18)F-FDG-PET was done according to evaluated criteria. The final diagnosis based on intraoperative findings in all cases including microbiological examinations.

RESULTS

For hip arthroplasty sensitivity/specificity of (18)F-FDG-PET towards implant loosening was 80%/87%. For infectious loosening of hip endoprostheses sensitivity/specificity was 67%/83%. In knee endoprostheses sensitivity/specificity for loosening was 56%/82% and 14%/89% for infection. The sensitivity of the results for knee and hip joints in regard to infectious versus aseptic loosening was significantly different.

CONCLUSION

We confirm that (18)F-FDG-PET is an appropriate tool to diagnose hip arthroplasty loosening. Differing from that (18)F-FDG-PET showed a significant lower sensitivity/specificity in detecting septic loosening of knee endoprostheses. It may therefore be necessary to use different methods to diagnose loosening of endoprostheses depending on the type of implant which is examined.