Diagnosing infection in the failed joint replacement: a comparison of coincidence detection 18F-FDG and 111In-labeled leukocyte/99mTc-sulfur colloid marrow imaging.

UNLABELLED: The objectives of this study were to investigate (18)F-FDG imaging, using a coincidence detection system, for diagnosing prosthetic joint infection and to compare it with combined (111)In-labeled leukocyte/(99m)Tc-sulfur colloid marrow imaging in patients with failed lower extremity joint replacements.

METHODS: Fifty-nine patients--with painful, failed, lower extremity joint prostheses, 40 hip and 19 knee--who underwent (18)F-FDG, labeled leukocyte, and bone marrow imaging, and had histopathologic and microbiologic confirmation of the final diagnosis, formed the basis of this investigation. (18)F-FDG images were interpreted as positive for infection using 4 different criteria: criterion 1: any periprosthetic activity, regardless of location or intensity; criterion 2: periprosthetic activity on the (18)F-FDG image, without corresponding activity on the marrow image; criterion 3: only bone-prosthesis interface activity, regardless of intensity; criterion 4: semiquantitative analysis--a lesion-to-background ratio was generated, and the cutoff value yielding the highest accuracy for determining the presence of infection was determined. Labeled leukocyte/marrow images were interpreted as positive for infection when periprosthetic activity was present on the labeled leukocyte image without corresponding activity on the marrow image.

RESULTS: Twenty-five (42%) prostheses, 14 hip and 11 knee, were infected. The sensitivity, specificity, and accuracy of (18)F-FDG, by criterion, were as follows: criterion 1: 100%, 9%, 47%; criterion 2: 96%, 35%, 61%; criterion 3: 52%, 44%, 47%; criterion 4: 36%, 97%, 71%. The sensitivity, specificity, and accuracy of labeled leukocyte/marrow imaging were 100%, 91%, and 95%, respectively. WBC/marrow imaging, which was more accurate than any of the (18)F-FDG criteria for all prostheses, as well as for hips and knees separately, was significantly more sensitive than criterion 3 (P < 0.001) and criterion 4 (P < 0.001) and was significantly more specific than criterion 1 (P < 0.001), criterion 2 (P < 0.001), and criterion 3 (P < 0.001).

CONCLUSION: Regardless of how the images are interpreted, coincidence detection-based (18)F-FDG imaging is less accurate than, and cannot replace, labeled leukocyte/marrow imaging for diagnosing infection of the failed prosthetic joint.