PROSTHESES INFECTION: A PRELIMINARY STUDY WITH PET

Abstract

Introduction: Discomfort and pain are common but unspecific symptoms in orthopaedic prosthetics. The majority of these symptoms are secondary to mechanical failure or loosening, while only a small proportion is related to infection. The differentiation between synovitis, loosening or infection is important for a correct therapeutical management, but it is often difficult using noninvasive techniques.

Positron emission tomography (PET) with 2-deoxy-2-[18F]fluoro-D-glucose (FDG) has evolved from a research imaging modality to a clinical practice for the assessment of malignancies. FDG, a nonspecific tracer of increased intracellular glucose metabolism, has been found to accumulate not only in malignant cells but also in infection and inflammation foci.

Aim of the study was to evaluate the usefulness of FDG PET scan in patients with joint replacement.

Materials and Methods: In this study we describe PET findings in 33 patients (age 42–88 yrs.) with hips (n. 16) and knees (n. 17) prostheses who had a complete operative and/or clinical follow-up; 42.5% had a pattern of mobilization. All patients underwent PET scan 60 minutes after i.v. injection of 185 MBq of 18F-FDG (transmission-emission, 3D acquisition). PET tomograms were evaluated by nuclear physicians without knowledge of the clinical diagnosis by visual interpretation, which was graded on a four-point scale according with common clinical classification (0 = normal pattern: not significant locoregional uptake; 1 = synovitis: synovial localized uptake; 2 = prosthesis loosening: synovial and soft tissues uptake; 3 = prosthesis infection: synovial, soft and bone tissues diffuse uptake).

Results: The results will be discussed in detail and correlated with clinical findings. The diagnostic value of PET, in terms of sensitivity, specificity and accuracy was compared with traditional radionuclear techniques (dynamic bone scan, 99mTc-labelled granulocytes).

Conclusion: We underline a good correlation between PET and clinical pattern (88% of cases). Particularly PET was able to correctly differentiate the prostheses loosening in the 100% of cases without infection and in the 77% of patients with infectious disease suggesting its usefulness in clinical practice also for detecting only inflammatory tissue such as synovitis. Moreover, the capability of PET to quantificate the inflammatory activity could be useful in the monitoring of the therapy. Further evaluation in a large group of patients is indicated.