OTS8 FDG imaging in identifying infected total joint arthroplasty. (Orthopaedic & Trauma Surgery).

OTS8 FDG IMAGING IN IDENTIFYING INFECTED TOTAL JOINT ARTHROPLASTY. Kevin M. Trapp, MD, Charito Love, MD, Christopher J. Palestro, MD, and Scott E. Marwin, MD. Long Island Jewish Medical Center; New Hyde Park, NY.

Infection and aseptic loosening must be considered in a patient with unrelenting pain after total joint arthroplasty. Distinguishing between these two entities is imporant in determining surgical management. Recently, FDG-PST imaging for diagnosing suspected joint arthroplasty infection has been reported. The procedure is simple with readily available results. A prospective study was undertaken to evaluate its utility in identifying an infected total joint. 30 patients with 35 joint replacements (15 hip and 20 knee) were included. Thirty patients had a single arthroplasty, and 5 had bilateral arthroplasties (1 hip and 4 knee). Imaging was done using a Hybrid PST system, with measured attenuation correction, after the administration of 150 mEq F-iS FDG. Increased periprosthetic uptake compared with the adjacent normal activity was interpreted as positive for infection. Final diagnoses were based on histopathologic/micobiologic results available in 21 patients and on final clinical disposition in 9 patients. Te n of 35 joint arthroplasties were infected. Sensitivity, specificity, and accuracy were 100%, 44%, and 60%, respectively. The positive predictive value was 42%, and the negative predictive value was 100%. Excluding 4 asymptomatic arthroplasties in 4 patients with bilateral joint arthroplasty, the sensitivity, specificity, and accuracy were 100%, 33%, and 55%. When only the symptomatic THA were considered, the sensitivity, specificity, and accuracy were 100%, 40%, and 57%, while those of the TKA, the corresponding values were 100%, 36%, and 59%, respectively. FDG is sensitive but not specific for diagnosing the infected joint arthroplasty. Its role may be limited to that of a screening test. If negative, another cause of patients' symptoms should be sought.