Limited strength evidence supports the clinical utility of nuclear imaging to aid in the diagnosis of PJI.

Rationale
18F-FDG PET: There were two moderate strength studies, with conflicting results. In one study of 41 patients with hip arthroplasties (Chacko 2002), 18F-FDG was 91.7% sensitive and 96.6% for infection. In another investigation (Stumpe 2004), 18F-FDG PET studies performed on 35 patients were reviewed by two readers independently. Sensitivity of 18F-FDG PET for the two readers was 33% and 22%, and specificity was 81% and 85% respectively.

Combined labeled leukocyte/bone: One moderate strength investigation (Savarino 2004) studied 26 hip arthroplasties with combined bone and techenetium-99m labeled leukocyte imaging and found that the combined test was 31% sensitive, and 100% specific for infection. Thus, the test is good for ruling in, but not for ruling out prosthetic hip infection. It may not be possible to extrapolate these data to knee arthroplasties.

Combined labeled leukocyte/marrow: Moderate evidence supports the use of combined leukocyte/marrow imaging for diagnosing prosthetic joint infection. One moderate strength investigation (Segura 2004) studied 77 lower extremity arthroplasties with combined technetium-99m labeled leukocyte and bone marrow imaging and found that the combined test was 92.8% sensitive, and 98% specific for infection.

Indium-111-labeled leukocyte imaging: In one moderate strength investigation (Rand 1990) studied 38 painful knee arthroplasties and found that the test was 83% sensitive, and 85% specific for infection. In one high strength investigation of 153 scans of lower extremity arthroplasties (Scher 2000) the test was 77% sensitive and 86% specific for infection.

Technetium-99m-labeled leukocyte imaging: There were two moderate strength papers with conflicting results. In one investigation of 77 lower extremity arthroplasties (Segura 2004) the test was 96% sensitive and 30% specific. In another investigation of 40 lower extremity arthroplasties (Chik 1996) the test was 70% sensitive and 100% specific.

Technetium-99m bone imaging: There were five moderate strength papers with conflicting results. Three investigators reported that the test was 100%  sensitive (Segura 2004, Chik 1996, Larikka 2001[hip only]). One investigator (Levitsky 1991) reported 33% sensitivity and another (Hill 2017, hips only) reported 29% sensitivity. Specificity varied from 0% to 86% among the five studies.

POSSIBLE HARMS OF IMPLEMENTATION
There may be a radiation dose associated with imaging of the site but it is small enough to pose no real risk to the patient. Some metal implants are not MRI safe which must be determined prior to imaging. Caution should be used with intravenous administration of iodinated and gadolinium based contrast agents to patients with impaired renal function (https://www.acr.org/Clinical-Resources/Contrast-Manual). Additionally, not all test options are available at each center which may have resource, access to care, and cost implications not fully delineated in these recommendations.

FUTURE RESEARCH
More high-quality evidence is needed to determine if ultrasound and MRI are useful in diagnosis of PJI, and higher quality diagnostic evidence is needed in order to create stronger recommendations.
 
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