Delank et al [74], in a series of both hip and knee prostheses, found that a negative PET scan excluded infection (100% sensitivity). If the scan was positive, differentiation between wear and infection was not possible. Prandini et al [75] performed a meta- analysis of the diagnostic performance of different radiotracers in peripheral osteomyelitis and prosthetic joint infections, yielding results for FDG-PET with a sensitivity of 94%, a specificity of 87%, a PPV of 87%, an NPV of 94%, and an overall accuracy of 92%. Although metal artifacts have very little impact on nuclear medicine examinations (except as photopenic defects) and create negligible scatter [68,76,77], high PET attenuation coefficients in the area of metal can lead to an overestimation of the PET activity in that region and thereby to a false-positive PET finding. Nonattenuated PET images, which do not manifest this error, can be used in these cases to aid the interpretation of these metal-induced artifacts. Synovitis and aseptic loosening (in hip prostheses) may cause increased FDG uptake [69]. Sterner et al [78] examined 14 patients with painful TKA to detect early aseptic loosening. Overall accuracy was 71% (sensitivity, 100%; specificity, 56%). In addition, Stumpe et al [79] found diffuse synovial and focal extrasynovial FDG uptake in patients with component malrotation. They concluded that this test is noncontributory in individual patients with persistent pain. Studies in patients with hip prostheses have shown that postoperative remodeling can result in artifactual periprosthetic FDG uptake for up to 6 months after implant insertion [80]. Noting the lack of specificity for detection of periprosthetic infection on conventional FDG-PET, Aksoy et al [70] explored the use of FDG- labeled leukocyte PET/CT for imaging patients with painful joint prostheses and found a sensitivity of 93%, a specificity of 97%, a PPV of 93%, and an NPV of 97%. However, this examination is not in general use.
Imaging After Total Knee Arthroplasty. Delank et al [74], in a series of both hip and knee prostheses, found that a negative PET scan excluded infection (100% sensitivity). If the scan was positive, differentiation between wear and infection was not possible. Prandini et al [75] performed a meta- analysis of the diagnostic performance of different radiotracers in peripheral osteomyelitis and prosthetic joint infections, yielding results for FDG-PET with a sensitivity of 94%, a specificity of 87%, a PPV of 87%, an NPV of 94%, and an overall accuracy of 92%. Although metal artifacts have very little impact on nuclear medicine examinations (except as photopenic defects) and create negligible scatter [68,76,77], high PET attenuation coefficients in the area of metal can lead to an overestimation of the PET activity in that region and thereby to a false-positive PET finding. Nonattenuated PET images, which do not manifest this error, can be used in these cases to aid the interpretation of these metal-induced artifacts. Synovitis and aseptic loosening (in hip prostheses) may cause increased FDG uptake [69]. Sterner et al [78] examined 14 patients with painful TKA to detect early aseptic loosening. Overall accuracy was 71% (sensitivity, 100%; specificity, 56%). In addition, Stumpe et al [79] found diffuse synovial and focal extrasynovial FDG uptake in patients with component malrotation. They concluded that this test is noncontributory in individual patients with persistent pain. Studies in patients with hip prostheses have shown that postoperative remodeling can result in artifactual periprosthetic FDG uptake for up to 6 months after implant insertion [80]. Noting the lack of specificity for detection of periprosthetic infection on conventional FDG-PET, Aksoy et al [70] explored the use of FDG- labeled leukocyte PET/CT for imaging patients with painful joint prostheses and found a sensitivity of 93%, a specificity of 97%, a PPV of 93%, and an NPV of 97%. However, this examination is not in general use.