The addition of blood-pool and flow scans was investigated to determine if hyperemia led to a match of bone marrow-labeled leukocyte uptake (and therefore a false-negative scan). These additional scans decreased the number of false- negative findings (sensitivity, 83%; specificity, 94%; PPV, 83%; NPV, 94%). Overall, the performance of the labeled leukocyte marrow scan protocol was nonetheless thought to be of limited clinical utility [106]. In contrast, Love et al [69] found the combination of In-111-labeled leukocyte/Tc-99m-labeled sulfur colloid marrow scanning to be the reference standard for diagnosing periprosthetic infection. The authors found the combination of labeled WBC and marrow scanning to be 100% sensitive and 100% specific for diagnosing infection in TKA [69]. Semiquantitative assessment of WBC scans using a combination of early and delayed imaging as a substitute for bone marrow imaging produced a >90% sensitivity and specificity in one series [99]. Love et al [109] examined 150 failed joint prostheses with histopathologic correlation and found that leukocyte/marrow imaging yielded a sensitivity of 96%, a specificity of 87%, and an accuracy of 91%. They found that leukocyte/marrow imaging was significantly more accurate than bone scan (50%), bone/gallium scan (66%), and leukocyte/bone imaging (70%) in their population. WBC scan and sulfur colloid scan may have a role in the workup of suspected infection in knee arthroplasty. Variant 3: Pain after total knee arthroplasty. Infection excluded. Suspect aseptic loosening or osteolysis or instability. Additional imaging following radiographs. Imaging of rotational instability of a TKA is discussed in greater detail under Variant 5. If a patient has undergone a full workup and infection has been excluded, then loosening should be considered as the potential cause of knee pain and periprosthetic lucency. In multiple studies, aseptic loosening has been found to be a common cause of TKA failure [13,110-112].
Imaging After Total Knee Arthroplasty. The addition of blood-pool and flow scans was investigated to determine if hyperemia led to a match of bone marrow-labeled leukocyte uptake (and therefore a false-negative scan). These additional scans decreased the number of false- negative findings (sensitivity, 83%; specificity, 94%; PPV, 83%; NPV, 94%). Overall, the performance of the labeled leukocyte marrow scan protocol was nonetheless thought to be of limited clinical utility [106]. In contrast, Love et al [69] found the combination of In-111-labeled leukocyte/Tc-99m-labeled sulfur colloid marrow scanning to be the reference standard for diagnosing periprosthetic infection. The authors found the combination of labeled WBC and marrow scanning to be 100% sensitive and 100% specific for diagnosing infection in TKA [69]. Semiquantitative assessment of WBC scans using a combination of early and delayed imaging as a substitute for bone marrow imaging produced a >90% sensitivity and specificity in one series [99]. Love et al [109] examined 150 failed joint prostheses with histopathologic correlation and found that leukocyte/marrow imaging yielded a sensitivity of 96%, a specificity of 87%, and an accuracy of 91%. They found that leukocyte/marrow imaging was significantly more accurate than bone scan (50%), bone/gallium scan (66%), and leukocyte/bone imaging (70%) in their population. WBC scan and sulfur colloid scan may have a role in the workup of suspected infection in knee arthroplasty. Variant 3: Pain after total knee arthroplasty. Infection excluded. Suspect aseptic loosening or osteolysis or instability. Additional imaging following radiographs. Imaging of rotational instability of a TKA is discussed in greater detail under Variant 5. If a patient has undergone a full workup and infection has been excluded, then loosening should be considered as the potential cause of knee pain and periprosthetic lucency. In multiple studies, aseptic loosening has been found to be a common cause of TKA failure [13,110-112].