MRI with metal artifact reduction technique has also been shown to detect osteolysis that is not visible on radiographs [96,97]. US Knee US has a limited role in the workup of periprosthetic infection, but it can be readily used to assess soft tissues, including the presence of edema, hyperemia, and fluid collections about the knee joint in patients with TKA. This may be beneficial in certain situations (eg, practices that may perform fluoroscopy-guided aspiration). Imaging After Total Knee Arthroplasty injection of the radiolabeled WBCs [63]. Comparison of activity on the WBC image with activity on a bone scan (usually a 3-phase bone scan) has been advocated. A positive study for infection generally requires focal increased activity on the WBC study in the same location and distribution as the positive 3-phase bone scan [100]. Using a sequential combination of bone and In-111-labeled leukocyte scans in patients with loose or painful knee prostheses found a sensitivity of 88%, a specificity of 78%, a PPV of 75%, and an NPV of 90% for diagnosis of infection. They noted an area of potential utility for leukocyte scans, specifically that a negative indium leukocyte scan might support the absence of infection in otherwise equivocal cases and in situations in which a musculoskeletal pathologist is not available to interpret an intraoperative frozen section [100]. A small sample of indium scans in uncomplicated postoperative TKA patients has shown that inflammation can persist around the operative site in the absence of infection [100]. Bernard et al [50] reported a multicenter trial of various methods for diagnosing hip and knee infections. Scans using tagged WBCs or radiolabeled immunoglobulin demonstrated a sensitivity of 74% and a specificity of 76% for diagnosing infection. A literature review indicates sensitivities of 40% to 96% and specificities of 76% to 100% for WBC scans of joint prostheses [49,50,99-104].
Imaging After Total Knee Arthroplasty. MRI with metal artifact reduction technique has also been shown to detect osteolysis that is not visible on radiographs [96,97]. US Knee US has a limited role in the workup of periprosthetic infection, but it can be readily used to assess soft tissues, including the presence of edema, hyperemia, and fluid collections about the knee joint in patients with TKA. This may be beneficial in certain situations (eg, practices that may perform fluoroscopy-guided aspiration). Imaging After Total Knee Arthroplasty injection of the radiolabeled WBCs [63]. Comparison of activity on the WBC image with activity on a bone scan (usually a 3-phase bone scan) has been advocated. A positive study for infection generally requires focal increased activity on the WBC study in the same location and distribution as the positive 3-phase bone scan [100]. Using a sequential combination of bone and In-111-labeled leukocyte scans in patients with loose or painful knee prostheses found a sensitivity of 88%, a specificity of 78%, a PPV of 75%, and an NPV of 90% for diagnosis of infection. They noted an area of potential utility for leukocyte scans, specifically that a negative indium leukocyte scan might support the absence of infection in otherwise equivocal cases and in situations in which a musculoskeletal pathologist is not available to interpret an intraoperative frozen section [100]. A small sample of indium scans in uncomplicated postoperative TKA patients has shown that inflammation can persist around the operative site in the absence of infection [100]. Bernard et al [50] reported a multicenter trial of various methods for diagnosing hip and knee infections. Scans using tagged WBCs or radiolabeled immunoglobulin demonstrated a sensitivity of 74% and a specificity of 76% for diagnosing infection. A literature review indicates sensitivities of 40% to 96% and specificities of 76% to 100% for WBC scans of joint prostheses [49,50,99-104].