Love et al [109] reported WBC/marrow sensitivity, specificity, and accuracy as 96%, 87%, and 91%, respectively, for 150 total hip and knee replacements. Joseph et al [106] reported preoperative WBC/marrow imaging in 58 total hip and knee replacements with a sensitivity, specificity, and accuracy of 46%, 100%, and 88%, respectively. Palestro et al [107,134] described >90% accuracy and a specificity with a high sensitivity for WBC/marrow studies in the assessment of prosthetic joints. In the setting of chronic infection, differentiating chronic prosthetic infection from loosening can be more challenging, given that, in comparison with acute infections, chronic infections tend to have significantly fewer neutrophils, which are the predominant type of WBC labeled in an In-111 or Tc-99m-HMPAO WBC study, and radiolabeled WBCs are predominantly neutrophils. A decreased WBC sensitivity in osteomyelitis has also been attributed to a bacterial protective membrane or biofilm and to the effect of antibiotics [66]. Nonetheless, WBC/marrow scans to include SPECT/CT appear to be the imaging procedures of choice, with a high degree of accuracy for the failed joint prosthesis in the setting of a positive 3-phase bone scan because a negative WBC/marrow study does not include aseptic loosening [66]. In-111 WBC and Tc-99m sulfur colloid studies are not useful for assessment of instability. Variant 4: Pain after total knee arthroplasty. Suspect periprosthetic or hardware fracture. Additional imaging following radiographs. Periprosthetic fractures may occur either during or after surgery and can involve the femur, tibia, or patella. Among periprosthetic fractures, supracondylar distal femur fractures are most common, whereas patellar fractures are rare [135,136]. Supracondylar fractures occur in 0.3% to 2.5% of TKA, usually within 2 to 4 years after surgery, and often occur in the setting of low-energy trauma [136]. Tibial fractures are associated with loose components and malalignment.
Imaging After Total Knee Arthroplasty. Love et al [109] reported WBC/marrow sensitivity, specificity, and accuracy as 96%, 87%, and 91%, respectively, for 150 total hip and knee replacements. Joseph et al [106] reported preoperative WBC/marrow imaging in 58 total hip and knee replacements with a sensitivity, specificity, and accuracy of 46%, 100%, and 88%, respectively. Palestro et al [107,134] described >90% accuracy and a specificity with a high sensitivity for WBC/marrow studies in the assessment of prosthetic joints. In the setting of chronic infection, differentiating chronic prosthetic infection from loosening can be more challenging, given that, in comparison with acute infections, chronic infections tend to have significantly fewer neutrophils, which are the predominant type of WBC labeled in an In-111 or Tc-99m-HMPAO WBC study, and radiolabeled WBCs are predominantly neutrophils. A decreased WBC sensitivity in osteomyelitis has also been attributed to a bacterial protective membrane or biofilm and to the effect of antibiotics [66]. Nonetheless, WBC/marrow scans to include SPECT/CT appear to be the imaging procedures of choice, with a high degree of accuracy for the failed joint prosthesis in the setting of a positive 3-phase bone scan because a negative WBC/marrow study does not include aseptic loosening [66]. In-111 WBC and Tc-99m sulfur colloid studies are not useful for assessment of instability. Variant 4: Pain after total knee arthroplasty. Suspect periprosthetic or hardware fracture. Additional imaging following radiographs. Periprosthetic fractures may occur either during or after surgery and can involve the femur, tibia, or patella. Among periprosthetic fractures, supracondylar distal femur fractures are most common, whereas patellar fractures are rare [135,136]. Supracondylar fractures occur in 0.3% to 2.5% of TKA, usually within 2 to 4 years after surgery, and often occur in the setting of low-energy trauma [136]. Tibial fractures are associated with loose components and malalignment.