87 SPECT/CT in the post-operative painful knee Figure 9 (A) CT and (B) fused SPECT/CT of loosening of fixational screw at tibial tuberosity after TKA and trauma (arrow). Image courtesy of Prof. Dr W.U. Kampen (Hamburg, Germany). Comparedwith planar scintigraphy, SPECT with andwithout CT substantially improves imaging complications after prosthesis, which next to BS also has been proven for 99mTc-labeled antigranulocyte antibodies and autologous leukocytes [51, 52]. Optimal accuracy can be obtained through enhanced anatomical localization and improved determination of the extent of the pathology [52]. Bone marrow (BM) imaging using colloids ([99mTc]-nanocolloid or [99mTc]-sulphur colloid) both target the reticuloendothelial system, and have a well-established role in the imaging of suspected prosthetic joint infection (PJI), in conjunction Indium-111 or Technetium-99m white blood cell scintigraphy (WBC) [63]. CombinedWBC and BM scintigraphy using colloid is regarded positive for infection if increased activity in the periprosthetic region on the WBC images without corresponding activity on the BM images [59]. Until today, the majority of studies indicate that WBC imaging (using the correct acquisition protocols and interpretation criteria), and preferably the combination of WBC and BM scintigraphy is the best technique for diagnosing PJI [45, 47, 59, 64]. The role of FDG-PET/CT in diagnosing PJI remains questionable, mainly because of low specificity [45, 47, 64]. Low specificity of FDG-PET/CT for PJI can be explained by the fact that FDG-PET is in itself non-specific in discriminating between sterile inflammation and infection as it displaysmacrophage activity. In all patients with TKA sterile inflammation plays a role to some extent: in the formof either synovitis, post-operative inflammation at the bone-prosthesis interface, reaction to fixating cement or reaction to polyethylene inlay wear. Stumpe, et al. described already in 2006 that using FDG-PET/CT diffuse synovial and focal extra-synovial uptake is commonly found in patients withmalrotation of the femoral component and is not related to pain location [64]. 3