Uptake of technetium 99m-labelled phosphate compounds (TCN-MDP) by bone is increased in areas of higher vascularity, including infections and bone healing. With infection, a 3-phase bone scan shows increased uptake of labelling in all 3 scan phases.
Absence of uptake suggests impaired vascularity, or bone necrosis. Bone scanning detects increased bone remodeling that is present around all fractures for 12-24 months. Bone scanning cannot differentiate aseptic hardware loosening from infection. Bone scans are of negligible value in the early postoperative period of acute fractures.
Indium111-labelled white blood cell scans are more specific for inflammation and infection. The illustration shows a larger area of uptake, surrounding hyperemia and inflammation with TCN-MDP (b) than with the indium111 white blood cell technique (a). However, false positives and false negatives still occur, and such scans can be positive in un-united fractures.