Comparative 18F-FDG PET of experimental Staphylococcus aureus osteomyelitis and normal bone healing

Abstract

PET using (18)F-FDG is a promising imaging modality for bone infections, based on intensive consumption of glucose by mononuclear cells and granulocytes. The method may have limitations in distinguishing uncomplicated bone healing from osteomyelitis. Bone healing involves an inflammatory phase that represents a highly activated state of cell metabolism and glucose consumption, mimicking infection on PET images. This laboratory study of a standardized model was designed to compare the (18)F-FDG PET characteristics of normal bone healing with those of local osteomyelitis.

Methods: A localized osteomyelitis model of the rabbit tibia was created by modifying a previously reported canine model. In the osteomyelitic group (n = 8), a standardized metaphyseal defect of the proximal right tibia was surgically created and filled with a block of orthopedic bone cement, followed by injection of a predetermined amount (0.1 mL) of Staphylococcus aureus (strain 52/52A/80, 1 x 10(5)/mL) into the space around the cement. The control group of animals with normal bone healing (n = 8) underwent the same procedure, but the bacterial injection was replaced by a sterile saline injection. The bone cement was surgically removed during debridement at 2 wk. Osteomyelitis was confirmed with positive bacterial cultures during the debridement and 6 wk later at the time of sacrifice. (18)F-FDG PET and peripheral quantitative CT were performed 3 and 6 wk after the debridement. The presence of osteomyelitic bone changes on plain radiographs was classified according to a previously published system.

Results: Before surgery, the standardized uptake values of (18)F-FDG did not differ markedly between the right and left tibias. In the control animals, uncomplicated bone healing was associated with a temporary increase in (18)F-FDG uptake at 3 wk (P = 0.007), but it returned almost to normal by 6 wk. In the experimental animals, localized osteomyelitis resulted in an intense continuous uptake of (18)F-FDG, which was higher than that of healing and intact bones at 3 wk (P = 0.014 and P < 0.001, respectively) and at 6 wk (P < 0.001).

Conclusion: (18)F-FDG PET seems to be an efficient tool in the differentiation of uneventful bone healing from bone healing complicated by localized osteomyelitis.