The use of 18F-fluoride and 18F-FDG PET scans to assess fracture healing in a rat femur model

Purpose Currently available diagnostic techniques can be unreliable in the diagnosis of delayed fracture healing in certain clinical situations, which can lead to increased complication rates and costs to the health care system. This study sought to determine the utility of positron emission tomography ( PET) scanning with F-18- fluoride ion, which localizes in regions of high osteoblastic activity, and F-18-fluorodeoxyglucose ( FDG), an indicator of cellular glucose metabolism, in assessing bone healing in a rat femur fracture model. Methods Fractures were created in the femurs of immunocompetent rats. Animals in group I had a fracture produced via a manual three- point bending technique. Group II animals underwent a femoral osteotomy with placement of a 2- mm silastic spacer at the fracture site. Fracture healing was assessed with plain radiographs, F-18- fluoride, and F-18-FDG PET scans at 1, 2, 3, and 4- week time points after surgery. Femoral specimens were harvested for histologic analysis and manual testing of torsional and bending strength 4 weeks after surgery. Results All fractures in group I revealed abundant callus formation and bone healing, while none of the nonunion femurs were healed via assessment with manual palpation, radiographic, and histologic evaluation at the 4- week time point. F-18- fluoride PET images of group I femurs at successive 1- week intervals revealed progressively increased signal uptake at the union site during fracture repair. In contrast, minimal tracer uptake was seen at the fracture sites in group II at all time points after surgery. Data analysis revealed statistically significant differences in mean signal intensity between groups I and II at each weekly interval. No significant differences between the two groups were seen using F-18- FDG PET imaging at any time point. Conclusion This study suggests that F-18- fluoride PET imaging, which is an indicator of osteoblastic activity in vivo, can identify fracture nonunions at an early time point and may have a role in the assessment of longitudinal fracture healing. PET scans using (18F)- FDG were not helpful in differentiating metabolic activity between successful and delayed bone healing.