ACL graft metabolic activity assessed by 18 FDG PET-MRI.

BACKGROUND: To demonstrate the use of 18 Fluorodeoxyglucose positron emission tomography (PET) and magnetic resonance imaging (MRI) in combination (18 FDG-PET) to assess the metabolic activity of ACL graft tissue and evaluate the utility of this technique for ligament imaging.

METHODS: Twenty-one knees with intact ACL grafts in 19 patients at multiple time points following ACL reconstruction were recruited to participate. PET-MRI imaging was performed using a custom device to place knees in the same position for both studies. Images were co-registered for quantification of 18 FDG-PET standardized uptake value (SUV) for the proximal, middle, and distal ACL was quantified. Signal in extra-articular muscle tissue in the index knee was also recorded as a control. Signal from each location was compared based on how far post-operative each knee was from ACL reconstruction (<6months, six to 12months, 12-24months, or >24months).

RESULTS: Significant differences in 18 FDG PET SUV between the four time points were observed in the proximal (p=0.02), middle (p=0.004), and distal (p=0.007) portions of the ACL graft. The greater than 24months group was noted to be different from other groups in each case. No difference in PET 18 FDG SUV was noted in the extra-articular muscle in the index knee in each time group (p=0.61).

CONCLUSIONS: Metabolic activity was noted to be significantly lower in grafts imaged greater than two years post-reconstruction relative to those grafts that had been in place for shorter periods of time.