ACL graft metabolic activity assessed by ¹⁸FDG PET-MRI

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

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 ¹⁸FDG-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).

Significant differences in ¹⁸FDG 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 ¹⁸FDG SUV was noted in the extra-articular muscle in the index knee in each time group (p=0.61).

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.