Delayed Gadolinium-Enhanced MRI of Cartilage (dGEMRIC) 12 Months after ACL Reconstruction

INTRODUCTION: Anterior cruciate ligament (ACL) injuries place the knee at risk for early osteoarthritis (OA), and there is evidence to suggest that ACL reconstruction, the standard of care for ACL injuries, does not reduce this risk. An in vivo method that can detect early changes in articular cartilage integrity could provide insight into the mechanisms by which post-traumatic OA develops in these patients, which could lead to more effective treatment strategies. Delayed Gadolinium-Enhanced MR Imaging of Cartilage (dGEMRIC) has been used to study changes in articular cartilage glycosaminoglycan (GAG) content following ACL injury [1, 2]. GAG is an important structural molecule of cartilage, and its loss is associated with articular cartilage degeneration [3]. dGEMRIC involves the creation of T1 maps of hyaline cartilage after the administration of an IV dose of an anionic gadolinium [Gd(DTPA)] contrast agent. Because cartilage matrix is composed largely of negatively charged GAG molecules, it repels the negatively charged ions of the contrast agent. Subsequently, the Gd(DTPA) concentration is higher in cartilage regions with lower GAG concentration; the cartilage T1gd relaxation time is thereby reduced [3]. The resulting dGEMRIC index is correlated with cartilage GAG concentration. For the purpose of this study, both knees of subjects with a unilateral ACL injury were imaged following injury (just before ACL reconstruction), and again 12 months after ACL reconstruction. Our objective was to compare the dGEMRIC indices of the femoral and tibial articular cartilage in the ACL-injured and contralateral uninjured knees before and after reconstruction. We hypothesized that the dGEMRIC indices of the ACL-injured knees would be lower than those of the contralateral knees at both the 0(before surgery) and 12-month (after surgery) time points.