Biomechanical properties and vascularity of an anterior cruciate ligament graft can be predicted by contrast-enhanced magnetic resonance imaging - A two-year study in sheep

Magnetic resonance imaging has been used to determine graft integrity and s tudy the remodeling process of anterior cruciate ligament grafts morphologi cally in humans. The goal of the present study was to compare graft signal intensity and morphologic characteristics on magnetic resonance imaging wit h biomechanical and histologic parameters in a long-term animal model. Thir ty sheep underwent anterior cruciate ligament reconstruction with an autolo gous Achilles tendon split graft and were sacrificed after 6, 12, 24, 52, o r 104 weeks. Before sacrifice, all animals underwent plain and contrast-enh anced (gadolinium-diethylenetriamine pentacetic acid) magnetic resonance im aging (1.5 T, proton density weighted, 2-mm sections) of their operated kne es. The signal/noise quotient was calculated and data were correlated to th e maximum load to failure, tensile strength, and stiffness of the grafts. T he vascularity of the grafts was determined immunohistochemically by staini ng for endothelial cells (factor VIII). We found that high signal intensity on magnetic resonance imaging reflects a decrease of mechanical properties of the graft during early remodeling. Correlation analyses revealed signif icant negative linear correlations between the signal/noise quotient and th e load to failure, stiffness, and tensile strength. In general, correlation s for contrast-enhanced measurements of signal intensity were stronger than those for plain magnetic resonance imaging. Immunohistochemistry confirmed that contrast medium enhancement reflects the vascular status of the graft tissue during remodeling. We conclude that quantitatively determined magne tic resonance imaging signal intensity may be a useful tool for following t he graft remodeling process in a noninvasive manner.