Evaluation with contrast-enhanced magnetic resonance imaging of the anterior cruciate ligament graft during its healing process: a two-year prospective study

The aim of this study was to evaluate, with contrast-enhanced-magnetic resonance imaging (MRI), the changing imaging appearance of an anterior cruciate ligament (ACL) graft during the revascularization phase by quantitatively assessing the morphological and signal intensity changes taking place at its cross-sectional surface over time. Fifty patients underwent contrast-enhanced-MRI on the third postoperative day and at a mean of 6, 12, and 24 months time interval after surgery. Proton-density images were obtained to evaluate morphological and signal intensity characteristics. Oblique-axial T1-weighted images obtained before and after intravenous gadolinium administration were used for quantitative analysis. Enhancement index (EI: signal-to-noise quotient(after gadolinium)A center dot signal-to-noise quotient(before gadolinium)) and cross-sectional area (CSA) were calculated for two regions of interest: the transplanted graft and its surrounding hypervascular tissue, and at three distinct graft sites (intra-articular, intraosseous tibial tunnel, and intraosseous juxta screw sites). Comparisons of EI and CSA at every site and time interval were performed using analysis of variance. A variable MRI appearance of the graft during the different time intervals was attributed to the varying amount of the hypervascular tissue gradually surrounding the graft. Graft EI and peripheral tissue CSA progress in a parallel, time- and site-related pattern along the graft course. The initial heterogeneity with intermediate signal intensity at the intra-articular graft site reflected intense revascularization. A slower revascularization progress was noticed at the other two intraosseously enclosed sites. During the healing process the amount of revascularization tissue influences the MR imaging characteristics of the graft according to the examined site and the time interval after surgery. By 2 years postoperatively, revascularization completion coincides with the homogeneously low signal intensity of the graft, closely resembling native ACL.