Three-dimensional isotropic magnetic resonance imaging can provide a reliable estimate of the native anterior cruciate ligament insertion site anatomy.

Abstract

This study quantified the error in anterior cruciate ligament (ACL) insertion site location and area estimated from three-dimensional (3D) isotropic magnetic resonance imaging (MRI) by comparing to native insertion sites determined via 3D laser scanning. Isotropic 3D DESS MRI was acquired from twelve fresh-frozen, ACL-intact cadaver knees. ACL insertion sites were manually outlined in each MRI slice, and the resulting contours combined to determine the 3D insertion site shape. Specimens were then disarticulated, and the boundaries of the ACL insertion sites were digitized using a high-accuracy laser scanner. MRI and laser scan insertion sites were co-registered to determine the percent overlapping area and difference in insertion centroid location. Femoral ACL insertion site area averaged 112.7±17.9mm2 from MRI and 109.7±10.9mm2 from laser scan (p=0.345). Tibial insertion area was 134.7±22.9mm2 from MRI and 135.2±15.1mm2 from laser scan (p=0.881). Percentages of overlapping area between modalities were 82.2±10.2% for femurs and 81.0±9.0% for tibias. The root-mean-square differences for ACL insertion site centroids were 1.87mm for femurs and 2.49mm for tibias. The MRI-estimated ACL insertion site centroids were biased on average 0.6±1.6mm proximally and 0.3±1.9mm posteriorly for femurs, and 0.3±1.1mm laterally and 0.5±1.5mm anteriorly for tibias. Errors in ACL insertion site location and area estimated from 3D-MRI were determined via comparison with a high-accuracy 3D laser scanning. Results indicate that MRI can provide estimates of ACL insertion site area and centroid location with clinically applicable accuracy. MRI-based assessment can provide a reliable estimate of the native ACL anatomy, which can be helpful for surgical planning as well as assessment of graft tunnel placement.