Computer investigation of ACL orientation during passive range of motion.

No quantitative data are reported in the literature regarding the orientation of anterior cruciate ligament (ACL) fibers during passive range of motion. In this study we performed an original qualitative and quantitative analysis in eight cadaver knees, examining ACL elongation and 3D orientation. Computer elaboration of anatomical and kinematic data obtained by a six degrees-of-freedom electrogoniometer enabled a mathematical and statistical evaluation of the 3D behavior of the ACL. Our data confirmed the isometric behavior of ACL. The inclination of ACL with respect to the tibial plateau decreases with flexion from 56 degrees to 33 degrees. Orientation of ACL with respect to the femoral notch increases with flexion from 4 degrees to 58 degrees. The ACL orientation in a medio-lateral direction changes from 24 degrees to 52 degrees. The postero-lateral and the antero-medial bundle have different angular variations, mainly with respect to the tibial plateau and medio-lateral direction. This quantitative and qualitative information not only increases the anatomical knowledge of the ACL, but could also be important in developing or improving the surgical strategy for ACL reconstruction.