Measurement of the End-to-End Distances Between the Femoral and Tibial Insertion Sites of the Anterior Cruciate Ligament During Knee Flexion and With Rotational Torque

PurposeThe aim of this study was to determine the end-to-end distance changes in anterior cruciate ligament (ACL) fibers during flexion/extension and internal/external rotation of the knee.MethodsThe positional relation between the femur and tibia of 10 knees was digitized on a robotic system during flexion/extension and with an internal/external rotational torque (5 Nm). The ACL insertion site data, acquired by 3-dimensional scanning, were superimposed on the positional data. The end-to-end distances of 5 representative points on the femoral and tibial insertion sites of the ACL were calculated.ResultsThe end-to-end distances of all representative points except the most anterior points were longest at full extension and shortest at 90°. The distances of the anteromedial (AM) and posterolateral (PL) bundles were 37.2 ± 2.1 mm and 27.5 ± 2.8 mm, respectively, at full extension and 34.7 ± 2.4 mm and 20.7 ± 2.3 mm, respectively, at 90°. Only 4 knees had an isometric point, which was 1 of the 3 anterior points. Under an internal torque, both bundles became longer with statistical meaning at all flexion angles (P = .005). The end-to-end distances of all points became longest with internal torque at full extension and shortest with an external torque at 90°.ConclusionsOnly 4 of 10 specimens had an isometric point at a variable anterior point. The end-to-end distances of the AM and PL bundles were longer in extension and shorter in flexion.Clinical RelevanceThe nonisometric tendency of the ACL and the end-to-end distance change during knee flexion/extension and internal/external rotation should be considered during ACL reconstruction to avoid overconstraint of the graft.