Anterior cruciate ligament graft tensioning versus knee stability

Positioning of the graft for anterior cruciate ligament (ACL) reconstruction and securing the graft at various degrees of knee flexion are interrelated factors when attempting to restore a knee's normal kinematics. The interrelationships between graft positioning on the femur and tibia (graft 'isometricity'); securing the graft at various positions of knee flexion; and the resulting restoration or disruption of the knee kinematics were studied on ten fresh frozen cadaveric knee specimens. Well placed ('isometric') grafts appeared to restore almost normal knee kinematics regardless of the position of the knee at the time of securing the grafts. This was, however, not the case in non-ideally placed grafts. 'Nonisometric' ACL substitutes which became taut in extension, overconstrained the knee if the graft was secured in flexion. If the same graft was secured in extension, increased joint laxity in flexion occurred. In contrast, 'nonisometric' ACL substitutes which became taut in flexion overconstrained the knee if the graft was secured in extension. If the same graft was secured in flexion, the graft became slack during extension.