Tibiofemoral kinematics of the anterior cruciate ligament (ACL)-deficient weightbearing, living knee employing vertical access open "interventional" multiple resonance imaging.

BACKGROUND: Our current understanding of tibiofemoral kinematics in the anterior cruciate ligament (ACL)-deficient knee is very limited. Using vertical open-access MRI, it is possible to accurately analyze tibiofemoral motion in patients with isolated rupture of the ACL. STUDY: Prospective cohort study. PURPOSE: To assess if ACL rupture alters normal knee weightbearing kinematics. METHODS: Tibiofemoral motion was assessed through the arc of flexion from 0 degrees to 90 degrees in 10 patients with isolated rupture of the ACL in one knee and a normal contralateral knee. Midmedial and midlateral sagittal images were analyzed in all positions of flexion in both knees to assess the tibiofemoral relationship. RESULTS: In the lateral compartment of the knee, the tibial plateau is persistently subluxed anteriorly throughout the arc of flexion from 0 degrees to 90 degrees (flexion facet center to posterior tibial cortex distance of 15.8 mm +/- 2.9 in ACL-deficient knees compared to 21.4 mm +/- 1.4 in normal knees at 0 degrees extension, P <.0001) when compared to normal knees. The medial tibiofemoral relationship is unchanged compared to normal knees. CONCLUSION: Rupture of the ACL changes tibiofemoral kinematics producing anterior subluxation of the lateral tibial plateau. CLINICAL SIGNIFICANCE: Altered kinematics may explain, at least in part, the increased incidence of secondary osteoarthritis in patients with ACL rupture.