Evaluation of Kinematics of Anterior Cruciate Ligament-Deficient Knees with Use of Advanced Imaging Techniques, Three-Dimensional Modeling Techniques, and Robotics

Measuring knee biomechanics in six degrees of freedom with acceptable accuracy has been proven to be technically chal-lenging. At ourbioengineering laboratory,wehaveemployedbothan in vitro robotic testingsystemandan invivo combineddual fluoroscopicandmagnetic resonance imaging technique toanalyze the impactof anterior cruciate ligament ruptureon theknee joint. Whenmeasuring the tibiofemoral kinematics of nine cadaverswith the robotic testing system,we found that anterior cruciate ligament deficiency not only altered anterior translation and axial rotation of the tibia, but it also increased the medial translationof the tibia aswell. The in vivodual fluoroscopic imaging analysisof tibiofemoral kinematics in tenanterior cruciate ligament-deficient patients revealed analogous findings: an increased medial translation of the tibia of approximately 1 mm between 15 and 90 of flexion was found in anterior cruciate ligament-deficient knees, in addition to an increased anterior translation (approximately 3 mm) and internal rotation (approximately 2) of the tibia at low flexion angles. In a subsequent study of tibiofemoral cartilage contact, we found that the cartilage contact points shifted posteriorly—aswas expectedon the basis of the increased anterior tibial translation—as well as laterally on the surface of the tibial plateau. The data demonstrate how rupture of the anterior cruciate ligament initiates a cascade of events that eventually results in abnormal tibiofemoral cartilage contact in both the anteroposterior and mediolateral directions. If the restoration of normal knee homeostasis is the ultimate goal of ligament reconstruction, the normal function of the anterior cruciat