Concepts and measurement of in vivo tibiofemoral kinematics

Recent studies of tibiofemoral kinematics in 6 degrees-of-freedom have given us a new perspective and demonstrated lateral compartmental roll-back centered on a medially oriented axis over a relatively stable medial compartment during functional arcs of sagittal knee motion. This translates into coupled internal tibial rotation with increasing knee flexion, which is altered by anterior cruciate ligament (ACL) injury. During terminal extension, the tensioned ACL provides an internal torque to the lateral femoral condyle with tightening of the lateral collateral ligament, culminating in the 'screw-home mechanism'. Studies of tibiofemoral kinematics in the ACL-deficient knee have demonstrated posterior and medial shifts of the femur relative to the tibia reference point. In addition, the ACL-deficient knee also demonstrates different patterns of tibiofemoral kinematics during gait. Current ACL-reconstruction techniques will restore some functions of the ACL; however, some studies have suggested that anatomical ACL-reconstruction may better restore normal tibiofemoral kinematics. Although in vitro studies have contributed much to our knowledge of knee kinematics, increasingly accurate in vivo measurement techniques now offer new insight on rotational stability. The methodologies of in vivo kinematics include radiological techniques, video-based motion analysis, electromagnetic tracking devices, and ultrasound-based systems. As management of knee pathologies continue to evolve, development of reliable measures of rotational stability may be the next challenge in clinical and functional outcome assessment.