Functional activity of the anterior and posterior cruciate ligaments under in vivo gait and static physiological loads.

Abstract

The loading of the anterior and posterior cruciate ligaments (ACL and PCL) during normal gait has not been quantified. Also, it is not clear whether ligaments under "static" physiological loads commonly used in cadaveric studies behave similarly to normal gait experienced in vivo. We measured the in vivo kinematics of the stifle joint of sheep (N = 4) during "normal gait," then reproduced these gait paths using a robotic system. The loads borne by the cruciate ligaments were determined using the principle of superposition and plotted against each other. This indicated some functional interaction between the ACL and PCL under in vivo physiological loads. To examine this relationship under static loading conditions, cadaveric knees (N = 6) were tested in the anterior-posterior (AP) direction, along the axes of the ACL and the PCL, as well as under combined AP and tibial rotations. The same process was repeated after either the ACL (N = 3) or the PCL (N = 3) was transected. Our results show a mutually exclusive relationship in ACL and PCL load bearing under both "in vivo gait" and "static" loading conditions. High ACL loads were associated with low PCL loads and vice versa. This is a novel study quantifying the actions of the cruciate ligaments during gait and comparing them to commonly used static loading conditions in cadaveric studies.