ESTIMATION OF ACL FORCES BY REPRODUCING AVERAGE KNEE KINEMATICS

A non-invasive, non-contact methodology to estimate forces in the anterior cruciate ligament (ACL) in response to in vivo knee kinematics will allow ACL surgical procedures and rehabilitation protocols to be improved. The specific aim of this study is to evaluate the feasibility of a non-invasive, non-contact methodology for estimating force in the ACL by reproducing average differential kinematics in 6-degrees of freedom (DOF) from one set of porcine knees (source) onto a separate set of porcine knees (target). Differential kinematics are motions of the knee in 6-DOF relative to the passive path of flexion-extension 1. Differential kinematics from a set of source cadaveric porcine knees (n = 8) were recorded in response to an anterior load of 100 N and a valgus load of 5 Nm at 30°, 60°, and 90° of knee flexion. The in situ forces in the ACL of the target knees (n = 8) in response to reproducing average differential kinematics was compared to the in situ forces in the ACL of target knees resulting from the application of the same anterior and valgus loads. There was a significant difference in the in situ force in the ACL between applied loads and average differential kinematics for all flexion angles under anterior loading and at 60° of knee flexion for valgus loading. There was not a significant difference in the in situ force in the ACL for valgus loading at 30° or 90° of knee flexion. Under anterior loads, in situ force in the ACL from reproducing average differential kinematics and applied loads differed by up to 227% in two target knee; although, the anterior tibial translations were identical. These results indicate that average differential kinematics from a random sampling of knees does not account for the 6-(DOF) motion of the knee. This is because variations in knee laxity cause coupled motions to be averaged out of the differential kinematics, artificially constraining the knees' motion. In the future, cadaveric knees will be matched to the group of subject kinematics with similar anterior and internal-external knee laxity to improve estimates of the forces in the ACL