Strain distributions all around ACL during knee motion

Large and highly variable deformations of the anterior cruciate ligament (ACL) in the human knee cannot be adequately quantified by one-dimensional and/or localized measurements. In order to measure strains in the entire area of the ACL, we applied a photoelastic coating method and attempted to analyze stress on the basis of the strains. A specific kind of polyurethane, possessing optically high fringe-sensitivity, was found to be most suitable for the measurement purpose. A specially designed apparatus was used to allow a natural motion of the knee whose medial and lateral femoral bone parts were removed in order for the ACL to be exposed. The photoelastic observation was performed from all the directions around the longitudinal axis of the ACL. Measurement and analysis gave the continuous information of strain distribution including the variations of strain along the principal strain directions in the ACL