Graft tension of the posterior cruciate ligament using a finite element model

The aim of the study was to analyse the change in length and tension of the reconstructed single-bundle posterior cruciate ligament (PCL) with three different femoral tunnels at different knee flexion angles by use of three-dimensional finite element method.

The right knees of 12 male subjects were scanned with a high-resolution computed tomography scanner at four different knee flexion angles (0°, 45°, 90° and 135°). Three types of single-bundle PCL reconstruction were then conducted in a 90° flexion model: femoral tunnels were created in anterolateral (AL), central and posteromedial (PM) regions of the footprint. Length versus flexion curves and tension versus flexion curves were generated.

Between 0° and 90° of knee flexion, changes in length and tension in the PM grafts were not significant. Whereas the lengths and tension of the AL and central grafts significantly increased in the same flexion range. The length and tension of the PM grafts at 135° of knee flexion were significantly higher than those at 90° of knee flexion, whereas the AL and the central grafts showed only slight length changes beyond 90° of flexion. However, the tension of the AL graft increased significantly beyond 90° of flexion.

Changes in the graft length, and tension were generally affected by different femoral tunnels and knee flexion angles. In groups with the AL and PM single-bundle reconstruction, the graft tension increased beyond 90° of knee flexion when the graft is tensioned at 90° of flexion. These data suggest that final fixation angle at 90° for the AL or PM graft would induce graft overtension in high knee flexion of 135°. Whereas central graft which is fixed in 90° of flexion is desirable in terms of prevention of graft overtension. Because the graft tension within it was relatively constant beyond 90° of flexion.