A Biomechanical Study of Replacement of the Posterior Cruciate Ligament with a Graft. Part I

Abstract

Isometer readings from a trial wire attached to a point on the femur provided an accurate indication of the change in the length of a graft subsequently centered at that point. Anteriorly placed femoral tunnels should be avoided, as the isometer readings indicated increased tension, with flexion of the knee, in a graft placed in this region. The force in the intra-articular portion of the graft was always less than the force applied to the bone block in the tibial tunnel. Therefore, the femoral end of the graft should be tensioned to avoid frictional losses from the severe bend in the graft as it passes over the posterior tibial plateau. With correct pre-tensioning of a graft, normal anterior-posterior laxity at 0 to 90 degrees of flexion can be restored. However, because of the considerable range in the laxity-matched pre-tensions, we recommend that the pre-tension be greater than forty-three newtons for all patients to ensure that normal laxity is restored.