PCL reconstruction. In vitro biomechanical comparison of 'isometric' versus single and double-bundled 'anatomic' grafts.

We compared the ability of three different posterior cruciate ligament (PCL) reconstructions to restore normal anteroposterior laxity to the knee from 0 to 130 degrees of knee flexion. Cadaver knees were tested intact, after PCL rupture or after bone-patellar tendon-bone grafting. Grafts were performed isometrically or with a single bundle representing the anatomical anterior PCL fibre bulk (aPC) or with a double bundle that added the posterior PCL fibre bulk (pPC). The grafts were tensioned to restore normal knee laxity at 60 degrees of flexion, except for the pPC which was tensioned at 130 degrees. The isometric graft led to overconstraint as the knee extended resulting in high graft tension in extension and excess laxity in flexion. The aPC graft matched normal laxity from 0 to 60 degrees of flexion but was lax from 90 to 130 degrees of flexion. Only the double-bundled graft could restore normal knee laxity across the full range of flexion.