Biomechanical analysis of a posterior cruciate ligament reconstruction - Deficiency of the posterolateral structures as a cause of graft failure

We hypothesized that posterior cruciate ligament reconstructions are often compromised by associated injuries to the posterolateral structures. Theref ore, we evaluated a posterior cruciate ligament reconstruction in isolated and combined injury models using a robotic/ universal force-moment sensor t esting system. The resulting knee kinematics and the in situ forces in the native and reconstructed posterior cruciate ligament were determined under four external loading conditions. In the isolated injury model, reconstruct ion reduced posterior tibial translation to within 1.5 +/- 1.3 to 2.4 +/- 1 .4 mm of the intact knee at 30 degrees and 90 degrees under a 134-N posteri or tibial load. In the combined injury model, deficiency of the posterolate ral structures increased posterior tibial translation of the reconstructed knee by 6.0 +/- 2.7 mm at 30 degrees and 4.6 +/- 1.5 mm at 90 degrees of fl exion, External rotation increased up to 14 degrees while varus rotation in creased up to 7 degrees, In situ forces in the posterior cruciate ligament graft also increased significantly (by 22% to 150%) for all loading conditi ons. Our results demonstrate that a graft that restores knee kinematics for an isolated posterior cruciate ligament deficiency is rendered ineffective and may be overloaded if the posterolateral structures are deficient, Ther efore, surgical reconstruction of both structures is recommended in the set ting of a combined injury.