Isolated hamstrings activity generally had little or no effect on anterior cruciate ligament forces but significantly increased forces in the posterior cruciate ligament beyond approximately 30 degrees of flexion.

The single-bundle reconstruction produced graft forces, knee laxities, and coupled tibial rotations that were closest to normal. Adding a posterolateral graft to an anteromedial graft tended to reduce laxities and tibial rotations, but the reductions were accompanied by markedly higher forces in the posterolateral graft near 0 degrees that occasionally caused it to fail during tests with internal torque or anterior tibial force.

Reduction or elimination of the pivot-shift sign is an important goal for anterior cruciate ligament reconstruction. In our model, the results show that a single-bundle reconstruction was sufficient to restore intact knee kinematics during a simulated pivot-shift event. The higher graft forces with some double-bundle graft-tensioning protocols reduced the coupled rotations and displacements from an applied valgus moment to less than the intact levels. This overcorrection should theoretically make the knee less likely to pivot but could have unknown clinical consequences.

The need for a posteromedial graft during posterior cruciate ligament reconstruction is questioned, especially in view of the relatively high graft forces at full extension that could cause it to permanently elongate with time. If a double-bundle reconstruction is performed, there is no biomechanical advantage in making the bone bridge between tunnels less than 3 mm.

This study suggests that a posteromedial tunnel should not be used for single-bundle posterior cruciate ligament reconstruction.