Effects of twisting of the graft in anterior cruciate ligament reconstruction.

In an in vitro study on six knees from cadavers, the effect of bone-patellar tendon-bone graft twist on anterior knee laxity was measured at different knee flexion angles. A motion and loading rig was used to prescribe the flexion angle, to restrain axial rotation, and to apply 100 N anterior force to the tibia. Roentgen stereophotogrammetric analysis was used to measure the relative anteroposterior position of the tibia and femur. The tibial bone block was cemented in a cylinder that allowed rotation in the bone tunnel. The anterior cruciate ligament was transected and reconstructed with neutral, 90 degrees, and 150 degrees internal twists and 90 degrees and 150 degrees external twists. External and internal graft twists in the reconstruction resulted in significant reductions of anterior laxity, however, at the cost of a more posterior position of the unloaded tibia relative to the femur (anteroposterior-error). The results are explained by the anterior relocation of the graft insertion by twisting the tibial bone block. The inclination angle of the graft in the anteroposterior direction flattens, which could improve the anterior laxity. A consequent side effect is the increase of posterior shift of the tibia relative to the femur.