Determination of the in situ forces in the human posterior cruciate ligament using robotic technology. A cadaveric study.

We examined the in situ forces in the posterior cruciate ligament as well as the force distribution between its anterolateral and posteromedial bundles. Using a robotic manipulator in conjunction with a universal force-moment sensor system, we applied posterior tibial loads from 22 to 110 N to the joint at 0 degrees to 90 degrees of knee flexion. The magnitude of the in situ force in the posterior cruciate ligament and its bundles was significantly affected by knee flexion angle and posterior tibial loading. In situ forces in the posterior cruciate ligament ranged from 6.1 +/- 6.0 N under a 22-N posterior tibial load at 0 degree of knee flexion to 112.3 +/- 28.5 N under a 110-N load at 90 degrees. The force in the posteromedial bundle reached a maximum of 67.9 +/- 31.5 N at 90 degrees of knee flexion, and the force in the anterolateral bundle reached a maximum of 47.8 +/- 23.0 N at 60 degrees of knee flexion under a 110-N load. No significant differences existed between the in situ forces in the two bundles at any knee flexion angle. This study provides insight into the knee flexion angle at which each bundle of the posterior cruciate ligament experiences the highest in situ forces under posterior tibial loading. This information can help guide us in more accurate graft placement, fixation, and tensioning, and serve as an assessment of graft performance.