Effects of sectioning the posterolateral structures on knee kinematics andin situ forces in the posterior cruciate ligament

The objective of this study was to determine the effects of sectioning the posterolateral structures (PLS) on knee kinematics and in situ forces in th e posterior cruciate ligament (PCL) in response to external and simulated m uscle loads. Ten human cadaveric knees were tested using a robotic/universa l force-moment sensor testing system. The knees were subjected to three loa ding conditions: (a) 134-N posterior tibial load, (b) 5-Nm external tibial torque, and (c) isolated hamstring load (40 N biceps/40 N semimembranosus). The knee kinematics and in situ forces in the PCL for the intact and PLS-d eficient knee conditions were determined at full extension, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of knee flexion. Under posterior tibia l loading posterior tibial translation with PLS deficiency increased signif icantly at all flexion angles by 5.5 +/- 1.5 mm to 0.8 +/- 1.2 mm at full e xtension and 90 degrees, respectively. The corresponding in situ forces in the PCL increased by 17-19 N at full extension and 30 degrees of knee flexi on. Under the external tibial torque, external tibial rotation increased si gnificantly with PLS deficiency by 15.1 +/- 1.6 degrees at 30 degrees of fl exion to 7.7 +/- 3.5 degrees at 90 degrees, with the in situ forces in the PCL increasing by 15-90 N. The largest increase occurred at 60 degrees to 1 20 degrees of knee flexion, representing forces two to six times of those i n the intact knee. Under the simulated hamstring load, posterior tibial tra nslation and external tibial and varus rotations also increased significant ly at all knee flexion angles with PLS deficiency, but this was not so for the in situ forces in the PCL. Our data suggest that injuries to the PLS pu t the PCL and other soft tissue structures at increased risk of injury due to increased knee motion and the elevated in situ forces in the PCL.