Effect of Posterior Cruciate Ligament Deficiency on In Vivo Translation and Rotation of the Knee During Weightbearing Flexion

Background: The effect of posterior cruciate ligament (PCL) deficiency on 6 degrees of freedom in vivo knee-joint kinematics is unclear. Hypothesis: In addition to constraining anterior-posterior translation, the PCL also functions to constrain the medial-lateral translation and rotation of the knee during weightbearing flexion of the knee. Study Design: Controlled laboratory study. Methods: Eight patients with a PCL injury in 1 knee and the other intact were scanned with magnetic resonance imaging, and 3-dimensional models of the femur and tibia were created for both knees. Each knee was imaged during quasistatic weight-bearing flexion (from 0° to 105° ) using a dual-orthogonal fluoroscopic system. The translation and rotation of the PCL-deficient knee were compared with the intact contralateral control. Results: Posterior cruciate ligament deficiency caused an increase in posterior tibial translation beyond 30° of flexion compared with the intact contralateral knees. At 90° of flexion, PCL deficiency increased posterior tibial translation by 3.5 mm ( P < .05). In the medial-lateral direction, PCL deficiency resulted in a 1.1 mm increase in lateral tibial translation at 90° of flexion ( P < .05). With regard to rotation, PCL deficiency caused a significantly lower varus rotation (on average, 0.6° lower) at 90° of flexion. Posterior cruciate ligament deficiency caused a decreased internal tibial rotation throughout the range of flexion, but no significant difference was detected. Conclusions: This study quantitatively describes the effect of PCL injury on 6 degrees of freedom kinematics of the knee during quasistatic weightbearing flexion. Using the intact contralateral side as a control, we found that PCL injuries not only affect anterior-posterior tibial translation but also medial-lateral translation and rotation of the knee. Clinical Relevance: These data provide baseline knowledge of the in vivo kinematics of the knee after PCL injury. Surgical reconstruction of the injured PCL, either using single-bundle or double-bundle technique, should not only focus on restoration of posterior stability of the knee but also the medial-lateral stability as well as the rotational stability. These findings may help to explain the long-term degenerative changes seen in PCL-deficient knees. Keywords: posterior cruciate ligament (PCL) PCL injury in vivo knee kinematics PCL reconstruction