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 weightbearing flexion (from 00 to 105 degrees) 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 301 of flexion compared with the intact contralateral knees. At 901 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 901 of flexion (P < .05). With regard to rotation, PCL deficiency caused a significantly lower varus rotation (on average, 0.6 degrees lower) at 90 degrees 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.