In vivo function of the posterior cruciate ligament during weightbearing knee flexion

Background: Current knowledge of posterior cruciate ligament function is mainly based on in vitro cadaveric studies. There are few studies on the in vivo function of the posterior cruciate ligament. The objective of the study was to quantify the multidimensional deformation of the posterior cruciate ligament. Hypothesis: During in vivo weightbearing flexion, the posterior cruciate ligament undergoes complex 3-dimensional deformations, including elongation, twist, and changes in orientation. Study Design: In vivo biomechanical study. Methods: Magnetic resonance images of 5 human knees were used to create 3-dimensional computer models of each subject's knee, including the insertion areas of the posterior cruciate ligament. Orthogonal fluoroscopic images of each subject's knee were acquired as a quasi-static lunge was performed. The images and computer models were used to reproduce the in vivo motion of the knee. The relative motion of the femoral and tibial insertions was described in terms of elongation, twist, elevation (the angle between the tibial plateau and posterior cruciate ligament, measured in the sagittal plane), and deviation (mediolateral orientation, measured in plane of tibial plateau). Results: The length of the posterior cruciate ligament increased significantly with increasing flexion. It twisted almost 801 as the knee flexed from 0degrees to 90degrees. The elevation angle remained relatively constant at 50degrees. The deviation angle was medially oriented by 20degrees at full extension, then decreased to approximately 10degrees at 30degrees through 90degrees of flexion. Conclusion: The posterior cruciate ligament undergoes a complex twisting motion as it elongates with flexion. Clinical Relevance: During reconstruction, the tunnels and graft may need to be placed such that the multidimensional deformation of the intact posterior cruciate ligament is reproduced.