Technology Brings New Information About the Posterior Cruciate LigamentEngineering experts have new information for us on the function of the posterior cruciate ligament (PCL). Using fluoroscopy and three-dimensional (3-D) computer models, the knees of patients with PCL injuries were examined. Fluoroscopy is a type of X-ray imaging that allows a view inside the moving joint.
MRIs were used to scan both knees of each patient in the study. The information was used by a computer to create a 3-D model of the patient's knees. The computer program created a coordinate system for the tibia (lower leg bone) and the femur (thighbone). This information was used to identify the axis (center) of motion for flexion.
A fluoroscopic system was used to measure and record knee joint kinematics. This was done with the patient in a standing (weight-bearing) position while lunging forward. Kinematics refers to joint motion that occurs from all angles and directions.
Using these two systems together, the engineers were able to map out and measure tibial translation (glide) in all planes of motion. They looked at how far the tibia moved backwards, sideways, and in a rotatory direction in the PCL-deficient knee. These measures were compared with the normal knee.
The results showed that the tibia moves forward relative to the femur during knee flexion. The amount of forward translation was less in the PCL-injured knees. As the knee bent to 90-degrees of flexion, the tibia also slipped sideways in the PCL-injured knees. Internal rotation of the tibia during flexion was the same between the injured and normal knees.
Many studies have shown degenerative changes occur over time in PCL-deficient knees. The authors of this study suggest these osteoarthritic changes may be caused by the change in contact points and increase in contact pressures within the joint when the PCL is damaged. The lateral movement of the tibia may shift these contact points.
Kinematic studies like this one show that the PCL's function in the knee is more complex than just to maintain posterior stability (keep the tibia from sliding backwards). Surgeons must take this information into consideration when reconstructing the knee after a PCL injury.
Guoan Li, PhD, et al. Effect of Posterior Cruciate Ligament Deficiency on In Vivo Translation and Rotation of the Knee During Weightbearing Flexion. In The American Journal of Sports. March 2008. Vol. 36. No. 3. Pp. 474-479.
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