Abstract
Introduction
In posterior cruciate ligament (PCL)-preserving total knee arthroplasty (TKA), it is important to determine whether the PCL is properly functioning after surgery. As the PCL is partly damaged during the operation, we cannot rule out the possibility that excessive tension further damages the remaining PCL resulting in dysfunction or that initial functioning of the PCL is lost due to excessively low tension. However, it is normally difficult to examine whether the PCL has remained intact and is still functional after TKA. The objective of this study was to visualize knee joint flexion after TKA by MRI and evaluate the PCL based on these images.
Method
PCL-preserving TKA was performed in 41 knees using the Fine Total Knee System® (Nakashima Medical, Okayama, Japan) where a titanium component can be selected for both the femur and the tibia. We visualized knee flexion positions by MRI at 6 months after surgery and evaluated visualization or non-visualization of the PCL, the relationship between knee flexion angle and PCL elevation angle against the plane of the tibial joint vertical to the tibial axis, and the forms of PCL based on the MRI data.
Results
The PCL was visualized in 40 of the 41 knees. These 40 knees showed a strong positive correlation (correlation coefficient 0.85) between the knee flexion angle (mean 95.8 degrees, 59 to 129 degrees) and the PCL elevation angle (mean 60.4 degrees, 38 to 79 degrees) by MRI. As the PCL was visualized as a straight line in 6 of 13 knees at a knee joint flexion angle of less than 90 degrees, sufficient tension was considered to be transmitted; however, 7 knees showed superior protrusion or S-shaped forms, indicating that the tension in the PCL was not strong. No superior protrusion of the PCL was observed in 27 knees at the flexion angle of 90 degrees or more; 19 knees showed straight-line forms and 7 knees showed inferior protrusion due to posterior pressure from the femur, and the flexion angle was 105 degrees or greater in all knees with inferior protrusion. At the knee flexion angle of 90 degrees or greater, the tension in the PCL was confirmed in 26 knees (96%) by MRI.
Conclusion
To date, there have been no morphological evaluations of postoperative PCL in PCL-preserving TKA. While tension in the PCL was determined to be insufficient in some knees at the knee flexion angle of less than 90 degrees, the elevation angle of the PCL against the tibia increased with tension as the knee flexion angle increased. Postoperative MRI indicated that the PCL functions as a stabilizer between the femur and the tibia in knees that have undergone PCL-preserving TKA, especially at the knee flexion angle of 90 degrees or greater.
