Mean tensile strength of the PCL in TKA depends on the preservation of the tibial insertion site

Purpose

The tibial insertion of the posterior cruciate ligament (PCL) frequently becomes damaged when performing a tibial cut in a PCL-retaining total knee replacement (TKA). The aim of this study was to quantify the functional effect of this structural damage on the tensile strength and failure load.

Methods

Six paired knees from fresh-frozen cadaver specimens were used. All soft tissues but the PCL were removed. In the left-sided specimens, a classic tibial cut at a depth of 9 mm with 3° of posterior slope was made, while in the right-sided specimens, a bone block was left in front of the tibial PCL insertion. After cementing a tibial tray, the specimens were mounted in a loading frame in 60° of flexion. The femur was translated anteriorly at a constant velocity rate of 0.5 mm/s. Tensions in the PCL were measured continuously until failure occurred.

Results

In one specimen, the tibial PCL insertion was completely removed by the tibial cut. In the other five paired specimens, the mean tensile strength of the PCL was 380.6 ± 154.7 N in the left-sided knees. In the right-sided knees, the mean tensile strength was 738.4 ± 166.7. The average right-to-left ratio was 2.2 ± 0.7 (p = 0.006).

Conclusion

The results of this study indicate that the conventional technique for tibial preparation in cruciate-retaining total knee arthroplasty can result in a significant decrease in tensile strength of the PCL, rendering it susceptible to failure and subsequent midflexion instability. Therefore, we recommend leaving the posterior tibial cortex anterior to the PCL insertion intact when performing a cruciate-retaining TKA.