An Analysis of the Posterior Cruciate Ligament Isometric Position Using an In Vivo 3-Dimensional Computed Tomography–Based Knee Joint Model

Purpose

This study aimed to review the isometric point of the posterior cruciate ligament (PCL) based on insertional locations identified in recent anatomic studies by use of a 3-dimensional knee model.

Methods

Ten living subjects with healthy knees were evaluated. High-resolution computed tomography scans were performed at 3 positions of 0°, 90°, and 135°, and 3-dimensional knee images were constructed. Customized software was used to define tibial and femoral insertion points of the PCL, based on recently described anatomy. The femoral attachment site of the PCL was divided into 4 sectors (labeled A through D), and the tibial attachment site was divided into 6 sectors (labeled 1 through 6). Twenty-four virtual PCL bundles were created between these sectors, and their length was measured in the 3 knee flexion positions.

Results

In 0° and 90° of knee flexion, the virtual bundle showing the least amount of length change (1.10 ± 0.66 mm) was at sector D-6, that is, a posteromedial bundle inserting into the most posterior femoral sector (sector D) and the most distal tibial sector (sector 6). This change was not significantly different compared with all other virtual bundles with tibial points connected to femoral sector D (P > .05). An isometric position for the PCL (length change <2 mm) could not be found in 135° of knee flexion because of lengthening of all virtual bundles.

Conclusions

Our data suggest that the femoral attachment point is more important than the tibial attachment point: any of the 6 tibial bundles attached to the most posterior femoral sector had similar isometric properties.

Clinical Relevance

Reproducing normal tibial and femoral anatomy underpins PCL surgical reconstruction. These findings suggest that to perform an isometrically accurate PCL reconstruction, particular attention should be paid to the location of the femoral attachment site, once the tibial footprint has been established. There were no isometric points in any virtual PCL bundle in the fully flexed knee because of excessive lengthening. Therefore, to avoid lengthening of the reconstructed graft, we recommend that fixation is performed at knee flexion angles between 0° and 90° and that patients avoid high flexion during postoperative rehabilitation.