Femoral insertion site in medial patellofemoral ligament reconstruction.

Background: The optimal femoral insertion point in MPFL (medial patellofemoral ligament)-reconstruction still remains ambiguous. Three-dimensional knee simulations based on computerized tomography (CT) images acquired under physiological loading conditions give further insights to predict the optimal femoral insertion site of the MPFL. The hypothesis of the present study is that the optimal insertion point is not as reliable as thought and is dependent on subject-specific anatomical factors.

Methods: High-resolution 3D images of the knee were acquired in ten weight-bearing knees of healthy subjects in five flexion angles (0 to 120°). The distance between different femoral insertion points and two defined patellar points was computed in each position to quantify length of respective bundles and isometry of the femoral insertion site.

Results: The median length of both bundles was maximal in full extension (proximal bundle: 62.2mm and distal bundle: 59.9mm). The shortest ligament length was obtained in the flexion position 90° for bundle I (57.3mm) and 30° for bundle II (85.3mm). The calculated most isometric femoral attachment point showed a non-uniform distribution pattern related to anatomic landmarks. The radiographic landmark showed the worst isometric score value compared to virtually defined spots by surgeons and the computed most isometric point.

Conclusions: This study provides results on the MPFL path length under physiological loading conditions using high-resolution bone geometry. The most important finding of this study was that the computed, best isometric femoral insertion point showed a variable anatomical distribution. This suggests that the optimal position for femoral MPFL-graft fixation is patient specific.