Simulation of the optimal femoral insertion site in medial patellofemoral ligament reconstruction

To develop and validate a new simulation system to predict the optimal femoral insertion site of the medial patellofemoral ligament (MPFL) using preprogrammed conditions of graft length change.

A computed tomography scan was performed for constructing bone surface models of the patella and the femur. Lateral radiographs of the knee and axial radiographs of the patellofemoral joint at knee flexion were used for constructing a three-dimensional patellofemoral joint model by 3D–2D image matching at each knee flexion angle. To determine the optimal femoral insertion site, the following three conditions were devised: (1) MPFL behaves isometric from 0° to 60°, (2) MPFL is most taut at full extension, and (3) MPFL is slack at more than 60° of knee flexion. Every condition was applied to the femoral bone surface model, and the area that fulfilled all three conditions was defined as the optimal femoral insertion site of MPFL. Twenty knees of ten healthy volunteers were assessed to verify the simulation. Comparison between simulated optimal femoral insertion and anatomical insertion was done.

The mean simulated optimal femoral insertion was close to the anatomical insertion site. There were no significant differences in the proximal–distal position and anterior–posterior position between the simulated insertion and the anatomical insertion sites.

The system can be useful for predicting the optimal femoral insertion site as a part of a preoperative plan for MPFL reconstruction, and it may help surgeons to determine the optimal femoral insertion site during MPFL reconstruction.