Introduction: This study examined the role of the medial patellofemoral ligament (MPFL) and medial patellotibial ligament (MPTL) in patellar stability at various flexion angles.
Methods: Nine cadaveric knees were used. The MPFL and MPTL were isolated and marked. The knees were potted and rigidly fixed to a materials testing system (Instron, Norwood, MA). A wire was threaded through two concentric holes in the patella allowing it to translate laterally. The knees were secured in different angles of flexion (0o, 10o, 20o, 30o, 40o, 50o, and 60o). At each angle the knees were tested with both structures intact, one or the other transected, the MPFL reconstructed alone, both structures reconstructed and the MPTL reconstructed alone. A repeated measures ANOVA was conducted to examine the difference between force and strain using SPSS statistical software.
Results: The force needed to displace the patella 1 cm was significantly less at all flexion angles when the MPTL and MPFL were transected compared with intact, MPFL reconstruction, MPTL reconstruction and both reconstructed (p<0.05). With an increase in flexion the stiffness increased as well. Stiffness was significantly higher at 30°, 40°, 50° and 60° (p<0.001) for the MPFL reconstruction compared to the intact knee. When both the MPFL and the MPTL reconstructions together were compared to the intact state, the reconstructions at 40°, 50° and 60° of flexion had a significantly high stiffness p=0.025, p=0.022 and p=0.007 respectively.
Discussion: The MPFL remains the primary medial stabilizer of the patella. Our initial thoughts were that the MPTL could provide a possible alternative in reconstruction techniques for patellar instability. After our study was completed, we determined that the native MPTL provides little functional importance to preventing lateral displacement of the patella. Our reconstruction results did provide some increased benefit of reconstructing the MPTL and MPFL. This is most likely due to replacing the native ligament with a profoundly more robust ligament under tension.
Medial patellofemoral ligament (MPFL), Medial patellotibial ligament (MPTL), Biomechanics, Reconstruction