Force measurements on the fibular collateral ligament, popliteofibular ligament, and popliteus tendon to applied loads

Background: Little information is known about the forces seen on the main individual structures of the posterolateral knee to applied loads. This information is needed to determine which structures should be reconstructed and also the relative strengths needed for reconstruction grafts. Purpose: To determine in vitro forces in the fibular collateral ligament, popliteofibular ligament, and popliteus tendon for various posterolateral knee loading conditions. Study Design: Cadaveric study. Results: The fibular collateral ligament was loaded in varus, internal rotation, and external rotation. The highest amount of force seen on the fibular collateral ligament was at 0degrees of knee flexion with external rotation, with the mean load response to external rotation significantly less at 90degrees. Fibular collateral ligament varus load response at 0degrees, 30degrees, and 60degrees was fairly constant, with a significant decrease at 90degrees compared to 30degrees of knee flexion. The popliteus tendon and popliteofibular ligament were loaded with an external rotation moment and were noted to have similar loading patterns. The mean load response on both the popliteus tendon and the popliteofibular ligament peaked at 60degrees of knee flexion. The mean popliteus tendon and popliteofibular ligament load response at 0degrees was significantly less than the mean load response at 30degrees, 60degrees, and 90degreesdegrees of knee flexion. Conclusions: High relative loads were seen on the fibular collateral ligament with varus and external rotation and on the popliteus tendon and popliteofibular ligament, with external rotation. A reciprocal relationship of load sharing in external rotation depending on knee flexion angle was revealed that has not been previously reported. The force on the fibular collateral ligament with external rotation loads was higher than the load on the popliteus complex at lower flexion angles, with the popliteus complex having higher load sharing at 60degrees and 90degrees of knee flexion. These results provide a measure of the potential for failure of these structures with joint loading and guidelines for both graft strength requirements for surgical reconstructions and postoperative rehabilitation protocols.