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 0 degrees of knee flexion with external rotation, with the mean load response to external rotation significantly less at 90 degrees . Fibular collateral ligament varus load response at 0 degrees , 30 degrees , and 60 degrees was fairly constant, with a significant decrease at 90 degrees compared to 30 degrees 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 60 degrees of knee flexion. The mean popliteus tendon and popliteofibular ligament load response at 0 degrees was significantly less than the mean load response at 30 degrees , 60 degrees , and 90 degrees 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 60 degrees and 90 degrees 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.

An analysis of an anatomical posterolateral knee reconstruction: an in vitro biomechanical study and development of a surgical technique.

BACKGROUND: To date, no surgical technique to treat posterolateral knee instability anatomically reconstructs the 3 major static stabilizing structures of the posterolateral knee: the fibular collateral ligament, the popliteus tendon, and the popliteofibular ligament. HYPOTHESIS: Static varus and external rotatory stability would be restored to the reconstructed knee with a posterolateral knee injury. METHODS: The anatomical locations of the original fibular collateral ligament, popliteus tendon, and popliteofibular ligament were reconstructed using a 2-graft technique. Ten cadaveric specimens were tested in 3 states: intact knee, knee with the 3 structures cut to simulate a grade III injury, and the reconstructed knee. RESULTS: For the varus loading tests, joint stability was significantly improved by the posterolateral reconstruction compared to the cut state at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. There were no significant differences between the intact and reconstructed knees at 0 degrees, 60 degrees, and 90 degrees for varus translation. For the external rotation torque tests, external rotation was significantly higher for the cut state than for the intact or reconstructed posterolateral knee. There was no significant difference in external rotation between the intact and reconstructed posterolateral knees at any flexion angle. CONCLUSIONS: This 2-graft technique to reconstruct the primary static stabilizers of the posterolateral knee restored static stability, as measured by joint translation in response to varus loading and external rotation torque, to knees with grade III posterolateral injuries.