Relative role changing of lateral collateral ligament on the posterolateral rotatory instability according to the knee flexion angles: a biomechanical comparative study of role of lateral collateral ligament and popliteofibular ligament

Abstract

This cadaveric study assessed the relative role of the lateral collateral ligament (LCL) and popliteofibular ligament (PFL) in limiting tibia external rotation. Eight paired cadaveric knees were divided into two groups. The specimens were mounted on a rotational wheel and 5 Nm external rotation torque was applied before and after cutting the ligaments at 0A degrees-30A degrees-60A degrees-90A degrees knee flexion. Three cutting steps were applied: (1) PT (popliteus tendon)-, (2) LCL-, (3) PFL in group I, and (1) PT-, (2) PFL-, (3)LCL in group II. Increased external rotation at each step was taken as the ratio of final external rotation at the end of step 3. Repeated measure ANOVA and a Mann-Whitney U test were used for statistical analysis. At step 2, the ratio of increased external rotation after cutting the LCL (group I) was similar to the ratio after cutting the PFL (group II) at 0A degrees and 30A degrees flexion, but that of group I was lower than group II at 60A degrees and 90A degrees flexion (p = 0.029 and p = 0.029). At step-3, the ratio after cutting the LCL (group II) was less than the ratio after cutting the PFL (group I) at 90A degrees flexion (p = 0.029). The PFL and LCL play equally important roles in limiting external rotation at the knee extended position (0A degrees, 30A degrees) but the LCL contribution becomes smaller than PFL at the flexed position (60A degrees, 90A degrees).