Summary

The peripheral ligamentous structures of the knee act as secondary restraints to posterior tibial translation in neutral rotation and can become primary stabilizers in internal, or external rotation, depending on flexion angle.

Abstract

Background

The posteromedial and posterolateral structures of the knee were previously shown to be secondary restraints to posterior tibial translation (PTT). The effect of these structures may be increased, when performing a posterior drawer in internal, or external rotation.

Purpose

The purpose of this study was to investigate the influence of the peripheral stabilizers on restricting PTT in neutral, external, and internal tibial rotation.

Methods

A sequential cutting study was performed on twenty-four fresh-frozen human knee specimens, utilizing a validated six degree of freedom robotic test setup. After determining the native knee kinematics from 0-90° knee flexion, an 89 N posterior drawer in neutral, internal, and external rotation was performed in 0°, 30°, 60°, and 90° knee flexion angle. In eight knees, a motion-controlled protocol was performed replaying the native motion, while constantly measuring forces. The reduction of the restraining force presented the percentage contribution of each cut, according to the principle of superposition. In sixteen knees, a force-controlled protocol was performed, determining the increases in PTT after each cut. After determining the native knee kinematics, the posterior cruciate ligament (PCL) was cut, followed by randomized sectioning of the posteromedial (medial collateral ligament / posterior oblique ligament) and posterolateral (lateral collateral ligament / popliteus complex) structures. Mixed linear models with posthoc Dunn’s correction was used for statistical analysis.

Results

During motion-controlled testing, performing a posterior drawer in rotation, significantly decreased the contribution of the PCL in restraining the posterior drawer. The PCL was the primary restraint to PTT in neutral rotation in all flexion angles (24.4 – 61.2 %). The primary restraint to PTT in internal rotation was the posterior oblique ligament in 0° (24.2 ± 14.1 %), the medial collateral ligament in 30° (33.6 ± 11.4 %), and the PCL in 60-90° (46.2 – 57.8 %). In external rotation, the primary restraint was the lateral collateral ligament in 0° (24.7 ± 10.5 %), and the popliteus complex in 30-90° of flexion (56.4 – 65.2 %). During force-controlled testing, PTT in the PCL-deficient knee was significantly decreased when performing the posterior drawer in rotation. Insufficiency of the posterolateral, or posteromedial structures during posterior drawer in neutral rotation, led to a significant increase in PTT of up to 7.6 mm, in addition to the insufficiency caused by sectioning of the PCL. When performing the posterior drawer in external rotation, an insufficiency of the posterolateral structures led to a significant further increase in PTT of up to 11.8 mm. When performing the posterior drawer in internal rotation, an insufficiency of the posteromedial structures led to a significant additional increase in PTT of up to 14.9 mm.

Conclusion

The peripheral stabilizers act as secondary restraints to PTT in neutral rotation and can become primary stabilizers in internal, or external rotation. This study may guide the clinician in diagnosing combined deficiencies of the PCL, and the posteromedial, or posterolateral corner of the knee.