Motion of the distal tibiofibular syndesmosis under different loading patterns: A biomechanical study

The distal tibiofibular syndesmosis is an important structure for ankle stability. The objective of this study was to evaluate the motion of the syndesmosis under different loading patterns and determine the characteristics of the syndesmotic motion.

Six fresh cadaveric lower extremity specimens with the knee reserved were tested in this study. The skin and muscles were removed with all ligaments around the syndesmosis and knee and ankle joint intact. An axial load of 600 N was applied to the specimens with the ankle joint in 10° dorsiflexion, neutral position, and 15° plantar flexion using a universal material testing machine. Then, with the ankle joint positioned neutrally, a combination of 600-N axial and 5-Nm torsional external rotation loading was applied to the specimens. The medial-lateral and anterior-posterior displacement and rotation of the distal fibula relative to the distal tibia were measured.

Under the axial loading, the distal fibula tended to move medially and anteriorly and rotate internally with the ankle positioned from the neutral position to 15° plantar flexion. Meanwhile, when the ankle was positioned from the neutral position to 10° dorsiflexion, the distal fibula tended to move laterally and posteriorly and rotate externally. Under the combined loading, with respect to the isolated axial loading, the distal fibula tended to move medially and posteriorly, and rotate externally relative to the distal tibia.

Micro motion existed in the syndesmosis. The relative motion of the syndesmosis was correlated to the ankle position and loading patterns.