Objective:

To compare the biomechanical effects of different fixation heights and anterior tilt angles in syndesmotic fixation for Weber B ankle fractures using a finite element model.

Approach:

• Model Development: A 3D finite element ankle model was created from CT/MRI data of a healthy adult, simulating residual instability by transecting ligaments after anatomical reduction and fixation.
• Fixation Models: Eighteen fixation models were created using tricortical screws or suture-buttons, placed at heights of 20, 30, or 40 mm above the tibial plafond with anterior tilt angles of 12.5°, 27.5°, or 42.5°.
• Outcome Measures: Outcomes included peak tibiotalar contact stress, fibular displacement, and peak implant von Mises stress under axial loading and external rotation.

Key Findings:

• Residual instability increased peak tibiotalar contact stress by 36.8% and fibular translation.
• Fixation at 20–30 mm restored near-physiologic mechanics, while 40 mm fixation showed biomechanical deterioration.
• Tricortical screws better restrained fibular translation compared to suture-buttons, which preserved more micromotion but had higher implant stress concentrations.

Interpretation:

Fixation height had a larger biomechanical effect than anterior tilt angle, with optimal fixation recommended at 20–30 mm above the tibial plafond.

Limitations:

• The study was based on a single-subject model, limiting generalizability.
• Material properties and loading conditions were derived from literature rather than measured from the individual.

Conclusion:

The study found that fixation height had a larger biomechanical effect than anterior tilt angle.