Subtalar arthrodesis alignment: the effect on ankle biomechanics

Area of Science:

• Biomechanics
• Orthopedic Surgery
• Lower Extremity Function

Background:

• Lower extremity joint alignment significantly impacts adjacent joint function and overall limb performance.
• Limited literature exists on the biomechanics of subtalar arthrodesis and its specific effects on ankle biomechanics.
• Understanding these effects is crucial for optimizing surgical outcomes.

Purpose of the Study:

• To investigate the impact of subtalar arthrodesis position on sagittal plane ankle biomechanics.
• To quantify changes in ankle muscle strength and moment arms based on subtalar joint alignment.

Main Methods:

• A validated 3D computational model of the lower extremity was utilized.
• Subtalar arthrodesis was simulated across a range of varus and valgus (20 degrees each).
• Ankle muscle fiber force, moment arm, and moments were calculated throughout physiological motion.

Main Results:

• Plantarflexion strength peaked at 10 degrees of subtalar valgus (221 Nm), with minimal variation (2.6%).
• Dorsiflexion strength maximized at 5 degrees of subtalar valgus (46.8 Nm), with variation up to 7.5%.
• Changes in strength were attributed to altered muscle fiber force capacities and moment arms.

Conclusions:

• Subtalar arthrodesis positioned between 5 and 10 degrees of valgus demonstrates a biomechanical advantage.
• This finding provides a biomechanical rationale supporting positive clinical outcomes observed in previous studies.