Unlocking the talus by eversion limits medial ankle injury risk during external rotation

Area of Science:

• Biomechanics
• Orthopedics
• Sports Medicine

Background:

• Ankle eversion preceding external foot rotation predisposes the anterior tibiofibular ligament (ATiFL) to injury.
• Despite high foot rotation, the anterior deltoid ligament (ADL) is protected from failure in an everted position.
• Understanding the differential joint kinematics is crucial for elucidating injury mechanisms.

Purpose of the Study:

• To quantify subtalar and talocrural joint rotations during external foot rotation.
• To compare joint motion in neutral versus pre-everted ankle configurations at sub-failure levels.
• To investigate the kinematic basis for ADL protection during eversion.

Main Methods:

• Utilized fourteen cadaver lower extremities (seven pairs).
• External rotation of 20° was applied in neutral and pre-everted ankle positions.
• Motion capture tracked tibia, talus, and calcaneus; joint coordinate systems analyzed subtalar and talocrural motion.

Main Results:

• Talocrural joint rotation was significantly greater in the neutral ankle (13.3°) compared to the pre-everted ankle (10.5°).
• Subtalar joint rotation was significantly greater in the pre-everted ankle (2.4°) compared to the neutral ankle (1.1°).
• Overall, talocrural rotation (11.9°) exceeded subtalar rotation (1.8°).

Conclusions:

• A 'locking' mechanism in the neutral position and 'unlocking' in the everted position may explain altered joint rotations.
• Increased subtalar and decreased talocrural motion in the pre-everted state likely contributes to ADL protection.
• Findings offer insights into external rotation kinematics and ankle injury risk factors.