False” sprains refer to overstretching of the ligaments and/or capsule.

True sprains refer to tear of some fibres of the ligaments.

Because of the tight fit in the tenon-mortise configuration, dislocation without malleolar fracture is rare.

Commonly caused by forced external rotation and over-eversion of the foot.

The talus is externally rotated forcefully against the lateral malleolus.

Consequently:

•  The torsion effect on the lateral malleolus causes it to fracture spirally.
•  The talus moves laterally, medial ligament becomes taut
•  If the talus is forced to move further, its rotatory movement results in its violent contact with the posterior inferior margin of the tibia, which shears off.

When the joint has to be immobilized e.g. a plaster cast, it is done in slight plantarflexion / neutral since:

• In dorsiflexion , there is tension on the ligaments, and the anterior stractures would shorten while the posterior would be overstretched.
• In plantarflexion, the posterior structures would shorten, and the anterior ones overstretched.