Causes
The Achilles tendon is most commonly injured by sudden plantarflexion or dorsiflexion of the ankle, or by forced dorsiflexion of the ankle outside its normal range of motion.
Other mechanisms by which the Achilles can be torn involve sudden direct trauma to the tendon, or sudden activation of the Achilles after atrophy from prolonged periods of inactivity. Some other common tears can occur from overuse while participating in intense sports. Twisting or jerking motions can also contribute to injury.
Fluoroquinolone antibiotics, famously ciprofloxacin, are known to increase the risk of tendon rupture, particularly achilles.
Read more about this topic: Achilles Tendon Rupture