The Achilles tendon takes a significant load and crosses two joints. If there is any weakness in the tendon at the same time as the two joints (knee and ankle) that the tendons and muscles cross move in different directions at the same time, then there is a high risk for a rupture. The rupture is usually ‘heard’ and is usually very obvious what has happened.
The treatment for an achilles tendon rupture is either a surgical repair or a plaster cast. The research shows almost similar outcomes between the two approaches, so there is no clear reason to have one over the other.