How did Santa Anna lose his leg?

Answer 1

Santa Anna lost his leg twice. He lost his real leg fighting against the Spanish when Mexico became independent from Spain. Later, US forces narrowly missed capturing Santa Anna, but they did capture his wooden leg which he had abandoned in his coach to escape on horseback. It was often exhibited at state fairs, but is now on display in the Oglesby Mansion (Illinois State Military Museum) in Decatur, Illinois.

Answer 2

He was hit with a cannon ball while retreating from a battle during the Pastry War.

Answer 3

In the so called Pastry War of 1838 and 1839.