When Anakin Skywalker met Count Dooku on Geonosis, the duel resulted in the former losing his arm; the Count had cut it off at the elbow. Why cut off the arm instead of killing the young Jedi? Probably because Dooku was rather upset by something Anakin had done, and he wanted the lad to suffer!
Many thanks to Lego, and our apologies -- they do not sell Anakin like this! These figures are from the Dooku "Jedi Duel" set, and the Anakin "Tusken Raider Encounter" set.