How did Peeta get hurt during the hunger games?

Peeta was cut on his upper leg by Cato, the District 2 tribute. According to Katniss, the cut went straight to the bone. Because of not treating the wound properly, infection set in and blood poisoning resulted. He also received multiple tracker jacker stings on his upper body.

Later in the book, Peeta's leg is mauled/ripped badly by one of the wolf muttations. The wound is so bad Katniss must create a tourniquet to staunch the flow of blood that, if allowed to continue, would have killed Peeta.

Peeta's leg was hurt so badly, at the following Victor's interviews Katniss discovers he has a prosthetic leg.