A disturbed boy kills his father with his farm tractor and his arm is mangled in the process. He's taken to a mental hospital where he's outfitted with a hook to replace his lost hand and, years later, he's eventually released from the asylum. He returns home to find his mother has remarried, which sets him off on a murderous rampage.
Scream Bloody Murder
A deranged kid murders his father and has his arm crushed by the farm tractor. After being discharged from the mental hospital with an amputee, he discovers that his mother has remarried, prompting him to go on a homicidal rampage.