Hitler had been shot at a Nazi demonstration in Munich in the late 20s, which at least temporarily immobilized his arm. In the attempted bomb assassination his arm was badly injured. The one with the bad arm all along was the Nazi from Berlin, Goebbels, the propaganda expert.
"Hitler had been shot at a Nazi demonstration in Munich in the late 20s"
No. Hitler dislocated his shoulder when he and others were shot at during the "Beerhall Putsch" of 1923.
"In the attempted bomb assassination his arm was badly injured."
No. In fact, Hitler joked that the blast had done away with his palsey in his left arm. But it later returned.
His arm palsey from probably from Parkinson's. Though others have offered other possibilities.