What happened to his hand isn't really clear. His Walk of Fame page says that he got permanent nerve damage after falling through a glass door when he was 14-years-old. Author Ted Schwarz wrote The Peter Lawford Story, and in it said that his hand apparently began to atrophy. The doctor's choice of treatment was to force his hand to be in an open position so the muscles will learn to relax that way. It always lacked in strength and he couldn't use it.