My mom's looking for a book she read when she was ten, please help!!

Hihi, my mom's been looking for a book she read at the age of ten for about thirty years now and I want to help her find it for mother's Day or something, I had her describe the book here since she can still remember it well

"70's/80's novel. Psychological thriller/horror. Preteen boy only child is a psychopath. Parents are wealthy and emotionally distant. Breaks his own arm or hand with a fire poker in front of his father to get him in trouble/arrested. Possibly green cover."

She also said it doesn't have anything supernatural so nothing with ghosts like some Google searches keep showing.

Thank you so much and I'm sorry if this isn't enough to find it.