What is Tom's handicap and what conclusion can we draw because of it?

Chapter 18 is when Tom Robinson's handicap is revealed. Jem is shocked when he sees it. Reverend Sykes explains what happened to Tom as follows:

"He got it caught in a cotton gin, caught it in Mr. Dolphus Raymond's cotton gin when he was a boy . . . like to bled to death . . . tore all the muscles loose from his bones—" (186).

Mayella and Bob Ewell claim that Tom choked, beat, and raped Mayella, but there's no way he could have because his left arm is about a foot shorter than his right, and the hand is shriveled and completely useless to him. The prosecution still maintains that because he is a young, strong man, he overpowered the nineteen-year-old girl. The problem with that is the rest of the Ewells' story. Mayella also claims that Tom choked her, but usually that involves two hands, not one. She also claims he beat her, but most of her wounds were on her right side, suggesting that a left-handed man hurt her. Therefore, because of Tom's handicap, he could not have choked or beaten her; and if he didn't do those things to her, he more than likely did not rape her.