This is not a normal injury, in the sense that it is not done normally by robbers and others, but is typically done by somebody who is intimate with the person whose penis has been cut off. It is quite normal that even in a husband and wife relationship, for the wife to cut the penis of such a person, means that their relationship is in a pretty bad state; and in such cases, it is quite normal for a criminal trial to happen. In the current case. the wife cut off the penis of the husband and threw it in the garbage dump, with the intention that the penis could be re-attached. In the trial, she was convicted of the crime and was sentenced for life (link to article):
A judge sentenced a Southern California woman who cut off her estranged husband's penis and tossed it in the garbage disposal to life in prison with the possibility of parole. Catherine Kieu, 50, was convicted by an Orange County jury in April of aggravated mayhem and torture following the July 2011 assault on her ex-husband. Kieu drugged her former spouse before tying him up and severing his penis with a knife. She then threw it into the garbage disposal unit.