You Can "Break" Your Penis? Wait! What?
The specific injury in question, penile fracture, is luckily rare and, when it does occur usually completely fixable via emergency surgery. It happens when the tunica albuginea, which is sort of like a thick, slightly elastic wrapping around the spungy, blood-filling parts of the penis part is torn by some form of blunt trauma (my mission today is apparently to make you all associate penises with the least sexy things imaginable). Basically, penile fractures are caused by essentially hitting an erect penis too hard and at the wrong angle. They are, not surprisingly, extremely painful and as every single article I've found on the subject makes sure to point out, when they happen there's usually a popping or cracking sound. And of course, everything goes soft because a) the tunica albuginea makes maintaining erections possible and if it's torn that ain't gonna happen and b) you will be freaking the fuck out because YOUR PENIS JUST BROKE. Also the blood that was formerly filling your erect penis leaks out of the spungy bits and you end up with one helluva nasty look bruise. The injury most commonly occurs during heterosexual sex while the woman is on top and she accidentally bears down on the penis at the wrong angle, causing her pelvic bone to smash against it.
Anyway, back to the study at hand: University of Maryland urologist Andrew Kramer reviewed the medical histories of 16 men who had come to the university for repair of such an injury between 2007 and 2011. (The numbers are so low because it really is pretty rare, honest guys.) In particular he looked at the intake interviews in which the patients described the circumstances leading to their injury. In most cases the author had himself been involved in this interview, and, according to the paper's abstract the men were, "remarkably forthcoming with the personal social dynamics of the sexual encounter." (I picture the informed consent conversation going something like this, doctor: "We'd like to use your information to better understand how penile fracture occurs and possibly help prevent other men from experiencing the same thing." Patient: "Yes. That is a noble cause, ask of me what you will.")
The major factor leading to injury was not, as so many outlets are reporting, being with someone other than your partner (although a full half of the men were cheating at the time the injury happened), but the location in which the men were having sex. Only three were injured while in the bedroom. The others were injured while trying to have sex in significantly less convenient places, like a car, elevator, or public restroom. The real relationship to cheating here is that cheaters, because of the need to keep their affairs secret, are more likely to have sex in such cramped spaces than other men. The actual breakdown from the study is: 14 of the men claimed to have sustained their injuries after sex (no explanation of how the other two managed to do break their members, but the author speculates that they were just lying about not having sex when the injury occurred). Eleven of those who admitted they were having sex at the time of the injury were not having sex in a 'typical' scenario. One was having sex in an elevator, 3 were having sex at work, 2 were having sex in a public bathroom, and the other 2 were having sex in a car. In general these are scenarios that would involve rushed sex (an elevator?) and potentially awkward positions that would increase the likelihood of an accident of this type. In some cases, not surprisingly, alcohol was also involved. The good news is that this data implies that penile fracture fairly easy to prevent in most cases: don't go having sex in elevators or the back of a car, and if you do it's probably best to go with doggy style, not some contorted form of woman-on-top (or receptive partner on top in the case of gays). And you should probably make sure your partner isn't so drunk he/she has lost motor control.
While the media would love to make this study about karmic payback for cheating on one's spouse, that's not really what the study findings imply (although I'd love to hear the evo-psych interpretation, if only for a good laugh). Cheating is wrong in 99% of circumstances because it hurts other people (see Dan Savage's rules of cheating for reasonable exceptions), but there's no karmic retribution in penile fractures (beyond, maybe, having to explain to one's partner how the fracture occurred). Mother nature may be a bitch, but she's a random bitch, not a righteous one. The lesson of the paper is not so much "Don't cheat," as, "throw down the money for a hotel room, you cheap foolish bastard." That and that you really shouldn't rush through sex because injuries can occur and sometimes they're really, really shitty injuries, like a broken motherfucking penis.