Usually, penile trauma arrives quietly -- via small tears in just a few layers of the stretchy tunica albuginea. These don't qualify as fractures and often don't even hurt. But experts believe the unnoticed damage can build up and lead to unmistakable problems: the curved penis of Peyronie's, which affects about 1 in 10 middle-aged men. (Exact numbers are tough to know; estimates range from 1% to 24%.)
Get developments in medicine, nutrition and fitness delivered to your inbox with our The Health Report newsletter. Sign up »
The body relies on blood flow to repair damaged tissue without leaving a scar, yet very little blood circulates in a penis -- except when it's erect, of course. As a consequence, extensive scars can build up in the organ's elastic layers over time.
Imagine inflating a hot-dog-shaped balloon while pinching one side. As the balloon expands, it bends toward the pinched side. Likewise, a penis with Peyronie's disease looks normal when flaccid but curved when erect. And the greater the scarring, the greater the curve.
Most men who encounter the disease do so in their early 50s. One possible reason is that penile tissue can weaken with passing years. Elastic layers in a middle-aged penis are more likely to give out during vigorous intercourse than in a youthful one.
Also, erections soften with age, which makes even unathletic sex more accident-prone. Just as it's easier to bend and twist a half-blown balloon than a fully inflated one, less-than-rigid penises buckle more easily during intercourse.
The topside, mid-shaft of the penis usually bears the brunt of this buckling pressure, so scars often form there -- giving most affected penises a skyward curve. In severe cases, the penis resembles a hook, curling back to touch the abdomen.
A bend causes dual problems: erection difficulties and logistical issues with intercourse. "Some people will have a rigid penis, but it's so curved that there's nothing they can do," Lue says.
Erectile dysfunction medications such as Viagra might protect some men -- and harm others. In men with mild erection problems, the drugs can bring a medium-soft erection up to full strength, "so there's less chance of injury during normal sexual activity," Montague says.
But for men with severe erectile dysfunction, the drugs might make matters worse, by providing an erection that's just about firm enough for penetration but still soft enough to buckle easily during intercourse.
Cardiovascular problems -- particularly diabetes, high blood pressure and high cholesterol -- boost the risk of Peyronie's as much as six times, according to a 2006 study. Smoking and drinking alcohol each increase chances five-fold. These tend to soften erections and change the structure of the stretchy penile tissue.
Healing from prostate surgery can cause problems, and genetics is probably involved too.
Treatment for Peyronie's disease is still tricky. Dr. Francois de la Peyronie -- who wrote about the condition in 1743 -- suggested that men apply mineral water and mercury to their organs. Electricity, arsenic, cow's milk and a deep heating of the rectal muscles have also been recommended in past times.
Medicines used today directly target the scars on the elastic sheath of the penis. But most have not been tested in large, convincing clinical trials. Two drugs -- interferon and verapamil, both of which help stop new scar tissue from forming -- have shown promise in smaller trials.
Currently underway by Auxilium Pharmaceuticals is a large clinical trial for collagenase, an enzyme that might break down scar tissue in the penis. Also planned is a smaller study by Allergan to investigate the use of botulinum toxin -- Botox -- which might relax penis muscles and reduce scarring.
About 10% of the time, untreated penises with Peyronie's disease will straighten on their own. If not, doctors may recommend surgery after a year or so. Options for reducing the curve include implanting a prosthesis (which adds firmness but requires set-up before sex); permanently pinching a bit of elastic tissue opposite the scar (which also shortens the penis); or replacing scar tissue with a tissue graft (which can sometimes cause other problems, such as numbness or complete loss of erections).
The best approach to Peyronie's disease involves preventing penile trauma in the first place, urologists say.
A bit of biomechanical common sense helps: Stay well-lubricated during sex to reduce friction. Be aware of pubic bones and other hazards, especially during entry and reentry. Keep thrusting motions along the length of the shaft. And avoid maneuvers that bend, twist or buckle the penis.
In short, be careful. It's not a toy.
Read more The Mating Game columns at latimes.com/matinggame.