Priapism is one indicator of severe spinal injury/trauma in falls or MVCs. Also

"Priapism is a prolonged and painful erection that can last from several hours up to a few days. The priapismic erection is NOT associated with sexual thoughts or sexual activity. What happens is that blood flows into the penis, but is unable to drain as it would in a normally flaccid penis. Considering that the penis provides little room for blood to circulate, the blood becomes stagnant after a while, acidifies, and loses oxygen. Without oxygen, the red blood cells become stiff, and even less able to squeeze their way out of the penis.

Very few cases of priapism are without an obvious cause. In most cases, priapism results from one of two things: certain medications or medical conditions. Under the category of medications, there are two primary culprits. For one, penile injections used to treat some forms of impotence can cause priapism; however, this usually only happens when a man decides, on his own, to increase the dosage. Second, psychiatric medications, such as anti-depressants, seem to cause some cases of priapism; however, how these drugs affect priapism is unclear. The second major cause of priapism is certain medical conditions and diseases -- generally, any that cause the blood to thicken, or cause red blood cells to lose their flexibility and mobility. Sickle-cell anemia and leukemia are probably the most common conditions that cause priapism."