When a trans man begins testosterone therapy, the clitoris will begin to grow. As it’s analogous to the head of the penis, it’ll respond to testosterone in much the same way that an adolescent boy’s does during puberty. Unfortunately, it’s much smaller and the structures that make up a penis in a male are spread out throughout the female genitalia, so it’s not going to actually grow into a full-sized, functional penis, but it will try its best. It may grow up to about two inches in length.
Wanting greater length, some trans men will resort to topical DHT cream and “pumping”, wherein a device is used to apply suction to the clitoris and encourage blood flow. There’s still some debate about whether or not this help, but a number of surgeons recommend it.
Many trans men go without the “bottom surgery” at all, because it’s difficult, expensive, prone to complications, and the results are typically unsatisfactory. Metoidioplasty is the most common surgical option and preferred among trans men. The ligament that holds the clitoris in place is cut, allowing the full length–most of which is internal–to be utilized. Its position is changed so that it more closely corresponds with the position of the penis. Some surgeons are experimenting with combining that surgery with one where the urethra is moved as well, so that the man can urinate through his neophallus, but in most cases that’s reserved for a second surgery as it is actually more likely to result in complications due to the nature of the urinary tract. Some trans men have achieved up to four inches in length through this method.
A phalloplasty is what MatthewGerlach refers to. An erectile pump may be used or rods. Since non-genital tissue is used, most of it lacks erotic sensation. The clitoral nerves can be utilized in the phalloplasty in a number of ways, but there is a risk of losing erotic sensation entirely. A *best *case scenario involves retaining the ability to orgasm. Most men don’t want to take the risk of less than best. A phalloplasty can be used to form an average-sized penis, unlike the metoidioplasty.
The metoidioplasty may result in a smaller penis, but it also results in less scarring since only the genitals are involved in the surgery and greater erotic satisfaction, even if penetrative sex might be somewhat difficult. It also has erectile tissue in it, so no implants are required.
Looking at these two surgery options, you should be able to see why a penile transplant wouldn’t actually be that useful for a trans man. Once we have the capability of nerve grafting to the degree that a penile transplant wouldn’t result in a loss of sensation, that same technology can be used to make the phalloplasties more satisfactory. Why have someone else’s tissue and risk rejection when you can do the same thing with your own tissue?
I have declined from including links here, as they include drawings, photographs, or graphic descriptions of genitalia and surgery. If someone is interested in more information, I’d suggest looking at metoidioplasty dot com, which outlines the surgical techniques and outcomes in greater detail.