We can't really GET a definitive answer.

We've been told, more than once, that those who are not physically able to go through AIT can be screened by WTMD and hand swabs. However, there are still plenty of reports of people with shoulder issues being told by individual TSOs that they are opt-outs, and being forced to undergo the enhanced pat-down. Since the rules are not enforced, there is absolutely no way to know what you will encounter, because you don't know whether you'll encounter TSOs and TSMs who follow the rules or not.

Meanwhile, if you're medically unable to go through WTMD, you're told that the only alternatives are AIT or the pat-down. If you're physically unable to walk through the WTMD or AIT, such as those confined to wheelchairs, then your only alternative is the pat-down.

Whatever fluff the TSA propaganda machine may put out to the contrary, people in wheelchairs are, quite simply, forced to undergo a physical search every time they transit a c/p. How extensive, invasive, and abusive this search is depends entirely on the TSOs conducting it.