While I think travelers should have the pat-down in plain view of everyone, rather in a "private room," I think your case is an exception. You should explain your medical/pain issue and ask for private screening. You need your own witness, if you don't have an appropriate travel companion the airline should supply an employee to accompany you as your witness.

If they balk, ask for the airline Complaints Resolution Officer (all airlines are required to have them, see FT's Disability forum for the recent thread with more information). If you have problems, get a supervisor and a LEO involved.

I would think if the TSO visualizes the area of concern, no touching should be involved. You might have to swipe the area with your fingers, then have your fingers swabbed for explosives detection. Ask for gloves. Allow a lot of extra time for all this, at least one hour.

If I had any sort of recent surgery, this is how I would handle the pat-down. This includes breast cancer, ostomies, etc. The indignities are bad enough, we cannot allow the government to cause physical pain to us just because we are using commercial air as transportation.

The very fact that this is an issue is a travesty. Good luck with your travel this evening.