I'm thinking that when my arm is out in certain positions it does cut off the pulse/blood supply to that arm. That causes the muscles and the nerves to act up- I would think.

and that will cause the delayed?? sx increases and pain

plus-

the fact that you probably aren't used to having your arm out at that position for any length of time - so you muscles are being stretched & held like that for an hour or so or however long the surgery takes.

Something to ask about??
If they would be able to change your arm positions every 10 mins or so that might help..
{Is there a real reason ?? does it have to be out like that??}

It wouldn't hurt to tell them you have a shoulder/arm problem and it hurts for days/weeks after being in certain positions.
{since they may not know much about TOS anyway- simplify it for them-LOL}