For new patients, I usually have the history already in the chart (we have people to do that), labs and MRIs, etc, along with a pain diagram, so I have a pretty good idea of what the pain generator is, what has been done and what the next steps are likely to be. Sometimes things change while in the exam room and we take a different route.
For follow-ups, it's basically are they better enough to stop treatment or keep going with the current plan of care, or do we need to change course and if so, what's the next step.
Physiatrists tend to see a lot of neck and back pain patients. There is so little really known about these, that it is almost all anecdotal experience and heuristics. What I do is probably different than what the guy down the street does, but we probably end up at the same place most of the time.
I would say 75% of the time, my assessment and plan are confirmed in the exam room and 25% take me in a different direction.
It's not unusual to be stumped and need someone else's opinion. I have a coccydynia pt today that I've tried everything I know and suggested she see an pain anesthesiologist to see if they have any better ideas. Yesterday I sent a patient to neurology after repeat EMG showed a rapidly-progressing PPN of the BUE w/o LE symptoms. I often send patients to orthopedic and neurosurgeons when I can't resolve their symptoms.
And for most of what we do, there is no "best" treatment option. There is so little research to guide us for most of what we do, it's mostly what you have learned through clinical practice.
I can interpret most labs, x-rays, spine MRIs and EMGs. If I do the EMG, I can usuaklly give a concrete dx, but some are confusing and need more thought, maybe more testing. probably 90% of spine MRI's are interpreted the same by the radiologist as how I see them, 10% of the time they see something I miss (and probably 5% of the time I see something they miss...).
I could not interpret a hip or shoulder MRI to save my soul. I've missed subtle fxs on xrays. I've seen weird stuff on MRI's and xrays, called the radiologist and s/he says "Bah, it's nothing."
If it got to the point where nothing surprised me, I'd lose my interest in medicine. But I am far enough along that my guesses are right more than they are wrong.