Good idea to start PhD with a potentially obstructive medical condition? [EDIT] I have a medical condition, diagnosed after I received and accepted my PhD offer. I am wondering if i should defer or have the surgery in the middle of my program. [/EDIT]

The condition makes it difficult  for me to stand for long periods of time (due to vertebra slippage). I'm still able to function on my desk job. Taking classes should not be an issue. However, working in the lab (somewhat unavoidable in my field) might be challenging.

There is surgery to fix this issue, by fixing the vertebra. But that is not the first line of treatment and is used only if the problem gets worse. 

I'm unsure if I should start the program and then take a quarter off for the surgery or wait for the surgery and then start my program. Your comments/ideas/advice on evaluating my situation are welcome.

P.S. It might be relevant, I am an international student accepted at a US university.
Part way through my PhD I was diagnosed with ovarian cancer, requiring major surgery followed by chemotherapy. I went to one course unit for a quarter, so that I kept my connection to the department and parking pass, but was not expected to do much work.

I don't know whether the school where you will be doing your PhD will allow that sort of option.

I agree with the advice in comments to discuss with whichever professor is responsible for first quarter students.