What is the ruling if an orthopaedic surgeon misses salah time due to being in surgery?

As an exception, for example, if you're going to be in surgery then try and plan in advance. So if you know it's a lengthy procedure, pray dhuhr and asr together maybe earlier at dhuhr time or later at asr time, whichever is easier. It shouldn't be the norm. The norm is not to join the prayers only for specific exceptions.