Trucking companies and their insurance companies set those requirements. They vary a lot. Some companies just want you to show up with a valid DOT Medical Card and some require you to use their selected doctor or clinic. Generally speaking, your physical fitness/agility is only tested at time of hire, not during each medical exam (2 years). Flatbed companies often have the most strenuous requirements. I’m posting the link below as an example of how strict s=one of the better flatbed companies can be. Their procedure is “worst-case scenario” for anyone with some sort of health issue. https://www.youtube.com/watch?v=qyMlvfb51wI
I would suggest you contact individual companies and ask for their physical requirements.
There are many drivers with some sort of joint issues driving for various companies. The 2 big causes of medical disqualifications for truck drivers are high blood pressure and insulin-dependent diabetes. The blood pressure can be controlled with medication and that usually means getting yearly re-checks, rather than the standard 2 year DOT Medical Card. If someone’s diabetes can be controlled with pills you may still qualify for a Medical Card. If insulin injections are required that’s disqualifying, as far as I know.