I had shoulder surgery right before the start of 3rd year and it turned out fine. I took 2 weeks off post-op, did some BS electives for 4 weeks, and started a core rotation 6 weeks post-op. During the elective, I was still in a sling so it was obvious I was crippled so people gave me more slack and assumed I couldn't do anything besides observe and talk to patients. Even after the core rotation started at 6 weeks with no sling, I was exhausted all the time because I wasn't sleeping well since it's impossible to get comfortable after shoulder surgery/it hurts for a while. But it was alright in the end.
I know it's a different limb so a shoulder didn't affect my walking/rounding like an ACL might (although at 3 months post-op, it shouldn't either), but I started on Neuro so I was unable to do a lot of the exams since I was still mostly one-armed. I explained to people that I had just had shoulder surgery and was still limited in my ability to use my arm and everyone was super understanding. For example, as long as I demonstrated proper technique of a cranial nerve exam with my other arm or describe how I would've done it, then they understood that I knew my stuff and checked me off for skills during the standardized patient exam. Similarly, with patients, if I couldn't do a proper exam on my own, I would just use the resident's physical exam for my presentations but formulate the plan on my own. Usually, I was able to figure out how to do most of the things one-armed / adapt technique a bit / take a bit longer. But it's not like the residents relied on the medical students' exams anyways, so my not doing them did not make more work them at all and didn't affect anything in the long run.
It would've been very different had I started on Ob or Surgery, so I had arranged my 3rd year schedule to accommodate my recovery, limitations, and PT. Not sure if you have that luxury but it's something to consider.
Mostly, talk to your rotation coordinator and your residents/attendings if on your rotation your ACL is causing issues. Unless they're total a**hats, they should understand and be able to accommodate you.
Good luck with your surgery and recovery!
