I was cutting a box one time, and the knife slipped. I ended up stabbing my leg really deep. I knew nothing of tetanus at the time, and it didn't hurt, since I guess I missed the nerves.
anyway, turns out I was fine, except: I couldn't lift my leg over a bike seat. That particular motion used the muscle that I had stabbed, so I couldn't do it.
so one particular muscle was... inoperable somehow. Otherwise, I felt fine.
your not being able to walk up stairs reminded me of that somehow