I live in Michigan. Obviously if you can no longer do stairs because of a recent handicap it is good cause for breaking a lease. Just get a statement from the doctor as to what your condition is and whether or not it is expected to be permanent.
What I'd like to know is just how is it you are doing those stairs now? Unless you are being carried up, it would seem that your handicap isn't that severe. Being unable to do stairs at all and being able to do them with difficulty is two different things. If only with difficulty then I see no reason why you can't remain until the end of the lease.
It depends on where you are. This is a global site. No one can tell where you are. Housing rules and regulations differ greatly from place to place.
NOT happening here legally maybe in ur country
pay whatever penaly has to be paid