A walker or a cane can often get you to the front of the line. It is best to contact airline personel if there is a long line and you need assistance-- don't just walk up to the ID-checking podium waving a disabled parking plackard.
Just find someone from the airline and ask for help [getting to the front of the line] if you are not going to request a wheelchair.
A cane is a very good alternative. I have a folding one that I recently bought due to a motorcycle accident.