I am afraid you might have the stairs to contend with - only terminal B has air bridges (and I am not sure every flight gets to use them, not sure) the others still use the stairs. It looks from a quick glance, that Copa is not terminal B.

They may be able to arrange for someone to carry you on / off? Although if it were me I would wear a pair of old jeans and come down the steps on my butt rather than have someone carry me and risk knocking my knee (and yes, I did have people carry me when I had my bust knee, but not in an airline setting). You might also be able to manage a slow hop up / down (take advantage of pre-boarding, and stay on the plane until everyone else is off so you can take your time). You could request a wheelechair for use in getting from the plane through the airport (it can be a bit crazy at times, so this might reduce your time stood in line).